© 2009, Elsevier Limited. All rights reserved. The right of Juriy Wladimiroff and Sturla Eik-Nes to be identified as editors of this work has been asserted by them in accordance with the Copyright, Designs and Patents Act 1988. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior permission of the Publishers. Permissions may be sought directly from Elsevier's Health Sciences Rights Department, 1600 John F. Kennedy Boulevard, Suite 1800, Philadelphia, PA 19103-2899, USA: phone: (+1) 215 239 3804; fax: (+1) 215 239 3805; or email: h
[email protected]. You may also complete your request online via the Elsevier homepage (www.elsevier.com), by selecting ‘Support and contact’ and then ‘Copyright and Permission’. ISBN-13: 978-0-444-51829-3 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Notice Neither the Publisher nor the Editors assume any responsibility for any loss or injury and/or damage to persons or property arising out of or related to any use of the material contained in this book. It is the responsibility of the treating practitioner, relying on independent expertise and knowledge of the patient, to determine the best treatment and method of application for the patient. The Publisher
The publisher's policy is to use paper manufactured from sustainable forests
Printed in China
✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Contributors
Domenico Arduini MD Associate Professor Cattedra Medicina dell’Eta Prenatale Universita di Tor Vergata Rome Italy Fetal biometry, estimation of gestational
Bruno Cacciatore MD, PhD Professor of Obstetrics and Gynaecology Department of Obstetrics and Gynaecology Helsinki University Hospital Helsinki, Finland
age, assessment of fetal growth
Doppler ultrasonography in gynaecology
Bernard Benoit Hôpital Princesse Grace Monaco
José M. Carrera PhD Professor of Obstetrics and Gynaecology Fetal Medicine Unit Department of Obstetrics and Gynaecology Institute University Dexeus Barcelona Spain
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Harm-Gerd K.Blaas MD, PhD National Centre for Fetal Medicine St Olav’s Hospital University Hospital Trondheim Trondheim Norway
Investigation of early pregnancy
Investigation of early pregnancy
vii
Contributors
✩ ✩✩✩✩✩✩✩✩✩✩✩ Rabih Chaoui Centre for Prenatal Diagnosis and Human Genetics Berlin Germany Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Frank A. Chervenak MD Given Foundation Professor and Chairman Department of Obstetrics and Gynecology Weill Medical College of Cornell University New York USA Ethics and patient information
Werner Diehl Department of Prenatal Diagnosis and Therapy AK Barmbek Hamburg Germany Multiple pregnancies
Francis A. Duck PhD, DSc Medical Physicist Department of Medical Physics and Bioengineering Royal United Hospital Bath UK Biological effects and safety aspects
Sturla H. Eik-Nes Professor of Obstetrics and Gynaecology Department of Obstetrics and Gynaecology National Centre for Fetal Medicine University Hospital of Trondheim Trondheim Norway Physics and instrumentation
viii
Amniotic fluid and placental localization Examining the cervix by transvaginal ultrasound
Annegret Geipel MD Priv. Doz. Dr. Med Leitende Oberärztin Pränatalmedizin Abteilung für Geburtshilfe und Pränatale Medizin Universitätsklinikum Bonn Sigmand-Freud-Str. 25 53105 Bonn Germany Evaluation of fetal and uteroplacental blood flow
Ulrich Gembruch Professor of Obstetrics and Gynaecology Abteilung fur Praenatale Medizin und Geburtshilfe Zentrum fuer Geburtshilfe und Frauenheilkunde Rheinische Friedrich-WilhelmsUniversitaet Bonn, Germany Evaluation of fetal and uteroplacental blood flow
Francesco Giacomello MD Professor Department of Surgery University Tor Vergata Rome Italy Fetal biometry, estimation of gestational age, assessment of fetal growth
Kurt Hecher Professor of Obstetrics and Gynaecology Department of Prenatal Diagnosis and Therapy AK Barmbek Hamburg, Germany Multiple pregnancies
✩✩✩✩✩✩✩✩✩✩✩ ✩
Assessment of the placenta and umbilical cord
Davor Jurkovic MD, PhD Consultant Early Pregnancy and Gynaecology Ultrasound Unit Department of Obstetrics and Gynaecology King’s College Hospital London UK Gynaecological pathology: the uterus
Laurence B. McCullough PhD Dalton Tomlin Chair in Medical Ethics and Health Policy Professor of Medicine and Medical Ethics Associate Director for Education Center for Medical Ethics and Health Policy Baylor College of Medicine Houston Texas USA Ethics and patient information
Hylton B. Meire Consultant Radiologist (Ultrasound) Bromley UK Medico-legal implications of ultrasound imaging in obstetrics and gynaecology
Israel Meizner md Professor Ultrasound Unit Department of Obstetrics and Gynecology Rabin Medical Center – Beilinson Campus Petah-Tikun and Sackler Faculty of Medicine Tel Aviv University Tel Aviv, Israel
Contributors
Eric Jauniaux MD, PhD, MRCOG Professor in Obstetrics and Fetal Medicine Academic Department of Obstetrics and Gynaecology UCL EGA Institute for Women’s Health Royal Free and University College London London UK
Prenatal diagnosis of fetal anomalies
Ana Monteagudo MD Professor of Obstetrics and Gynecology Department of Obstetrics and Gynecology New York University School of Medicine New York USA Scanning techniques in obstetrics and gynaecology
Eduard J.H. Mulder Msc, PhD Professor Department of Perinatology and Gynaecology University Medical Center Utrecht The Netherlands Fetal movement patterns and behavioural states
Kypros H. Nicolaides MD Professor of Fetal Medicine Department of Obstetrics & Gynaecology Kings’s College Hospital London UK Prenatal diagnosis of fetal anomalies
David A. Nyberg MD Seattle Ultrasound Associates Seattle USA Normal fetal anatomy at 18–22 weeks
ix
Contributors
✩ ✩✩✩✩✩✩✩✩✩✩✩ Rüdiger Osmers MD, PhD Professor of Obstetrics and Gynaecology Department of Obstetrics and Gynaecology University Hospital Gottingen Gottingen Germany Gynaecological pathology: tubes and ovaries Doppler ultrasonography in gynaecology
Gianluigi Pilu MD Associate Professor of Obstetrics and Gynaecology Department of Obsetrics and Gynaecology University of Bologna Bologna Italy Prenatal diagnosis of fetal anomalies
Roberto Romero MD Professor of Obstetrics and Gynecology Wayne State University and Chief of the Perinatology Research Branch of the National Institute of Child Health and Human Development National Institutes of Health Bethsedu, MD USA Prenatal diagnosis of fetal anomalies
Rehan Salim MRCOG Early Pregnancy and Gynaecology Ultrasound Unit Department of Obstetrics and Gynaecology King’s College Hospital London UK Gynaecological pathology: the uterus
x
Kjell Å. Salvesen Dr Med, PhD National Centre for Fetal Medicine St Olav’s Hospital University Hospital Trondheim Trondheim Norway Examining the cervix by transvaginal ultrasound
Waldo Sepulveda Professor of Obstetrics and Fetal Medicine University of Santiago de Chile San Jose Hospital and Director Fetal Medicine Center Clinica Las Cordes Santiago, Chile Prenatal diagnosis of fetal anomalies
Povilas Sladkevicius MD, PhD Department of Obstetrics and Gynaecology Malmö University Hospital Lund University Malmö Sweden Normal gynaecological anatomy (uterus, tubes, ovaries)
Vivienne L. Souter MD, MRCOG Seattle Ultrasound Associates Seattle USA Normal fetal anatomy at 18–22 weeks
Ilan E. Timor-Tritsch MD Professor of Obstetrics and Gynecology Department of Obstetrics and Gynecology New York University School of Medicine New York USA Scanning techniques in obstetrics and gynaecology
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal gynaecological anatomy (uterus, tubes, ovaries)
Yves Ville MD Professor of Obstetrics and Gynaecology Service Gyneco/Obstetrique Centre Hospitalier Inter Communal Poissy France
Kim Wherey MD Seattle Ultrasound Associates Seattle USA Normal fetal anatomy at 18–22 weeks
J. W. Wladimiroff Emeritus Professor of Obstetrics & Gynaecology Department of Obstetrics & Gynaecology Erasmus University Medical Centre Dr Molewater plein 40 3015 GD Rotterdam The Netherlands
Contributors
Lil Valentin MD, PhD Professor in Obstetrics and Gynaecology Department of Obstetrics and Gynaecology Malmö University Hospital Lund University Malmö Sweden
Amniotic fluid and placental localization
Invasive procedures in obstetrics
Gerard H.A. Visser MD, PhD Professor of Obstetrics and Gynaecology Department of Perinatology and Gynaecology University Medical Center Utrecht The Netherlands Fetal movement patterns and behavioural states
xi
✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Preface
This textbook is the result of a joint venture between the International Society for Ultrasound in Obstetrics and Gynaecology (ISUOG) and the European Board and College of Obstetrics and Gynaecology (EBCOG). Both organizations play an important role in training. The book aims to provide the reader with the information necessary for everyday ultrasonography in obstetrics and gynaecology, rather than a summary of the latest developments in the field. The book follows the traditional pattern of starting with the physical and biological aspects of diagnostic ultrasound, followed by a wide range of clinical applications in obstetrics and gynaecology. Each chapter has been written by one or more experts actively involved in ultrasound teaching. Ultrasound images are presented either in the text or separately on a CD at the end of the book. Multiple choice questions are presented at the end to allow the reader to test his or her knowledge. We hope that this textbook will serve all those who are active in day-to-day ultrasound scanning. Juriy W. Wladimiroff, Sturla H. Eik-Nes
xiii
1 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Physics and instrumentation Sturla H Eik-Nes
Abstract This chapter provides an overview of the fundamental physical principles that make it possible to produce images of human tissue using sound. The physical laws are explained without the use of complicated formulas. Sound is a mechanical vibration in a medium such as air or human tissue. The upper frequency limit for sound to be heard by humans is 20 kHz. Frequencies above 20 kHz are called ultrasound. Medical images are made with a frequency above 3 MHz. The basic principle for making images of human tissue is to send a pulse into the tissue with a transducer and detect the echoes emerging from structures in the tissue. Imaging may be done in real time by electronic scanning. A variety of sizes and shapes of transducers have been produced for the various applications of ultrasound in medical diagnosis. A proper transducer must be used for a specific task. The ultrasound beam is the essential tool to make images. It must be focused by the user and the image must be properly adjusted with respect to the gain. Measurements can be made and a basic understanding of the resolution in the three planes is necessary for measurements and interpretation of the images. The main artifacts such as edge shadows, attenuation shadows, enhancements and reverberation must be understood. Basic principles of ultrasound scanning must be followed to extract the maximum information from the scan.
Keywords A-mode, artifacts, B-mode, focus, M-mode, real-time scanning, technical principles of ultrasound in obstetrics and gynaecology, time gain compensation.
Introduction In the practice of clinical ultrasound in obstetrics and gynaecology, it is essential that the examiner has a basic understanding of the physics that makes it possible
1
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ to produce images of human tissue using sound. In addition, the examiner must be able to handle artifacts properly, know about the basic performance of the instrument and be aware of artifacts, safety and risk factors. This chapter provides an overview of the fundamental physical principles without the use of complicated formulas to explain the physical laws. The focus is to give the reader an overall understanding of how an ultrasound machine works and the skill to operate the machine and to manage the necessary adjustments in order to produce images of high quality for diagnostic use. For indepth knowledge of the physics of ultrasound, the reader is referred to excellent textbooks. (See selected list at the end of this chapter.)
Sound Sound is mechanical vibrations travelling in a physical medium such as air, water, metal or even human tissue. Whether the airborne vibrations come directly from the source or are reflected, they produce impressions on the eardrums of our vestibular organs. We interpret these vibrations as sound. Sound may be categorized according to various frequency levels:
• infrasound (0–20 Hz) • audible sound (20–20 kHz) • ultrasound (>20 kHz) • diagnostic ultrasound (1–20 MHz). Humans do not hear the infrasound but other species such as whales, dolphins, elephants, hippopotamuses and rhinoceros do; they use infrasound to communicate with other members of their species over long distances. The upper frequency limit for humans is 20 kHz. Frequencies above 20 kHz are called ultrasound. Some species may hear sound frequencies which for humans are categorized as ultrasound, for example mice (10–70 kHz), dogs (40–60 kHz) and bats (20–200 kHz). There is even some evidence that bats utilize the change in pitch of the echo to determine the relative movement of the object that reflects sound – the Doppler effect. Marine mammals may produce very complex signals ranging from low frequencies for long-range use to high frequencies for local chatting!
Short History of the Development of Ultrasound in Medicine
2
In 1912, the passenger ship Titanic hit an iceberg on its maiden trip crossing the Atlantic from Southampton to New York. In the time that followed, physicists took an interest in using sound to detect large objects submerged in water. Initially their research for that purpose was unsuccessful. During World War I, the French physicist Paul Langevin was responsible for developing the hydrophones needed to detect submarines; this underwater sonar technology resulted in the first sinking of a German submarine in 1916. In 1917, Langevin invented the quartz sandwich transducer which served as the basis for the modern ultrasonic era. Between
✩✩✩✩✩✩✩✩✩✩✩ ✩
Physics and instrumentation
World War I and World War II, the development of sonar (Sound Navigation and Ranging System) and radar (Radio Detection and Ranging) took place. The latter technique used electromagnetic waves rather than ultrasound. The next important step was the use of ultrasound to detect flaws in metal using high-frequency ultrasound. The metal flaw detectors became increasingly important as World War II was approaching, but were reported after the war.2,4 After World War II, Howry and Bliss, in Denver, started to experiment with sonar equipment and amplifiers from the navy.7 They developed a pulse-echo technique in 1948–49, and later produced cross-sectional images of a human partly submerged in water. At the same time, Wild in Minneapolis developed a breast scanner and actually made a diagnosis of breast lesions with his device.12 The Swedish physician Inge Edler and physicist Helmut Hertz, at the University of Lund, borrowed a metal flaw detector from Kockum's Shipyard in Malmö, Sweden. In 1953, they managed to trace the movements of the human cardiac valves by means of the sound waves emitted and received by their modified instrument.5 This was the start of a new era in cardiology relying on sound technology.6 The next breakthrough was by the Scottish physician Ian Donald, in Glasgow, who conducted the basic research for the development of a machine for clinical use employing ultrasound to make two-dimensional images of human tissue. Donald had served in the Air Force during World War II and his past experience influenced his prototype machine, which consisted of two metal flaw detectors. His Lancet paper of 1958, ‘Investigation of abdominal masses by pulsed ultrasound’, is considered to be one of the most important for the development of clinical ultrasound.3 Since the late 1950s, the development of ultrasound in medicine in general and in the field of obstetrics and gynaecology in particular has continued in an exponential way. Breakthrough advances have been repeatedly made in spite of claims that the development of ultrasound in medicine has reached its physical limits.
Sound, Waves and Propagation Sound is a mechanical vibration in a medium. The medium may be, for example, air, water or human soft tissue. The sound wave propagates through the medium as a longitudinal compression wave. When we think of waves we may picture a stone being thrown into a quiet lake and observe the concentric rings that propagate from the centre, or we may think of the waves in the ocean as seen from the shore or from a boat. These waves are transversal waves. Sound waves, however, are longitudinal waves and the medium that they travel through is subject to cyclic variations in pressure as the medium is being compressed or rarefied (Fig. 1.1). Make a small experiment by putting your index finger on the top of your larynx, then make the sound of a z-z-z. With your finger you will feel the vibrations caused by your vocal cords that are your own sound system, that cause the z-z-z to be heard in the room. You have now produced longitudinal sound waves that travel
3
Distance
λ
Compression
Decompression
Pressure
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Distance
Moves with wave velocity, c Fig. 1.1 (Upper panel) A schematic illustration of a sound wave as it travels in a medium causing periodic compressions and rarefaction of the medium. (Lower panel) The dislocation of the particles.
4
through the room and cause compression and rarefaction of the air in their path. When the sound waves hit the eardrums of someone in the room, the process is reversed and causes the eardrums to vibrate and the person will hear your z-z-z. The sound wave is a longitudinal wave caused by compression and rarefaction of a physical medium in the direction of the movement of the wave. This sound wave may further be described by intensity and frequency. If you have a piano, you can carry out a small experiment in your living room by hitting A above middle C. You will hear a chamber tone with a frequency of 440 Hz. If you move up one octave on your piano and hit A, you will hear it at a frequency of 880 Hz. If you move up one more octave to the next A, you will hear an A note with the frequency of 1760 Hz. The frequency tells us about the degree of highness or lowness of a tone. The frequency is the number of vibrations per second that produce the sound. Hit the A on your piano very lightly and you will barely hear the chamber tone of 440 Hz; hit the key with force and you will hear the same chamber tone with the frequency of 440 Hz, but much louder. This tells us that the same tone may differ in intensity or loudness. The intensity tells us something about the loudness or strength of the sound signal. A sound wave travelling in a medium produces compression and rarefaction of the medium as shown in Figure 1.1. The velocity of propagation of the sound wave is dependent on the medium and is 330 m/s in air, 1480 m/s in water, 1589 m/s in
✩✩✩✩✩✩✩✩✩✩✩ ✩
λ=
v f
(1)
A chamber tone (440 Hz) has a wavelength of 0.75 m, propagating in air at the velocity of 330 m/s. It is obvious from equation 1 that the wavelength will vary with the frequency and velocity of sound in the tissue. The higher the frequency, the shorter the wavelength; the higher the velocity of sound, the longer the wavelength. Because the speed of sound in human tissue has been standardized at 1540 m/s in the equation, the wavelength will vary with the frequency (Table 1.1). The higher the frequency of ultrasound in human tissue, the shorter the wavelength. An ultrasound wave with a frequency of 5 MHz (M is the Greek abbreviation for mega which means big, but used in acoustics it means million) has a wavelength of 0.31 mm. It is important to understand what really happens when a sound wave moves through the medium. A scene we all are familiar with will demonstrate the principle (Fig. 1.2). When a sound wave propagates through a medium, the wave moves while the medium remains in place. Thus, when ultrasound propagates through human tissue, it is the wave that moves, not the tissue. Let's go back to the sound waves. Low-frequency sound (a human voice, music) will spread all over a room. You can easily hear the voice of a person talking with his back turned to you. Very high-frequency sound behaves like light – it moves like a beam along a straight line. High-frequency ultrasound propagates through tissue in a relatively narrow beam and may be focused by acoustic lenses. In order to make a simple ultrasound machine, we need to be able to produce high-frequency sound. In the 1880s the Curie brothers discovered the piezoelectric effect which implies that a crystal, for example a quartz crystal, will produce an electrical current if subject to mechanical pressure. Conversely, an electrical current that is applied to a quartz crystal will cause the crystal to change its shape. The change in shape will have an impact on the surrounding medium. If alternating
Physics and instrumentation
muscle and 3500 m/s in bone. The hardness or stiffness of the medium is the main factor determining the propagation velocity of sound. Ultrasound machines are now standardized and calibrated to use 1540 m/s as the speed of sound in human tissue. Based on the propagation of the sound wave in a particular medium (v) with a particular frequency (f), we arrive at the first important equation for the wavelength λ:
Table 1.1 Various ultrasound frequencies and the corresponding wavelength Frequency (MHz)
Wavelength (mm)
3.5 5 8 10
0.44 0.31 0.19 0.15
5
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Wave motion
6
Fig. 1.2 The person on the shore throws a stone into the water. The stone creates waves in the form of concentric rings that approach the cork. Instead of being ‘pushed away’ the cork moves up and down as the wave passes by.
current is applied to the crystal, the crystal will repeatedly change its shape and the movements of the crystal will produce a wave transmitted through the medium. By using a piezoelectric material (quartz crystal) it is possible to produce highfrequency sound waves that emerge from the crystal into human tissue. The same crystal can be made to pick up the echoes emerging from the depth of the tissue. Such echoes will have an impact on the crystal that produces an electric pulse that we may detect and process further. If you have been at an outdoor rock concert in front of a full-blast subwoofer, you will have experienced the impact that sound can have on your body, in particular on your air-filled chest cavity. Imagine the sound level scaled down to an impact you cannot feel and then a very sensitive instrument introduced to detect the sound waves; then you have a demonstration of the basic principle of receiving low-impact echoes. Making images with sound is about sending and receiving sound waves in the form of a pulse (Fig. 1.3). We now have enough knowledge to make a one-dimensional ultrasound image of the fetal skull the way it was done in the late 1950s and early 1960s. It was called A-mode (A stands for amplitude) (Fig. 1.4). In the early days of the clinical use of ultrasound, A-mode technology made it possible to measure the fetal biparietal diameter and the conjugata vera, to locate the placenta, including placenta praevia, and to diagnose polyhydramnion, detect the fetal heart activity, diagnose a molar pregnancy and a variety of other diagnoses. The interpretation of such images was difficult and required extensive training and imagination of the examiner. Still, sophisticated diagnoses were made by dedicated pioneers.9
✩✩✩✩✩✩✩✩✩✩✩ ✩
Physics and instrumentation Fig. 1.3 (Bottom) An electric current is applied to the transducer and a pulse is sent out. (Top) A pulse is received and generates an electric current that can be displayed by the instrument. The stronger the returned pulse (echo), the higher the amplitude of the electric current.
The natural step forward was to make two-dimensional images. The strength of the echoes was then displayed as a white dot instead of as an amplitude; the higher the intensity of the returned echo, the larger the dot. This was called B-mode (B stands for brightness). In a one-dimensional system, these signals were impossible to interpret but moving the transducer in a plane across the area to be examined (scanning) during sending and receiving made it possible to display all the echoes emerging from structures in that plane. Together, these were converted into a relatively easy-to-read two-dimensional image (Fig. 1.5). This manual scanning made it much easier to produce and interpret two-dimensional images produced with ultrasound. The image quality was further improved by the development of the analogue scan converter, so that grey scaling could be applied as well as scaling of the image and calliper movements on the screen. The next technical step was to produce real-time two-dimensional images. This was achieved mechanically in the 1960s by Krause and Soldner in Erlangen, Germany.10 A more sophisticated way was to align a set of crystals to make a linear transducer, described by Nicolaas Bom in Rotterdam, in 1971.1 The principle was further developed by Martin Wilcox who produced a clinically most successful real-time scanner in 1972 (Fig. 1.6). The principle of displaying the returned signals appropriately is simple: the speed of sound is known and the time from when a pulse is emitted until it comes back can be calculated. It is obvious that each submitted pulse will hit many structures in the path of the beam, thus many echoes will be returned separated by a short time interval. Electronic real-time scanning implies that the transducer sends a pulse, and then it switches to the listening mode. A linear transducer may typically have 196 or more crystals aligned in a row. Typically crystals number 1–50 are fired, and then number 2–52, etc. The examiner is presented with an image frame rate of approximately 30 per second, which for the human eye will make the on-screen image appear flicker free with movements in real time.
7
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
8
Fig. 1.4 A-mode. A single ultrasound beam is sent through the fetal skull and, in sequence reflected from the parietal bone closest to the transducer, the falx cerebri, the skull bone distal to the transducer and, finally, the posterior uterine wall. Depending on the strength of the returned pulses (echoes), the quartz crystal will generate a high- or low-amplitude current.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Physics and instrumentation
Fig. 1.5 Twin pregnancy. B-mode image obtained in 1964 by Diasonograph, Nuclear Enterprises Ltd, Edinburgh, UK. The image is made by ‘compound scanning’, i.e. by rocking the probe back and forth during the process of moving the scanning arm slowly across the pregnant abdomen. Reproduced by permission from Bertil Sundén.11
Finally, we need to understand the physical principle of M-mode (M stands for motion). M-mode is used to trace the movement of a structure. For example, tracing the movement of a heart valve or the movement of the atrial wall and the ventricular wall of the fetal heart simultaneously on the very same image makes it possible to discriminate a dissociation of the rhythm, i.e. supraventricular tachycardia, various kinds of AV block, etc. During an M-mode recording, we register the movements of the echoes along one single line in our image (the y-axis) while time runs along the x-axis. The principle is easy to understand if we imagine that we put a long paper strip on our desk, hold a pen against the paper and move the pen up and down while pulling the paper strip in a direction perpendicular to the movement of the pen. In our example, the pen represents the moving echoes and the up-and-down movement of the pen will result in a curved line on the paper reflecting the movements of the pen. An M-mode scan is shown in Figure 1.7.
One Transducer for each Purpose A variety of sizes and shapes of transducers have been produced for the various applications of ultrasound in medical diagnosis. Transducers have various sizes of ‘footprints’, i.e. the part of the transducer that touches the skin or other tissue. Transducers with a small footprint are necessary in, for example, cardiology, for sending a beam between the ribs to reach the heart as a target organ. To reach the heart and thoracic aorta, even an oesophageal transducer may be used; in urology and proctology, the prostate or lower part of the intestines is reached by inserting a transducer into the rectum. The gastroenterologist may examine the liver from the surface of the abdomen or insert a slim transducer through the gastric scope to reach the surrounding organs including the ductus pancreaticus and the pancreas.
9
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 1.6 (Upper panel) The ADR linear scanner (in Europe manufactured under the name of ADR-Kranzbühler, image by courtesy of the company, 1980). (Lower panel) The basic principle of scanning in real time. The crystals fire the sound beams, which travel into the human tissue, hit structures and are reflected. The reflected echoes are picked up and displayed accordingly on a screen.
10
In vascular surgery, imaging through a catheter has been developed for target organs such as the neck vessels and coronary arteries. In the field of obstetrics and gynaecology, curvilinear transducers are extensively used for transabdominal examination (Fig. 1.8). The shape of the transducer fits well to the pregnant and non-pregnant abdomen, the footprint is small, while the view deep in the tissue is wide due to the sector-shaped image. The use of a convex transducer also reduces the effect of reverberations and wave front aberrations (see later). Transducers designed for transvaginal scanning make the early pregnancy and the non-pregnant uterus accessible at a close range; thus, they are widely used in gynaecology and obstetrics. Transducer technology has become complex. The essential unit, the sound-emitting crystal, was made of natural materials such as quartz. Nowadays most of the crystals are made of artificial ceramics mixed with plastic materials with various
✩✩✩✩✩✩✩✩✩✩✩ ✩
Movement with time
Depth
M-mode
Physics and instrumentation
A-mode
Movement with time Grey-scale amplitude along beam at fixed time
Time
Fig. 1.7 The principle of M-mode. The basic principle is described in the text.
Fig. 1.8 Sector, curvilinear, linear and transvaginal transducers.
forms of damping material to produce a clean pulse and a pulse of short duration. The electrical excitement is made through thin silver electrodes connected to the ceramic material. The basic principle for producing a pulse wave and receiving an echo, which generates a current, remains the same, as illustrated in Figure 1.8.
The Ultrasound Beam Near Field and Far Field Ideally, an ultrasound beam would emerge from a crystal, be narrow and circular and shoot into the tissue along a straight line. Then it would return along the same line from structures it may hit, to the very same crystal, which would be excited by the echoes and produce an electrical current. In real life, the beam is not ‘narrow and circular’ but advanced engineering has, over time, worked to
11
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ modify the beam towards the ideal form. Put simply, the beam has a near field and a far field. In the near field we may influence the shape of the beam by focusing. In the far field we cannot do that. When we make our images we are operating in the near field. So from an imaging point of view, we would like the beam to have a long near field (Fig. 1.9). The depth (d) at which the transition of the beam from the near field to the far field takes place is given by equation 2. r is the diameter of the circular transducer: (2) r2 d= λ This equation tells us that the near field is relatively long if the diameter of the circular transducer is large and/or the wavelength (λ) is short, i.e. the frequency is high. It follows that the near field is relatively short if the transducer has a small diameter and/or the wavelength is long, i.e. the frequency is low.
Focusing This brings us to the next important feature, which is the focusing of the beam. The required effect of focusing the beam is to reduce the width of the beam. Focusing may be achieved by employing lenses in various forms. F ×λ (3) BW = 2r Figure 1.10 shows the trade-off of having a narrow beam width as an effect of focusing: an increased divergence of the beam distal to the focal distance. Considering equations 1–3, we may conclude that a focused transducer with a large diameter (aperture) and a high frequency (short wavelength) will provide a narrow beam in our region of interest (at the focal distance). So why do we not settle for transducers with a large aperture and a high frequency? The quick answer is that a large aperture may not be acceptable for a particular application and high-frequency ultrasound is absorbed to a greater extent than low-frequency ultrasound. The range of a relatively low-frequency transducer is longer than for a relatively high-frequency transducer. Near field
Far field
2r Transducer d
12
Fig. 1.9 Schematic illustration of an ultrasound beam emerging from a transducer with a circular surface with a diameter 2r. The beam has a near field reaching into the depth of d and a far field.
✩✩✩✩✩✩✩✩✩✩✩ ✩ Near field
Far field
2r Transducer
Lens
BW
Fig. 1.10 Schematic illustration of an ultrasound beam emitted from a transducer with a circular surface with a diameter 2r. The focal distance is set at F and the beam width (BW) is the effect of the focusing.
Physics and instrumentation
F
The solution is to use high frequency if we are looking at structures close to the transducer and low frequency if we are looking at structures further away. Let us go back to the ultrasound beam. Ideally, one would like the ultrasound beam to be thin and round, and shoot into the tissue along a straight line, hitting structures which cause echoes that return to the transducer along the same line. Then only structures in the thin path of the beam would cause echoes. We have learned that this is not so. The beam has a near field where we may manipulate the beam and a far field where the beam diverges due to diffraction, where it is not possible to manipulate the beam. The beam has a main lobe and side lobes (Fig. 1.11). The side lobes may be considered ‘skirts’ around the main lobe body. When such a complex beam is shot into the tissue, all the structures hit by the
Side lobe Main lobe
Fig. 1.11 Schematic sketch of an ultrasound beam, demonstrating the main lobe and the side lobes.
13
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ main lobe and structures which in reality are located on the side of the main lobe, but within the side lobes, will cause echoes to be returned to the transducer and be displayed along the centre of the imaginary line through the centre of the main lobe. This will cause a ‘smear-out’ effect of the image. The presence of side lobes in addition to the main lobe reduces the quality of our image. Structures outside the main lobe will be picked up by the side lobes and on the final image they will be displayed along the centre line through the main lobe. Improving the overall beam quality is accomplished through the focusing process which may be achieved in various complex ways. One technique, dynamic focusing, may help us understand the principle of focusing. One submitted pulse may cause many returned echoes which hit the transducer surface over a time period, depending on how far the echoes have travelled on their way down to the various reflectors and then back. Focusing is a process that may be done on the way out and on the return of echoes. Focusing on the returned echoes is always done. Since we know when a pulse has been transmitted, we may focus the returned echoes by changing the focus level in the tissue at certain time intervals following the transmission of the pulse. This will cause echoes, which originate from a depth of, for example, 2, 4, 6, 8 and 10 cm, to be focused separately on return. Thus, the focusing process will affect the area between 2 and 10 cm, in the example above. Additionally, we may focus our area of interest especially on the way out to obtain the highest image quality possible in the specific area where we are looking. Arrows along the side of the image indicate the manually set foci. Optimum quality is usually achieved employing two to three foci in the area of interest. The process of directing the focus of our beam to the area we are looking is one of the most important manual adjustments we make during ultrasound scanning. Unfortunately, focusing is one of those manual adjustments which are most often forgotten, a practice that exemplifies a lack of technical understanding of the person performing the scanning.
Resolution
14
To be able to interpret our image, define discrete structures and make precise measurements on an ultrasound image, we need to understand the basic principles of resolution. Resolution is defined as the smallest distance we can have between two structures and still be able to distinguish them as two separate structures. On a two-dimensional ultrasound image, we have an axial plane, a lateral plane and an elevation plane (Fig. 1.12). The resolution in these three different planes is determined by various physical laws that we have to understand to optimize the adjustment of our machine settings, select the best transducer for our purpose and make measurements as precise as possible. The axial resolution may be called the range resolution or the radial resolution. The resolution in the axial plane is the best of the three. The axial resolution is mainly determined by the length of the transmitted pulse. A ‘pulse’ always consists of a few oscillations in spite of effective damping factors. The absolute length
✩✩✩✩✩✩✩✩✩✩✩ ✩ Transducer
Physics and instrumentation
Axial plane
Azimuth plane
Elevation plane Fig. 1.12 The three planes on an ultrasound image: the axial, the azimuth and the elevation plane.
5 MHz 2.5 MHz
5 MHz 2.5 MHz 5 MHz 2.5 MHz Fig. 1.13 In the upper part, a 5 MHz pulse is shown travelling towards a target, which may be a blood vessel. The pulse is short enough to be able to hit the anterior and posterior walls separately, thus two separate echoes will be reflected and make two separate dots on the screen when they hit the transducer. Below, the 2.5 MHz pulse is longer and the echoes from the anterior and posterior walls of the vessel will overlap, so only one large dot will be displayed on our screen. The 2.5 MHz pulse was not able to resolve the two vessel walls as two separate structures.
of a pulse may therefore be reduced by increasing the ultrasound frequency. The principle of the axial resolution is demonstrated in Figure 1.13. The total pulse length of a 5 MHz pulse is typically shorter than that of the 2.5 MHz pulse. A good axial resolution requires a short pulse. Several factors may contribute to a short pulse: one of them is the wavelength. A high frequency (i.e. short wavelength) will make the pulse relatively short and improve the axial resolution.
15
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The lateral resolution affects measurements across the azimuth plane, which is perpendicular to the direction of the beam. The lateral resolution is governed by different physical laws from the axial resolution and is poorer than the axial resolution. Among the factors that affect the lateral resolution are the quality of the beam and the size of the side lobes (see Fig. 1.11). In the process of optimizing the beam quality, the aim is to have a thin main lobe and small side lobes. The lateral resolution perpendicular to the direction of the beam is poorer than the axial resolution. Measurements made in the axial direction are more precise than those made across the image perpendicular to the beam.
Measurement Generally, when we measure a distance in the axial direction, we put one electronic calliper on an echo and move the next calliper to another echo to assess the distance between the two. However, we are not actually measuring the distance between the two, but rather the time it takes for a pulse to travel from the transducer to the structure closest to the transducer and to the structure further away. So when we measure a distance, our calculations are based on time rather than on a physical distance. We have to take into account that of the two, axial resolution is better than lateral resolution. If we measure in the plane perpendicular to the beam, the beam quality will influence our measurement. A relatively thick beam will make the endpoint of a structure appear blurred and make the distance between two points appear slightly larger than in reality. This phenomenon has a consequence for the measurements across the screen, for example the occipitofrontal diameter of the skull and even the femur length.8
Time Gain Compensation
16
When a pulse propagates through the tissue, it will gradually lose its energy. This loss is caused mainly by power absorption and to a smaller extent by reflection, scattering and geometric spread. This process takes place as the pulse travels away from the transducer and as the echo is on its way back to the transducer. The absorption of ultrasound energy increases with increasing frequency. The attenuation causes the reflected echoes from structures deep in the tissue to be weaker than those emerging from nearby structures. If we do not compensate for this phenomenon, our image will appear imbalanced (Fig. 1.14). The speed of sound in the human tissue is constant; the echoes emerging from the deeper areas arrive later than those from the upper structures. Thus, we may compensate for the loss of power from the late-arriving echoes by inserting a time variable gain in the receiver amplifier. This is called time gain compensation (TGC). The basic TGC is preset in modern machines, but we may have to adjust manually to fine-tune our image. Usually it is possible to make an overall adjustment of the gain as well as adjustments affecting the local area ranging from the near to the far field of the image. The setting of the TGC also affects our measurements and it is an important part of the training to learn how to set it correctly. A TGC adjusted too high will produce blurry edges and measurement of distance between structures will be longer than in real life.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Physics and instrumentation
Fig. 1.14 A section through the planum biparietale. The area close to the transducer is correctly adjusted while the distal area has hardly visible low-energy echoes as a consequence of the insufficient compensation for the attenuation of sound emerging from the deeper sections of the tissue.
The fine-tuning of our image using the TGC is one of the most important adjustments we make. The grey-scale level of the image ought to appear well balanced from the upper to the lower part of the image. The adjustment must aim at achieving the full register of grey tones between the black areas and the white highlights. The setting of the TGC has an influence on our measurements.
Artifacts Artifacts in ultrasound imaging may be distortions or any form of incorrect appearance affecting an image and giving misleading information as we try to interpret from the image. The imaging process using ultrasound technology may cause numerous artifacts that we have to be aware of. Some of the main artifacts are as follows:
• Edge shadows • Attenuation shadows • Enhancement • Reverberations. Edge Shadows In obstetrics, edge shadows are mainly observed during scanning of the fetal head. When the sound enters a round structure such as the fetal head it emerges from tissue with a velocity of 1540 m/s through the bone of the fetal skull that has a sound velocity of ≈3000 m/s. The sound will then be refracted and leave a shadow-like impression on both sides of the fetal skull (Fig. 1.15).
Attenuation Shadows Bone absorbs ultrasound and the echo amplitude will then be reduced behind ossified structures. This is frequently observed during fetal heart scanning when the image of the heart may be in the shadow of the ribs or the vertebrae. In gynaecology, dense structures such as myomas may to a lesser degree reduce the
17
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 1.15 Edge shadows. On both sides of the fetal skull, the ultrasound beam is refracted and then leaves a shadow below.
amplitude of the sound. Such shadows may give us information about the structure that is causing the shadow.
Enhancement Enhancement is the opposite of attenuation shadow. The phenomenon may be seen behind cysts (Fig. 1.16). This artifact may also be used to characterize the structure causing the enhanced area.
18
Fig. 1.16 Simple cyst demonstrating the enhancement artifact. The sound that is passing through the cyst is not attenuated in the same degree as the sound passing through the tissue on the right and left side of the cyst. Therefore, the amplitude of the sound immediately below the cyst is higher than on the sides and consequently it looks as if the area below the cyst has been enhanced by selectively turning up the time gain compensation.
✩✩✩✩✩✩✩✩✩✩✩ ✩
ReverberationS Physics and instrumentation
The artifact referred to as reverberation or multiple reflections is common and may distort the image in several ways. The basic principle of making an image using sound is to send a pulse, wait for the pulse to return as an echo and then a dot is put on the screen corresponding to the time the pulse has taken to travel on its way down to the reflecting structure and back again. A pulse may also be reflected back and forth between interfaces before returning to the transducer. The extra travel time this process takes will cause the false echoes to arrive later than echoes emerging directly from the original structure so that then several lines on the image may present themselves as copies of the original (Fig. 1.17). Such reverberations may easily be recognized. Layers of fat may also cause reflections and reverberations in the image that presents itself as a diffuse cloud of noise and is thus not so easy to recognize as artifacts. The lower mechanical impedance of sound in fat (sound velocity ≈1420 m/s) and muscle tissue (sound velocity ≈1560 m/s) may cause reverberations. Reverberations may be complex in their appearance and not always easy to detect. Using a curved array transducer may reduce the effect of reverberations. The echoes are scattered out of the field, which causes the curved array to have a good near-field view.
Main echo
Reverberation
Object
Image
A
Main echo Reverberation
Object
Image
B Fig. 1.17 Two examples of reverberations. In the upper panel (A) the main echo schematically is represented by a blood vessel. A ‘copy’ of these echoes may be found as reverberations at a lower level. Fatty tissue may also cause reverberations which may show up as a diffuse haze (B).
19
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
References 1. Bom N, Lancée CT, v Zwieten G, Kloster FE, Roland J. Multiscan echocardiography I. Technical description. Circulation 1973;48(5):1066–1074 2. Desch CH, Sproule DO, Dawson WJ. The detection of crack in steel by means of supersonic waves. J Iron Steel Inst 1946; 153:319 3. Donald I, Wicar WA, Brown TG. Investigation of abdominal masses by pulsed ultrasound. Lancet 1958;1:1188 4. Firestone FA.The supersonic reflectoscope, an instrument for inspecting the interior of the solid parts by means of sound waves. J Acoustic Soc America 1946;17:314 5. Edler H, Hertz CH. The use of ultrasonic reflectoscope for the continuous recording of movements of heart walls. Kgl Fysiograph Saellskap Lund Förh 1954;40:23 6. Edler I. Ultrasound cardiography. The diagnostic use of ultrasound in heart disease. Acta Med Scand 1955;308(suppl):32
7. Howry, DH, Bliss WR. Ultrasonic visualisation of soft tissue structures of the body. J Lab Clin Med 1952;40:579 8. Jago JR, Whittingham TA, Heslop R. The influence of ultrasound scanner beam width on femur length measurements. Ultrasound Med Biol 1994;20(8):699–703 9. Kratochwil A. Ultraschalldiagnostik in Geburtshilfe und Gynäkologie. Georg Thieme Verlag, Stuttgart, 1968 10. Krause W, Soldner R. Ultraschallbildverfahren (B-Scan) mit hoher Bildfrequenz für medizinische Diagnostik. Elektromedica 1967;4:1 11. Sundén B. On the diagnostic value of ultrasound in obstetrics and gynæcology. Acta Obstet Gynaecol Scand 6(suppl):114 12. Wild JJ, Reid JM. Application of echoranging techniques to the determination of structure of biological tissues. Science 1952;28:226–230
Further reading Angelsen B. Ultrasound Imaging. Waves, Signals, and Signal Processing. Basic Principles, Wave Generation, Propagation, and Beam forming in Homogenous Tissue. Vol I. Emantec, Trondheim, Norway, 2000. www.ultrasoundbook.com Angelsen B. Ultrasound Imaging. Waves, Signals, and Signal Processing. Propagation and Scattering in Homogenous, Nonlinear Tissue with Contrast Agent. Imaging and Doppler Measurement. Vol II. Emantec, Trondheim, Norway, 2000. www.ultrasoundbook.com Hatle L, Angelsen B (eds). Doppler ultrasound in cardiology. Physical principles and clinical applications. Lea and Febiger, Philadelphia, 1986 Kremkau FW. Diagnostic ultrasound. Principles and Instruments, 7th edn. WB Saunders, Philadelphia, 2006 Maulik D (ed). Doppler ultrasound in obstetrics and gynecology. Springer, New York, 1997 Woo J A short history of the development of ultrasound in obstetrics and gynecology. www.ob-ultrasound.net/history1.html
20
2 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Biological effects and safety aspects Francis A Duck
Abstract Full exploitation of diagnostic ultrasound requires careful consideration of potential risks. Ultrasound causes small increases in tissue temperature. Whilst commonly of only fractions of a degree, some conditions can give temperature increases which could approach 10°C, particularly at exposed bone during Doppler modes. Safety thresholds are derived from studies into thermal teratology. Tissues can also be damaged mechanically by gas body activation, although this mechanism appears to be of very minor concern for most obstetric applications. Another bioeffects mechanism is radiation pressure, whose presence is demonstrated by acoustic streaming. Epidemiological studies have yet to demonstrate unequivocally any causal relationship between exposure to ultrasound in utero and developmental changes, although all published studies relate to earlier, low-intensity exposure regimens. There is yet insufficient understanding of the interaction between ultrasound and the developing embryo and fetus at all stages in pregnancy, and this lack of detailed knowledge still advises care and prudence in the use of ultrasound in obstetrics. On-screen safety indices may assist clinical users to make improved safety judgements.
Keywords Epidemiology, exposure, gas body activation, mechanical index, non-thermal effects, regulations, thermal effects, thermal index, ultrasound safety.
Introduction Diagnostic ultrasound has an enviable reputation for safety, and the lack of evidence of significant hazard and consequent risk has been one of the key factors which has established it as the pre-eminent imaging method in obstetrics. Whilst the severe biological effects associated with x-radiation became abundantly clear
21
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ very early, ultrasound gives no obvious evidence of tissue damage until very high intensities are used. However, it is now appreciated that even diagnostic levels of ultrasound can cause small but potentially significant tissue responses. Therefore, both the design and clinical use of equipment which uses ultrasound for diagnosis must be subject to the general rule that the diagnostic benefit must be sufficient to outweigh the potential for harm – a risk/benefit judgement has to be made. Until about a decade ago, manufacturers designed ultrasound scanners for particular applications – for example for cardiology, ophthalmology, obstetric or vascular scanning. Regulation in the USA restricted output intensity from obstetric scanners to be about eight times lower than the highest available. These limits served also to constrain output from equipment available in other countries. In the early 1990s regulations in the USA were relaxed, in part to allow Doppler modes to be used in obstetrics, allowing the highest output to be used for all applications. Manufacturers now sell equipment for obstetric use that can operate at levels previously reserved only for peripheral vascular applications. They are required also to display values of safety indices, which reflect the changing output of the machine as it is used clinically for different applications and patients. These values of the mechanical index (MI) and thermal index (TI) are intended to allow users to make a risk/benefit judgement. In order to do this, clinicians and other users of the equipment must know of the potential hazards inherent in using ultrasound, and be advised about the interpretation of the safety indices. This chapter is intended to introduce the reader to these issues. More detailed information may be found in other publications2,10,11 and in a series of safety tutorial articles which are available on the web page of the European Federation of Societies for Ultrasound in Medicine and Biology (www.efsumb.org/ecmus. htm) and the International Society for Ultrasound in Obstetrics and Gynecology (www.isuog.org).
Acoustic Output of Diagnostic Ultrasound Scanners
22
Exposure to ultrasound at sufficiently high levels is capable of causing lethal damage to tissues. Knowledge of acoustic output serves to ensure that diagnostic exposures are limited to levels that may be used safely. Broadly, two aspects of the ultrasound beam are measured, which guide answers to two questions: how much energy is in the beam and how big are the pulses of ultrasound? The energy may be described in terms of total acoustic power (energy per second) or acoustic intensity (power through a specific area). Both of these are related to the temperature rise in tissue. Commonly the spatial-peak temporalaverage intensity is quoted rather than the acoustic power (Ispta, in milliwatts per square centimetre). The size of the pulse is usually measured by its peak rarefactional pressure, pr, in megapascals (MPa). One megapascal is approximately equal to 10 atmospheres. This quantity is related to the potential for gas body activation or acoustic cavitation. Normally, tables giving Ispta and pr present the highest values reached anywhere, and these are found typically near to the focus of the ultrasound beam.
✩✩✩✩✩✩✩✩✩✩✩ ✩ Table 2.1 Summary of median and maximum values of spatial peak, temporal average intensity, Ispta, from a 1998 survey22 Maximum value, mW cm−2
A- or M-mode
81
604
Real-time B-mode
94
1330
Colour Doppler
328
2030
Spectral Doppler
1420
7500
There have been a number of published surveys of output, and these have been summarized by Whittingham.22 He shows that the peak rarefaction pressure used for all modes is about the same, with median about 2.5 MPa and maximum about 5 MPa, whether operating in imaging mode, M-mode, spectral Doppler or Doppler imaging. Thus gas body effects are equally likely to occur whatever mode is in use. The situation is different when considering Ispta. This is shown in Table 2.1, which summarizes the median and maximum values reported by Whittingham for a 1998 survey. Two remarks may be made. First, on average, intensities become higher as the mode is changed from M-mode, through B-mode and colour Doppler, to become highest in spectral Doppler mode. This trend occurs in both the maximum and median values. Therefore, on average, the highest intensities and hence probably the greatest heating are associated with Doppler modes, particularly spectral Doppler. However, the second remark is perhaps of greater general importance. The overlap between peak intensities in each mode is very large. It is possible to find B-mode intensities on one scanner which exceed the highest Doppler intensities on another. Moreover, for any selected transducer it is often true that the intensity used for Doppler imaging exceeds that used for spectral Doppler. For this reason it is now becoming common only to give general advice on safety rather than to give specific advice for the use of pulsed Doppler. Surveys have also demonstrated a trend towards increased output during the past 20 years or so. Increases have occurred in output from ultrasound scanners used for obstetrics, partly due to the changed regulations in the USA, and partly because of a general trend to design scanners that operate towards the top end of the available performance range.
Biological effects and safety aspects
Median value, mW cm−2
Tissue Warming by Diagnostic Ultrasound The fundamental biochemical processes controlling the behaviour and function of living cells depend strongly on temperature. Mammalian tissues can survive and operate effectively within quite a small range of temperatures, and elevated temperatures sustained for extended times may alter cell function and can result in cell death. Temperature elevation is a potent teratogen, and thus it is appropriate to establish the extent by which ultrasound scanners are capable of increasing temperature within tissue.
23
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
24
Ultrasound pulses lose energy as they penetrate tissue, a fact ultimately limiting the ability to scan to great depths. Almost all the energy lost from the ultrasound wave is deposited as heat in the tissue and this causes small rises in temperature in this tissue.3 The temperature rise is affected by a number of factors. The first is the energy in the beam: the higher the intensity, the greater the heating. The energy distribution is also important, for example whether the beam is narrowly focused, and whether it is scanned. The thermal and acoustic properties of tissue also determine the temperature elevation. Amongst these properties, the two most important are the acoustic absorption coefficient of the tissue and its blood perfusion rate. Bone is the tissue which absorbs ultrasound energy to the greatest extent and so, wherever the ultrasound scan plane intercepts bone, it will be here that the temperature rise will be most rapid and of greatest elevation. In obstetric scanning, the developing fetal skeleton warms first and to the highest temperature. As the fetal bones mature throughout gestation, the absorption of ultrasound increases, and so does the temperature they may attain (see Fig. 2.1). Blood perfusion controls temperature elevation, returning local temperature towards the core temperature. This effect is seen most strongly near large blood vessels. Fetal tissue is adequately, though not strongly, perfused, and so this may not be a significant factor in controlling ultrasound-induced warming. Tissues may also be warmed as a secondary effect from an elevated temperature in a nearby structure. This is important when considering heating of fetal central nervous tissue, which is known to be particularly sensitive to thermal damage.3 Whilst fetal brain itself has a relatively low ultrasound absorption coefficient, the brain tissue which lies alongside the skull heats as a secondary effect of skull heating. It is therefore the bone temperature that is critical for safety judgements. The second situation when secondary heating may be important is transducer self-heating. Ultrasound transducers heat because the electrical power is converted rather inefficiently into ultrasound power, the remaining power being dissipated as heat in the transducer. Tissues close to the transducer can have their temperature raised by several degrees, by contact heating. Whilst this probably is not important for a skin-coupled transducer, a transducer for transvaginal scanning could, in principle, pose a problem. International standards for transducer design now limit the contact temperature rise to 6°C, and the contact temperature to 43°C.9 Currently available clinical scanners are capable of causing temperature elevations in bone which approach 10°C, and in soft tissues of about 3°C, when operating in pulsed Doppler mode. Whilst these results relate to rather extreme experimental conditions, which omit the protection given by any overlaying tissue layers, they emphasize that present clinical scanners are easily able to cause significant heating within tissues when operated at the extreme upper limits of output. One example of bone heating is shown in Figure 2.1, which shows measured temperature rises in samples of human fetal vertebrae, exposed to ultrasound in vitro.5 In this case the frequency was 3 MHz, and the acoustic power, 50 mW, can be easily achieved in vivo with modern scanners.
✩✩✩✩✩✩✩✩✩✩✩ ✩ 2.0
1.6
39 weeks
Temperature rise, C
1.4 1.2 1.0 0.8 0.6 0.4
14 weeks
0.2 0.0
0
50
100
150 200 250 Time, seconds Fig. 2.1 Measured surface heating curves for two human fetal vertebrae, exposed in vitro to 3 MHz focused ultrasound at a diagnostic power (50 mW); 14 weeks and 39 weeks gestation. Redrawn from reference 5 with permission.
From the scientific evidence of the effects of hyperthermia, it is generally accepted that tissues containing a large component of actively dividing cells are particularly sensitive to heat. Abnormalities in cell pathology and biochemical processes can occur following an increase in temperature above normal basal levels. There are critical periods during gestation when the embryo and fetus are particularly sensitive to thermal effects. During formation of the neural plate and closure of the neural tube, animal studies have demonstrated that elevated temperature can result in neural defects, retarded brain development, exencephaly and microphthalmia. Exposure at preorganogenesis stages can result in cardiovascular abnormalities, whilst later heating can affect skeletal and visceral systems. There is now a substantial literature on thermal teratology7 which suggests that an elevated temperature of 2–2.5°C, if sustained for an extended period, is sufficient to cause major developmental abnormalities, at least in small mammals. Recognizing the difficulty of transferring animal data to humans, these data still serve as a reminder that remarkably small changes in fetal temperature are capable of causing developmental changes of major significance. It is not possible to interpret thermal bioeffects studies without considering the time over which the temperature elevation is generated and the time for which it is sustained. Review of the thermal teratology literature has led the World Federation for Ultrasound in Medicine and Biology to recommend that ‘a diagnostic exposure that elevates embryonic and fetal in-situ temperature above 41°C (4°C above normal temperature) for 5 minutes or more should be considered potentially hazardous’.11,12 Of course, clinical scanning commonly takes place in a manner such that regions are not examined continuously for more than a few seconds at a time. Exceptions to this are most probably in cardiovascular studies, when the
Biological effects and safety aspects
1.8
25
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
26
time variation of a particular region is of interest. Exposed bone can approach a steady-state temperature within about 30 seconds (see Fig. 2.1), soft tissue somewhat longer. Assuming that bone may be exposed anywhere within the examined volume, it is prudent to take particular care to limit output if the examination requires the probe to be stationary for more than 30 seconds.
Non-Thermal Mechanisms and their Safety Implications Ultrasound pulses can alter cells in other ways than by heating the tissue. Broadly, heating changes rates of biochemical reactions, whereas the damage from mechanical effects is primarily to the cellular and tissue structures. Non-thermal mechanisms fall into two classes: those which involve ‘gas bodies’ and those which do not.
Gas Body Effects of Diagnostic Ultrasound It is now accepted that diagnostic ultrasound does not cavitate soft tissues. That is, microscopic gas bubbles are not generated within tissue by diagnostic ultrasound pulses under normal conditions. However, cells and tissue can be damaged when exposed to diagnostic ultrasound pulses if they lie close to a region of gas already contained within tissue. The shear forces generated at the tissue/gas interface may be sufficient to cause damage. Known examples include the rupture of capillaries at the lung surface, resulting in extravasation of blood components into the extracellular space, and the formation of petechiae in the intestine. Gas bubble contrast agents are being introduced into the practice of clinical ultrasound and similar shear forces are created at the surface of these agents when exposed to ultrasound. A process known as ‘sonoporation’ can occur, which is the transient opening of ‘pores’ or gaps in cell membranes, allowing the passage of larger biomolecules into the intracellular space. At sufficiently high acoustic pressures, haemolysis occurs. The response of gas-filled structures to an ultrasound field has been termed ‘gas body activation’ because it differs in many respects from acoustic cavitation. One common factor, however, is that all effects are related to thresholds in acoustic pressure. Judgements about safety therefore depend on an estimate of these thresholds, and a comparison with estimates of acoustic pressure in vivo. The displayed MI is intended to inform these judgements. In the context of obstetric ultrasound, much of the safety discussion about gas bodies has little relevance. Cavitation is not initiated in soft tissues. There are no pre-existing gas bubbles within the uterus so no gas body activation can occur. It is appropriate to use caution when using gas bubble contrast agents for hysterocontrast salpingography, using the displayed MI to limit the possibility of inertial cavitation of free bubbles released when the contrast agent is destroyed. Present advice is to avoid the use of intravenous contrast agents during pregnancy, because it is yet to be determined whether fragments may pass the placental barrier and enter the fetal circulation.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Other Mechanical Bioeffects Mechanisms
Evidence from Epidemiology This section summarizes briefly the outcome of the more important epidemiological studies into ultrasound exposure in utero. Fuller reviews may be found elsewhere.10 There have been three well-managed case–control studies into ultrasound and childhood malignancies, all of which were of sufficient size to have statistical validity. No association between childhood malignancy was found in any study. Some early studies suggested an association between exposure and birthweight or subsequent growth, but subsequent studies have been unable to demonstrate such an association. In view of the conflicting evidence presented by these studies, the present consensus is that there is no association between exposure to ultrasound and birthweight. A range of neurological functions has been examined and no association between ultrasound exposure in utero and subsequent hearing, visual acuity, cognitive function or behaviour has been found. An association with dyslexia reported earlier14 was not found in later larger studies.15,16 Studies have suggested a possible association between ultrasound exposure and handedness,17 with a gender-biased tendency towards left-handedness.18 At present, there is no explanation of this association and no firm conclusions can be drawn.19 A controlled randomized study from Australia indicated the relationship between repeated Doppler examinations and growth restriction in the fetus20 but the same research group could not find any effect on postnatal follow-up of the children.21 In summary, there is no independently verified evidence to suggest that ultrasound exposure in utero may cause an alteration in the development and growth of the fetus. All studies have either proved to be negative, or, when positive findings have appeared, they have not been verified or have been shown to result from poorly designed studies. New studies will be difficult to structure, because of the difficulty of finding an unexposed control group, resulting from the widespread use of ultrasound during pregnancy throughout the world. It is necessary to sound
Biological effects and safety aspects
A brief mention should be made of a further means of interaction between ultrasound and tissue – radiation pressure. Ultrasound waves push the material through which they pass. If the medium is a liquid, such as amniotic fluid or blood, the result is movement of the liquid. This is called acoustic streaming and may sometimes be observed with modern scanners. Whilst streaming itself is not apparently a hazard, the radiation pressure causing it is also exerted on all tissues within the beam. The forces are small but it is important to recognize that little is known of their effects. Radiation pressure can induce neurological and auditory effects at sufficiently high levels, and some cells can respond to the effects of external shear forces. Caution is needed here as elsewhere as diagnostic techniques are being developed.
27
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ a note of caution, however. There are no studies which have explored outcomes following exposure to pulsed Doppler or Doppler imaging, where intensities and powers are known to be higher than in pulse-echo imaging. While the results of epidemiological studies so far are comforting, they cannot be used to support an argument that it is safe to extend exposure in utero to higher levels. Further epidemiological studies focused specifically on Doppler exposure would be needed before such confidence can be claimed.
The Management of Safety The successful management of safety in medical ultrasound practice operates at several levels. It involves manufacturers, users and international and national professional and regulatory bodies. Manufacturers must comply with standards and regulations intended to make the equipment safe. Users must make sure that they use the equipment in an appropriate and safe manner. Basic scientists provide the evidence from which safety judgements are made, and which informs the recommendations of national and international bodies.4
The Users' Responsibility Clinicians using ultrasound equipment should have specific training in safety aspects of its use. From this training they are expected to be able to use the real-time safety indices to manage the machine settings with appropriate attention to safety. A summary of the meaning and function of these safety indices follows.
28
Thermal indices Since it is impossible for the user to know the temperature increase in the body, thermal indices (or TI) have been developed to provide guidance. A TI is a rough estimate of the increase in temperature that occurs in the region of the ultrasound scan. A TI of 2.0 suggests that a temperature rise may reach 2°C, if the transducer is held stationary for long enough. There are three thermal indices – one for soft tissue (TIS), one for bone at depth (TIB) and one for bone at the surface (TIC). These TI values are more helpful than any other information available to the user, because they are informative about the state of the machine output as it is being used. However, the methods for calculating TI include some important simplifications and as a result the true temperature rise may be somewhat higher or lower than the value indicated, perhaps by as much as a factor of 2. Whilst the displayed TI values are the best information currently available, they should be used only as rough, rather than absolute, indicators of the thermal hazard. They may be useful, however, to identify which machine settings are more likely to generate significant temperature increases in tissue, so that particular care may be made to avoid their use for critical examinations. On current equipment, TI values can usually be found around the edge of the scanner screen, often in the top right corner, indicated by the letters TIS, TIB or TIC
✩✩✩✩✩✩✩✩✩✩✩ ✩
Mechanical index At high enough pressure amplitudes, cavitation becomes ‘inertial’ and its potential for damage increases considerably. An analysis of inertial cavitation has resulted in the formulation of a mechanical index (MI). The MI was developed to quantify the likelihood of onset of inertial cavitation, for which a threshold of MI 0.2 if bubbles pre-exist has been suggested. The MI is proportional to the peak rarefactional pressure, and has a weak frequency dependency. It has since been related also to thresholds for lung damage, and contrast behaviour. The MI is displayed on the scanner screen together with, or instead of, the TI. For applications in obstetrics and gynaecology, the MI is of use primarily when contrast agents are to be used.
Biological effects and safety aspects
followed by a number which changes when the scanner controls are altered. The most cautious approach is to display TIB most of the time. TIS should be displayed only if there is no bone, developing bone or cartilage anywhere in the region being scanned.
The Manufacturers' Obligations The Medical Device Directive in Europe and the Food and Drug Administration (FDA) regulations in the USA both make demands of manufacturers regarding the safe design and performance of their scanners and provision of output information to users. Europe sets no upper limit to the allowed output from ultrasound equipment; the USA, through the FDA, has such limits in place. Intensity (Ispta) must not exceed 720 mW cm–2 and the MI must not exceed 1.9. In order to use these output levels, manufacturers must provide a real-time display of safety information by means of the TI and MI.1,9 Manufacturers must also comply with international standards as set by the International Electrotechnical Commission for electrical and thermal safety.9
Safety Practice Keeping up to date with current thinking on ultrasound safety and risk minimization allows clinicians to make the best decisions on how to maximize the benefit to the patient whilst reducing the risk. Present estimates of risk encourage clinicians primarily to use equipment in such a way as to maximize the opportunity to make a good diagnosis. There is more chance of causing harm by misdiagnosis than through heating or cavitation. With this in mind, the following sections summarize the particular safety considerations relating to obstetric scanning early and late in pregnancy, and to the scanning of patients with fever.
Diagnostic Ultrasound During the First Trimester Probably the most critical question concerns the exposure of the embryo during the early stages of pregnancy.6 This is a period of rapid development and complex biochemical change, which includes organ creation and cell migration.
29
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ There is widespread evidence that during this period the developing embryo is particularly sensitive to external agents, whose effect on subsequent development may range from fatal developmental malformation to minor and subtle biochemical disturbance. It is because of this sensitivity that the ISUOG13 and EFSUMB 8 have recommended caution with the use of Doppler in early pregnancy. The EFSUMB have advised that ‘until further scientific evidence is available, investigations using pulsed or colour Doppler should be carried out with careful control of output levels and exposure times’.8 This statement recognizes both that there are gaps in our knowledge and understanding of the way in which ultrasound may interact with embryonic tissue, and that any adverse effect may result in developmental problems because of the particular sensitivity of the tissue at this time. Moreover, this sensitivity may be cyclic, with some tissues being sensitive only during particular time-bands of rapid cell development and differentiation. Heat is a teratogen and any temperature increase from the absorption of ultrasound can disturb subsequent development, if of sufficient magnitude and maintained for sufficiently long. Fortunately, the tissue with the greatest tendency to heat, bone, only starts to condense at the end of the first trimester. In the absence of bone, current evidence suggests that temperature elevations greater than 1.5°C are unlikely to occur within embryonic tissue at present diagnostic exposures. This suggests that significant developmental changes probably do not occur. The kinetics of biochemical processes are known to be temperature sensitive, however, and little research has investigated the influence of small temperature changes induced locally on membranes and signal transduction pathways. There is no evidence for cavitation, as there are no gas bubbles to activate within the uterus. The effects of radiation pressure on the developing embryo and fetus are unknown. Thus, although our current understanding suggests that present practice is safe, there is sufficient uncertainty about the detailed interaction processes to advise caution.
Scanning During the Second and Third Trimesters
30
Bone ossification is the main developmental change during the second and third trimesters of pregnancy that is of significance to ultrasound safety. As bone condenses, it forms local regions of high ultrasound absorption. Ultrasound energy is absorbed more by the fetal skeleton than by fetal soft tissues, and so it is preferentially heated. This is important in part because soft tissues alongside this bone will also be warmed by thermal conduction, reaching a higher temperature than expected from ultrasound absorption alone. Neurological tissues are known to be particularly sensitive to temperature rise, and the development of brain tissue, and of the spinal cord, could be affected if adjacent skull or vertebral bone were heated too much. Within the fetal haematopoietic system, the bone marrow is the main site of blood formation in the third trimester of pregnancy. Neither cavitation nor gas body activation will occur because of the absence of nucleation sites and pre-existing bubbles.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Obstetric Scanning on PatIents with Fever
Conclusion Ultrasound has an enviable record for safety. Indeed, it is partly its lack of toxicity which has allowed it to grow to the point where ‘more than one out of every four imaging studies in the world is an ultrasound study’. All the evidence points to the conclusion that past and current practice presents no actual risk to the patient, and may be considered as safe. Nevertheless, there is ample evidence that modern scanners, designed in accordance with national and international standards and regulations, can warm tissues by several degrees under some circumstances. If gas bubbles or other pockets of gas lie in the ultrasound field, the tissues may be damaged from stresses caused by cavitation-like oscillations. Current scanning equipment displays safety indices, allowing users greater feedback for safety judgements to be made. Safety in diagnostic ultrasound depends both on manufacturers to produce equipment that is safe to use, and on the users of ultrasound in managing their scanning practice.
Biological effects and safety aspects
It is noted in the WFUMB recommendations12 that ‘care should be taken to avoid unnecessary additional embryonic and fetal risk from (heating due to) ultrasound examinations of febrile patients’. If a mother has a temperature, her unborn child is already at risk of maldevelopment as a result of the elevated temperature. This being so, it is sensible not to increase this risk unnecessarily. This does not mean withholding obstetric scanning from patients if they have a temperature. The methods of limiting exposure, including minimizing the TI, limiting the duration of the scan and avoiding casual use of Doppler techniques, should be employed with particular vigilance in these cases.
References 1. American Institute for Ultrasound in Medicine/National Electrical Manufacturers' Association. UD 3-1992: standard for real-time display of thermal and mechanical acoustic output indices on diagnostic ultrasound equipment. American Institute for Ultrasound in Medicine/National Electrical Manufacturers' Association, Rockville, MD, 1992 2. Barnett SB, Kossoff, G (eds). Safety of diagnostic ultrasound: progress in obstetric and gynaecological sonography series. Parthenon, London, 1998 3. Barnett SB, Rott H-D, ter Haar GR, Ziskin MC, Maeda K. The sensitivity of biological tissue to ultrasound. Ultrasound Med Biol 1997;23:805–812
4. Barnett SB, ter Haar GR, Ziskin MC, Rott H-D, Duck FA, Maeda K. International recommendations and guidelines for the safe use of diagnostic ultrasound in medicine. Ultrasound Med Biol 2000;26:355–366 5. Doody C, Porter H, Duck FA, Humphrey VF. In vitro heating of human fetal vertebra by pulsed diagnostic ultrasound. Ultrasound Med Biol 1999;25:1289–1294 6. Duck FA. Is it safe to use diagnostic ultrasound during the first trimester? Ultrasound Obstet Gynecol 1999;13: 385–388 7. Edwards MJ. Hyperthermia as a teratogen: a review of experimental studies and their clinical significance. Teratogen Carcinogen Mutagen 1986;6:563–582
31
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
32
8. European Federation of Societies for Ultrasound in Medicine and Biology. Clinical safety statement for diagnostic ultrasound. 2008: www.efsumb.org 9. International Electrotechnical Commission 2002 IEC Standard 60601-2-37: medical electrical equipment – particular requirements for the safety of ultrasound medical diagnostic and monitoring equipment. International Electrotechnical Commission, Geneva 10. Salvesen KJ, Eik-Nes SH. Ultrasound during pregnancy and birthweight, childhood malignancies and neurological development. Ultrasound Med Biol 1999;25:1025–1031 11. Ter Haar G, Duck FA (eds). The safe use of ultrasound in medical diagnosis. British Medical Ultrasound Society/British Institute of Radiology, London, 2000 12. World Federation for Ultrasound in Medicine and Biology Symposium on Safety of Ultrasound in Medicine. Conclusions and recommendations on thermal and non-thermal mechanisms for biological effects of ultrasound. Ultrasound Med Biol 1998;24(suppl 1):1–55 13. Abramowicz JS, Kossoff G, Marsal K et al. Safety statement, 2000 (reconfirmed 2003). International Society of Ultrasound in Obstetrics and Gynecology (ISUOG). Ultrasound Obstet Gynecol 2003;221:100 14. Stark CR, Orleans M, Haverkamp AD et al. Short- and long-term risks after exposure to diagnostic ultrasound in utero. Obstet Gynecol 1984;63:194–200
15. Salvesen KA, Bakketeig LS, Eik-Nes SH et al. Routine ultrasonography in utero and school performance at the age 8–9 years. Lancet 1992;339:85–89 16. Salvesen KA, Vatten LJ, Jacobsen G et al. Routine ultrasonography in utero and subsequent vision and hearing in primary school age. Ultrasound Obstet Gynecol 1992;2:243–247 17. Salvesen KA, Vatten LJ, Eik-Nes SH. Routine ultrasonography in utero and subsequent handedness and neurological development. BMJ 1993;307:159–164 18. Kieler H, Axelsson O, Haglund B et al. Routine ultrasound screening in pregnancy and the children's subsequent handedness. Early Hum Dev 1998;2:233–245 19. Salvesen KA, Eik-Nes SH. Is ultrasound unsound? A review of epidemiological studies of human exposure to ultrasound. Obstet Gynecol 1995;4:293–298 20. Newnham JP, MacDonald J, Hall C. Characterisation of the possible effect on birthweight following frequent ultrasound examinations. Early Hum Dev 1996;45:203–214 21. Newnham JP, Doherty DA, Kendall GE et al. Effects on repeated ultrasound examinations on childhood outcome up to 8 years of age: follow-up of a randomized controlled trial. Lancet 2004;364: 2038–2044 22. Whittingham TA. Acoustic outputs of diagnostic machines. In: Ter Haar G, Duck FA (eds) Safety of medical diagnostic ultrasound. British Institute of Radiology, London, 2000, pp 16–91
3 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Scanning techniques in obstetrics and gynaecology Ilan E Timor-Tritsch Ana Monteagudo
Abstract In the last 25 years ultrasonography became the ‘right hand’ of modern obstetricians and gynaecologists. This was possible due to the advances of ultrasound transducer technology and the ‘explosion’ of computer science. In order to realize the power of ultrasound diagnostics and the ultrasound-guided procedures, the astute provider of women's health has to understand how and when to apply the different scanning techniques. This chapter enumerates the different ways in which ultrasound is used in obstetrics and gynaecology. However, it starts with the very basic concepts of how to set up a simple but efficient ultrasound examining room and the ways to approach scanning the everyday patient in a simple office setting. The text leads the reader through the scanning of specific organs as well as some of the mandatory protocols of obstetric and gynaecological examination. Certain more prevalent clinical entities are mentioned in greater detail than others. The interested reader should be clear that ultrasound technology like any other technology based upon electronics, is developing rapidly and without any doubt, by the time these pages are read, there will be new and exciting ways to help us provide better, faster and more accurate diagnoses for our patients. Constant reading and updating our knowledge in ultrasonography is mandatory.
Keywords Colour Doppler, gynaecology, obstetrics, transabdominal ultrasound, transvaginal ultrasound, ultrasound.
Introduction The subject of scanning techniques in obstetrics and gynaecology can be presented from various angles. One way is to start with the purely physics aspects of
33
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ scanning. This, however, may deter some clinicians from reading through this part of the book. The other angle for introducing the ways we scan in the office and in the dedicated ultrasound laboratories is to describe and discuss the practical aspects of the daily use of ultrasound in its clinical set-up. We decided to take this route, thinking that it has more practical value. An additional decision had to be made: to avoid discussion of older scanning techniques which were ‘cutting edge’ in their time, but which have no practical use at the time of this writing.
General Aspects We will deal with the basic requirements as far as the ultrasound equipment, orientation and aspects of the technicalities involved in conducting the gynaecological ultrasound examination are concerned. If additional information is needed, the reader is referred to some of the more detailed resources in the literature.6,8,14,16,17,20,28,33,35,40,57
Empty or Full Bladder It is now known almost to everyone engaging in obstetric and gynaecological scanning that transabdominal ultrasound is performed most of the time with a full bladder. The full bladder serves as an acoustic window and pushes the bowel out of the sound path (Fig. 3.1). However, transvaginal sonography is best performed with an empty bladder, which enables the pelvic organs to reach a closer proximity to the tip of the high-frequency transvaginal probe. The difference between the two approaches lies in the different physical properties of the transabdominal and transvaginal probes.10,22,25,27,48,50 The transabdominal probe produces a more or less panoramic view of the pelvis, showing the interrelationship of the major anatomical structures within the pelvis and their possible pathology. The transvaginal probe, however, is able to furnish a more targeted image of the organ of interest. The transvaginal probe,
34
Fig. 3.1 Orientation using transabdominal scanning. (A) Directions in the sagittal plane. (B) Directions in the transverse plane.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Scanning techniques in obstetrics and gynaecology
therefore, will permit an effective imaging usually to not more than 7–10 cm in depth. Lately more advanced probe technologies as well as signal processing have enabled deeper penetration with minimal loss of resolution. The bowel interferes with transvaginal sonography mainly in cases in which the uterus has been removed and the available space is taken up by the gas/fluid of the bowel. Depending on the goal of the scan, the sonographer can select the transabdominal or the transvaginal scanning method. It is important to stress the fact that it is easier and faster to empty the urinary bladder than to fill it up, and this should always be considered before the patient is sent to empty her bladder. The protocol of most laboratories is to perform first a general transabdominal scan of the pelvis, which requires a full bladder to get an overview of the anatomy. However, if a patient presents with an empty bladder, the scan should not be postponed, and transvaginal sonography can be performed as a first-line imaging technique. If transabdominal examination of the pelvis is still required, it should be performed after filling the bladder. Benacerraf et al questioned whether a full bladder is still necessary for pelvic sonography.3 After scanning 206 consecutive patients prospectively, they concluded that transvaginal sonography (TVS) with an adjunctive transabdominal sonography (TAS) with an empty bladder approach can replace the full bladder technique for routine pelvic sonography. Filling the bladder may help in imaging a low-lying placenta, diagnosing placenta accreta overlying the bladder or outlining the cervix in the median plane, and at the time of chorionic villus sampling, it may help to ‘straighten’ the uterine body to match the axis of the cervix and the vagina for better approach by the sampling catheter. If the patient is suspected of having an ectopic pregnancy, extreme caution should be exercised to prevent the patient drinking water, because an emergency surgery can be required if a bleeding ectopic pregnancy is diagnosed. In this case, if it is really necessary to obtain abdominal views, the bladder should be filled using an indwelling catheter or by infusing about 1 L of IV fluids.
Patient Information Patient information is important regardless of the gynaecological or obstetric procedure plan. Informing the patient about the transabdominal or transvaginal sonography is essential. Patients usually have a general idea about ultrasound but we should not take this for granted. There are still countries and communities in which, due to mostly religious views, transvaginal scanning is not accepted and therefore not used. The kind of examination she is about to undergo should be explained to the patient in several short sentences. This information can be conveyed in three ways. The first, which is probably the best way, is at the time of the bimanual pelvic examination in the office of the gynaecologist or in the emergency room. At this time, the words ‘transabdominal’ and ‘transvaginal’ should be mentioned and explained. A second way to inform the patient is by the way of brochures available in several languages and placed in the waiting area, or given to the patient by the receptionist. The third and probably the worst way to explain the scanning to the patient is at the time of the scan itself, while she is seated on the examination table. At this time,
35
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ the patient does not have the opportunity to ask many questions or she is under stress and does not really remember the right questions to be asked. The similarity between the familiar vaginal speculum, or the Papanicolau test, and the vaginal transducer could be used as an effective comparison. The patient also should be reassured that the dimensions of the probe are small, and it is helpful to show her the probe. Some laboratories allow the patient to insert the probe into her own vagina. However, in general, this is not regulated in any way. Over the years, patient information regarding the use of the transvaginal probe will probably become redundant. Remember that several years ago, when transabdominal sonography was introduced, emphasis was placed on patient information, and today patients know enough about transabdominal sonography that can be used almost without any in-depth explanation. At times transvaginal scanning is contraindicated. Almost similar quality images can be obtained by using the transrectal approach. The vaginal probe is inserted in the rectum55 and after its insertion the same protocol as for a vaginal probe can be followed. The biggest ‘hurdle’ is to properly explain to the patient the harmless nature of such a scan.
The Examination Table It should be explained at the outset that any ultrasound examination can, and if necessary should, be carried out on any available examination table or even in the patient's bed. Certain additions, such as elevating the pelvis for a better transvaginal ultrasound examination, may be necessary. More and more gynaecological and obstetric pelvic scans, however, are performed with the patient on a gynaecological examination table. This is equipped with a footrest, which allows the patient to assume the lithotomy position for convenient transvaginal scanning, and a retractable leg support, which can be extracted for a better transabdominal sonographic evaluation of the patient. It is rather cumbersome and almost impossible to perform transvaginal ultrasound scanning on a flat table, unless an elevation below the pelvis is provided. Such an elevation will enable the backward tilt of the probe handle. The newer probes that have the ability to electronically or mechanically steer the scanning plane may be used even with a flat examination table. Some gynaecological examination tables are fitted with a swinging arm and a small platform that can support a small portable ultrasound box, similar to the swinging arm on the other side of the table supporting the colposcope (Fig. 3.2). Remember that, for specific reasons, such as a detailed examination of the cervix, the patient can be scanned, using the transvaginal probe, in a standing position.
Bimanual Pelvic Examination Preceding the Scan
36
Patients undergoing transvaginal or even transabdominal sonography usually have a pelvic exam that precedes the imaging procedure. If transvaginal ultrasonography is to be performed in the gynaecologist's office, a bimanual exam should definitely be
✩✩✩✩✩✩✩✩✩✩✩ ✩
performed before the scanning. If the patient is referred to the imaging laboratory, the gynaecologist should explain the palpatory finding for which the patient is referred for further imaging studies. The imaging laboratories rely on the information provided by the obstetrician-gynaecologist and are guided by these findings. These specialized ultrasound laboratories usually do not subject the patient to a routine pelvic examination. It is, however, a good idea to take the time to examine the patient before or even after the ultrasound examination to correlate the findings with the image obtained. Such a pelvic palpatory examination is even more important if a discrepancy between the image obtained and the image expected occurs. A basic distinction between the transvaginal ultrasound examination in the gynaecologist's office and that performed in the specialized laboratory must be made. In the gynaecologist's office, a bimanual examination is performed after taking the history of the patient. This examination usually guides the clinician as to the necessity of performing other laboratory tests. Among these laboratory tests, ultrasound may be considered. If ultrasound equipment is available in the office, the gynaecologist may proceed to complement and enhance his or her bimanual palpatory examination with this simple imaging technique. In this case, the bimanual pelvic examination and the transvaginal ultrasound complement each other to arrive at the clinical decision. If referral of the patient to a more sophisticated and usually remotely situated imaging laboratory is selected, the targeted pelvic ultrasound exam is performed by imaging specialists who must rely on the pelvic examination previously performed by the referring physician.
Scanning techniques in obstetrics and gynaecology
Fig. 3.2 A gynaecological table fitted with a swinging arm on which the small, portable ultrasound machine is placed. This can be used during examinations performed with the patient on the table.
Equipment The practical aspects of using the equipment are discussed below. The first step in scanning a patient is to prepare the equipment before the patient is examined. This preparation is even more crucial when a transvaginal scan is planned.
37
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
38
The patient's demographic data, her last menstrual period and important pertinent observations should be entered. We found it useful to have the last menstrual period appear on the screen of the ultrasound machine next to the patient's name; thus it will be visible on each of the printed pictures, and it will therefore be easy to calculate the gestational age of a pregnancy or, in a gynaecological scan, the day of the patient's cycle. Recording devices should be switched to a stand-by position that enables their instantaneous operation. Ultrasound machines now enable recording onto CDs and even electronic data transmission over networks and the Internet. It is helpful to have a separate foot-switch which freezes the screen and even a second one to take hard copies of the desired images. This becomes important when transvaginal sonography is performed, because the operator needs both hands free, one to manipulate the transvaginal probe and the second to place on the abdominal wall and facilitate the location and mobilization of the pelvic structures. All operators should use gloves when scanning. They should at least put a glove on the hand handling the probe during the examination. This protects the users from a possible transmittable infection and reassures the patient as to a procedure performed under clean circumstances. Transabdominal probes are usually not covered with a probe cover (unless a sterile procedure is contemplated). However, they should be cleaned between patients. Probe cleaning is of the utmost importance. Both the transabdominal and transvaginal probe should be wiped, with gel first and then some means of probe cleanser can be applied. An alcohol spray or sponge or some other disinfectant (usually a quaternary alcohol compound) may be used to clean the probe. Ordinary bleach also can be used for this. However, it is important to ask the probe manufacturers about their preferred method of disinfecting the probe. Odwin et al provided guidelines to the different solutions and their efficacy in cleaning the probes.36 Local disinfection protocols should be followed carefully to minimize the spread of infection and the liability of the operators. A clean condom or the digit of a surgical rubber glove should cover the transvaginal probe. These must be clean but need not be sterile. Ultrasound coupling gel should be placed inside the protective cover to enable smooth passage of the sound waves from the transducer to the pelvic organs. A ready-to-use, prelubricated, individually prepackaged, thin plastic transvaginal probe cover is available for use. This cover is particularly useful if the patient is allergic to latex. Latex allergy is more widespread than believed, therefore it is a good routine to ask patients about such allergies before using a latex product at scanning. It is also a good idea to post a sign in the waiting area which asks the patients to report any previously known latex allergy before the actual scanning. Coupling gel should be applied to the tip of the probe before its insertion into the vagina. Coupling gels seem to be important to generate a clear and clinically meaningful ultrasound picture on the screen. K-Y gel (Johnson & Johnson, Skillman, NJ) or the ultrasound coupling gel, which is basically clean to begin with, can be used for this purpose. Mineral oil is a good inexpensive coupling agent if the more expensive gels are not available. However, infertility patients
✩✩✩✩✩✩✩✩✩✩✩ ✩ approaching their midcycle should be scanned using normal saline because coupling gels may be detrimental for sperm motility and viability.
Orientation using transabdominal probes is simple. On the monitor or any hardcopy picture, it is sufficient to annotate which is the patient's right or left side. This is much like the conventional orientation used in radiology. On a longitudinal, sagittal transabdominal scan the direction toward the patient's head (cephalad or superior) is displayed usually on the left side and the direction toward the patient's feet (caudad or inferior) is displayed on the right side of the monitor or picture. Anterior (or ventral) points upward and posterior (or dorsal) points downward on the monitor or the picture (see Fig. 3.1). In transvaginal sonography, the orientation is entirely different. The images created are oriented perpendicularly (rotated 90 ° counterclockwise), compared to those generated by the transabdominal probe. Sonologists from around the world display sonographic pictures according to different rules.4 Displaying of the sonographic image requires some explanation, because it becomes important to understand the onscreen image orientation. The sonographic picture generated by transvaginal sonography can be displayed with the apex of the ‘pie’ pointing upward (Fig. 3.3A) or downward (Fig. 3.3B). Some countries, as well as individuals, believe that displaying images with the apex pointing down seems more logical. However, at this time, a uniform worldwide display is highly unlikely to occur. Some sonologists think that displaying a transvaginal picture with the apex of the ‘pie’ pointing to the bottom and a transabdominal picture with the apex pointing to the top would enable a distinction regarding the scanning routine. For example, in Germany (and in a number of other countries), one could distinguish between a transvaginal and a transabdominal picture by looking at the picture orientation. It is important and also useful to introduce some standardization regarding this issue.58 In the United States and many other countries, the images are displayed as follows.
Scanning techniques in obstetrics and gynaecology
Orientation
• If a fetus is scanned, the left and right sides will be determined according to
the position of the fetal stomach and the fetal heart. • In the case of a gynaecological scan, on the longitudinal plane, the bladder appears on the upper left side of the screen with the external cervical os pointing toward the right. If the uterus is anteverted, the fundus appears on the same side as the urinary bladder (Fig. 3.3A). If the fundus in a retroverted uterus points toward the opposite side of the bladder, the retroversion can be ascertained (Fig. 3.3C). • In the cross-section of the pelvis in the transverse (coronal) plane, the patient's right side will be seen on the left side of the monitor (or picture) and the left side of the patient on the right side of the monitor (or picture), as on any radiographic image performed using the coronal plane (Fig. 3.3A).
39
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
40
Fig. 3.3 Orientation in the pelvis using the transvaginal probe. (A) The uterus is displayed with the apex of the ‘pie’ pointing upward. The general directions within the body are marked on the pictures. The left image is the picture of the uterus in the sagittal plane, whereas that on the right side depicts the transverse section. (B) The uterus is displayed with the apex of the ‘pie’ pointing downward (the European approach). (C) A retroverted uterus and its relationship with the bladder. The major directions in the pelvis are identical with the sagittal section of the uterus in Fig 3.3A.
✩✩✩✩✩✩✩✩✩✩✩ ✩
• If the cervix is scanned usually in the sagittal plane, it is customary that in
– On the coronal planes, the fetal right side should be kept on the left side of the picture and the fetal left side on the right side of the image. This is similar to any coronal x-ray picture of the head (Fig. 3.5A). – On the sagittal planes it is customary to orient the forehead (anterior or frontal) to the left and the occiput (posterior or occipital) to the right side of the picture (Fig. 3.5B). – Using TVS, a series of coronal and sagittal brain sections can be obtained for better definition of eventual pathology.30,56 Some authors recommend the use of transverse and anteroposterior planes only if transvaginal sonography is used.12 A somewhat better approach is to use the relative position of the target organ within the pelvis, which does not necessarily match the cardinal and classic anatomical planes of the pelvis. This scanning method is called ‘organ-oriented scanning’ (Fig. 3.6).38,61 It is practical to refer to the longitudinal axis of the scanned organ, such as the fallopian tube or the ovary (e.g. ‘the longitudinal image of the tube’, etc.), instead of using the conventional orientation of the scanning planes with the known pelvic co-ordinates. Lately the issue of orientation using three-dimensional (3D) ultrasound has surfaced. Interestingly, the major textbooks on the subject of 3D ultrasound in obstetrics and gynaecology have not discussed adequately, or at all, orientation in the acquired volume. It should be stressed that this orientation, mainly in the reconstructed volumes, is a real but surmountable problem. Some machines have a convenient
Fig. 3.4 Sagittal sections of the cervix with a cervical suture. Note that by convention the external os of the cervix with an anteverted uterus is oriented towards the right of the picture.
Scanning techniques in obstetrics and gynaecology
an anteverted pregnant uterus the external os is pointing towards the right side of the picture, while the internal os is on the left side of the image (Fig. 3.4). Of course, the bladder is kept constantly on the upper left side of the picture. In the case of a retroverted uterus the bladder is kept on the upper left side of the picture while the external and internal os are oriented respectively to the left and right side of the picture. • If the fetal brain is scanned, a careful assessment of the left and right side is necessary regardless of TAS or TVS.
41
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 3.5 Orientation in scanning the fetal brain regardless of the scanning route. (A) The coronal plane. (B) The sagittal plane. Note that the face is on the left side.
labelling protocol which enables the user to label the major directions (right, left, cranial, caudal, anterior, posterior) at the onset of scanning and incorporate it automatically in the displayed images (Medison, Kretz and General Electric systems). These, of course, make orientation in such 3D volumes easier. If, however, such orientation display is not available, the operator should use extreme care to correctly label the image generated. This may avoid later confusion and medical liability. The most important message regarding orientation is the fact that it is mandatory to label all images at all times to be able to correctly indicate left and right, cranial and caudal, sagittal, coronal and axial (horizontal) sections (Fig. 3.7).
Scanning Routine Regardless of the route selected to perform the scan, a methodical and systematic scanning routine should be followed. The following order was found to be helpful.
42
Fig. 3.6 The concept of ‘organ-oriented’ scanning in the female pelvis. (A) The tube (chronic hydrosalpinx) is imaged to display its longest diameter. This is not necessarily in any fixed plane of the pelvis. It is obtained by trial and error. This is correct also if the ovary is scanned. (B) Ninety degrees to any plane that detects the longest measurement of the pelvic organ (in this case an acute salpingitis with the ‘cogwheel sign’) will display the cross-section of that organ.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Obstetric Scanning Different countries use different protocols for the structures to be included in obstetric scans. These requirements should be kept in mind when performing ultrasound examinations of the fetus. It is customary to divide the scanning routine in obstetrics as follows: firsttrimester scan, basic exam and comprehensive fetal exam. When performing the first-trimester scan (usually between 11 and 14 postmenstrual weeks), a transabdominal or transvaginal probe may be used.1,9,13,29,34,42-44,51,60 The following information should be obtained.
Scanning techniques in obstetrics and gynaecology
Fig. 3.7 Three-dimensional image of the uterus. The upper left image is in the sagittal plane, the upper right in the axial plane, the lower left in the coronal plane. The lower right image is the rendering of the uterine cavity in the coronal plane which is almost never achieved using two-dimensional transvaginal scanning.
• Presence or absence of an intrauterine gestational sac • Identification of embryo or fetus • Yolk sac • Fetal number • Presence or absence of fetal cardiac activity • Crown–rump length (CRL) • Evaluation of uterus and adnexal structures • Evaluation and measurement of the nuchal translucency. I f any obvious anomaly is seen, which may be the case if high-resolution equipment is used, this should trigger a more intensive scan and obviously a follow-up scan. The basic fetal exam should provide the following information.
• Fetal number • Fetal presentation • Documentation of fetal life • Placental location • Assessment of amniotic fluid volume • Assessment of gestational age • Survey of fetal anatomy for gross malformations • Evaluation of the ovaries and possible maternal pelvic masses.
43
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ This is primarily a biometric examination. Nonetheless, a brief survey of fetal anatomy and maternal pelvic organs should be performed. Some major structural malformations of the fetus may be identified during basic examinations, and some basic examinations may suggest the need for a more comprehensive survey.13,29,34,60 In certain circumstances, a ‘limited’ ultrasound examination may be appropriate and desirable. Such circumstances commonly relate to the specific nature of the information required or the urgent nature of the clinical situation. A limited examination may be useful to collect information such as the following.
• Assessment of amniotic fluid volume – amniotic fluid index (AFI) • Fetal biophysical profile (BPP) testing • Ultrasonography-guided amniocentesis, chorionic villus sampling (CVS) • Nuchal translucency measurement9,34,44 • Perumbilical blood sampling (PUBS) • External cephalic version • Confirmation of fetal life or death • Localization of placenta in antepartum haemorrhage • Confirmation of fetal presentation. A comprehensive ultrasound examination may be indicated for a patient who is suspected of carrying a physiologically or anatomically defective fetus by history, clinical evaluation or prior ultrasound examination. A limited examination, as defined above, may be performed by ultrasonographers or specially trained personnel. The basic examination, however, should be performed or reviewed by an appropriately trained operator. An operator with experience and expertise in such scanning should perform the comprehensive examination. In some situations, it may not be possible to perform a full fetal survey. These include:
• oligohydramnios • hyperflexed position of the fetus • engagement of the head • compression of some fetal parts • maternal obesity. Biophysical profile Biophysical profile testing consists of a non-stress test with the addition of four observations made by real-time ultrasound, each receiving a score of two. The five components are as follows.
• Reactive non-stress test. • Fetal breathing movements (one or more episodes of rhythmic fetal breathing movements of 30 seconds or more within 30 minutes).
• Fetal movement (three or more discrete body or limb movements within 44
30 minutes). • Fetal tone (one or more episodes of extension of a fetal extremity with return to flexion).
✩✩✩✩✩✩✩✩✩✩✩ ✩
• Quantitation of amniotic fluid volume. There is no universal agreement
With this method, a score of 2 (normal) or 0 (abnormal) is assigned to each of the five observations. A score of 8–10 is normal; a score of 6 is considered equivocal (a fetus should be retested in 12–24 hours) and a score of 5 or less is abnormal. In the presence of oligohydramnios, further evaluation may be warranted.26,39 See also Chapter 7.
Gynaecological Scanning If transabdominal sonography is performed, the sonographer may select other target areas for the scanning, such as looking for free fluid in the abdominal cavity, in Morrison's pouch, along the right axial line or below the liver, or scanning the patient's kidneys. It should be stressed that adequate training should preclude scanning non-gynaecological structures. It is important to use the largest possible magnification, which enables orientation as well as recognition of organs and their pathologies. Magnification usually does not alter the resolution of high-frequency probes. The following routine has proven to be effective.2
Scanning techniques in obstetrics and gynaecology
as to the optimal method of assessing amniotic fluid volume. Some investigators consider the detection of a single pocket of amniotic fluid exceeding 2 cm in two perpendicular planes to be adequate. A semiquantitative, four-quadrant assessment of amniotic fluid depth (AFI) is widely used, and cross-sectional nomograms have been developed.32,39 Ideal cut-off levels for intervention using the AFI have yet to be established.
The uterus When evaluating a suspected uterine mass, the practitioner should identify the appropriate anatomical structures. The initial step is to identify the bladder anteriorly and the rectosigmoid posteriorly. The position of the uterus depends on the distension of the bladder and rectosigmoid, masses that may be present extrinsic to the uterus, and intrinsic uterine masses. The normal uterus appears sonographically as a uniform structure. By resting a hand on the abdomen and using the intermittent pressure of a transvaginal probe, the practitioner can determine the mobility of the uterus, the ovaries or any pelvic structure. This sliding movement of the organs can be related to each other or the stationary pelvic floor (‘sliding organs sign’).57 The origin of structures (e.g. ovary versus a pedunculated fibroid) or adhesions can be diagnosed using this manoeuvre. Testing for pain is also possible, with the vaginal probe identifying the touched structure in question on the screen. Lately 3D ultrasound became the most informative and powerful technique to image the uterus. Its main strength is that along with the sagittal and transverse planes, the coronal plane can be displayed. The cervix Scanning the uterine cervix is an integral part of the gynaecological as well as the obstetric ultrasound examination. A wide variety of pathologies ranging from benign or prevalent Nabothian (inclusion) cysts to cervical fibroids or the rare
45
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
46
cervical pregnancy can be identified. The importance of transvaginal ultrasound scanning of the cervix has increased in recent years as it has been found to be predictive of preterm deliveries. Usually the closed cervical canal length is measured. If funnelling is seen the funnel length and width can be measured. Cervical sutures can and should also be evaluated periodically. The myometrium The sonographic appearance of the myometrium and the arcuate vessels within the myometrium should be noted. Leiomyomata tend to be discrete, multiple, spherical masses of varying size. They can be found almost entirely within the endometrial cavity (submucosal) (Fig. 3.8A–C), within the myometrium (intramural) or on the surface of the uterus (subserosal). Ultrasonographically, a leiomyoma often appears hypoechogenic. However, its appearance may vary depending on its location and whether it has undergone internal changes, such as hyaline degeneration, fatty degeneration, calcification or haemorrhagic necrosis. These changes will alter the sonographic appearance of the leiomyoma; for example, the presence of calcium will result in an increase in echogenicity, whereas degeneration will produce a cyst-like structure. Submucosal leiomyomata may give the appearance of a bulge in the endometrial lining. A more detailed investigation of this sign is warranted. This can be accomplished by instilling normal saline via a thin catheter placed in the uterine cavity. The saline will serve as a contrast medium and will outline the mass (Fig. 3.8D,E). Serial ultrasonography can be used to determine whether the leiomyomata are growing or shrinking. This can be especially useful in patients entering menopause. When the uterus of a reproductive-age woman with leiomyomata is evaluated,
Fig. 3.8 Examples of submucous fibroids enhanced by saline infusion sonohysterography. (A,B) Almost entirely intracavitary submucous myoma. (C) It is possible to study the Doppler signal of the feeding vessel to the fibroid. (D,E) Partially submucous myoma bulging into the cavity with approximately 30–40% of its volume.
✩✩✩✩✩✩✩✩✩✩✩ ✩
The endometrium Sonographically, the interface of the two endometrial surfaces appears as a thin, echogenic line that can be evaluated throughout the menstrual cycle. The endometrium varies in thickness and appearance depending on the stage of the menstrual cycle or the use of exogenous hormones. Measurement of the endometrial thickness should be done on the long axis, with a combined anterior–posterior wall measurement. If fluid is found in the uterine cavity, the measurement should exclude that fluid interface (Fig. 3.9). In postmenopausal women with bleeding, studies indicate that when there is a thin distinct endometrial echo less than 4–5 mm maximum anteroposterior thickness read from a long axis view, this finding is consistently associated with lack of significant tissue on sampling. Thus, such patients may be able to avoid invasive sampling and its risks, expense and discomfort. Presence of an endometrial echo greater than 5 mm is not compatible with atrophy and thus, depending on hormonal status, may indicate the need for sampling. Saline infusion sonohysterography can be used to distinguish symmetrically thickened endometrium in
Fig. 3.9 The technique of measuring endometrial thickness in the presence of intracavitary fluid.
Scanning techniques in obstetrics and gynaecology
the practitioner should be alert to the possibility of a small (4–6 weeks of gestation size) chorionic sac. These small gestations may be difficult to detect and may be found in odd locations. Adenomyosis is diagnosed by noting the presence of endometrial tissue in the stroma of the myometrium. Although this condition may be suspected by the presence of small sonolucent areas and linear shadowing within the myometrium, it cannot be confirmed only on that basis. Usually the anterior or posterior wall containing the adenomyosis is thicker than the other wall. The diagnosis rests on clinical parameters and histological confirmation.
47
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
48
which the process is global from endometrial changes that may be focal. In the former, blind sampling is appropriate, whereas the latter requires hysteroscopically directed evaluation. It is to be hoped that current research in 3D techniques, particularly in volume rendering, may prove to be an added source of information distinguishing benign from malignant pathology. Finally 3D techniques are proven to be useful in diagnosing the different degrees of uterine malformations by displaying the contour of the fundus and the cavity at the same time (Fig. 3.10).31 It is also important to examine carefully the entire length of the myometrial– endometrial interface. If the endometrium is irregular or if there is an enlarged area of echogenicity, endometrial pathology should be suspected. An endometrial biopsy or dilation and curettage should be performed to determine the histological status of the endometrium. The myometrial–endometrial interface should be evaluated by continuously shifting the transducer through its long axis and corresponding coronal planes. Increasing attention is being given to the presence of heterogeneous central uterine changes in women who receive tamoxifen for breast cancer. In some such cases, changes originally interpreted as endometrial are actually in the proximal myometrium. Sonohysterography may be used to determine the location (endometrial vs proximal myometrial) of such heterogeneous echoes. During the follicular phase, the endometrium is thin, with a ‘pencil-line’ echo of the cavity and hypoechoic functional endometrium on both sides of the cavity line (three-line sign). This phase is followed by gradual thickening, which reaches its peak immediately prior to ovulation. Following ovulation, coincidental with the rise in progesterone, the echogenicity of the endometrium on both sides of the cavity line increases and equals that of the cavity line, which gradually disappears within the hyperechoic endometrium. This hyperechoic endometrium is then ‘broken down’ at the time of the menstrual flow. The endometrium can be
Fig. 3.10 Three-dimensional rendering of the uterus in the coronal plane. Note the clear contours of the fundus (arrows) and the septated uterus.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Scanning techniques in obstetrics and gynaecology
measured throughout the first part of the cycle. The endometrium can serve as a natural contrast material in the uterus, leading to better definition of the endometrial–myometrial interface and detection of polyps or submucous leiomyomata, or both. Patients with irregular uterine bleeding may have an endometrial polyp, submucosal myoma or adenomatous hyperplasia. Polyps can occur in patients of any age but tend to be more common in perimenopausal women. Polyps are usually seen as a prominent endometrial echo complex; rarely, discrete masses occupying the endometrial cavity are found. Sonohysterographic fluid enhancement through a thin intrauterine catheter may improve diagnostic capability.18 The branching appearance of the feeding blood vessel can be detected by turning on the colour Doppler feature. Although neither transvaginal nor transabdominal ultrasound evaluation can confirm the presence or absence of cancer of the endometrium, ultrasonography can provide information to aid in diagnosis. In early stages, endometrial carcinoma can appear as a change in the thickness of the endometrial lining and in the endometrial echogenicity. Advanced endometrial or cervical carcinoma may appear as hydrometra, pyometra or haematometra. These conditions will appear sonographically as fluid collection within the uterine cavity. The endometrial– myometrial interface should be defined and monitored to detect pathology at that level. Other conditions that may be detected by ultrasound examination of the endometrium are Asherman syndrome and retained products of conception following spontaneous abortion, therapeutic abortion or delivery. A diagnosis of Asherman syndrome can be strengthened by the presence of an irregular echogenic picture and, occasionally, by the finding of calcification. On ultrasonography, calcification is intensely echogenic and causes acoustic shadowing. The diagnosis can be firmly established by hysteroscopy. Retained products usually can be detected if an irregularly shaped, dilated endometrial cavity containing echogenic material is noted. Asherman syndrome can best be distinguished from retained products of conception by evaluating the patient's history. Uterine anomalies including septae, bicornuate uteri and didelphys may be identified especially when using 3D ultrasonography using ‘thick-slice’ or inversion rendering. Sonohysterography may be useful to measure a fundal septum prior to hysteroscopic resection when habitual abortion is present.
Adnexal Masses Ultrasonographic examination of the adnexa encompasses evaluation of the ovaries, fallopian tubes and parametrial areas. It is important that the examiner be familiar with other anatomical structures in this area, such as the external and internal iliac artery and vein, ureter and bowel. The ovaries usually lie in the ovarian fossa found along the lateral pelvic wall. The ovary can be located by identifying a pulsating linear echo; superior to this is the external iliac artery and posterior and inferior to this the ureter.
49
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The normal ovary of teenagers and young adults measures approximately 2 × 2 × 3 cm. The size of the ovary should be measured according to the largest diameter in the three planes. Some investigators have recommended determining ovarian volume, using the formula (length × width × height)/2. The ovarian volume in teenagers and young adults can reach 14 cm3. In postmenopausal women, the average ovarian volume is 2.5 cm3 or less. The following aspects of an adnexal mass should be evaluated. – the mass should be moved by the vaginal probe or by the hand • Mobility
of the operator that is resting on the abdomen (‘sliding organs’ sign).57 – its location should be established by watching the on-screen picture • Pain when touching different organs with the tip of the transvaginal probe. structure – features of an ovarian mass, such as thickness and outer • Wall and inner surface irregularities and papillae, should be described and measured. • Septations – the thickness of the septations should be reported. of the mass – the mass can be completely sonolucent and may • Echogenicity have low-level echogenic contents, may be with or without an echogenic core, may have mixed echogenicity containing all of these components or may be completely echogenic. The presence of the following conditions may make it more difficult to detect ovarian or adnexal masses with ultrasonography.
• Fluid-filled loop of bowel • Faeces in loop of bowel • Closed-loop bowel obstruction • Artifact of multipath reflection of sound waves (stratified echo pattern
resulting from echoes bouncing back and forth) from fluid-filled structure (e.g. bladder) • Mesenteric cysts • Peritoneal inclusion cysts (postoperative or after infections) • Nabothian cysts • Hydrosalpinges (acute and chronic) • Large fibroids.
50
The clinical findings of acute salpingitis may be strengthened by ultrasonographic findings of tubo-ovarian complexes of a fluid-containing structure with thickened walls sensitive to the touch of the probe, adnexa adherent to loop of bowels, or collection of fluid in the cul-de-sac. Chronic salpingitis can be diagnosed on the basis of a painless (to the touch of the probe), thin-walled, pear-shaped, fluidfilled adnexal structure. Abscesses can be detected by ultrasonography, which can also be used to characterize the abscess as unilocular or multilocular and determine the thickness of the abscess wall and anatomical location. This information should be integrated into clinical findings (e.g. pain, fever) and is helpful in determining whether the abscess may be drained percutaneously or transvaginally or whether surgical intervention is required.54
✩✩✩✩✩✩✩✩✩✩✩ ✩
Peritoneal Fluid Scanning techniques in obstetrics and gynaecology
Small amounts of fluid in the lower pelvis can be visualized with ultrasonography. The fluid should be examined for the presence or absence of floating debris, which will appear as low-level echoes. The tip of the probe can be used to rock the fluid slightly, thus aiding in the observation of floating particles. If the nature of the fluid must be determined, culdocentesis can be accomplished with the aid of transvaginal sonography, which offers the best guidance for needle placement through the needle guide mated to the shaft of the probe. Attempts to assess the quantity of pelvic fluid have been reported in the literature. The smallest amount of fluid that can be detected is about 20–30 mL if a 5 MHz transvaginal probe is used. Although experienced sonographers can estimate the approximate amount, this should be done with extreme caution. Figure 3.11 demonstrates how the approximate amount of free or loculated pelvic fluid collection can be estimated using perpendicular scanning planes. If a larger amount of abdominal or pelvic fluid is suspected, the space between the liver and the right kidney (the Morrison pouch) should be examined. This can be achieved by placing an abdominal transducer parallel to the sagittal plane and overlying the right upper abdomen. One should distinguish between free fluid in the pelvis and loculated fluid. The loculated fluid is found usually as a consequence of pelvic surgery or an inflammatory process. It is characterized by flimsy or denser adhesions creating the pseudoseptations in the fluid. The wall of the pseudocyst is the pelvic wall itself.
Urinary Bladder Ultrasonography can be used to examine the bladder for the presence of extrinsic or intrinsic pathological masses. The urethra and the bladder can be viewed on the sagittal and on an extremely anteriorly directed coronal plane. A transverse scan through the superior portion of the bladder reveals the bladder to be rounded. If the bladder is scanned inferiorly, it will appear square, whereas a longitudinal scan will make it appear triangular. The thickness of the bladder and the
Fig. 3.11 The technique of estimating the almost free (or loculated) pelvic fluid. The formula of the ovoid is used (a × b × c) 0.523 = mL.
51
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 3.12 Using transvaginal colour Doppler, the ureteral jets of the left (A) and right (B) ureter can be studied.
presence of polyps or bladder stones will be outlined by the sonolucent urine. A scan performed at the base of the bladder, just proximal to the urethrovesical junction, will permit visualization of the urethral orifices. Ultrasonography may be used to estimate the volume of postvoid residual and, in incontinent women, the mobility of the urethrovesical junction. Observing the urinary jets arising from the two ostia by using grey-scale or colour Doppler, it is possible to determine ureteral patency (Fig. 3.12).52,53
Other Findings Other pathologic processes that can affect organs in the lower pelvis can also be detected. The most prevalent bowel diseases that can be observed are diverticulosis and various degrees of dilation of the small bowel. Dilation of the bowel that can be mistaken for cystic structures can often be differentiated by the presence of peristalsis. Ectopic or low-lying horseshoe kidneys can also be detected by sonography. Transabdominal sonography can be used to identify appendicitis; however, considerable experience is required to do so.
Colour Doppler Studies An increasing number of laboratories are now offering colour flow-directed measurements such as pulsatility and resistance indices as well as flow velocities.2,13,26,29,32,39,57,60 Some colour flow studies are still considered investigational in the USA. The pulsatility index is calculated by the following formula: Systolic Velocity − Diastolic Velocity Mean Velocity The resistance index is calculated by the following formula: 52
Systolic Velocity − Diastolic Velocity Systolic Velocity
✩✩✩✩✩✩✩✩✩✩✩ ✩
Screening for Ovarian Masses
Scanning techniques in obstetrics and gynaecology
Subsequent chapters will discuss the technique and clinical use of colour Doppler and power Doppler measurements. Preliminary results raise the possibility of detecting increased vascularity and new vessel formation in cases of malignant ovarian masses. In general, vessels in malignant tumours lack the muscle layer and have lower impedance. However, increased flow may also be seen with pelvic inflammatory processes. The presence of a corpus luteum not only may be misleading in the structural evaluation of an adnexal mass since the flow measurement values overlap with those found in ovarian cancer. The corpus luteum is known to have new vessel formation, which lowers the resistance to flow while present. Recent studies have suggested a possible role for colour Doppler in the diagnosis of adnexal torsion.15,23 These studies suggest that, at the site of the torsion, the diameter of the vessels proximal to the occlusion is increased; the disruption of flow is identified on colour Doppler. Within the twisted adnexa, there is significantly diminished flow or no flow at all. The cost–benefit ratio of colour flow studies is still under investigation, and the value of such studies is as yet not fully determined. Moreover, the technique requires a great deal of training, and measurement remains a subjective process.
Transvaginal sonography, with or without colour flow-directed measurements of resistance to flow and flow velocities, has been suggested as a means of screening for ovarian cancer.5,7,24 Although transvaginal sonography is probably the best means of determining the morphological structure of adnexal masses, its efficacy in screening for ovarian cancer has not been adequately established. Both modalities – transvaginal sonography and colour flow-directed measurements – are experimental for these uses.11,49,59 Several studies are under way to determine whether transvaginal sonography and colour Doppler in conjunction with biological markers (proteins) can be used to screen a selected population at high risk for ovarian cancer. Other studies are being done to examine the feasibility of using transvaginal sonography as a first-line modality for screening. Doubts about the value of colour Doppler in the diagnosis of ovarian masses have also been expressed.45-47
Transperineal and Transrectal Scanning This chapter would not be complete without mentioning other scanning routes. The transperineal route is also called translabial scanning. It is mainly used if transvaginal scanning is not possible (no transvaginal transducer is available or a contraindication prevents its use).21,41 A linear or curvilinear transducer is inserted in a glove and applied to the vulvar area in a sagittal fashion. The authors' experience is that there are very few contradictions to the use of transvaginal probes in favour of a transperineal scan. Even in the case of premature
53
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ rupture of the membranes, it was found that one transvaginal scan can be more useful than one digital examination to predict premature delivery.19,37 In cases where transvaginal scanning is not feasible or is contradicted, transrectal scanning can be used.55
Ultrasound-Guided Puncture Procedures There are two kinds of ultrasound-guided puncture procedures: those guided by a transabdominal transducer and performed transabdominally and those guided by a transvaginal transducer and performed transvaginally. Transabdominal puncture procedures can be done using the ‘free hand’ method or a fixed needle guide. The former requires some degree of experience and good eye–hand co-ordination. Transvaginal puncture procedures should always be performed using a fixed needle guide which is ‘mated’ to the shaft of the transvaginal probe.
Conclusion The technique and clinical aspects of transabdominal and transvaginal ultrasound have been discussed. Those who intend to perform hands-on scanning of obstetric and gynaecological patients should familiarize themselves with the described techniques. In addition, the more specific and detailed texts and published articles should be read. Based upon our experience, the evolution of understanding in this imaging specialty is closely related to advances in the fields of electronics, acoustics and computer sciences as well as to the ability to miniaturize most components of the ultrasound equipment. References
54
1. American College of Obstetricians and Gynecologists 1993 ACOG technical bulletin no. 187. American College of Obstetricians and Gynecologists, Washington, DC 2. American College of Obstetricians and Gynecologists 1995 ACOG technical bulletin no. 215. American College of Obstetricians and Gynecologists, Washington, DC 3. Benacerraf BR, Ship TD, Bromley B. Is a full bladder still necessary for pelvic sonography? J Ultrasound Med 2000;19:237–241 4. Bernaschek G, Deutinger J. Current status of vaginosonography – a world-wide inquiry. Ultrasound Obstet Gynecol 1992;2:352–356 5. Bourne TH, Hampson J, Reynolds K, Collins WP, Campbell S. Screening for early ovarian cancer. Br J Hosp Med 1992;48:454–459
6. Callen PW. Ultrasonography in obstetrics and gynecology, 4th edn. WB Saunders, Philadelphia, 2000 7. Campbell S, Bourne T, Bradley E. Screening for ovarian cancer by transvaginal sonography and colour Doppler. Eur J Obstet Gynecol Reprod Biol 1993;49:33–34 8. Chervenak FA, Isaacson GC, Campbell S. Ultrasound in obstetrics and gynecology. Little, Brown, Boston, 1993 9. Cicero S, Sacchini C, Rembouskos G, Nicolaides KH. Sonographic markers of fetal aneuploidy – a review. Placenta 2003;24 (suppl B):S88–98 10. Coleman BG, Arger PH, Grumbach K et al. TVS and TAS sonography: prospective comparison. Radiology 1988;168:639–643 11. Daskalakis G, Kalmantis K, Skartados N et al. Assessment of ovarian tumors using
✩✩✩✩✩✩✩✩✩✩✩ ✩ 25. Lavery MJ, Benson CB. Transvaginal versus transabdominal ultrasound. In: TimorTritsch IE, Rottem S (eds) Transvaginal sonography, 2nd edn. Chapman and Hall, New York, 1991 26. Manning FA, Harman CR, Morrison I, Menticoglou SM, Lange IR, Johnson JM. Fetal assessment based on fetal biophysical profile scoring. IV. An analysis of perinatal morbidity and mortality. Am J Obstet Gynecol 1990;162:703–709 27. Mendelson EB, Bohm-Velez M, Joseph N, Neiman HL. Gynecologic imaging: comparison of TAS and TVS sonography. Radiology 1988;166:321–324 28. Merz E. Three-dimensional ultrasound in obstetrics and gynecology. Lippincott Williams and Wilkins, Philadelphia, 1998 29. Michailidis GD, Papageorgiou P, Economides DL. Assessment of fetal anatomy in the first trimester using twoand three-dimensional ultrasound. Br J Radiol 2002;75:215–219 30. Monteagudo A, Reuss ML, Timor-Tritsch IE. Imaging the fetal brain in the second and third trimester using transvaginal sonography. Obstet Gynecol 1991;77:27–32 31. Monteagudo A, Timor-Tritsch IE. First trimester anatomy scan: pushing the limits. What can we see now? Current Opin Obstet Gynecol 2003;15:131–141 32. Moore TR. Superiority of the four-quadrant sum over the single-deepest-pocket technique in ultrasonographic identification of abnormal amniotic fluid volumes. Am J Obstet Gynecol 1990;163:762–767 33. Nelson TR, Downey DB, Pretorius DH, Feuster A. Three-dimensional ultrasound. Lippincott Williams and Wilkins, Philadelphia, 1999 34. Nicolaides KH. Nuchal translucency and other first-trimester sonographic markers of chromosomal abnormalities. Am J Obstet Gynecol 2004;191:45–67 35. Nyberg DA, Hill LM, Bohm-Velez M, Mendelson EB. Transvaginal ultrasound. Mosby-Yearbook, St Louis, MO, 1992 36. Odwin CS, Fleischer AC, Kepple DM. Probe covers and disinfectants for transvaginal transducers. J Diagn Med Sonogr 1990;6:130–135 37. Rizzo G, Capponi A, Angelini E, Vlachopoulou A, Grassi C, Romanini C. The value of transvaginal ultrasonographic examination of the uterine cervix in predicting preterm delivery in patients with preterm premature rupture of membranes. Ultrasound Obstet Gynecol 1998;11:23–29
Scanning techniques in obstetrics and gynaecology
transvaginal color Doppler ultrasonography. Eur J Gynaecol Oncol 2004;25:594–596 12. Dodson MG, Deter RL. Definition of anatomical planes for use in transvaginal sonography. J Clin Ultrasound 1990;18: 239–242 13. Economides DL, Whitlow BJ, Braithwaite JM. Ultrasonography in the detection of fetal anomalies in early pregnancy. Br J Obstet Gynaecol 1999;106:516–523 14. Fleischer AC, Romero R, Manning FA et al. The principle and the practice of ultrasonography in obstetrics and gynecology, 5th edn. Appleton and Lange, Stamford, CT, 1996 15. Fleischer AC, Stein SM, Cullinan JA, Warner MA. Color Doppler sonography of adnexal torsion. J Ultrasound Med 1995;14:523–528 16. Goldstein SR, Timor-Tritsch IE (eds). Ultrasound in gynecology. Churchill Livingstone, New York, 1995 17. Goldstein SR. Endovaginal sonography, 2nd edn. Wiley-Liss, New York, 1991 18. Goldstein SR. Use of ultrasonohysterography for triage of perimenopausal patients with unexplained uterine bleed. Am J Obstet Gynecol 1994;170:565–570 19. Gomez R, Galasso M, Romero R et al. Ultrasonographic examination of the uterine cervix is better than cervical digital examination as a predictor of the likelihood of premature delivery in patients with preterm labor and intact membranes. Am J Obstet Gynecol 1994;171(4):956–964 20. Hendrick WR, Hykes DL, Starchman DE. Ultrasound physics and instrumentation, 3rd edn. Mosby, St Louis, MO, 1995 21. Hertzberg BS, Bowie JD, Weber TM, Carroll BA, Kliewer MA, Jordan SG. Sonography of the cervix during the third trimester of pregnancy: value of the transperineal approach. Am J Roentgenol 1991;157: 73–76 22. Kossoff G, Griffith KA, Dixon CE. Is the quality of transvaginal images superior to transabdominal ones under matched conditions? Ultrasound Obstet Gynecol 1991;1:29–35 23. Kupesic S, Aksamija A, Vucic N, Tripalo A, Kurjak A. Ultrasonography in acute pelvic pain. Acta Med Croatica 2002;56:171–180 24. Kurjak A, Shalan H, Matijevic R, Predanic M, Kupesic-Urek S. Stage I ovarian cancer by transvaginal color Doppler sonography: a report of 18 cases. Ultrasound Obstet Gynecol 1993;3:195–198
55
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
56
38. Rottem S, Thaler I, Goldstein SR, TimorTritsch IE, Brandes JM. Transvaginal sonographic technique: targeted organ scanning without resorting to ‘planes.’ J Clin Ultrasound 1999;18:243–247 39. Rutherford SE, Phelan JP, Smith CV, Jacobs N. The four-quadrant assessment of amniotic fluid volume: an adjunct to antepartum fetal heart rate testing. Obstet Gynecol 1987;70:353–356 40. Sabbagha RE. Diagnostic ultrasound applied to obstetrics and gynecology, 3rd edn. Lippincott, Philadelphia, 1994 41. Scanlan KA, Pozniak MA, Fagerholm M, Shapiro S. Value of transperineal sonography in the assessment of vaginal atresia. Am J Roentgenol 1990;154:545–548 42. Souka AP, Nicolaides KH. Diagnosis of fetal abnormalities at the 10–14-week scan. Ultrasound Obstet Gynecol 1997;10: 429–442 43. Souka AP, Pilalis A, Kavalakis I et al. Assessment of fetal anatomy at the 11–14week ultrasound examination. Ultrasound Obstet Gynecol 2004;24:730–734 44. Spencer K, Nicolaides KH. Screening for trisomy 21 in twins using first trimester ultrasound and maternal serum biochemistry in a one-stop clinic: a review of three years experience. Br J Obstet Gynaecol 2003;110:276–280 45. Tekay A, Jouppila P. Blood flow in benign ovarian tumors and normal ovaries during the follicular phase. Obstet Gynecol 1995;86:55–59 46. Tekay A, Jouppila P. Controversies in assessment of ovarian tumors with transvaginal color Doppler ultrasound. Acta Obstet Gynecol Scand 1996;75:316–329 47. Tekay A, Jouppila P. Intraobserver variation in transvaginal Doppler blood flow measurements in benign ovarian tumors. Ultrasound Obstet Gynecol 1997;9: 120–124 48. Tessler F, Schiller VL, Perrella RR et al. TAS versus endovaginal pelvic sonography: prospective study. Radiology 1980;170: 553–556 49. Timmerman D, Valentin L, Bourne TH et al. Terms, definitions and measurements to describe the sonographic features of adnexal tumors: a consensus opinion from the International Ovarian Tumor Analysis (IOTA) Group. Ultrasound Obstet Gynecol 2000;16:500–505 50. Timor-Tritsch IE, Bar-Yam Y, Elgali S, Rottem S. The technique of TVS
sonography with the use of 6.5 MHz probe. Am J Obstet Gynecol 1988;158:1019–1024 51. Timor-Tritsch IE, Bashiri A, Monteagudo A, Arslan AA. Qualified and trained sonographers in the US can perform early fetal anatomy scans between 11 and 14 weeks. Am J Obstet Gynecol 2004;191:1247–1252 52. Timor-Tritsch IE, Haratz-Rubinstein N, Monteagudo A, Lerner JP, Murphy K. Transvaginal color Doppler sonography of the ureteral jets: a potential method to detect ureteral obstruction. Obstet Gynecol 1997;89:113–117 53. Timor-Tritsch IE, Haratz-Rubinstein N, Murphy K, Monteagudo A. Transvaginal ultrasound in the detection of ureteral jets. Contemporary Reviews in Obstetrics and Gynecology 1997;143–148 54. Timor-Tritsch IE, Lerner JP, Monteagudo A, Murphy KE, Heller DS. Sonographic markers of inflammatory tubal disease. Ultrasound Obstet Gynecol 1998;12:56–66 55. Timor-Tritsch IE, Monteagudo A, Rebarber A et al. Transrectal scanning: an alternative when transvaginal scanning is not feasible. Ultrasound Obstet Gynecol 2003;21: 473–479 56. Timor-Tritsch IE, Monteagudo A. Transvaginal fetal neurosonography: standardization of the planes and sections used by anatomic landmarks. Ultrasound Obstet Gynecol 1996;8:42–47 57. Timor-Tritsch IE, Rottem S (eds) Transvaginal sonography, 2nd edn. Elsevier, New York, 1991 58. Timor-Tritsch IE. Standardization of ultrasonographic images: let's all talk the same language! Ultrasound Obstet Gynecol 1992;2:311–312 59. Ueland FR, DePriest PD, Pavlik EJ, Kryscio RJ, van Nagell JR Jr. Preoperative differentiation of malignant from benign ovarian tumors: the efficacy of morphology indexing and Doppler flow sonography. Gynecol Oncol 2003;91:46–50 60. Whitlow BJ, Chatzipapas IK, Lazanakis ML, Kadir RA, Economides DL. The value of sonography in early pregnancy for the detection of fetal abnormalities in an unselected population. Br J Obstet Gynaecol 1999;106:929–936 61. Zimmer EZ, Timor-Tritsch IE, Rottem S. The technique of transvaginal sonography. In: Timor-Tritsch IE, Rottem S (eds) Transvaginal sonography, 2nd edn. Elsevier, New York, 1991
4 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Investigation of early pregnancy Harm-Gerd K Blaas José M Carrera
ABSTRACT The preferred approach for the first-trimester examination is transvaginal sonography (TVS) although transabdominal sonography (TAS) could be and sometimes should be used to get a better overview. The presentation of images made by TVS and TAS should be standardized. In early pregnancy, use established measurement methods and measure several parameters: the crown–rump length (CRL), the head width, the heart rate, the diameter of the amniotic cavity and the diameter of the yolk sac; if possible, describe the anatomy. Looking at the heart activity alone is an incomplete examination. A detailed description of the embryonic development starting at week 4 and ending at week 10 is presented.
Keywords Early pregnancy loss, ectopic pregnancy, first trimester ultrasound, miscarriage, sonoembryology.
Introduction Approximately 12–15% of all pregnancies end in recognizable miscarriages.1 The most common indication for emergency referral in early pregnancy is vaginal bleeding. However, there are many other reasons for a pregnant woman to visit her doctor, such as abdominal pain, poor obstetric history, recurrent miscarriages, previous pregnancy with anomalous embryonic/fetal development, check-up following assisted fertilization, possible teratogenic exposure, uncertain gestational age or general anxiety. Today an ultrasound assessment of the pregnancy is a natural part of a first-trimester clinical examination.
57
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ An ultrasound examination in the first trimester is expected to provide answers to important questions. Is the embryo/young fetus alive? Is the pregnancy properly located in the cavity of the uterus? Is it a single or multiple pregnancy, and in cases of multiple pregnancy, what is the chorionicity and amnionicity? What is the age of the conceptus? The examiner must recognize the signs of early pregnancy failure such as embryonic demise, spontaneous abortion, ectopic pregnancy, hydatidiform mole, and be able to identify normal anatomy and/or anomalies in very early viable pregnancies.2 The characteristics of the early conceptus are its small size, its constantly changing anatomical appearance, and its uniform development and constant growth. Therefore, the prerequisite for any early scan, in addition to adequate ultrasound equipment, is a thorough knowledge of the normal sonographic appearance of the developing embryo and its associated structures.2 The transvaginal approach is preferred. In this chapter, fetal age is always given in completed weeks and completed days based on the last menstrual period, i.e. the standard in obstetrics.
Description of the Sonoanatomic Development During the last two decades, systematic ultrasound studies have provided important and extensive knowledge about the development of the living embryo up to 10 weeks and the young fetus from 10 weeks on with detailed anatomic descriptions of embryonic organs and extraembryonic structures.3–9 4.5 weeks After approximately 4.5 weeks (LMP-based), a tiny gestational sac (diameter 2 mm) becomes visible within the decidua surrounded by the echogenic trophoblastic ring. 5 weeks 0–6 days, CRL ª0–3 mm At 5 weeks the thin-walled yolk sac usually appears (Fig. 4.1). After ≈5.5 weeks the yolk sac is always visible, which indicates that the pregnancy is properly located in the uterine cavity, even if the embryo is not yet identified. The embryonic pole appears adjacent to the yolk sac. Since the connecting stalk is short, the embryonic pole is located near the wall. The heart rate is about 80–100 beats per minute (bpm) at the end of this week. 6 weeks 0–6 days, CRL ª4–8 mm The embryonic pole, yolk sac and the heart activity are always present. The heart rate increases to 130 bpm (Fig. 4.2).
58
7 weeks 0–6 days, CRL ª9–14 mm In sagittal section, the embryonic body appears as a triangle. The sides consist of the back and the roof of the rhombencephalon, and the frontal part includes the head, the basis of the umbilical cord, and the embryonic tail (Fig. 4.3). The embryonic body is slender in the coronal plane. The limbs appear as short hypoechogenic
✩✩✩✩✩✩✩✩✩✩✩ ✩
Investigation of early pregnancy
Fig. 4.1 5 weeks 1 day old pregnancy: retroverted uterus, trophoblastic ring in fundus; (arrow) small secondary yolk sac.
Chor cavity Yolk sac
Heart
Embryo
Fig. 4.2 6 weeks 1 day old pregnancy: CRL 5.2 mm. The embryo and the yolk sac lie close to the wall (future placenta). The beating heart can easily be identified by real-time ultrasound.
outgrowths. The hypoechogenic brain cavities can be seen. The shallow rhombencephalic cavity is also visible from 7 weeks on. It has a well-defined rhombic shape in the cranial pole of the embryo. The heart can easily be recognized by real-time ultrasound as a relatively large beating structure below the embryonic head. It is large and echogenic, the frequency has increased from 130 to 160 bpm. The thin amniotic membrane surrounding the embryo becomes visible. The mean diameter of the amniotic cavity is approximately identical with the CRL.
59
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
B
A
Mesencephalon Rhombencephalon
Diencephalon
Fig. 4.3 7 weeks, CRL 13 mm. (A) Sagittal section through body; dotted line = section of B. (B) Horizontal section through the head showing measurement of head width and OFD (occipitofrontal diameter).
8 weeks 0–6 days, CRL ª15–22 mm The brain cavities are easily seen as large ‘holes’ in the embryonic head (Fig. 4.4). Choroid plexuses become visible as echogenic areas in the enlarged lateral ventricles and in the roof of the fourth ventricle. The third ventricle is still rather wide, as is the mesencephalic cavity. The mesencephalon is on top of the head. The spine is seen as two echogenic parallel lines. It is possible to recognize the fluidfilled stomach as a small hypoechogenic area on the left side of the upper abdomen below the heart. The physiological herniation of the gut can be identified as an echogenic area in the umbilical cord at the abdominal insertion. Within a few days, this echogenic structure becomes more distinct. At the end of the week, the fingers may be distinguishable.
60
9 weeks 0–6 days, CRL ª23–31 mm (Fig. 4.5) At week 9 it is possible to obtain acceptable images of the embryonic profile. The lateral ventricles are always visible. They are best seen in the parasagittal plane, where the C-shape becomes apparent. The bright choroid plexuses of the lateral ventricles are regularly detectable at 9 weeks. The width of the diencephalic cavity narrows gradually while the mesencephalon remains wide.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Investigation of early pregnancy
Mes Chorionic cavity 3. ventr Rhomb Mes
Lat Lower ventr limb
Lower limb Umb
Amn cavity
Amn cavity 3. ventr
Lower limb
Fig. 4.4 8/1 weeks, CRL 15 mm, sagittal section through embryo lying in amniotic cavity; the dotted line indicates section of image on the right side, horizontal section through the head. Mes, mesencephalic cavity; Rhomb, rhombencephalic cavity.
The choroid plexuses of the fourth ventricle are echogenic landmarks which divide the fourth ventricle into a rostral and a caudal compartment. The cerebellar hemispheres are easily detectable. The spine is still characterized by two echogenic parallel lines. During week 9 the heart rate reaches a maximum of mean 175 bpm. The midgut herniation is now a large hyperechogenic mass in the umbilical cord (Fig. 4.6). 10 weeks 0–6 days, CRL ª32–42 mm, and 11 weeks 0–6 days, CRL ª43–54 mm The fetus has developed a human appearance. The head is relatively large with a marked chin, a prominent forehead and a flat occiput. Ossification starts at about 11 weeks with the occipital bone,10 then the ossification of the spine becomes apparent. The lateral ventricles fill the anterior part of the head and conceal the diencephalic cavity. The cerebellar hemispheres seem to meet in the midline during weeks 11 and 12. The heart rate slows down to 165 bpm at the end of week 11. Anatomical details of the heart become obvious. The midgut herniation has its maximal extension at the beginning of week 10; it returns into the abdominal cavity during weeks 10–11. Fetuses that are older than 12 weeks do not demonstrate any sign of the midgut herniation. The stomach is always visible at 11 weeks. During weeks 9–11 the shape of the yolk sac alters and its wall becomes thinner. The yolk sac enlarges in some cases, while in other cases it shrinks.9
61
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Chorionic cavity 3rd ventricle Mesencephalic cavity Choroid plexus of 4th ventricle
Amniotic cavity
Spine
Fig. 4.5 Approximately 9-week-old embryo, CRL 22 mm, sagittal section through the embryo in the amniotic cavity. A
Echogenic midgut herniation in umbilical cord
B
Echogenic midgut herniation in umbilical cord
Cord cyst (normal phenomenon in early first trimester)
Body
62
Fig. 4.6 Sagittal (A) and horizontal (B) section through an embryo (CRL 28 mm) at the end of week 9. The midgut herniation of the bowel is identified as an echogenic area in the umbilical cord. In (B) horizontal section through the embryonic abdomen; the arrows point at the abdominal insertion of the umbilical cord, containing echogenic bowel.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Measurements of the Embryo/Early Fetus Investigation of early pregnancy
The crown–rump length (CRL) is measured as the greatest length in a straight line from the cranial to the caudal end of the body in the straightest possible position of the embryo/fetus (Fig. 4.7). The CRL diagram presented by Robinson in 1975 is still widely used for the evaluation and dating of the early pregnancy.11 The width of the head, also designated as the biparietal diameter (BPD), is measured in the horizontal section perpendicular to the body axis. Due to the development of the brain, the largest width alters its position in relation to cerebral landmarks during the embryonic and early fetal period (Fig. 4.8). At 7 weeks, BPD is measured at the height of the rhombencephalon. In the early fetal period the future cranium becomes more distinguished such that the BPD can be obtained by placing the calipers at the outer border of the not yet ossified
10 weeks Correct measurement of the crown−rump length (CRL)
C
9 weeks B 7 weeks A
70
mm
50
30
n = 29
10 6
7
8 9 10 11 12 LMP-based gestational age (weeks)
13
Fig. 4.7 The CRL is measured as the greatest length in a straight line from the cranial to the caudal end of the body in the straightest possible position of the embryo/fetus. At 7 weeks, the rhombencephalic cavity lies at the top of the head; later, the midbrain is at the top. Below: Growth curve of CRL in 29 healthy embryos (reproduced from reference 9 with permission).
63
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
A Head “BPD”
7 weeks B
9 weeks C
13 weeks Fig. 4.8 Measurement of the head at 7, 9 and 13 weeks. The reference plane and landmarks change during the first trimester. At 13 weeks, the third ventricle is visible. The cavum septi pellucidi is not yet developed.
64
cranium in a horizontal section at the level of the thalamus. The anteroposterior diameter of the embryonic head, designated as the occipitofrontal diameter (OFD), is measured in the same section perpendicular to the BPD. The embryonic head circumference (HC) measurement is usually calculated from the BPD and the OFD, using the formula for an ellipse. Measurements of the embryonic trunk (abdominal circumference, AC) have been introduced as a possible parameter for the estimation of embryonic age
✩✩✩✩✩✩✩✩✩✩✩ ✩
Investigation of early pregnancy
during first-trimester biometry.12 It is advantageous to use comparable parameters when describing embryonic and fetal biometry. Instead of measuring the mean diameter of the abdomen and multiplying it with the constant 2π to obtain the AC, one may use a simpler parameter such as mean abdominal diameter (MAD)9 alone. This parameter is derived from two perpendicular measurements taken in the horizontal plane through the upper embryonic abdomen below the heart and above the umbilicus/midgut herniation (Fig. 4.9). Longitudinal examinations of the BPD and MAD in 29 normal pregnancies showed that the growth of the healthy embryo is constant (Figs. 4.7, 4.10).9 In 1973, Robinson showed that the heart rate reached a maximum at 9 weeks in the first trimester.13 The heart can easily be recognized by real-time ultrasound
Spine
Stomach 11 weeks Fig. 4.9 Measurement of the abdomen at 11 weeks. The reference plane is in the height of the embryonic/fetal stomach (arrow). The MAD is calculated from two perpendicular measurements. The abdominal circumference is also calculated from these diameters.
25
BPD
mm
20 15 10 5 0
n = 29 6
20
7
8
9
10
11
12
13
MAD
mm
15 10 5 n = 29 0
6
7 8 9 10 11 12 LMP-based gestational age (weeks)
13
Fig. 4.10 Growth curves of the head width (BPD) and MAD in 29 pregnancies showing that the growth of the healthy embryo is constant (reproduced from reference 9 with permission).
65
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ as a relatively large beating structure below the embryonic head. The heart rate should be analysed electronically using the M-mode facility (Fig. 4.11). ‘Manual’ counting results in lower maximum heart rates, which again may result in incorrect counselling and poorer management of the patient. In normal pregnancies, the heart rate develops in a specific pattern, increasing from approximately 100 bpm at the end of 5 weeks to a peak mean of 175 bpm at 9 weeks, and slowly decreasing to 150 bpm in the second trimester (Fig. 4.12). The physiological midgut herniation is recorded by measuring the length of the protruded bowel into the cordal coelom. It is usually detectable at 8 weeks, has its maximal extension at the beginning of week 10, and can be seen until the end of week 11.8,14,15 Significant ossification of the long bones is not seen before 10 LMP weeks and later.16 This was confirmed in a study on the development of the skeleton comparing longitudinal ultrasound imaging from living embryos/fetuses with radiographs
Fig. 4.11 M-mode registration of embryonic heart activity (upper arrows) and maternal pulse (lower arrows). The embryonic heart rate is measured as beats per minute, here 168 bpm.
Heart rate 200
bpm
150
100
50 n = 448 0
66
5
6 7 8 9 10 11 12 13 14 CRL-based gestational age (weeks)
Fig. 4.12 Embryonic and fetal heart rate in 448 examinations; the age of the embryos/ fetuses is based on CRL measurements.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Extraembryonic Structures: the Three Sacs The gestational sac corresponds to the chorionic cavity. Its size has been used to evaluate normal progress of the early pregnancy. The amniotic membrane is easily depicted by transvaginal ultrasound at 7 weeks. For measurements, the calipers are placed on the thin membranes of the chorionic and amniotic cavities. As with the chorionic sac, the amniotic sac is measured by three perpendicular diameters and the arithmetical mean of these diameters is calculated. The yolk sac appears as a small ring with rather bright walls lying within the chorionic cavity (extraembryonic coelom), and lying outside the amniotic cavity after 7 weeks. Due to the loss of its physiological function, the yolk sac alters its shape during weeks 9–11.9 The wall of the yolk sac is thinner than 0.3 mm, but because of the transducer-dependent point spread function and the gain setting, the echogenic wall of the yolk sac appears significantly thicker in the ultraound image. Therefore, the calipers should be placed outside–inside or just on the middle of the yolk sac wall to avoid possible measurement bias. Thus, the measurements that most likely represent the true diameters are obtained by ‘outer–inner’ or ‘middle–middle’ placement of the calipers on the wall of the yolk sac. The growth of the amniotic cavity and the yolk sac is uniform and constant in healthy pregnancies9 (Figs. 4.13, 4.14).
Fig. 4.13 The three sacs: chorionic cavity and measurement of the amniotic cavity and the yolk sac.
Investigation of early pregnancy
obtained from aborted silver nitrate-impregnated embryos and fetuses.10 At 10.5 weeks the ossified part of the femur was just measurable to 2.1 mm by ultrasound. In a 10-week-old silver nitrate-impregnated embryo, the femur length was even shorter. Therefore, measurement of limbs does not have clinical significance in the first trimester.
67
✩ ✩✩✩✩✩✩✩✩✩✩✩ 60
Amniotic cavity diameter
mm
40 30 20 10 0
mm
Ultrasound in obstetrics and gynaecology
50
8 7 6 5 4 3 2 1 0
n = 29 6
7
8
9
10
11
12
13
Yolk sac diameter
n = 29 6
7 8 9 10 11 12 LMP-based gestational age (weeks)
13
Fig. 4.14 Growth curves of the mean amniotic cavity diameter and mean yolk sac diameter in 29 healthy pregnancies showing that the growth of extraembryonic structures is constant. (Arrow) At approximately 9 weeks the physiological function of the yolk sac ceases (reproduced from reference 9 with permission).
Multiple Pregnancy: Determination of Chorionicity and Amnionicity The chorionicity and amnionicity can be explained quite easily, considering the developmental stage at which the twinning event occurs.16 Late twinning will be incomplete and will result in conjoined twins. The ‘cleavage’ or twinning event does not take place after 5 completed weeks. The spectrum varies from dichorionic (DC) diamniotic (DA) to monochorionic (MC) monoamniotic (MA) twins, where conjoined twins represent the extreme form of monoamniotic twins. MCDA twins have two yolk sacs; MCMA twins usually have only one. The chorionicity and amnionicity can be diagnosed at the end of week 5, when both embryo and yolk sac are detectable. MCDA twins always have thin dividing amniotic membranes that become visible at 7 weeks, while MCMA twins have a common amniotic cavity without dividing membranes (Fig. 4.15). DC pregnancies always have two thick trophoblastic tissue layers and two amniotic membranes between the twins; on the ultrasound image these layers and membranes appear as one thick wall.17 At the end of the first trimester and beginning of the second, trophoblastic tissue in the angle between two placentas and chorionic cavities constitutes the ‘lambda’ sign, which is characteristic for DC pregnancies.18 68
✩✩✩✩✩✩✩✩✩✩✩ ✩ A
Investigation of early pregnancy
B
Fig. 4.15 Twin pregnancies. (A) Dichorionic diamniotic twins at 7 weeks; notice the thick trophoblastic tissue between the gestational sacs. (B) Monochorionic diamniotic twin pregnancy at 8 weeks; the amniotic membrane (arrow) may be difficult to identify.
Evaluation of Early Pregnancy Failure Early Pregnancy Loss According to the literature on embryology and sonoembryology, the size and morphology of both embryonic and extraembryonic structures show little variation in pregnancies of the same age.6–9,16 Of extraembryonic structures, especially the yolk sac and the amniotic sac show a growth pattern that is closely related to embryonic development. Measurement of the gestational sac has been used for pregnancy evaluation, but one must be aware of the rather large variation of its size in normal pregnancies. This knowledge can be used as the basis for the evaluation of the early pregnancy, when significant departures from normal development and measurements are found. A threatened abortion is defined as a painless vaginal bleeding occurring before 24 weeks of pregnancy. A spontaneous abortion may be incomplete or complete. In first-trimester bleeding, neither statistical prediction models based on signs and symptoms nor clinical judgement are valid replacements for ultrasonographic assessment in establishing a diagnosis.19 No single ultrasound measurement of different anatomical features in the first trimester has been shown to have a high predictive value for determining early pregnancy outcome.20 Therefore a systematic evaluation of the early conceptus using combined biometric parameters is recommended.2 69
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Gestational sac (chorionic cavity) and amniotic cavity The size of the gestational sac (chorionic cavity) has been used to evaluate normal progress of the early pregnancy. An abnormal size of the chorionic cavity, compared with the size of the embryo, has traditionally been associated with impending early pregnancy loss21,22 but its significance has not been extensively documented.23 This is probably due to the large variability of its size in normal pregnancies.9 Abnormality is probable when the mean size of the chorionic cavity is >10 mm without a yolk sac or >20 mm without an embryo. Another method of evaluating development is to compare the size of the amniotic cavity with the CRL.23 Embryologists have shown the close relationship between the amniotic cavity volume and fetal size. This has been confirmed by ultrasound studies showing a remarkable similarity in the absolute values of CRL and the mean diameter of the amniotic cavity in normal pregnancies between 7 and 11 weeks.9 A significant discrepancy between these two parameters is a possible sign for abnormality. A mean amniotic cavity diameter that is significantly less or larger than the actual CRL or an amniotic sac that is smaller than the yolk sac, or even absent after 7 weeks, are suspicious signs of abnormal development. If the size of the gestational sac or the embryo is smaller than the expected age, the possibility of incorrect age should always be considered and a repeat scan should be performed after 1 week. Normal growth and appearance of additional anatomical details may then rule out an abnormal early development. Yolk sac The yolk sac plays an important role in the early nutrition of the embryo, and is the source of early haematopoiesis.16 Thus, abnormal embryonic development may be reflected in an abnormal appearance of the yolk sac. However, many pregnancies that end in abortion show normal appearance of the yolk sac at an initial early scan; conversely, changes of shape and echogenicity have been found in uncomplicated pregnancies.23 In general, the finding of a yolk sac which is <3.0 mm between 6 and 10 weeks, >7 mm before 9 weeks, absent or clearly irregular in shape indicates a possible abnormal early pregnancy.
70
Haematoma Intrauterine haematomas are blood accumulations that are subchorionic, retroplacental or both (Fig. 4.16). The results from numerous studies of the intrauterine haematoma are not unequivocal. Today, the importance of intrauterine haematoma for early pregnancy loss is played down.23 A study from 2001 even concludes that intrauterine haematomas do not have a deleterious effect on pregnancy outcome in a population with recurrent miscarriage.24 But it seems reasonable to assume that if the haematoma lies under the placenta and cord insertion, it has the potential to lead to placental separation and abortion; and that also very large subchorionic haematomas may cause uterine contractions with subsequent pregnancy loss.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Umbilical cord Uterus
Haematoma Embryo
Trophoblastic tissue
Investigation of early pregnancy
Chorionic cavity
Fig. 4.16 8/4 weeks pregnancy showing an intact normal embryo and its umbilical cord. There is a large haematoma on the outer side of the gestational sac. The amniotic membrane is not visible on this image.
Heart rate There is a good correlation between the heart rate and embryonic size and age. Alterations of the embryonic heart rate such as arrhythmia and/or bradycardia may be associated with maldevelopment.22,25 Embryonic heart rate measurements in early pregnancy may be useful in the prediction of first-trimester spontaneous abortion after ultrasound-proven viability, but a heart rate below the 95% confidence interval of normal does not necessarily indicate a poor outcome.26 A general rule is that if the embryo has a CRL of 6 mm or more, the lack of heart activity is highly suspicious for intrauterine embryonic/fetal death. A significant relationship to abortion has been found when the heart rate is less than 1.2 SD from the mean.21
Trophoblastic Disease Gestational trophoblastic diseases are complete, partial and invasive moles, placental site trophoblastic tumours and choriocarcinomas. An invasive hydatidiform mole is defined by penetration of molar villi into the myometrium or vasculature of the uterus. Both complete and partial moles can become invasive. Ultrasound has replaced all other techniques for early diagnosis and management of these conditions.27 However, a routine pre-evacuation ultrasound examination identifies less than 50% of hydatidiform moles, the majority sonographically appearing as missed or incomplete miscarriage.28 Testing β-hCG levels of maternal serum is still of major importance for the evaluation and follow-up of treatment.
71
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Complete hydatidiform mole Complete hydatidiform mole develops when the diploid chromosomal set of the conceptus is entirely derived from paternal chromosomes. Patients with complete hydatidiform mole present a large uterus, vaginal bleeding and abnormally high β-hCG levels. The latter causes hyperstimulation of the ovaries, resulting in enlargement through theca lutein cysts in 50% of cases. The ultrasound examination reveals a uterine cavity filled with multiple cysts and echogenic areas of variable size and shape (‘snow-storm’ appearance) in the absence of an embryo or fetus (Fig. 4.17). One must be aware that certain rare uterine tumours may resemble moles. Using ultrasound, approximately 79% of complete hydatidiform moles are detected.28 Partial hydatidiform mole In partial hydatidiform mole, a fetus is found in association with molar degeneration of the placenta. Partial moles are usually of triploid or diandric origin, having two sets of chromosomes of paternal origin and one of maternal origin (69,XXX or 69,XXY).27 Partial mole presents on ultrasound examination as an enlarged placenta; it is thicker than 4 cm at the level of the cord insertion at the second-trimester routine scan and contains many cystic areas (‘Swiss cheese’ appearance). The diagnosis of partial mole is more difficult than that of a complete mole; only 29% were detected in a large study by Fowler et al.28 Doppler investigation plays a limited role in diagnosis or management.27 The fetus is usually growth retarded and shows variable congenital anomalies. Invasive hydatidiform mole An invasive mole usually appears clinically with bleeding after surgical evacuation of a molar pregnancy. Sonographically, nodular areas of increased echogenicity are found in the uterine wall. The lesions may contain fluid-filled cavities.27 Doppler may be used to evaluate the effectiveness of medical therapy. Choriocarcinoma Choriocarcinoma is highly malignant, developing from trophoblastic tissue and metastasizing into lungs, liver or brain. Women with metastases may present
72
Fig. 4.17 Complete hydatidiform mole: uterine cavity filled with multiple cysts and echogenic areas of variable size and shape.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Ectopic Pregnancy A common cause for early pregnancy failure in the western world is ectopic pregnancy. The prevalence of this condition is nearly 2%, accounting for 9% of pregnancy-related deaths of reproductive-aged women in the first trimester in the USA.29 There are many risk factors, the highest risk being found in patients who have had tubal surgery including sterilization, previous ectopic pregnancy, in utero exposure to diethylstilboestrol, IUD and documented tubal pathology.30 Early diagnosis of an ectopic pregnancy is important because it contributes to a decline in morbidity, maternal deaths and treatment costs. As the identification of an ectopic pregnancy can be difficult, the first step in ruling out ectopic pregnancy should be to identify intrauterine pregnancy which can virtually always be identified after 5.5 weeks by transvaginal ultrasound. Quantitative hCG serum analysis is an important additional test, when an intrauterine pregnancy cannot be seen. Ectopic pregnancy should be assumed when the hCG serum test is above the discriminatory zone in which a pregnancy should always be detected by transvaginal sonography (TVS) (β-hCG concentrations =1500 IU/L).30 Sonographically, an extrauterine gestational sac surrounded by an echogenic ring consisting of the trophoblast at the implantation is usually seen (Fig. 4.18). Other ultrasound signs for ectopic pregnancy are any non-cystic extraovarian adnexal mass, complex cystic or solid masses and, of course, a living ectopic pregnancy, which is found in approximately 5–15% of cases. Viability of ectopic pregnancies can be evaluated by transvaginal Doppler ultrasound because of the good vascularization of the trophoblastic ring. The scan for ectopic pregnancies must be performed thoroughly and systematically. One must be aware of special ectopic locations such as interstitial pregnancy, which occurs in 1–6% of all ectopic pregnancies,31 or cervical pregnancy, which accounts for only 0.15%.32 The ultrasound diagnosis of an interstitial pregnancy is made when products of conception are visible in the upper lateral aspect of the uterus, outside the uterine cavity and at least partially surrounded by myometrium.31 In cervical pregnancies, the gestational sac is found below the internal os of the uterus. To miss the diagnosis of these two variants of ectopic pregnancy imposes extraordinary risks to affected women, because these conditions may lead to acute life-threatening bleeding, which may be difficult to treat. One must also be aware of the possibility of concomitant intrauterine and ectopic pregnancies. The occurrence of heterotopic pregnancies is increased in pregnancies achieved by assisted fertilization.
Investigation of early pregnancy
with dyspnoea, abdominal pain and neurological symptoms. The primary symptom is vaginal bleeding. Choriocarcinoma may be found after a molar pregnancy, a miscarriage or after an apparently normal pregnancy. The sonographic appearance of a choriocarcinoma resembles that of an invasive mole. The primary tumour of a choriocarcinoma in an apparently normal placenta is usually small, less than 8 mm. So far, such a primary tumour has not been described sonographically.27
73
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
A
Uterus Ovary
right
left
B
Ectopic pregnancy
Ovary
Fig. 4.18 Ectopic pregnancy. (A) Transverse section through the female pelvis; ovary on the right side of the uterus. (B) Laterally from the right ovary an ectopic pregnancy with a living embryo can be seen. See also standardization, Fig. 4.21.
A review of six different diagnostic algorithms for ectopic pregnancy concluded that a combination of ultrasound and hCG resulted in the best outcomes. Ultrasound as the first step was the most efficient and accurate method of diagnosing ectopic pregnancy.29
Early Anomalies
74
High-frequency transvaginal transducers have made it possible to disclose structural developmental disorders of the embryo (before 10 weeks) and the young fetus. An increasing number of studies, reviews and case reports describe ultrasound detection of early anomalies.33–37 Nuchal translucency (NT), which may be found at the early 11–13-week-scan, is a well-known transient marker for fetal disorders.38 Both the transabdominal and the transvaginal approach can be used. Though NT is seen in normal fetuses, it is not only highly associated with chromosomal aberrations, but it may also be found in fetuses with skeletal anomalies, neuromuscular disorders, rare genetic disorders, heart defects or infections.38 The likelihood for associated anomalies increases with the thickness of the oedema. Nicolaides and colleagues have described the criteria of NT measurements: CRL 45–83 mm, 11 weeks 0 days to 13 weeks 6 days, preferably but not necessarily TVS, and good sagittal section of the fetus with appropiate magnification. The maximum thickness of subcutaneous translucency is measured by placing the calipers on the inner lines.38
✩✩✩✩✩✩✩✩✩✩✩ ✩
Standardization of Transvaginal and Transabdominal Imaging in Gynaecology In 1992, Timor-Tritsch discussed an inquiry performed by Bernaschek and Deutinger 40 that revealed a world-wide discord about the way TVS images were displayed.41 Timor-Tritsch's recommendation was: ‘Let's all talk the same language!’. To help us talk the same language, we should review some of the basic rules taught at medical school, rules that probably represent a world-wide standard. When we examine a patient, we principally position ourselves on the patient's right side and face the patient. This is the starting point of every examination. When we look at the patient we see the patient's left shoulder on the right. We can imagine we are viewing a ‘screen’ with our own eyes. When gynaecologists perform an examination of the uterus and adnex, they will find the patient's left ovary/adnexa on the right side (of the screen/picture), and the patient's right ovary/adnexa on the left side.
Investigation of early pregnancy
The absence of nasal bone ossification at the end of the first trimester is another marker for possible abnormal development, namely trisomy 21. Evidence based on radiological, histomorphological and sonographic studies has shown that nasal bone abnormalities are significantly more common in trisomy 21 fetuses than in euploid fetuses.39
Imaging in Medicine Pictures of organs or parts of the body should present the normal anatomical relations as exactly as possible. The argument for displaying the TVS pictures on the monitor with the ‘footprint’ of the vaginal probe at the bottom of the screen close to the cervix, while the fundus of the uterus points towards the top of the screen, seems correct and self-explanatory.41 In essence, this would be the ‘natural’ way to display the uterus on the screen, at least through the eyes of a practising gynaecologist who performs a bimanual examination on a patient in the supine position. The cervix would be at the tip of the examining fingers and the fundus of the uterus further away, i.e. cephalad. An additional advantage of displaying the picture with the apex of the ‘pie’ pointing downward or upward would be the ability to tell instantly the difference between an image obtained by the transvaginal or transabdominal route: the apex of the ‘pie’ pointing to the bottom of the screen on the transvaginal picture and to the top of the screen on the transabdominal scan. There are more arguments for this form of imaging. If we move the transabdominal transducer from the midsagittal plane to the left or to the right, we will identify the ovaries lying close to and ‘below’ the iliac vessels. This is the normal relation: the ovary is in a mediodorsal position to the iliac vessels. In the TVS image display, this anatomical relation should be maintained. For the transverse plane, the transducer is rotated 90 ° to the left, imaging the right adnexa on the left side of the picture and vice versa for the left adnexa.
75
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Ventral
Cranial
Caudal
Dorsal Fig. 4.19 Transabdominal sonography (TAS) and transvaginal sonography (TVS) of the female pelvis; sagittal insonation angle.
Ventral
Cranial
Caudal
Dorsal Fig. 4.20 Direction of the sagittal imaging sectors of TAS and TVS through the female pelvis. Note that the cranial part of the pelvis points to the left side, and the caudal part points to the right side. Imagine that the observer's position is on the right side of the patient.
Ventral/cranial
Right
Left
90 Dorsal/caudal
76
Fig. 4.21 By turning the transducers 90˚, a transverse section of the pelvis is shown. Note that the right part of the pelvis is shown on the left side of the image, and the left part on the right side. Imagine that the observer looks at the patient's body from below.
✩✩✩✩✩✩✩✩✩✩✩ ✩
References 1. Regan L, Rai R. Epidemiology and the medical causes of miscarriage. Baillière's Clin Obstet Gynecol 2000;14(5):839–854 2. Blaas H-GK. Editorial: the examination of the embryo and early fetus: how and by whom? Ultrasound Obstet Gynecol 1999;14(3):153–158 3. Takeuchi H. Transvaginal ultrasound in the first trimester of pregnancy. Early Hum Dev 1992;29:381–384 4. Timor-Tritsch IE, Farine D, Rosen MG. A close look at the embryonic development with the high frequency transvaginal transducer. Am J Obstet Gynecol 1988;159:678–681 5. Timor-Tritsch IE, Peisner DB, Raju S. Sonoembryology: an organ-oriented approach using a high-frequency vaginal probe. J Clin Ultrasound 1990;18:286–298 6. Blaas H-G, Eik-Nes SH, Kiserud T, Hellevik LR. Early development of the forebrain and midbrain: a longitudinal ultrasound study from 7 to 12 weeks of gestation. Ultrasound Obstet Gynecol 1994;4:183–192 7. Blaas H-G, Eik-Nes SH, Kiserud T, Hellevik LR. Early development of the hindbrain: a longitudinal ultrasound study from 7 to 12 weeks of gestation. Ultrasound Obstet Gynecol 1995;5:151–160 8. Blaas H-G, Eik-Nes SH, Kiserud T, Hellevik LR. Early development of the abdominal wall, stomach and heart from 7 to 12 weeks of gestation: a longitudinal ultrasound study. Ultrasound Obstet Gynecol 1995;6:240–249 9. Blaas H-G, Eik-Nes SH, Bremnes JB. Embryonic growth. A longitudinal biometric ultrasound study. Ultrasound Obstet Gynecol 1998;12(5):346–354 10. Zalen-Sprock R, Brons JTJ, Vugt J, Harten H, Geijn H. Ultrasonographic and radiologic visualization of the developing embryonic skeleton. Ultrasound Obstet Gynecol 1997;9:392–397
11. Robinson HP, Fleming JEE. A critical evaluation of sonar ‘crown-rump length’ measurements. Br J Obstet Gynaecol 1975;82:702–710 12. Reece EA, Scioscia AL, Green J, O'Connor TZ, Hobbins J. Embryonic trunk circumference: a new biometric parameter for estimation of gestational age. Am J Obstet Gynecol 1987;156:713–715 13. Robinson HP, Shaw-Dunn J. Fetal heart rates as determined by sonar in early pregnancy. J Obstet Gynaecol Br Cwlth 1973;80:805–809 14. Cyr DR, Mack LA, Schoenecker SA et al. Bowel migration in the normal fetus: ultrasound detection. Radiology 1986;161:119–121 15. Timor-Tritsch IE, Warren WB, Peisner DB, Pirrone E. First trimester midgut herniation: a high frequency transvaginal sonographic study. Am J Obstet Gynecol 1989;161:466–476 16. O'Rahilly R, Müller F. Developmental stages in human embryos. Carnegie Institute Publications, Washington, DC 17. Monteagudo A, Timor-Tritsch IE. Early and simple determination of chorionic and amniotic type in multifetal gestations in the first fourteen weeks by high-frequency transvaginal sonography. Am J Obstet Gynecol 1994;170:824–829 18. Sepulveda W, Sebire NJ, Hughes K, Odibo A, Nicolaides KH. The lambda sign at 10–14 weeks of gestation as a predictor of chorionicity in twin pregnancies. Ultrasound Obstet Gynecol 1996;7(6):421–423 19. Waard MW, Bonsel GJ, Ankum WM, Vos J, Bindels PJE. Threatened miscarriage in general practice: diagnostic value of history taking and physical examination. Br J Gen Pract 2002;52(483):825–829 20. Jauniaux E, Johns J, Burton G. The role of ultrasound imaging in diagnosing and
Investigation of early pregnancy
By simply looking at the image, it should be easy to distinguish whether the scan was done by TVS or TAS. Further, it must be possible to correlate TVS and TAS images from the same patient. When TVS and TAS images are standardized as indicated above, it is easy to recognize a TAS (‘pie apex up’) from a TVS (‘pie apex down’). In the transverse plane we will expect to find the patient's left ovary on the right side of the image and in the sagittal plane we will expect to find the bladder on the right side. If the uterus is pointing towards the right in a sagittal plane it is anteflexion; if it is pointing to the left, it is retroversion – no further explanation needed.
77
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
78
investigating early pregnancy failure. Ultrasound Obstet Gynecol 2005;25:613–624 21. Falco P, Milano V, Pilu G et al. Sonography of pregnancies with first-trimester bleeding and a viable embryo: a study of prognostic indicators by logistic regression analysis. Ultrasound Obstet Gynecol 1995;7:165–169 22. Makrydimas G, Sebire NJ, Lolis D, Vlassis N, Nicolaides KH. Fetal loss following ultrasound diagnosis of a live fetus at 6-10 weeks of gestation. Ultrasound Obstet Gynecol 2003;22:368–372 23. Jauniaux E, Kaminopetros P, El-Rafaey H. Early pregnancy loss. In: Rodeck J, Whittle M (eds) Fetal medicine: basic science and clinical practice. Harcourt Brace, London, 1999: 835–847 24. Tower C, Regan L. Intrauterine haematomas in a recurrent miscarriage population. Hum Reprod 2001;16(9):2005–2007 25. Schats R, Jansen CAM, Wladimiroff JW. Abnormal embryonic heart rate pattern in early pregnancy associated with Down's syndrome. Hum Reprod 1990;5(7):877–879 26. Achiron R, Tadmor O, Mashiach S. Heart rate as a predictor of first-trimester spontaneous abortion after ultrasoundproven viability. Obstet Gynecol 1991;78:330–334 27. Jauniaux E. Ultrasound diagnosis and follow-up of gestational trophoblastic disease. Ultrasound Obstet Gynecol 1998;11:367–377 28. Fowler DJ, Lindsay I, Seckl MJ, Sebire NJ. Routine pre-evacuation ultrasound diagnosis of hydatidiform mole: experience of more than 1000 cases from a regional referral center. Ultrasound Obstet Gynecol 2006;27:56–60 29. Gracia C, Barnhart K. Diagnosing ectopic pregnancy: decision analysis comparing six strategies. Obstet Gynecol 2001;97:464–470 30. Pisarska M, Carson S, Buster J. Ectopic pregnancy. Lancet 1998;351(9109):1115–1120 31. Hafner T, Aslam N, Ross J, Zosmer N, Jurkovic D. The effectiveness of non-surgical
management of early interstitial pregnancy: a case report of ten cases and review of the literature. Ultrasound Obstet Gynecol 1999;13:131–136 32. Jurkovic D, Hacket E, Campbell S. Diagnosis and treatment of early cervical pregnancy: a review and a report of two cases treated conservatively. Ultrasound Obstet Gynecol 1996;8:373–380 33. Blaas H-G, Eik-Nes SH. First-trimester diagnosis of fetal malformations. In: Rodeck J, Whittle M (eds) Fetal medicine: basic science and clinical practice. Harcourt Brace, London, 1999: 581–597 34. Blaas H-GK, Eik-Nes SH, Isaksen CV. The detection of spina bifida before 10 gestational weeks using 2D- and 3D ultrasound. Ultrasound Obstet Gynecol 2000;16:25–29 35. Blaas H-GK, Eik-Nes SH, Vainio T, Isaksen CV. Alobar holoprosencephaly at 9 weeks gestational age visualized by two- and threedimensional ultrasound. Ultrasound Obstet Gynecol 2000;15:62–65 36. Rottem S, Bronshtein M. Transvaginal sonographic diagnosis of congenital anomalies between 9 weeks and 16 weeks menstrual age. J Clin Ultrasound 1990;18:307–314 37. Souka AP, Nikolaides KH. Diagnosis of fetal abnormalities at the 10–14-week scan. Ultrasound Obstet Gynecol 1997;10:429–442 38. Nicolaides KH, Sebire NJ, Snijders R. The 11–14-week scan. The diagnosis of fetal abnormalities. Parthenon, Carnforth, 1999 39. Sonek J, Cicero S, Neiger R, Nicolaides K. Nasal bone development in prenatal screening for trisomy 21. Am J Obstet Gynecol 2006;195(5):1219–1230 40. Bernaschek G, Deutinger J. Current status of vaginosonography: a world-wide inquiry. Ultrasound Obstet Gynecol 1992;2:352–356 41. Timor-Tritsch I. Opinion: standardization of ultrasonographic images: let's talk the same language. Ultrasound Obstet Gynecol 1992;2(5):311–312
5 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks David A Nyberg Vivienne L Souter
Abstract A screening obstetric ultrasound during the second trimester has been widely adopted around the world and can provide important information regarding the fetus and pregnancy. The fetus can be examined quite literally from head to toe, which has led to the concept of the fetal ‘anatomical survey’. A fetal anatomical survey requires a systematic approach that should be performed in all secondtrimester fetuses, regardless of the indication for the ultrasound. Familiarity with normal anatomy is essential to recognize deviations from normal or fetal anomalies. Centres should attempt to exceed basic guidelines.
Keywords Fetal abnormalities, fetus, normal, normal anatomy, prenatal sonography.
Introduction A screening obstetric ultrasound during the second trimester has been widely adopted around the world. This can provide important information regarding the pregnancy, including evaluation for placenta praevia, evaluation of the cervix and cervical incompetence and, most importantly, evaluation of the fetus. The fetus can be examined quite literally from head to toe, which has led to the concept of the fetal ‘anatomical survey’. Parents might even consider this their baby's first physical examination. In the vast majority of cases the fetus appears normal and parents can be reassured regarding the health of their baby. At the same time, a systematic fetal survey can now detect the majority of fetal malformations.1 A second-trimester scan is also desired by most prospective parents and has been found to be cost-effective, at least at centres that have reasonable accuracy for detection of fetal anomalies.2
79
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The timing of the second trimester ultrasound varies between centres. While later scans permit improved anatomical detail and greater sensitivity for many structural defects, earlier scans can both provide useful information earlier and also about the risk of fetal chromosome abnormality. For this reason, fetal surveys may be performed earlier at 15–18 weeks, coinciding with the time of genetic amniocentesis or second-trimester maternal serum screen. At our own centre, patients obtain a scan at 15–18 weeks if they are considering genetic amniocentesis or at 18–22 weeks if they are considered low risk. This approach supports other studies which suggest that, at least among low-risk women, a later scan will provide more information and is less likely to result in a repeat scan.3 Centres that perform a first-trimester (10– 14 weeks) ultrasound that includes nuchal translucency measurements and early fetal evaluation will also usually obtain a later scan at 18–22 weeks.
Scan Guidelines Guidelines for a normal anatomical survey have been published by various institutions.4,5 However, most centres now routinely include documentation of other anatomical structures beyond the basic set suggested by society guidelines. We have further modified the guidelines to reflect the completeness of a fetal survey performed at most obstetric centres (Box 5.1). Procedures that adhere to these guidelines should result in detection of the majority of major detectable anomalies. Because most anomalies are sporadic and occur in otherwise low-risk women, it is important that all scans performed during the second trimester include a fetal survey as an essential part, regardless of the reason for performing the scan. Detection of anomalies does not require a detailed understanding of pathology; it only requires thorough familiarity with normal anatomy. Deviations from normal or suspected anomalies can then be referred to a high-risk centre for a more detailed fetal ultrasound examination and clinical consultation.
Normal Fetal Anatomy Brain/Calvarium Views of the brain should include three standard axial views: transthalamic, transventricular and transcerebellar (Figs 5.1–5.4). These three views permit a reliable prenatal diagnosis of nearly all significant intracranial anomalies as well as providing important clues for the vast majority of spinal dysraphic defects before the time of viability.6–8,84
80
Transthalamic view The transthalamic view (see Fig. 5.1) is the standard plane used for obtaining biometric cranial measurements (biparietal diameter (BPD) and head circumference). At this level, one can also visualize the frontal horns of the lateral ventricles and the cavum septum pellucidum between the frontal horns. The cavum septum pellucidum (CSP), and its posterior extension the cavum vergae, is a fluid-filled midline structure located between the lateral ventricles. Sonographically, it is
✩✩✩✩✩✩✩✩✩✩✩ ✩
Box 5.1 Elements of fetal anatomical survey at 18–22 weeks
Face/Neck Face (lips, mouth, nose, orbits and ears) Neck (nuchal fold) Spine Longitudinal and transverse views Thorax Heart – documentation of venous–atrial, atrial–ventricular and ventricular–arterial connections which may include the following views: •• Four chamber •• Right ventricular outflow •• Left ventricular outflow •• Aortic arch •• Ductal arch Lungs Bony thorax
Normal fetal anatomy at 18–22 weeks
Head and Brain Calvarium Brain – documentation of thalami, hemispheres, lateral ventricles, cerebellum and vermis which includes the following views: •• Transthalamic •• Transventricular •• Transcerebellar
Abdomen Major organs (stomach, liver, spleen, gallbladder) Gut Anterior abdominal wall Genitourinary tract Kidneys Urinary bladder Genitalia Extremities, bony skeleton Upper extremities including both hands Lower extremities including both feet Data from reference 4. Evaluation should also include estimation of dates (or evaluation of growth). This should include, as a minimum, measurements of biparietal diameter, head circumference, abdominal circumference and femur length (humerus length). Obstetric ultrasound should also include assessment of the placenta, cervix, amniotic fluid and possible adnexa. Adapted from Yoo et al.44
usually identified as a fluid-filled structure anterior to the thalami on axial images. It should not be mistaken for the third ventricle which is smaller and located more posteriorly between the thalami. Presence of the CSP suggests proper formation of the midline cerebral structures.85 When specifically sought, the CSP can be identified in most cases. However, it may be difficult to visualize on standard views, especially before 20 weeks. Both the CSP and corpus callosum can be better seen on transvaginal scans (see Fig. 5.2).9 The corpus callosum shows gradual enlargement during pregnancy, from nearly
81
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.1 Transthalamic view. Axial view through the mid head shows normal thalami (Th). The cavum septum pellucidum (CSP) is a small midline fluid space anterior the thalami.
17 mm in length at 18 weeks' gestation to 44 mm at term. The ratio of the length of the corpus callosum to the anteroposterior diameter of the brain remains relatively constant from 20–21 weeks' gestation to term. Transventricular view The transventricular view is obtained at a plane just superior to the transthalamic view (see Fig. 5.3). Demonstration of the lateral cerebral ventricles in this view is essential for the early detection of hydrocephalus. Within the ventricular system lies the echogenic choroid plexus, best seen filling the body of the lateral ventricle from medial to lateral wall, and extending into the atrium (or trigone). The choroid plexus does not extend into the frontal horns, and they are identified as A
B
82
Fig. 5.2 Transvaginal scans show normal-appearing corpus callosum (CC) in (A) coronal and (B) sagittal planes. FH, frontal horns; CSP, cavum septum pellucidum.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks Fig. 5.3 Axial sequence images from superior to inferior as seen with tomographic ultrasound imaging (TUI). The images are set at standard 3 mm intervals in this case. Note that the choroid (CH) fills the lateral cerebral ventricles and this is located at a plane superior to the transthalamic view. TH, thalamus; C, cerebellar hemispheres; CM, cisterna magna.
prominent anechoic anterior components of the lateral ventricles. In contrast, the surrounding cerebral cortex is hypoechoic with scarcely more echogenicity than the CSF. After about 18 weeks, the posterior aspect of the lateral ventricles (atria and occipital horns) is drawn laterally with development of the temporal horns. Simultaneously, the ventricles and choroid appear less pronounced with growth of the cerebral hemispheres.
Fig. 5.4 Transcerebellar view. Slightly oblique scan through the posterior fossa shows cerebellar hemispheres (C) which show a normal biconvex shape, outlined by the cisterna magna (CM). This single normal view excludes nearly all open spinal defects.
83
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
84
The standard measurement of the cerebral ventricle is obtained in an axial plane through the atrium. Most studies have found the mean size of the ventricular atrium to be in the range of 5.4–6.5 mm, with 10 mm considered to be a cut-off for abnormal.10,11 However, even lesser degrees of ventricular dilation may prove to be significant during the second trimester.12 Although 10 mm is a commonly accepted cut-off for normal size, others have found that ventricle size over 8 mm is unusual before 25 weeks.13 Mild or borderline degrees of cerebral ventricular dilation pose a difficult dilemma since most fetuses are perfectly normal but some have underlying abnormalities or experience adverse outcome.14,15 Idiopathic lateral ventricular dilation is more common among male fetuses16 and in our experience, this is more common in those who are large for gestational age. Detection of borderline or mildly dilated cerebral ventricles is controversial. Careful techniques should be used to evaluate the ventricles. Off-axis or angled planes can overestimate the size of the lateral ventricles.17 Reverberation artifact from bone normally obscures the proximal hemisphere. A technique employing an oblique scan plane angled superiorly through the temporal bone affords markedly improved visualization of the proximal hemisphere.18,19 A common ‘normal variant’ on transventricular views is a choroid plexus cyst. These are identified as often as 3–4% at 15–18 weeks20 and approximately 1% at 18–22 weeks. Choroid plexus cysts have been the subject of much study and debate.21–24 There is now generalized consensus that they are of no direct consequence themselves. They appear to slightly increase the risk of fetal chromosome abnormality, especially trisomy 18. However, as an isolated finding in a low-risk patient, this risk is considered to be low and amniocentesis is not recommended.25 Transcerebellar view The transcerebellar or posterior fossa view is obtained by slightly angling the scan plane down posteriorly from the axial image for BPD determination until the cerebellum and cisterna magna are delineated (see Fig. 5.4).26,27,86 This view is important for identification of the Dandy–Walker malformation and cerebellar agenesis and can provide diagnostic information regarding the presence or absence of the Arnold–Chiari malformation, seen with nearly all cases of open spina bifida. This scan plane is also useful for evaluating the nuchal soft tissue thickness. The cerebellar hemispheres can easily be seen on each side of the echogenic midline vermis, anterior to the cisterna magna. The cerebellum appears slightly more echogenic than the cerebral hemispheres and is separated from supratentorial structures by the tentorium. The cerebellar hemispheres are biconvex in shape. The normal fourth ventricle can be occasionally visualized within the midbrain by high-resolution scans. It appears as a triangular-shaped small fluid space between the cerebellar hemispheres. The cisterna magna appears as a sonolucent space just posterior to the cerebral hemispheres and vermis near the base of the brain. The presence of a normal cisterna magna (CM) excludes nearly all open spinal defects. Standardized measurements of the cisterna magna, with a normal range of roughly 3–10 cm, are taken in the midline from the vermis to the occipital bone.28 Measured values
✩✩✩✩✩✩✩✩✩✩✩ ✩
Face and Neck
Normal fetal anatomy at 18–22 weeks
at the lowest end of this range are expected only early in gestation, while conversely a cisterna magna of large dimension is generally seen in the third trimester. Occasionally a measurement exceeds these standards, which is usually still normal if the vermis is well seen and intact and the transverse cerebellar diameter is normal for gestational age. An inappropriate scan plane can also lead to an abnormally large measurement of the CM or even the appearance of a Dandy–Walker variant.29 Caution should be exercised in diagnosis of incomplete closure of the vermis in the early second trimester;30 however, the normal vermis should be closed by 18 weeks. In most fetuses, 1–3 linear echoes can be seen traversing the CM posteriorly from the cerebellum. Although originally mistaken for the straight sinus, these lines are now attributed to ‘subarachnoid septa’31 or ‘dural folds’.32 Occasionally they may appear ‘cyst-like’ and simulate a posterior fossa cyst.
Examination of the face is not included in basic examination guidelines; however, it is generally easy to perform and may provide important information. Parents also desire and easily recognize views of the face. Views of the face are particularly important when other anomalies are suspected. For all these reasons, we believe views of the face should be included in any fetal survey at 18–22 weeks. Imaging of the fetal face can be accomplished in coronal, sagittal and axial planes as well as three-dimensional (3D) multiplanar ultrasound (Figs 5.5–5.8). Each scan plane has advantages and disadvantages, and a combination of scan planes is often desired, when positioning is favourable, to adequately delineate all anatomy. A midline sagittal scan, or profile view, is one of the most recognizable images of any fetus (see Fig. 5.5). It is useful for evaluation of size and position of the mandible for exclusion of micrognathia, the nose and nasal bridge, and the tongue. Coronal imaging of the soft tissues of the nose and upper lip can be easily shown at 18–22 weeks (see Fig. 5.6). This view is most useful for exclusion of cleft lip, with or without cleft palate. Although mild forms of cleft lip/cleft palate can be missed earlier, the majority of clefts should be visualized by 18–22 weeks.
Fig. 5.5 Midline sagittal view of the face shows normal structures including a normal nasal bone (NB).
85
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
86
Fig. 5.6 Coronal view through the superficial soft tissues shows a normal upper lip (L) and nose (N).
On the other hand, cleft palate without associated cleft lip (aetiologically distinct from cleft lip with or without cleft palate) remains undetected throughout pregnancy, with rare exceptions. Although the soft tissue view is most useful, coronal views more posteriorly within the face may show the oral cavity and deep nasal structures. This can be useful for showing the involvement of cleft palate when cleft lip is suspected. Transverse or axial views are also useful when cleft lip/palate is suspected. The upper lip and anterior maxilla can be imaged simultaneously in this plane, and the integrity of the alveolar ridge can be demonstrated.33 The oral cavity may also be nicely imaged in the axial plane. When the upper lip is evaluated on coronal images, the nose also comes into plane. The nose should be normal in size and shape; two ala should be demonstrated. Some familial and racial differences are probably evident in the appearance of the nose. The orbits are best imaged in the axial or coronal plane (see Fig. 5.7). Measurement of the outer orbital diameter (OOD), which correlates with gestational age,34 allows for detection of hypo/hypertelorism. Intraorbital anatomy that can be identified includes the globe, lens and hyaloid artery. The fetal ears are not frequently targeted for imaging, but when necessary can be easily identified as complex soft tissue protrusions external to the skull.35
Fig. 5.7 Axial image through the orbits shows normal measurements of the orbital diameter (OD), binocular diameter (BOD), and interocular diameter (IOD).
✩✩✩✩✩✩✩✩✩✩✩ ✩
Because of their complex shape, they are best imaged using 3D multiplanar ultrasound (see Fig. 5.8). Normal ear size has been documented in an effort to detect small ears as a sign of fetal chromosome abnormality.36 Fetal hair may be seen during the third trimester37 but is not seen at this time. Evaluation of the soft tissue of the back of the neck (nuchal fold or nuchal thickness) has proven to be one of the best sonographic ‘markers’ for trisomy 21 during the second trimester.38-40 Although detection of sonographic markers is generally performed earlier, with nuchal translucency assessed as early as 10–14 weeks, nuchal thickness can still be evaluated before 20 weeks, and probably as late as 22 weeks. It should be included on any routine fetal anatomical survey during the second trimester. Because nuchal thickness increases with gestational age, absolute cut-offs will be useful throughout the pregnancy. Other neck structures are not routinely sought during the anatomical survey. Normal thyroid size has been documented since 20 weeks.41 However, cystic hygromata or other neck masses can be detected.
Normal fetal anatomy at 18–22 weeks
Fig. 5.8 Face, 3D multiplanar ultrasound. A variety of normal structures on a single image, including normal mouth, jaw, lips, orbits and ear.
Spine The fetal spine is well developed at 18–22 weeks. Each vertebral segment is composed of three ossification centres which appear echogenic sonographically.42 The anterior centre is the developing vertebral body while the posterior centres are formed at the junction of the lamina and the pedicle on each side.43 The ossification centres lie in a symmetrical triangular configuration, with the posterior centres oriented towards the midline. Imaging of the fetal spine can be accomplished in three planes: parasagittal, coronal and transverse. While the parasagittal and coronal images give the best overall views of the spine (Fig. 5.9), transverse images permit simultaneous evaluation of both the ossification centres and the overlying soft tissues (Fig. 5.10). Although transverse images look only at a single level, the entire spine can be quickly evaluated with transverse images with real-time ultrasound. Threedimensional multiplanar ultrasound can also be used to evaluate the spine and other bony structures (Fig. 5.11).
87
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.9 Longitudinal view shows normal spine (Sp) extending to the sacral spine.
Parasagittal imaging of the entire spine demonstrates two rows of roughly parallel ossification centers, one being the vertebral bodies and the other one a row of posterior centres. While this plane of section nicely demonstrates the overall appearance of the spine and delineates the posterior soft tissues adjacent to the midline, it theoretically might be less sensitive for subtle widening between the paired posterior ossification centres. Coronal images may be oriented to show both posterior ossification centres. However, this plane does not show visualization of the posterior soft tissues.
Heart The 18–22-week scan is an ideal time to evaluate the fetal heart.87 Indeed, the heart can usually be evaluated in great detail at this time. In additional to the requisite four-chamber view, most centres have now adopted the policy of additional views of the outflow tracts and great vessels.44,87,88 A systematic approach using specific views will result in optimal detection of cardiac defects. However, specific views are not a substitute for understanding normal anatomical relationships. Also, it should be stressed that static images are not sufficient for evaluating complex anatomical structures. Nowhere is this more true than when evaluating the dynamic fetal heart.
88
Fig. 5.10 Spine. Transverse view shows normal anterior (Ant) and posterior (Post) ossification centres and overlying skin posteriorly.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks
Fig. 5.11 3D multiplanar view shows normal spine (Sp), ribs (R) and scapula (Sc).
Obtaining a good four-chamber view is usually not difficult at 18–22 weeks although it requires good ultrasound technique (Fig. 5.12).45-47 This view is best obtained from an anterior or left lateral approach to avoid the spine and ribs. The scan plane is transverse through the lower thorax; however, the transducer is actually tilted slightly cephalad toward the spine to include the atria which are located posterior and superior to the ventricles. This can be accomplished by beginning the plane inferior to the heart and angling up slightly to the thorax. Using the four-chamber view, evaluation of the heart begins by overall assessment of the position, axis and size of the heart.48,49 The heart lies anteriorly within the thorax, slightly to the left of midline. The cardiac apex, as determined by a line through the ventricular septum, is directed to the left side of the hemithorax at about a 45 ° angle from the midline or roughly equidistant from the anterior and lateral aspects of the chest.50 The heart should occupy about one-third of the thorax; an abnormal heart to thoracic ratio can help identify a variety of cardiac defects.51 Cardiac rate and rhythm should be noted, with a normal range of 120–160 beats per minute from the second trimester to term.
89
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.12 Normal four-chamber axial view of the heart. LV, left ventricle; RV, right ventricle; LA, left atrium; RA, right atrium; PV, pulmonary veins; Ao, aorta.
A checklist of normal anatomical relationships can be confirmed on the fourchamber view, including the following.
• There are two atria of approximately equal size. The left atrium is the most posterior chamber.
• The two atrioventricular valves (mitral and tricuspid) show normal mobility.
• There are two ventricles of approximately equal size and thickness. Both
show normal contractility. The right ventricle is anterior in the midline, just behind the sternum, and the left ventricle is positioned left and posterior to the right ventricle. • The atrial and ventricular septa meet the two atrioventricular valves (mitral and tricuspid) to form the crux of the heart. This crux has a slightly offset cross appearance since the septal leaflet of the tricuspid valve inserts slightly lower in the ventricular septum than the mitral valve. The left atrium is the most posterior chamber and is similar in size to the right atrium. The atrial septum is often difficult to image, but appears as a continuous thin structure with the exception of a physiological opening, the foramen ovale, through which blood flows in the fetus from right to left atrium. • The interventricular septum should appear intact.
90
The ventricular septum appears as a continuous thick muscular structure separating the ventricles, except for its short, thinner membranous portion near the atrioventricular (AV) valves. In some scan planes the ventricular walls or interventricular septum may have a component which is quite hypoechoic relative to the remaining muscle. This is a normal variant secondary to the complex orientation of the cardiac muscle fibres interacting variably as the scan plane changes.52 Fetal rotation or probe position changes may also alter the appearance
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fig. 5.13 Four-chamber view without (left) and with (right) colour flow. Colour flow helps to confirm an intact ventricular septum.
Normal fetal anatomy at 18–22 weeks
and identification of some intracardiac structures, such as the ventricular septum which can vary from appearing relatively thin to rather thick when imaging in orthogonal planes. Colour flow Doppler can help confirm an intact ventricular septum (Fig. 5.13). The moderator band may be seen in the right ventricle. A commonly seen normal variant, usually within the left ventricle, is an echogenic focus caused by a specular reflection from the papillary muscles and chordae tendinae.53–55 This has been referred to as an echogenic intracardiac focus or echogenic chorda tendinae. It is observed in approximately 3–4% of the normal population before 20 weeks, and appears to be even more common among Asian populations. It typically resolves later in gestation and has no direct functional significance. However, an echogenic intracardiac focus does appear to increase the risk of fetal chromosome abnormality, especially trisomy 21, at least in non-Asian populations. In addition to the four-chamber view, other views of the heart are required to show normal relationships (Figs 5.14–5.18).42,44,56,57 However, it is important to understand the normal anatomy and circulatory pattern while obtaining these views. This sequential segmental approach is most useful in the evaluation of the heart and especially in the diagnosis of congenital heart disease. In brief, blood enters the right atrium through the superior and inferior vena cavae. Oxygenated blood from the inferior vena cava is preferentially directed across the foramen ovale to the left atrium while deoxygenated blood from the superior vena cava is directed to the right ventricle through the tricuspid valve. Deoxygenated blood is pumped through the pulmonary artery and much of this continues through the ductus arteriosus to the aorta, returning to the placenta and lower fetus. A portion of pulmonary arterial flow goes to the lungs, returning via the pulmonary veins. This blood enters the left atrium where it mixes with oxygenated blood crossing the foramen ovale and then enters the left ventricle through the mitral valve. It is then pumped through the left ventricle into the aorta.
91
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
92
Fig. 5.14 Left ventricular outflow tract. Plane angled toward the right shoulder from the standard four-chamber view shows normal ascending aorta (Ao). Note the wall of the ascending aorta is continuous with the ventricular septum. RV, right ventricle; LV, left ventricle; LA, left atrium.
Other views help show these normal relationships including the venous–atrial, atrial–ventricular and ventricular–arterial junctions of both the left and right side of the heart. In addition to the four-chamber view described above, these include a view of the upper abdomen to show normal solitus, and views of the great vessels. Left and and right ventricular outflow views (see Figs 5.14, 5.15) should be obtained, if possible. A ‘three-vessel’ view (see Fig. 5.16) should also be attempted by continuing to angle the transducer superiorly from the four-chamber view. A more complete study would include the venous–atrial connections and longitudinal views of the ductal arch (see Fig. 5.17) and aortic arch (see Fig. 5.18). The venous–atrial connections of both the left and right heart can be seen on transverse views sweeping from the abdomen to the four-chamber view. As an optional view, the relationship of the inferior and superior vena cavae with the
Fig. 5.15 Right ventricular outflow tract. Plane angled toward the left shoulder from the standard four-chamber view shows the main pulmonary artery (MPA), and its continuation by way of the ductus arteriosus (DA) which joins the aorta. RPA, right pulmonary artery; RV, right ventricle; Ao, ascending aorta seen in cross-section.
✩✩✩✩✩✩✩✩✩✩✩ ✩
right atrium can also be seen on a longitudinal view through the right atrium. This plane shows the inferior vena cava entering the right atrium and the tricuspid valve between the right atrium and ventricle. The four-chamber view shows the atrial–ventricular connections. Demonstration of the ventricular–arterial connections and great vessels requires familiarity with normal anatomy. The pulmonary artery arises anteriorly, close to the chest wall, and is directed straight back towards the spine while the aorta arises centrally within the heart from the left ventricle and ascends to the right, posterior to the pulmonary artery (see Figs 5.15, 5.17). The right ventricular outflow tract and branching of the pulmonary artery can be identified on an axial plane just above the level for a four-chamber view with angling slightly toward the left shoulder (see Fig. 5.15) while the left ventricular outflow tract can be visualized by angling toward the right shoulder from the four-chamber view (see Fig. 5.14).
Fig. 5.17 Ductal arch. Midsagittal scan shows the ductal arch. Note the arch is relatively flattened and has no systemic vessels arising from it. Also note that the ductus arteriosus (DA) is a direct extension of the main pulmonary artery (MPA) and so receives most of the blood pumped through the right ventricle (RV). RPA, right pulmonary artery; DA, ductus arteriosus; Ao, ascending aorta in cross-section; Ao(D), descending aorta; PV, pulmonic valve.
Normal fetal anatomy at 18–22 weeks
Fig. 5.16 Three-vessel view. Axial view superiorly shows three vessels: the pulmonary artery (P) and its continuation via the ductus arteriosus, the aorta (Ao) at the level of the aortic arch, and the superior vena cava (SVC). (P)Ao, proximal or ascending aorta; (D)Ao, descending aorta; D, ductus arteriosus; LT, left; RT, right.
93
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.18 Aortic arch. The aorta (Ao) arises from the left ventricle. It is rounder in shape than the ductus arteriosus and also gives rise to the neck vessels (arrows). Ao(D), descending aorta.
Each of these views should also show the other great artery in cross-section. The left ventricular outflow view should also show continuity of the aortic wall and the ventricular septum. The ductal arch view is obtained on longitudinal midline plane which shows continuation of the ductus arteriosus from the pulmonary artery and its connection with the aorta just below the aortic arch (see Fig. 5.17). The aortic arch can be seen on transverse views above the heart as the aorta curves from right to left (see Fig. 5.16). However, the entire aortic arch and origin of the neck vessels can best be seen on an aortic arch view (see Fig. 5.18). This is an oblique longitudinal plane oriented from the right anterior chest to the left posterior chest. The descending aorta can be seen on longitudinal views, as well as transverse views where it is seen in cross-section just to the left and anterior to the spine. In summary, a checklist of the great vessels should make note of the following.
• The aorta arises from the centre of the heart and ascends as the aortic arch which can be confirmed by showing the origin of head and neck vessels.
• The pulmonary artery arises from the right ventricle and gives rise to the
pulmonary arteries and the ductus arteriosus. • The great arteries are similar in size but the pulmonary artery at the valve ring may be slightly bigger than the aorta. • The great arteries cross each other at their origin. • The ventricular septum is continuous with the aortic wall. The recent introduction of 3D and 4D fetal echocardiography has opened new possibilities of studying normal and abnormal fetal cardiac anatomy.89
Lungs and Thorax
94
In addition to views of the heart, images directed to the heart will also demonstrate surrounding structures, including the lungs, great vessels, bony thorax and extrathoracic structures. The lungs are observed as homogeneously echogenic structures surrounding the heart. They should be roughly equal in size. They should surround the pulmonary arterial branches and pulmonary veins. Lung size has been evaluated by various ratios, lung length, and more recently by volume using 3D ultrasound.58–60
✩✩✩✩✩✩✩✩✩✩✩ ✩
Abdomen The basic ultrasound examination of the fetal abdomen and pelvis includes identification of the stomach, kidneys, bladder, umbilical cord insertion and adjacent anterior abdominal wall, and measurement of an abdominal circumference for dating/growth. Other organs that can easily be documented, and in some cases measured, include the liver,61 spleen,62 adrenals,63 large and small bowel and gallbladder,64 as well as major vascular structures. Both axial (Fig. 5.19) and longitudinal (Fig. 5.20) views are useful for evaluating the abdomen. The abdominal circumference (AC) measurement, while useful as an adjunctive parameter for fetal dating, finds its greatest value in the evaluation of fetal growth in the latter part of pregnancy. Fetal growth disturbances are generally detected by a change in the size of the fetal liver. This is reflected sonographically on the AC measurement, obtained on an axial image through the fetal liver where the midline umbilical vein joins the portal venous system. Only a short portion of the umbilical vein deep within the liver should be imaged, since visualization of the vein more anteriorly is only possible with oblique scans as it passes inferiorly towards the umbilicus (see Fig. 5.19). The stomach is a variably sized fluid-filled structure in the left upper quadrant. For confirmation of normal solitus, the stomach should be confirmed to be on the same side as the apex of the heart. Situs inversus seen prenatally usually reflects one of the cardiosplenic syndromes (asplenia or polysplenia). Absence of a visible
Fig. 5.19 Abdomen, axial view, at the level where the abdominal circumference measurement is obtained. St, stomach; L, liver; UV, umbilical vein; IVC, inferior vena cava; Ao, aorta; Sp, spine.
Normal fetal anatomy at 18–22 weeks
The osseous components of the thorax are readily identified due to their inherent subject contrast with the adjacent soft tissue structures. In this location the rib cage is composed of cartilage, which is sonographically hypoechoic and allows good sound transmission. The scapulae, clavicles, ribs and dorsal spine can all be easily identified on directed scanning. Since shadowing caused by the overlying bones makes examination of the intrathoracic contents difficult, especially with advancing gestational age, scan planes that avoid the bony thorax are employed when feasible.
95
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.20 Longitudinal view in the right abdomen shows the normal liver, diaphragm and more echogenic lung.
96
stomach after 14 weeks is unusual. This may indicate underlying fetal abnormality or transient decrease in fetal swallowing. In this situation, a short-interval follow-up scan is indicated for confirmation.65,66 A more common presentation is a small or prominent stomach. However, it is often difficult to know what is too small or too prominent. To help in this situation, Pekindil et al67 proposed a ratio of stomach circumference to abdominal circumference expressed as a percent (SC/AC ratio). They found this was normally distributed from 15 to 39 weeks at a mean of 20.4% and ranged between 14.8% and 27.03% throughout pregnancy. Although the fetal stomach is a dynamically changing organ, the SC/AC ratio can be considered as a potentially useful parameter in assessing fetal stomach size. The fetal duodenum can be identified but dilated duodenum suggests underlying obstruction68 (double bubble sign). The gallbladder is often seen in the right abdomen near the inferior edge of the liver (Fig. 5.21). Care should be taken not to mistake the gallbladder for the umbilical vein. While both structures extend to the region of the porta hepatis, the umbilical vein is of uniform calibre, midline in position, and courses inferiorly to penetrate the abdominal wall; the gallbladder is clearly not in the midline, usually is somewhat teardrop shaped, and does not penetrate the abdominal wall. Persistent intrahepatic right umbilical vein is a relatively common normal variant in which the right umbilical vein persists rather than the left.69 Blazer et al69 observed this finding in 69 of 30,240 consecutive pregnancies at 14–26 weeks.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks Fig. 5.21 Oblique scan shows a normal gallbladder in the right abdomen. This can be easily confused with the umbilical vein, which is more central in location. St, stomach.
In this situation, the persistent right umbilical vein enters the right lobe of the liver, lateral to the gallbladder rather than medial to it. In the absence of other abnormalities, this variation is associated with a favourable outcome.69 The liver occupies the majority of the upper abdomen, with a prominent left lobe extending well into the left upper quadrant in the fetus. The smaller spleen is identified as a solid organ posterior to the stomach. Much of the remaining abdominal cavity is filled with bowel. Early in the second trimester bowel appears as an area of midlevel to increased echogenicity filling the abdomen from the liver to the bladder. The large bowel progressively enlarges with meconium throughout pregnancy, measuring 3–5 mm at 20 weeks.70,71 Normal small bowel is less distinct since it is smaller, circuitous in course, and changes with peristalsis. Small bowel segments can be transiently identified with small quantities of fluid, particularly with higher-resolution scanners. Echogenic bowel may be seen as a normal variant.72 However, moderate to markedly echogenic bowel has been associated with adverse outcome including chromosome abnormality, in utero infection, growth retardation and fetal demise.73
Anterior Abdominal Wall The site of the umbilical cord insertion into the abdominal wall must be evaluated to confirm a normal-sized cord penetrating into the abdomen. The adjacent abdominal wall must also be examined to confirm its integrity. The musculature of the fetal abdominal wall appears hypoechoic, and may be confused with fetal ascites.74 Knowledge of the hypoechoic nature of fetal musculature and close attention to anatomical detail should easily differentiate the normal from abnormal.
97
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
98
Confirmation of a normal three-vessel cord may be made by direct imaging of the cord to delineate the two smaller umbilical arteries and the larger umbilical vein. Alternatively, the paired umbilical arteries can be imaged within the fetus, extending along the anterior abdominal wall from the umbilicus to a position lateral to the fetal bladder (Fig. 5.22). This can easily be confirmed with colour flow imaging (Fig. 5.23), a valuable technique early in gestation when direct visualization of the arteries within the cord is suboptimal. The umbilical cord insertion site should be visualized on all routine fetal surveys. Detection of a normal cord insertion excludes the vast majority of anterior abdominal wall defects.
Urinary Tract By 18–22 weeks, the kidneys can be clearly seen as oval masses lateral to the psoas muscles and inferior to the adrenal glands (Figs 5.24, 5.25). Before this time, the kidneys may be difficult to identify with certainty so that guidelines refer to scanning through the kidney regions. Use of colour flow Doppler can be helpful for confirming the presence of two kidneys when they are difficult to visualize on standard grey-scale imaging (Fig. 5.26).
Fig. 5.22 Cord insertion site. Axial view shows the umbilical cord inserting into the umbilicus. The paired umbilical arteries are seen on this view; the umbilical vein deviates from the arteries immediately on entering the abdomen and courses cephalad to the liver. Because the cord insertion is inferior on the abdominal wall, the urinary bladder (B) can often be seen on this view.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks
Fig. 5.23 Urinary bladder. A slightly inferior plane with colour flow Doppler shows the paired umbilical arteries coursing around the urinary bladder. LUA, left umbilical artery; RUA, right umbilical artery.
The kidneys grow throughout gestation and standard measurements for renal circumference, volume, thickness, width and length have been reported as a function of menstrual age.75 The ratio of kidney circumference to abdominal circumference remains constant at 0.27 to 0.30 throughout pregnancy.76 In general, the normal kidney length spans approximately 4–5 vertebral bodies.
Fig. 5.24 Kidneys. Axial view with the spine anterior in position shows the normal paraspinal kidneys (K), outlined by arrows. A tiny amount of fluid is seen within the central renal pelvis of each kidney.
99
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.25 Kidneys, coronal view. Coronal view of the abdomen shows both kidneys (K). Again note the small amount of fluid within the central renal pelvis of each kidney.
High-resolution scans can identify normal renal architecture. The medullae are arranged in anterior and posterior rows around the pelvic sinus. The medullae appear hypoechoic, probably because the tubules are thin-walled and fluid-filled, compared to the more peripheral renal cortex. Recognition of this normal renal architecture is important in distinguishing normal kidneys from those with cystic dysplasia.
100
Fig. 5.26 Normal renal arteries. Colour Doppler, using the power mode, with the fetus in coronal plane shows both renal arteries arising from the aorta. This can be helpful when the kidneys are difficult to visualize on standard grey-scale imaging.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal fetal anatomy at 18–22 weeks
The central renal pelvis commonly contains small amounts of fluid (urine). Obvious dilation of the renal pelvis may reflect an underlying obstructive process. Therefore, it is important to attempt to distinguish normal physiological amounts of fluid from a true abnormality. An objective method of assessment is measurements of the renal pelvis, best obtained in the anterior–posterior plane with the fetus either spine anterior or posterior relative to the transducer. ‘Cutoffs’ for normal vary with gestational age and will also vary between centres. By 18–22 weeks, we use a cut-off of 5 mm or more for suggesting a possible renal abnormality.77 As a normal variant, mild degrees of renal pyelectasis occur more commonly among fetuses that are large for gestational age and males are affected more often than females. Kent et al78 found that 13 of 37 (35%) fetuses with renal dilation of 4–8 mm at 16–21 weeks went on to require medical or surgical intervention for significant urinary tract anomalies. These anomalies included pelviureteric junction obstruction, dysplastic kidney, vesicoureteric reflux and posterior urethral valves. Follow-up evaluation is suggested at 28 weeks when renal pelvic dilation is suggested. Although not part of the genitourinary tract, the adrenal glands are usually assessed at the same time as the kidneys due to their proximity. The adrenal glands characteristically appear as triangular hypoechoic shadows which outline the upper poles of the kidneys. The right gland is positioned immediately posterior to the inferior vena cava, while the left lies lateral to the aorta. Sonographically the adrenals are hypoechoic peripherally, with a central echogenic layer. The urinary bladder is a fluid-filled structure located low within the pelvis, in the midline. Changes in bladder volume over time are obvious and help differentiate the urinary bladder from other cystic pelvic structures. If in doubt, the umbilical arteries course along the lateral walls of the bladder and confirm it as the urinary bladder. Therefore, this view can confirm the presence of both the urinary bladder and both umbilical arteries.
Genitalia Evaluation of the genitalia is often desired by the prospective parents in order to determine gender, and is also sometimes medically indicated. Certainly fetal genitalia are well visualized by 18–22 weeks (Fig. 5.27), and fetal gender can probably be accurately determined by the late first trimester.79 The first finding with a male fetus is delineation of the penis, a solid structure in contrast to the fluid-filled umbilical cord which may lie between the thighs. The scrotum is a bulbous soft tissue structure increasingly apparent at the base of the penis as gestation progresses. Although the scrotum is visualized, testicular descent is not seen before 26 weeks. Longitudinal scans of the scrotum and penis may produce a ‘turtle’ appearance. Female genitalia are confirmed early in gestation via identification of several parallel linear echos representing the margins of the labia. In the third trimester the prominent soft tissues of the labia majora border the linear echoes of the labia minora.
101
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
102
Fig. 5.27 Normal genitalia. Axial images of the perineum show normal female (left) and male (right) external genitalia.
Skeleton and Extremities The bones of the extremities are readily identifiable due to their inherent subject contrast with the surrounding soft tissues, from the late first trimester to term. The femur is the only long bone which is routinely measured, however, being a primary parameter for fetal dating as well as a screen for the skeletal dysplasias. Humerus length is also commonly measured during the second trimester, especially as a potential marker for fetal Down syndrome (Fig. 5.28). Mild contour variation in the normal femoral shaft is often apparent, with a straighter appearance on the lateral aspect and a mild ‘bowed’ appearance medially.80 Only the ossified portions of the bone are measured, excluding the hypoechoic cartilaginous epiphyses of the femoral head and condyles distally.81 It is recommended that a survey of all extremities be performed to confirm a grossly normal appearance of the bones and soft tissues to the level of the feet and hands (Figs 5.29, 5.30). Use of 3D multiplanar ultrasound can also help to confirm normal extremities, including the hands and feet (Fig. 5.31). Imaging of specific bones is accomplished by careful progression from one known structure
Fig. 5.28 Longitudinal views of the femur (F, left) and humerus (H, right). These are similar in size during the second trimester.
✩✩✩✩✩✩✩✩✩✩✩ ✩
to the next, adjusting probe position as needed to obtain the desired images.82 Scanning beyond the femur will outline the hypoechoic cartilages of the distal femur and proximal tibia. Subsequently the tibia and fibula and orientation of
Fig. 5.30 View of a normal hand including the thumb. Note three bones (proximal phalanx, middle phalanx and distal phalanx) of each finger.
Normal fetal anatomy at 18–22 weeks
Fig. 5.29 Feet. Axial view shows normal paired feet (F).
103
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 5.31 Hand, 3D view. Three-dimensional ultrasound with surface rendering better shows the complex shape of the hand.
104
the leg to the foot can be shown. Measurement of foot length and documentation of digits are possible with appropriate fetal positioning and careful scanning. Similar scanning through the upper extremities can detail the humerus, radius and ulna, and hand. The clavicle and scapula define the shoulder girdle. The scapula imaged in long axis coronally has a characteristic shape resembling a ‘Y’ with the supraspinatus, subscapularis and infraspinatus muscles in their respective fossae. The scapula has a triangular shape when imaged posteriorly. The clavicles can be seen if not
✩✩✩✩✩✩✩✩✩✩✩ ✩
Conclusion A second-trimester scan has now become widely accepted throughout much of the developed world. We believe it should be considered an essential part of obstetric care, but only when performed by experienced sonographers or sonologists. Armed with a systematic approach, a good understanding of normal fetal anatomy and familiarity with normal sonographic appearances and common variants, the sonographer/sonologist can offer accurate reassurance in the vast majority of normal pregnancies, and at the same time detect the majority of major defects in anomalous fetuses. Finally, it will be of interest to see to what extent new techniques like echo-planar magnetic resonance will complement or even replace certain areas of fetal anatomic assessment.90
Normal fetal anatomy at 18–22 weeks
obscured by flexion of the fetal head. They grow at a linear rate of approximately 1 mm per week, reaching a length of 20 mm at 20 weeks and 40 mm at 40 weeks. The humeral head epiphyseal cartilage lies between the ossified distal clavicle, scapula and proximal humeral diaphysis. At the elbow, the non-ossified coronoid fossa delineates the medial and lateral humeral epicondyles. The more proximal extent of the ulna at the elbow distinguishes it from the radius. Demonstration of the ulna and radius ending at the same level at the wrist effectively excludes many radial ray defects. The non-ossified carpals produce a conglomerate zone of grey echoes antenatally, but the ossified metacarpal and phalanges are readily visualized if the fetus extends the hand. The foot length is similar to the ossified femoral shaft throughout much of pregnancy.83
References 1. Grandjean H, Larroque D, Levi S. The performance of routine ultrasonographic screening of pregnancies in the Eurofetus Study. Am J Obstet Gynecol 1999;181(2):446–454 2. Vintzileos AM, Ananth CV, Smulian JC, Beazoglou T, Knuppel RA. Routine secondtrimester ultrasonography in the United States: a cost-benefit analysis. Am J Obstet Gynecol 2000;182(3):655–660 3. Schwarzler P, Senat MV, Holden D, Bernard JP, Masroor T, Ville Y. Feasibility of the second-trimester fetal ultrasound examination in an unselected population at 18, 20 or 22 weeks of pregnancy: a randomized trial. Ultrasound Obstet Gynecol 1999;14(2):92–97 4. American Institute of Ultrasound in Medicine. Guidelines for performance of the antepartum obstetrical ultrasound examination. American Institute of Ultrasound in Medicine, Laurel, MD, 1994
5. American College of Obstetrics and Gynecology. Technical bulletin no. 187. Ultrasound in pregnancy. American College of Obstetrics and Gynecology, Washington, DC, 1993 6. Filly RA, Cardoza JD, Goldstein RB, Barkovich AJ. Detection of fetal central nervous system anomalies: a practical level of effort for a routine sonogram [see comments]. Radiology 1989;172(2): 403–408 7. Reece EB, Goldstein I. Three-level view of fetal brain imaging in the prenatal diagnosis of congenital anomalies. J Matern Fetal Med 1999;8(6):249–252 8. Pilu G, Perolo A, Falco P, Visentin A, Gabrielli S, Bovicelli L. Ultrasound of the fetal central nervous system. Curr Opin Obstet Gynecol 2000;12(2):93–103 9. Malinger G, Zakut H. The corpus callosum: normal fetal development as shown by transvaginal sonography. Am J Roentgenol 1993;161:1041–1043
105
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
106
10. Cardoza JD, Goldstein RB, Filly RA. Exclusion of fetal ventriculomegaly with a single measurement: the width of the lateral ventricular atrium. Radiology 1988;169:711–714 11. Alagappan R, Browning PD, Laorr A et al. Distal lateral ventricular atrium: reevaluation of normal range. Radiology 1994;193:405–408 12. Hertzberg BS, Lile R, Foosaner DE et al. Choroid plexus–ventricular wall separation in fetuses with normal-sized cerebral ventricles at sonography: postnatal outcome. Am J Roentgenol 1994;163:405–410 13. Farrell TA, Hertzberg BS, Kliewer MA, Harris L, Paine SS. Fetal lateral ventricles: reassessment of normal values for atrial diameter at US [see comments]. Radiology1994;193:409–411. Comment in: Radiology 1994;193(2):315–317 14. McGahan JP The fetal head: borderlines. Semin Ultrasound CT MR 1998;19: 318–328 15. Pilu G, Falco P, Gabrielli S, Perolo A, Sandri F, Bovicelli L. The clinical significance of fetal isolated cerebral borderline ventriculomegaly: report of 31 cases and review of the literature. Ultrasound Obstet Gynecol 1999;14(5):320–326 16. Patel MD, Goldstein RB, Tung S, Filly RA. Fetal cerebral ventricular atrium: difference in size according to sex. Radiology 1995;194:713–715 17. Heiserman J, Filly RA, Goldstein RB. Effect of measurement errors on sonographic evaluation of ventriculomegaly. J Ultrasound Med 1991;10(3):121–124 18. Browning PD, Laorr A, McGahan JP et al. Proximal fetal cerebral ventricle: description of US technique and initial results. Radiology 1994;192:337–341 19. Cronan MS, McGahan JP. A new ultrasound technique to visualize the proximal fetal cerebral ventricle. J Diagn Med Sonography 1991;6:333–335 20. Kraus I, Jirasek JE. Some observations of the structure of the choroid plexus and its cysts. Prenat Diagn 2002;22:1223–1228 21. Nyberg DA, Crane JP. Chromosome abnormalities. In: Nyberg DA, Mahony BS, Pretorius D (eds) Diagnostic ultrasound of fetal anomalies. Yearbook Publishers, Chicago, 1990: 676–724 22. Walkinshaw S, Pilling D, Spriggs A. Isolated choroid plexus cysts: the need for routine offer of karyotyping. Prenat Diagn 1994;14(8):663–667
23. Gross SJ, Shulman LP, Tolley EA et al. Isolated fetal choroid plexus cysts and trisomy 18: a review and meta-analysis. Am J Obstet Gynecol 1995;172:83–87 24. Snijders RJ, Shawa L, Nicolaides KH. Fetal choroid plexus cysts and trisomy 18: assessment of risk based on ultrasound findings and maternal age. Prenat Diagn 1994;14(12):1119–1127 25. Sullivan A, Giudice T, Vavelidis F, Thiagarajah S. Choroid plexus cysts: is biochemical testing a valuable adjunct to targeted ultrasonography? Am J Obstet Gynecol 1999;181(2):260–265 26. Filly RA, Cardoza JD, Goldstein RB et al. Detection of fetal central nervous system anomalies: a practical level of effort for a routine sonogram. Radiology 1989;172: 403–408 27. Nyberg DA. Recommendations for obstetric sonography in the evaluation of the fetal cranium. Radiology 1989;172:309–311 28. Mahony BS, Callen PW, Filly RA et al. The fetal cisterna magna. Radiology 1984;153:173–176 29. Laing FC, Frates MC, Brown DL et al. Sonography of the fetal posterior fossa: false appearance of mega-cisterna magna and Dandy–Walker variant. Radiology 1994;192:247–251 30. Bromley B, Nadel AS, Pauker S, Estroff JA, Benacerraf BR. Closure of the cerebellar vermis: evaluation with second trimester US. Radiology 1994;193:761–763 31. Knutzon RK, McGahan JP, Salamat MS, Brant WE. Fetal cisterna magna septa: a normal anatomic finding. Radiology 1991;180(3):799–801 32. Pretorius DH, Kallman CE, Grafe MR, Budorick NE, Stamm ER. Linear echoes in the fetal cisterna magna. J Ultrasound Med 1992;11:125–128 33. Goldstein I, Jakobi P, Tamir A, Goldstick O. Nomogram of the fetal alveolar ridge: a possible screening tool for the detection of primary cleft palate. Ultrasound Obstet Gynecol 1999;14(5):333–337 34. Jeanty P, Cantraine F, Cousaert E et al. The binocular distance: a new way to estimate fetal age. J Ultrasound Med 1984;3: 241–243 35. Birnholz JC. The fetal external ear. Radiology 1983;147:819–821 36. Lettieri L, Rodis JF, Vintzileos AM, Feeney L, Ciarleglio L, Craffey A. Ear length in second-trimester aneuploid fetuses. Obstet Gynecol 1993;81(1):57–60
✩✩✩✩✩✩✩✩✩✩✩ ✩ 52. Brown DL, Cartier MS, Emerson DS et al. The peripheral hypoechoic rim of the fetal heart. J Ultrasound Med 1989;8: 603–608 53. Schechter AG, Fakhry J, Shapiro LR, Gewitz MH. In utero thickening of the chordae tendinae. A cause of intracardiac echogenic foci. J Ultrasound Med 1987;6(12):691–695 54. Bromley B, Lieberman E, Laboda L, Benacerraf BR. Echogenic intracardiac focus: a sonographic sign for fetal Down syndrome. Obstet Gynecol 1995;86(6):998–1001 55. Manning JE, Ragavendra N, Sayre J et al. Significance of fetal intracardiac echogenic foci in relation to trisomy 21: a prospective sonographic study of highrisk pregnant women. Am J Roentgenol 1998;170(4):1083–1084 56. DeVore GR. The aortic and pulmonary outflow tract screening examination in the human fetus. J Ultrasound Med 1992;11:345–348 57. DeVore GR. Color Doppler examination of the outflow tracts of the fetal heart: a technique for identification of cardiovascular malformations. Ultrasound Obstet Gynecol 1994;4:463–471 58. Yoshimura S, Masuzaki H, Gotoh H, Fukuda H, Ishimaru T. Ultrasonographic prediction of lethal pulmonary hypoplasia: comparison of eight different ultrasonographic parameters. Am J Obstet Gynecol 1996;175(2):477–483 59. D'Arcy TJ, Hughes SW, Chiu WS et al. Estimation of fetal lung volume using enhanced 3-dimensional ultrasound: a new method and first result. Br J Obstet Gynaecol 1996;103:1015–1020 60. Laudy JA, Janssen MM, Struyk PC, Stijnen T, Wladimiroff JW. Three-dimensional ultrasonography of normal fetal lung volume: a preliminary study. Ultrasound Obstet Gynecol 1998;11(1):13–16 61. Vintzileos AM, Neckles S, Campbell WA et al. Fetal liver ultrasound measurements during normal pregnancy. Obstet Gynecol 1985;66:477–480 62. Schmidt W, Yarkoni S, Jeanty P et al. Sonographic measurements of the fetal spleen: clinical implications. J Ultrasound Med 1985;4:667–672 63. Rosenberg ER, Bowie JD, Andreotti RF et al. Sonographic evaluation of the fetal adrenal glands. Am J Roentgenol 1982;139:1145–1147
Normal fetal anatomy at 18–22 weeks
37. Petrikovsky BM, Vintzileos AM, Rodis JF. Sonographic appearance of occipital fetal hair. J Clin Ultrasound 1989;17:425–427 38. Benacerraf B, Frigoletto F, Laboda L. Sonographic diagnosis of Down syndrome in the second trimester. Am J Obstet Gynecol 1985;153:49–52 39. Gray DL, Crane JP. Optimal nuchal skinfold thresholds based on gestational age for prenatal detection of Down syndrome. Am J Obstet Gynecol 1994;171:1282–1286 40. Bahado-Singh RO, Oz UA, Kovanci E et al. Gestational age standardized nuchal thickness values for estimating midtrimester Down's syndrome risk. J Matern Fetal Med 1999;8(2):37–43 41. Ho SS, Metreweli C. Normal fetal thyroid volume. Ultrasound Obstet Gynecol 1998;11:118–122 42. Filly RA, Simpson GF, Linkowski G. Fetal spine morphology and maturation during the second trimester. J Ultrasound Med 1987;6:631–636 43. Gray DL, Crane JP, Rudloff MA. Prenatal diagnosis of neural tube defects: origin of midtrimester vertebral ossification centers as determined by sonographic water-bath studies. J Ultrasound Med 1988;7: 421–427 44. Yoo SJ, Lee YH, Cho KS, Kim DY. Sequential segmental approach to fetal congenital heart disease. Cardiol Young 1999;9(4):430–444 45. McGahan JP. Sonography of the fetal heart: findings on the four-chamber view. Am J Roentgenol 1991;156:547–553 46. Copel JA, Gianluigi P, Green J et al. Fetal echocardiographic screening for congenital heart disease: the importance of the fourchamber view. Am J Obstet Gynecol 1987;157:648–655 47. Cook AC, Yates RW, Andersson RH. Normal and abnormal cardiac anatomy. Prenat Diagn 2004;24(1):32–48 48. Brown DL, DiSalvo DN, Frates MC et al. Sonography of the fetal heart: normal variants and pitfalls. Am J Radiol 1993;160:1251–1255 49. Frates MC. Sonography of the normal fetal heart: a practical approach. Am J Roentgenol 1999;173:1363–1370 50. Comstock CH. Normal fetal heart axis and position. Obstet Gynecol 1987;70:255–259 51. Paladini D, Chita SK, Allan LD. Prenatal measurement of cardiothoracic ratio in evaluation of heart disease. Arch Dis Child 1990;65(1 Spec No):20–23
107
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
108
64. Hata K, Aoki S, Hata T et al. Ultrasonographic identification of the human fetal gall bladder in utero. Gynecol Obstet Invest 1987;23:79–83 65. Millener PB, Anderson NG, Chisholm RJ. Prognostic significance of non-visualization of the fetal stomach by sonography. Am J Roentgenol 1993;160:827–830 66. Pretorius DH, Gosink BB, Clautice-Engle T et al. Sonographic evaluation of the fetal stomach: significance of nonvisualization. Am J Roentgenol 1988;151:987–989 67. Pekindil G, Varol F, Yuce MA, Yardim T. The fetal stomach circumference/abdominal circumference ratio: a possible parameter in assessing fetal stomach size. Yonsei Med J 1998;39(3):222–228 68. Levine D, Goldstein RB, Cadrin C. Distention of the fetal duodenum: abnormal finding? J Ultrasound Med 1998;17(4):213–215 69. Blazer S, Zimmer EZ, Bronshtein M. Persistent intrahepatic right umbilical vein in the fetus: a benign anatomic variant. Obstet Gynecol 2000;95(3):433–436 70. Nyberg DA, Mack LA, Pattern RM et al. Fetal bowel: normal sonographic findings. J Ultrasound Med 1987;6:3–6 71. Parulekar SG. Sonography of normal fetal bowel. J Ultrasound Med 1991;10: 211–220 72. Perez CG, Goldstein RB. Sonographic borderlands in the fetal abdomen. Semin Ultrasound CT MR 1998;19:336–346 73. Nyberg DA, Dubinsky, Mahony BS, Luthy DA, Hickok DE, Sorenson T. Echogenic fetal bowel: clinical importance. Radiology 1993;188:527–531 74. Hashimoto BE, Filly RA, Callen PW. Fetal pseudoascites: further observations. J Ultrasound Med 1986;5:151–152 75. Cohen HL, Cooper J, Eisenberg P et al. Normal length of fetal kidneys: sonographic study in 397 obstetric patients. Am J Roentgenol 1991;157:545–548 76. Grannum P, Bracken M, Silverman R et al. Assessment of fetal kidney size in normal gestation by comparison of ratio of kidney circumference to abdominal circumference. Am J Obstet Gynecol 1980;136:249–254 77. Anderson N, Clautice-Engle T, Allan R et al. Detection of obstructive uropathy in the
fetus: predictive value of sonographic measurements of renal pelvic diameter at various gestational ages. Am J Roentgenol 1995;164:719–723 78. Kent A, Cox D, Downey P, James SL. A study of mild fetal pyelectasia – outcome and proposed strategy of management. Prenat Diagn 2000;20(3):206–209 79. Shapiro E. The sonographic appearance of normal and abnormal fetal genitalia. J Urol 1999;162:530–533 80. Goldstein RB, Filly RA, Simpson G. Pitfalls in femur length measurements. J Ultrasound Med 1987;6:203–207 81. Lessoway VA, Schulzer M, Wittmann BK. Sonographic measurement of the fetal femur: factors affecting accuracy. J Clin Ultrasound 1990;18:471–476 82. Mahony BS, Filly RA. High resolution sonographic assessment of the fetal extremities. J Ultrasound Med 1984;3: 489–498 83. Mercer BM, Sklar S, Shariatmadar A. Fetal foot length as a predictor of gestational age. Am J Obstet Gynecol 1987;156:350–355 84. Barnewolt CE, Estroff JA. Sonography of the fetal central nervous system. Neuroimaging Clin North Am 2004;14:255–271 85. Garel C. Fetal cerebral biometry: normal parenchymal findings and ventricular size. Eur Radiol 2005;15:809–813 86. Hashimoto K, Shimizu T, Shimoya K, Kanzaki T, Clapp YF, Muzeta Y. Fetal cerebellum: US appearances with advancing age. Radiology 2001;221:70–74 87. Caoni R, McEwing R. Three crosssectional planes for fetal color Doppler echocardiography. Ultrasound Obstet Gynecol 2003;21:81–93 88. Allan L. Technique of fetal echocardiography. Paediatric Cardiol 2004;25:223–233 89. De Vore GR. Three-dimensional and fourdimensional fetal echocardiography: a new frontier. Curr Opin Pediatr 2005;17: 592–604 90. Duncan KR, Issa B, Moore R, Baker PN, Johnson IR, Gowland PA. A comparison of fetal organ measurements by echo-planar magnetic resonance imaging and ultrasound. Br J Obstet Gynaecol 2005;112:43–49
6 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Amniotic fluid and placental localization Juriy W Wladimiroff Sturla H Eik-Nes
Abstract Various pathways determine amniotic fluid production and absorption, which include fetal swallowing, lung fluid and urine production and flow across the chorionic plate. Measurements of the amount of amniotic fluid include the 1 or 2 cm pocket rule and the amniotic fluid index. Oligohydramnios is associated with fetal renal pathology and fetal growth restriction, whereas polyhydramnios is often associated with a wide range of fetal congenital anomalies, maternal diabetes mellitus, multiple pregnancy and nonimmune hydrops. Ultrasound is the method of choice to locate the placenta. The most common indications for locating the placenta are in connection with first-trimester invasive procedures, bleeding in the second and third trimesters, as part of the routine second-trimester exam and prior to external version of the fetus in late pregnancy. The placenta is located in the fundal area, on the left or right lateral side, the posterior or the anterior side or a combination thereof. Clinically it is most useful to distinguish the relation between the inner os of the cervical canal and the edge of the placenta.
Keywords Amniotic fluid absorption, amniotic fluid production, amniotic fluid volume, management of abnormal placental location, oligohydramnios, placenta praevia, placental embryology, placental functional anatomy, placental location, polyhydramnios.
Amniotic Fluid The amount of amniotic fluid surrounding the fetus provides us with information about the fetal condition. To appreciate abnormal changes in amniotic fluid
109
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ volume, it is necessary not only to reliably measure amniotic fluid volume but also to understand the various pathways which determine amniotic fluid production and absorption.
Amniotic Fluid Physiology It is during the period of embryonic development that the amnion is formed and surrounds the embryo. In the beginning the amnion itself is surrounded by coelomic fluid which will disappear from 9–10 weeks of gestation and a rapid expansion of amniotic fluid volume will occur thereafter. Amniotic fluid is 98–99% water and its chemical composition varies with gestational age.10 There are five pathways playing a major role in the exchange of water and solutes between fetus and amniotic fluid.14 Excretion from the fetus into the amniotic cavity consists of fetal urine flow and lung flow. The onset of fetal micturition is associated with a reduction of amniotic osmolarity which will continue with advancing gestational age.10 Reabsorption of amniotic fluid takes place through fetal swallowing and absorption into the fetal circulation across the fetal surface of the placenta1 and exchange across the fetal skin before completion of the keratinization process at approximately 22 weeks of gestation. Finally, there appears to be excretion from the fetal salivary glands into the amniotic fluid. A short resumé of a few of the most important pathways will now follow. Fetal urinary production Fetal urine flow constitutes an important source of amniotic fluid, hence the development of severe oligohydramnios in bilateral renal agenesis or urethral obstruction. Diagnostic ultrasound has provided data on hourly fetal urinary production rates, with values from 2–3 mL/h at 20 weeks to 30–35 mL/h at term.17 This would result in a urinary production rate of 700–800 mL/24 h, which is approximately 25% of fetal body weight/day. Over the years different urine production rates have been reported as a result of different measuring techniques. It seems that the above figures are probably more or less correct. Fetal urine contributes not only to amniotic fluid volume but also to its composition, since osmolarity is about onehalf and chloride and sodium concentration are about one-third of plasma values. Lung fluid The production of lung fluid is 250–300 mL/24 h at term, which is approximately 10% of fetal body weight.9 A very small percentage of this fluid remains in the lungs for expansion with growth. Nearly 99% of the fluid leaves the lungs through the trachea. Beyond the trachea about 50% is swallowed and the remaining 50% will appear in the amniotic fluid.
110
Flow across the chorionic plate It is likely that the exchange from the amniotic cavity to the fetal blood compartment of water and solutes is quite considerable, with figures of 200–250 mL/day of water in normal fetal development near term.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Amniotic Fluid Volume
Methods of assessment Several methods of amniotic fluid assessment have been employed to detect adverse fetal conditions. Determination of total intrauterine volume reflecting the sum of the volume of all intrauterine contents (fetus, placenta, amniotic fluid) is achieved from longitudinal, transverse and anteroposterior uterine dimensions. This method was particularly applied for the early detection of fetal growth restriction, but has a low accuracy. A quantitative approach of assessing amniotic fluid volume is the 1 cm or, even better, the 2 cm pocket rule. Using ultrasound, the largest cord-free pocket of amniotic fluid is detected and the vertical and transverse diameter of this pocket is measured with the transducer always at right angles to the maternal abdominal wall. Amniotic fluid volume was considered normal if the pocket measured 1 cm or more in its largest vertical diameter and reduced if the diameter was less than 1 cm.8 However, this approach leads to a pick-up rate of fetal growth restriction of only 4%. Later it was demonstrated that amniotic fluid pockets greater than 1 cm but less than 2 cm should also undergo further investigation for fetal underdevelopment.2 Here, the single deepest pocket was identified. A semi-quantitative method of assessing amniotic fluid volume is the amniotic fluid index technique.13 Using the umbilicus as a reference point, the uterus is divided into an upper and a lower half. The linea nigra is subsequently used to divide the uterus into a right and a left half, resulting in four uterine quadrants. The ultrasound transducer is placed in each quadrant with the transducer head always at right angles to the floor. A more oblique positioning of the transducer head will result in an inaccurate amniotic fluid volume measurement. Moreover, the investigation should extend to the lateral margins of the uterus since often substantial amniotic fluid may be situated in the flanks of the pregnant woman when in the supine position. In each quadrant the largest pocket of fluid is sought according to the above technique. The vertical diameter of each of the pockets is then measured (Fig. 6.1). The numbers obtained from each quadrant are added up. The resulting figure in centimetres represents the amniotic fluid index for that particular pregnant woman. A normal amniotic fluid index ranges between 5 and 25 cm. The amniotic fluid index and single deepest pocket measurement appear to perform best for the identification of normal amniotic fluid volumes, whereas the identification of oligo- and polyhydramnios is of limited value.7 In another study, the amniotic fluid index was not significantly correlated with perinatal outcome.11 The amniotic fluid index seems to offer no advantage in detecting adverse outcomes compared with the single deepest pocket when performed with the biophysical profile.7 Three-dimensional ultrasound has been used in measuring amniotic fluid or gestational sac volume at 11–14 weeks of gestation,4 whereas later in pregnancy magnetic resonance imaging was found to be comparable with ultrasound evaluation for the prediction of oligohydramnios.18
Amniotic fluid and placental localization
Both amniotic fluid volume and its composition reflect the status of mother and fetus.
111
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
4.7 cm
5.8 cm
4.9 cm
6.2 cm
Fig. 6.1 Measurement of the vertical diameter in each of the four quadrants of the uterus. The numbers are added up to calculate the amniotic fluid index.
Normal amniotic fluid volume values Amniotic fluid volume increases from approximately 70 mL at 11 weeks of gestation to 800 mL at 28 weeks followed by a slower increase to about 1000 mL at 34 weeks. A decline in volume takes place during the last 6 weeks of gestation to about 800 mL at 40 weeks. Gestational sac volume appears to be a poor predictor of major chromosomal defects.4 Abnormal amniotic fluid volumes Abnormalities in amniotic fluid volume are associated with increased perinatal mortality and morbidity.
112
Oligohydramnios Oligohydramnios is defined as a deepest fluid pocket of less than 2 cm or an amniotic fluid index of 5 cm or less. It develops in 0.5–4.0% of all pregnancies and can be associated with fetal growth restriction as a result of reduced renal perfusion and urinary output. Severe oligohydramnios (deepest fluid pocket smaller than 1 cm) or even anhydramnios may develop in the presence of bilateral renal agenesis or urethral obstruction/stenosis. Pregnancies beyond 40 weeks may be complicated by reduced amounts of amniotic fluid with volumes down
✩✩✩✩✩✩✩✩✩✩✩ ✩
Polyhydramnios Polyhydramnios is defined as a deepest fluid pocket of more than 8 cm or an amniotic fluid index of at least 25 cm or more. Its incidence has been reported to range from 0.4% to 3.3%. Chronic polyhydramnios which develops gradually over weeks or months is more common than acute polyhydramnios. The aetiology of polyhydramnios is diverse and includes fetal congenital anomalies, notably neural tube defects and neuromuscular defects preventing adequate swallowing, on the one hand, and gastrointestinal obstruction resulting in fluid congestion on the other. Nearly one in five pregnancies with chronic polyhydramnios has been associated with fetal anomalies. Other abnormal maternal and fetal conditions associated with polyhydramnios are maternal diabetes mellitus, macrosomia, multiple pregnancy and non-immune fetal hydrops. Also, lesions of the umbilical cord and placenta have been associated with polyhydramnios. However, in approximately two-thirds of pregnancies with polyhydramnios, no specific cause can be established. Idiopathic polyhydramnios12 does not seem to be less associated with adverse perinatal outcomes than polyhydramnios in which one of the above fetal or maternal conditions has been identified. Polyhydramnios in itself may create obstetric problems such as premature labour, postpartum haemorrhage and PROM resulting in prolapsed cord.
Amniotic fluid and placental localization
to about 350 mL at 42 weeks of gestation. Oligohydramnios may also develop in association with drug therapies such as indometacin treatment in premature labour. Decreased renal perfusion may be the underlying mechanism for this. Another cause of oligohydramnios is premature rupture of the membranes (PROM), which occurs in approximately 10% of all pregnancies and is associated with increased perinatal mortality and morbidity due to premature labour, chronic fetal distress or infection. When severe oligohydramnios develops before 20–25 weeks of gestation, there is a high association with fetal pulmonary hypo plasia, fetal facial compression and abnormal position/contractures of hands/feet (oligohydramnion sequence).
Conclusions Various pathways determine production and absorption of amniotic fluid, amongst which are fetal swallowing, fetal urinary production, fetal lung fluid excretion, fluid transfer through the chorionic plate and to a minor extent fluid excretion by the fetal salivary glands. Normal amniotic fluid volumes display a wide distribution with a marked increase up to about 34 weeks and a gradual reduction thereafter. Determination of amniotic fluid volume includes single deepest pocket and amniotic fluid index measurement. Abnormal amniotic fluid volumes include both oligohydramnios and polyhydramnios. Whereas oligohydramnios is mostly associated with fetal pathology, polyhydramnios may be due to abnormal fetal or maternal conditions or may be idiopathic. The predictive value of amniotic fluid index and single deepest amniotic fluid pocket for oligo- and polyhydramnios appears to be limited.
113
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Measurement of the vertical diameter in each of the four quadrants of the uterus is undertaken. The numbers are added up to calculate the amniotic fluid index.
Placenta Localization The introduction of ultrasound technology represented a unique step forward in our ability to make a diagnosis regarding the human placenta. Rapidly, it became clear that the new technology had far more advantages than x-ray, thermography and scintigraphy in the ability to locate the placenta, and it left the old techniques obsolete. Even the particularly difficult problem of defining the exact delineation of the border in cases where placenta praevia was suspected is now of historical interest only as a consequence of high-resolution ultrasound and the transvaginal scanning approach.
Embryology The placenta is regarded as an organ of fetal origin as it develops solely from the outer cell layer of the blastocyst, the trophoblast. The contact with the uterine endometrium and the trophoblast induces a proliferation of the trophoblast. Some of the trophoblast cells lose their cell membrane and form a syncytium, the so-called syncytioblast. This process stimulates a decidual reaction in the endometrium that causes the stroma to become thicker and highly vascularized, then called decidua. A thin capsule of the decidua called decidua capsularis covers the part of the embryo which is protruding into the endometrial cavity. The decidua at the embryonic pole develops into the decidua basalis, which takes part in the formation of the future placenta. During early development, the vessels supporting the decidua capsularis regress and the smooth chorion or chorion laeve develops.6 The vessels supporting the decidua basalis are retained and the leafy chorion or chorion frondosum is developed and the growth process of the placenta, which takes most of the remaining time of the pregnancy, then commences (Fig. 6.2).
Chorion laeve Decidua capsularis
Chorion frondosum Decidua basalis
Decidua parietalis
114
Fig. 6.2 Status of the chorion and the decidua at approximately 8 weeks' gestational age.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Amniotic fluid and placental localization
Functional anatomy The human placenta is the interface between the circulations of the mother and fetus for the exchange of nutrients, respiratory gases and waste products.3 The physiological mechanism of the transfer of specific substances is complicated and remains a field for advanced research. This is in contrast to other organ systems where such a mechanism is mostly understood. The human placenta has approximately 120 cotyledons that together comprise the functional unit of the organ. Each of these cotyledons has a primary villus stem which arises from the chorionic plate and is supplied by the primary branches of the fetal vessels. Further down the vascular tree, these branches form the secondary and tertiary stem where the vascular exchange takes place. From the maternal side, the pulsative blood flow from the spiral arteries enters the intercotyledonary space and flushes the maternal side of the vascular space all the way up to the chorionic plate. Between the cotyledons, the blood filters into venous channels and returns to the decidual plate. There is complete separation between the fetal and the maternal blood and all exchange of nutrients and blood gases takes place through the vasculosyncytial membranes separating the two circulatory systems. Development of the placenta as evaluated by ultrasound technology During weeks 8–12 the development of the placenta may be followed and the chorion frondosum (placenta) may be easily differentiated from the chorion laeve (chorion) (Fig. 6.3). From week 12 onwards it becomes possible to differentiate between the placenta, the basal plate facing the maternal side of the placenta and the chorionic plate facing the fetus. The placenta grows as pregnancy progresses, allowing easy identification.
Indications for the Location of the Placenta
• First-trimester invasive procedures such as abdominal or transvaginal chorion villus biopsy
• Transabdominal amniocentesis in the second trimester and other invasive procedures performed any time later in the pregnancy
• Bleeding in the second and third trimesters • Evaluation of the placenta and its location and relation to the uterine wall in cases of suspected placental abruption • Routine fetal examination performed at 18–20 weeks • Prior to external version of the fetus in late pregnancy.
The most common indication for location of the placenta is during systematic evaluation of the uterus and the intrauterine contents during the second-trimester fetal examination or ‘routine fetal examination’ as it is frequently called. The fetal examination is best initiated by the inverted U-movement of the transducer starting at the symphysis, slowly moving the transducer in a transverse plane on one side of the uterus to the top of the uterus and then down to the symphysis
115
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 6.3 Pregnancy at 10 weeks' gestational age. The placenta and the chorion are clearly imaged, as is the amniotic sac surrounding the fetus. The amnion has not yet fused with the chorion.
on the contralateral side. During this procedure the placenta may be located and other important features such as the viability of the fetus, the position and the number of fetuses may be established. In early pregnancy, i.e. before the 18–20-week routine fetal examination, there is no reason to register the location of the placenta except for those indicated above. Various locations of the placenta In the second trimester, the chorionic plate or the fetal surface of the placenta is usually seen as a white line. The placenta is usually relatively echogenic, with equally distributed, fine-grained echoes through the full extent of the organ. The basal plate is not always easy to distinguish but the uterine tissue, which is about 1.5 cm thick, appears slightly darker in its fine-grained echo setting compared to the placenta, making the delineation between the placenta and the uterine tissue possible (Fig. 6.4). Normally, the placenta is located in the fundal area on the left or right lateral side, the posterior or the anterior side (Fig. 6.5) or a combination thereof. The most important clinically useful distinction of the location is
116
Fig. 6.4 Placenta located on the anterior wall. The uterine wall, the basal plate of the placenta facing the uterus and the chorionic plate facing the fetus are clearly seen.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Amniotic fluid and placental localization
Fig. 6.5 Placenta located on the anterior wall including a velamentous insertion of the cord.
the relation between the lower portions of the placenta and the internal os of the uterus (Fig. 6.6). Attempts should be made to demonstrate the lower portion of the placenta and the internal os on the same image. Care must be taken to distinguish between Braxton Hicks contractions and the placenta. The contraction appears darker and less echogenic (Fig. 6.7). The final location of the placenta may require additional sagittal and parasagittal scans. It is not difficult to locate the placenta except when it is on the lower posterior wall. The overview might be difficult due to extremities or a larger presenting part of the fetus casting a shadow on the deeper portion of the image. Scanning from the right or left side of the uterus or scanning transvaginally can help overcome the problem.
Fig. 6.6 The placenta is located on the posterior wall, covering the internal os of the cervical canal. The placental edge is marked with +.
117
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 6.7 The placenta is located on the posterior wall. A local contraction of the uterus behind the placenta can clearly be distinguished, making the placenta seem to be protruding into the amniotic fluid.
Placenta praevia The placenta may cover the internal uterine os (see Fig. 6.6). When this is the case, an exact delineation of the location of the placenta and a specific management protocol are required. If more than 2.5 cm of the placenta covers the internal os, it is characterized as placenta praevia. A transvaginal scan may assist in providing a more detailed location of the lower portion of the placenta. In addition to the detailed relation to the internal os, it is important to describe the main location of the placenta. Particular attention is required when the placenta covers the internal os and a major part of the placenta is located in the lower anterior portion of the uterus, which may interfere with a surgical approach to deliver the fetus. Suggested management protocol for suspected placenta praevia Management when the placental edge related to the internal os at 18–20 weeks is:
• =1 cm from internal os. No further scans. Placenta praevia is unlikely. • <1 cm from or <2.5 cm overlying the internal os. Repeat scan at 35 weeks (or earlier in case of bleeding).
• 2.5 cm overlying the internal os. Most likely placenta praevia at term. Plan for a caesarean section at 38 weeks following verification of placental location.
Placental Morphology
118
Sometimes small sonolucent areas may be located within the regular fine-grained texture of the placenta, usually towards the basal plate (Fig. 6.8). They are usually referred to as placental lakes and represent areas without any fetal villi which consist of slowly moving blood. They have no clinical significance.15 Placental cysts may be located close to the chorionic plate. They are superficial vessels seen in cross-section or as longitudinal tubes. They have no clinical significance. The placental texture changes during the course of a pregnancy. These morphological changes have not been proven to have any clinical implications16 but
✩✩✩✩✩✩✩✩✩✩✩ ✩
it is useful to have knowledge of the described changes, which are part of the gradual ageing process of the placenta. Grannum, who classified them into grades 0, I, II and III, has described these changes, called placental grading, in detail.5 Grade 0 represents the normal finegrained homogenic placenta. Grade I presents with multiple echogenic areas, grade II has echogenic areas towards the base and comma-like indentions in the chorionic plate. Grade III has, in addition to grade II, cystic areas within the placenta and echogenic irregular areas beneath the chorionic plate.
Amniotic fluid and placental localization
Fig. 6.8 Anterior placenta with a placental lake.
Conclusion The placenta is regarded as an organ of fetal origin as it develops from the trophoblast. It is the interface between the maternal and fetal circulation. The human placenta has approximately 120 cotyledons, each of which derives its vascular supply from the fetus. The development of the placenta may be followed from week 8 onwards. By week 12, distinction of the placenta, with the basal plate facing the uterus and the chorionic plate facing the fetus, is possible. The indications for localization of the placenta are in connection with intrauterine invasive procedures, with bleeding in the second trimester, as part of the routine second-trimester scan and prior to external version in late pregnancy. The distinction of the relation of the inner cervical os and the placental edge is important. A management protocol for placenta praevia must be followed. References 1. Brace RA. Current topic: progress toward understanding the regulation of amniotic fluid: water and solute fluxes in and through the fetal extraplacental membranes. Placenta 1995;16:1–18 2. Chamberlain PF, Manning FA, Morrison I, Harman CR, Lange IR. Ultrasound
evaluation of amniotic fluid volume. I. The relationship of marginal and decreased amniotic fluid volumes to perinatal outcome. Am J Obstet Gynecol 1984;150:245–249 3. Doughty IM, Sibley CP. Placental transfer. In: Hanson A, Spencer JAD, Rodeck C (eds)
119
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
120
Fetus and neonate. Physiology and clinical applications. Cambridge University Press, New York, 1995: 3–29 4. Falcon O, Wegrzyn P, Faro C, Peralta CF, Nicolaides KH. Gestational sac volume measured by three-dimensional ultrasound at 11 to 13+6 weeks of gestation: relation to chromosomal defects. Ultrasound Obstet Gynecol 2005;25:546–550 5. Grannum PAT, Berkowitz RL, Hobbins JC. The ultrasonic changes in the maturing placenta and their relations to fetal pulmonic maturity. Am J Obstet Gynecol 1982;133:915–922 6. Larsen W. Fetal development and the fetus as a patient. In: Essentials of human embryology. Churchill Livingstone, New York, 1998: 317–330 7. Magann EF, Doherty DA, Field K et al. Biophysical profile with amniotic fluid volume assessments. Obstet Gynecol 2004;104:5–10 8. Manning FA, Hill M, Platt LD. Qualitative amniotic fluid determination by ultrasound. Am J Obstet Gynecol 1981;139:254–260 9. Mescher EJ, Platzker ACG, Ballard PL, Kitterman JA, Clements JA, Tooley WH. Ontogeny of tracheal fluid, pulmonary surfactant and plasma corticoids in the fetal lamb. J Appl Physiol 1975;39:1017–1021 10. Modena AB, Freni S. Amniotic fluid dynamics. Acta Biomed Ateneo Parmense 2004;75:11–18
11. Ott WJ. Reevaluation of the relationship between amniotic fluid volume and perinatal outcome. Am J Obstet Gynecol 2005;192:1803–1809 12. Panting-Kemp A, Nguyen T, Chang E, Quillen E, Castro L. Idiopathic polyhydramnios and perinatal outcome. Am J Obstet Gynecol 1999;181:1079–1082 13. Phelan JP, Smith CV, Broussard P, Small M. Amniotic fluid volume assessment with the four-quadrant technique at 36–42 weeks gestation. J Reprod Med 1987;32:540–542 14. Seeds AE. Current concepts of amniotic fluid dynamics. Am J Obstet Gynecol 1980;138:575–586 15. Thompson MO, Vines SK, Aguilina J, Wathen NC, Harrington K. Are placental lakes of any clinical significance? Placenta 2002;23:685–690 16. Vosmar MB, Jongsma HW, van Dongen PW. The value of ultrasonic placental grading: no correlation with intrauterine growth retardation or with maternal smoking. J Perinat Med 1989;17:137–143 17. Wladimiroff JW, Campbell S. Fetal urinary production rates in normal and complicated pregnancy. Lancet 1974;ii:151–154 18. Zaretsky MV, McIntire DD, Reichel TF, Twickler DM. Correlation of measured amniotic fluid volume to sonographic and magnetic resonance predictions. Am J Obstet Gynecol 2004;191:2148–2153
7 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Assessment of the placenta and umbilical cord Eric Jauniaux
ABSTRACT With improvement of ultrasound equipment, obstetricians are now able to examine the placenta and the cord in detail before delivery and to investigate the placental circulations in vivo. Over the last two decades ultrasound has gained an important role in the prenatal diagnosis and management of: ■■ ■■
■■ ■■ ■■
■■
■■
first- and second-trimester intrauterine haematomas which are associated with premature rupture of the membranes and preterm onset of labour placenta accreta which is characterized by myometrial invasion by villi tissue and occurs when the decidua basalis is partially or completely absent vascular chorioangiomas which are associated with an increased incidence of polyhydramnios and fetal growth retardation complete and partial hydatidiform mole which can both be associated with persisting gestational trophoblastic tumours vascular placental lesions such as large thrombosis and infarcts which are usually found during the third trimester and are associated with fetal growth restriction the absence of one umbilical artery which is found in association with many fetal anatomical defects and which when isolated leads to poor fetal growth in about 20% of the cases abnormal cord insertion and position which can be associated with severe obstetric complications.
These findings demonstrate that the differential diagnosis of placental and cord abnormalities is now possible in utero and that placental examination should be part of all routine ultrasound examinations.
Keywords Placenta, trophoblast, tumour, umbilical cord.
121
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Introduction Before the development of ultrasound imaging, morphological examination of the placenta and the cord was only of epidemiological value and was therefore of little influence on pregnancy management.With the advent of modern ultrasound equipment, it is now possible to examine the placenta and the cord in detail from the beginning of the first trimester. A gestational sac of 2–3 mm can be detected as early as 4 weeks and 1 or 2 days menstrual age. In fact, the term ‘gestational sac’ refers to the chorionic cavity and the rim of placental villi and underlying decidual proliferation, which is the first evidence of a pregnancy. Determining placental position in utero was one of the first aims of ultrasound examination in the 1960s. Visualization and localization of the placenta by ultrasound became rapidly superior to all other imaging techniques such as radiographic placentography or scintigraphy and is now an essential part of routine prenatal examinations. The ultrasound features of most placental or cord vascular lesions may undergo major changes within a few days. When a placental or cord abnormality, which could be associated with perinatal complications, is suspected, serial sonographic examinations should be performed. The information which can now be obtained by high-resolution ultrasound or Doppler techniques places additional demands on the clinician who requires more extensive knowledge of the anatomy and physiology of the vascular circulatory changes that occur during pregnancy.1–30 In this chapter, the sonographic differential diagnoses and pathophysiology of the principal abnormalities of the placenta and the umbilical cord will be presented.
Major Structural Abnormalities of the Placenta In describing placental lesions, ultrasonographers have used many inaccurate and misleading expressions. This is probably due to the fact that little attempt has been made to compare ultrasound and pathological findings. One should always refer to the histopathological terminology to categorize these lesions and evaluate their clinical significance.
Congenital Abnormalities Abnormalities of placentation
122
Placenta extrachorialis This is a common abnormality, found in about 25% of all placentas, and characterized by a transition of membranous to villous chorion at a distance from the placental edge.9 Insertion of the membranes within the placental margin results in placental tissue not covered by the chorionic plate (extrachorialis) and in a smaller than normal amniotic cavity.9 Two forms can be distinguished: the circummarginate placentas and the circumvallate. Only the latter has clinical significance because the abnormal insertion of membrane contains amnion, chorion and decidual tissue. As the uterine wall stretches during the second half of gestation, the placenta cannot adapt and there is tearing of membranes from the edge of the chorionic plate
✩✩✩✩✩✩✩✩✩✩✩ ✩
Placenta accreta This has been defined as a placenta with abnormal adherence, either in whole or in part, to the uterine wall.6,16 This abnormality is characterized by myometrial invasion by the villi and occurs when the decidua basalis is partially or completely absent. According to the degree of myometrial invasion, this condition is subdivided into placenta accreta vera, when the villi are simply attached to the myometrium, placenta increta, when the villi deeply invade the myometrium, and placenta percreta, when the villi penetrate the entire thickness of the uterine wall.16 Placenta accreta is a rare but very serious abnormality. All conditions or procedures which affect the integrity of the internal uterine walls, such as caesarean section and other uterine surgery, curettage, sepsis or fibroids, are predisposing factors for abnormal villous penetration.6 In many patients there is a combination of aetiological factors and the association of high parity with prior caesarean scars and anterior low placental insertion (praevia) is a particular risk. Placentas accreta have an overall maternal and fetal mortality of around 10% due to antepartum or postpartum bleeding, uterine rupture and uterine inversion. Placenta percreta is clearly the most dangerous condition, with a perinatal mortality rate approaching 96%.6,16 On ultrasound, the decidual interface between placenta and myometrium (hypoechoic retroplacental zone) is absent at the level of the abnormal villous penetration.4,6,16,29 Most placentas accreta can be detected as early as 11–14 weeks of gestation in most at-risk patients by visualization of irregular vascular spaces within the placenta basal area.4 Colour Doppler sonography highlights areas of increased vascularity with dilated blood vessels crossing the placenta and uterine wall.16,29 In addition, in placenta percreta, an irregular uterine serosa is found in greyscale ultrasonography and thinning of the uterine wall, found in magnetic resonance imaging, contributes to the diagnosis.29 The diagnosis of placenta accreta is rarely achieved antenatally by routine ultrasound examination.6 However, by contrast with placenta circumvallate, the prenatal diagnosis of this condition allows the surgical team to demarcate which areas of the placenta are accreta, increta or percreta before surgery and prepare for a caesarean hysterectomy and more extensive pelvic surgery if a partial resection is impossible. This approach has not been investigated prospectively on many patients but there is little doubt that prenatal diagnosis of major placenta increta and percreta will reduce fetal and maternal perinatal mortality allowing transfer to centres that are equipped for major pelvic surgery and intensive care.
Assessment of the placenta and umbilical cord
and intrauterine bleeding with formation of a subchorionic haematoma (see below). Circumvallate placentation is therefore accompanied by a risk of premature rupture of the membrane, vaginal bleeding and preterm onset of labour. This form of placentation is also associated with an increased incidence of low-birthweight infants.9,13 The obstetric risks linked with circumvallate placentas has never been evaluated prospectively. Multiple subamniotic sonolucent areas of various size and shape, located in the periphery of the placenta, are the main ultrasound features of this form of placentation.9 However, the accuracy of sonography of the placenta for revealing circumvallation appears to be limited.8
123
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Placental tumours
124
Mesenchymal tumours Chorioangioma or placental hemangioma is the most common benign tumour of the placenta with an incidence at delivery of 0.5–1% of placentas examined.9,16 The incidence of large chorioangiomas is lower and varies from 1 in 8000 to 1 in 50,000 pregnancies.16 Chorioangiomas are hamartomas, which arise as a malformation of the primitive angioblastic tissue of the placenta. There are two main histopathological types of chorioangiomas: angiomatous, which are formed of numerous blood vessels, and cellular, which consist of loose mesenchymal tissue, containing a few ill-formed vessels. Degenerative changes such as necrosis, calcification, hyalinization or myxoid changes are frequently present in large tumours.9 Most chorioangiomas are small, single, round, encapsulated and intraplacental. They are occasionally observed during routine ultrasound examination14 and are likely to be discovered only by histopathological examination. Large chorioangiomas are of variable shape, divided by fibrous septa, and most commonly protrude from the fetal surface of the placenta near the cord insertion.9 These tumours are well circumscribed, have a different echogenicity from the rest of the placental tissue and have been documented sonographically from 16 weeks of gestation.14 Chorioangiomas can be complicated by fetal hydrops due to the chronic shunting of large volumes of fetal blood through the tumour or to polyhydramnios.9,14 The development of polyhydramnios is independent of the size of the tumour but rather linked to its vascular nature.14,30 The fetal risk depends more on the proportion of angiomatous versus myxoid tissue inside the tumour than on its exact size.14 Thus ultrasound examination of the vascularization of the tumour is a pivotal determining factor of pregnancy outcome (Fig. 7.1). If the tumour is avascular, no specific complications should be expected. If the tumour is vascularized, and in particular if it contains numerous large vessels, serial ultrasound and Doppler examinations are warranted to detect polyhydramnios and early features of fetal congestive heart failure. Novel intrauterine treatment options include intravascular transfusion, fetoscopic laser devascularization, microcoil embolization, and
Fig. 7.1 Heterogeneous vascular placental mass at 30 weeks, protruding from the fetal plate near the cord insertion (star). The pregnancy was complicated by polyhydramnios. Pathological examination demonstrated a vascular chorioangioma.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gestational trophoblastic tumours (GTD) Hydatidiform transformation (Fig. 7.2) of the villous tissue is a common finding in placental trophoblastic tumours. Complete or classic hydatidiform moles (CHM) are described as a generalized swelling of the villous tissue, diffuse trophoblastic hyperplasia and no embryonic or fetal tissue.3 Classically, patients with CHM present with vaginal bleeding, uterine enlargement greater than expected for gestational age and abnormally high level of maternal serum human chorionic gonadotropin (MShCG). Medical complications include pregnancy-induced hypertension (PIH), hyperthyroidism, hyperemesis, anaemia and the development of ovarian theca-lutein cyst. With earlier diagnosis, the incidence of these complications has decreased. Molar changes can now be detected from the second month of pregnancy by ultrasound which typically reveals a uterine cavity filled with multiple sonolucent areas of varying size and shape (‘snow-storm appearance’) without associated embryonic or fetal structure.18,21 Theca-lutein cysts secondary to the very high MShCG levels may be diagnosed in up to 30% of cases producing either soap bubble or spoke wheel appearance of the ovaries, which are enlarged. Elevated
Fig. 7.2 Typical ‘Swiss cheese’ appearance of the placenta on ultrasound corresponding to hydatidiform transformation in a partial mole.
Assessment of the placenta and umbilical cord
intravascular injection of absolute alcohol. Quantitative flow data obtained using three-dimensional power Doppler may indicate altered haemodynamics in the tumour which can influence the management.28
125
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ MShCG levels, combined with these specific sonographic features, are highly indicative of the presence of hydatidiform mole, even before the final histopathological diagnosis is confirmed. Ultrasound features of CHM may be different at earlier gestations and accuracy of diagnosis varies between studies. The ultrasound diagnosis of complete mole usually poses little problem from the third month of pregnancy onward and can be made prenatally in around 80% of cases.2,13,29 Partial hydatidiform moles (PHM) refer to the combination of a fetus with localized placental molar degenerations, characterized by focal swelling of the villous tissue – focal trophoblastic hyperplasia.19 The abnormal villi are being scattered within macroscopically normal placental tissue, which tends to retain its shape. Partial moles are usually triploid and of diandric origin, having two sets of chromosomes from paternal origin and one from maternal origin. Most have a 69,XXX or 69,XXY genotype derived from a haploid ovum with either reduplication of the paternal haploid set from a single sperm or, less frequently, from dispermic fertilization. Triploidy of digynic origin, due to a double maternal contribution, is not associated with placental hydatidiform changes. Vaginal bleeding in the first or second trimester with a total incidence of 47% is the most common maternal symptom reported in both types of triploidies.19 The phenotypic expression of both diandric and digynic triploidies includes growth restriction and disturbance of organogenesis that becomes obvious in fetuses surviving into the second trimester. From 16 weeks, almost all triploid fetuses have at least one measurement below the normal range and more than 70% present with severe growth restriction.19 Structural fetal defects are observed antenatally in about 93% of cases. The most common are abnormalities of the hands, bilateral cerebral ventriculomegaly, heart anomalies and micrognathia. Triploid partial moles are not associated with specific fetal anomaly but almost always with symmetrical growth restriction. Classically, triploid partial mole presents on ultrasound as an enlarged placenta (thickness >4 cm at 18–22 weeks) containing multicystic avascular sonolucent spaces (see Fig. 7.2) – ‘Swiss cheese’ appearance. Following uterine evacuation, 18–29% of patients with a CHM and 1% of those with a PHM will develop a persistent trophoblastic tumour.3,19 If the incidence of maternal complication has been reduced by an early diagnosis, the incidence of persistent GTD has remained unchanged since the introduction of routine ultrasound examination during pregnancy. This highlights the importance of training sonographers working in early pregnancy units in the detection of placental molar changes as many cases of complete and partial moles will present as miscarriages. MShCG is significantly higher in both CHM and PHM and, in conjunction with transvaginal ultrasound, may provide the screening test required.
Secondary Abnormalities Vascular abnormalities
126
Thrombosis and infarcts Both lesions are usually found during the third trimester of pregnancy.1 Placental thromboses are the result of focal coagulation of blood in the intervillous spaces
✩✩✩✩✩✩✩✩✩✩✩ ✩
Assessment of the placenta and umbilical cord
and occur more frequently in pregnancies complicated by rhesus isoimmunization.9,15,17 Large hypoechoic areas with low flow laterally and relatively high flow in the central part on real-time imaging can be observed in the early stages of the development of an intervillous thrombosis. Abnormal haemodynamic flow in the intervillous space may result from the failure of the cotyledon to expand in response to the increasing flow of the corresponding uteroplacental artery and compression of the surrounding villi which gradually atrophy as fibrin is laid down in the periphery.15 This process causes a progressive increase of the echogenicity of the lesion. Finally the maternal blood coagulates in the placental tissue, obliterating, focally, the intervillous circulation. Placental infarcts are the result of obstruction of a uteroplacental artery leading to focal degeneration of the overlying villous tissue.15,17 Extensive infarcts are found in pregnancies complicated by pre-eclampsia or essential hypertension and are associated with an increase in perinatal mortality and intrauterine growth retardation. Sonographically, placental infarcts appear as large intraplacental areas, irregular and hyperechoic in the acute stage and isoechoic in a more advanced stage.9,17 Identifying thrombo-occlusive placental lesions before the development of pregnancy complications may prove useful in the design of trials to study the effectiveness of heparin in the prevention of clinical complications resulting from thrombo-occlusive uteroplacental disease.9 Haematomas Extravasation of maternal or fetal blood can result in a localized collection of blood or haematoma forming in the placenta. Such lesions may be subamniotic, subchorionic or retroplacental and can be identified on prenatal ultrasound examination.5,20 The terminology used to describe placental vascular lesions is confusing, with ultrasound descriptions often unrelated to the pathological findings. Various terms such as subchorionic cyst, membranous cyst, thrombotic cyst and subchorionic haemorrhage have been used in the literature to describe lesions of the fetal plate of the placenta. A subchorionic or retroplacental haematoma reflects bleeding of maternal origin and is identified sonographically as a hypoechoic area between the chorion and uterine wall. Such lesions are seen in more than 10% of pregnancies, commonly in the first trimester, and may carry an increased risk of miscarriage, stillbirth, preterm labour and abruptio placentae.9,17 On the other hand, subamniotic haematoma are found situated under the amniotic layer covering the fetal (chorionic) plate of the placenta and result from the rupture of fetal vessels branching from the cord (Fig. 7.3). These are considerably less common, with the majority reported in the third trimester or as a result of excessive traction on the umbilical cord at delivery.17 The sonographic appearance is of a single mass protruding from the fetal plate and surrounded by a thin membrane. While the newly formed clot is echogenic, with time the lesion becomes less so as the clot resolves.
Major Structural Abnormalities of the Umbilical Cord The umbilical cord anatomy can often be visualized from 12 weeks' gestation by grey-scale imaging but a precise diagnosis of a particular cord abnormality may be
127
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 7.3 Hypoechoic mass protruding from the fetal plate of the placenta (star) and corresponding after delivery to subamniotic haematoma due to the rupture of a fetal vessel.
difficult and time consuming before 18–20 weeks. Various factors such as oligohydramnios or multiple loops in the cord can make accurate visualization of the cord vessels impossible, even near term.17 High-resolution colour Doppler imaging has an important role in early and accurate diagnosis of cord abnormalities and is also of clinical value in viewing invasive procedures such as amniocentesis or cordocentesis.
Congenital Abnormalities Abnormalities of the cord insertion Velamentous insertion of the cord or placenta velamentosa is a well-defined pathological entity with a frequency of around 1% of pregnancies.17 From a clinical point of view, attachment of the cord to the extraplacental membranes is important because of the risk of severe fetal haemorrhage during labour. Antenatal diagnosis of attachment of the cord to the membranes rather than the placental mass can be easily performed before labour by means of grey-scale and colour Doppler imaging.17,27 Systematic assessment of the placental cord insertion site at routine obstetric ultrasound has the potential to identify pregnancies with velamentous insertion and, therefore, those at risk for obstetric complications, including vasa praevia.
128
Single umbilical artery (SUA) syndrome The absence of one umbilical artery (Fig. 7.4) is amongst the most common congenital fetal malformations with an incidence of approximately 1% of all deliveries.17 The highest incidence of SUA is found among western Europeans and there is no evidence of familial tendency for this anomaly. SUA occurs three to four times more frequently in twins and almost invariably accompanies the acardia malformation and sirenomelia or caudal regression syndrome.17 There is also a sixfold increase of the incidence of velamentous insertion of the cord among SUA infants.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fetal major anatomical defects are largely responsible for the high fetal and neonatal loss from this pathology.23 Fetal malformations are present in about 50% of cases of SUA and can affect any organ system. The comparison of sonographic and postnatal findings in cases of SUA syndrome has shown that minor malformations of the musculoskeletal and cardiovascular systems or of the genitourinary tract are often misdiagnosed by ultrasonography, in particular when they are isolated.17 The discovery of a SUA in the perinatal period justifies a detailed ultrasound examination of the neonate to exclude minor anomalies of internal organs such as the kidney or heart, which may lead to deleterious sequelae if untreated until late infancy. The antenatal discovery of a SUA together with another fetal structural abnormality should raise the question of antenatal chromosome invasive testing,23 in particular in early pregnancy24 when the diagnosis of structural defect is less accurate. However, it is most likely that, as for many other isolated fetal defects, an isolated SUA does not increase the risk for trisomy 21.17 Thus, the SUA is not a specific marker of chromosomal abnormalities and the higher incidence of SUA found in trisomies 13 and 1824 is probably only related to the higher incidence in these cases of major fetal defects which are known to be associated with the aplasia or atrophy of one of the umbilical arteries. The detection rate of SUA remains low in routine ultrasound.7 However, the incidence of fetal growth restriction (FGR) is significantly elevated among fetuses with a SUA and may be present without any other congenital anomalies in about 20% of cases.17 Since the incidence of FGR is about 10% in the third trimester of pregnancy then 1 in 10 neonates with a low birthweight may have a SUA. The presence of a single umbilical artery is associated with a poorer perinatal outcome compared to that in fetuses with three vessels in the cord.7 Recognizing the importance of this cord anomaly in counselling and management of pregnancies should provide the stimulus to improve detection rates. Cord tumours Umbilical cord tumours are infrequent perinatal findings and are always benign. From a pathological point of view, primary cord tumours can be divided into
Assessment of the placenta and umbilical cord
Fig. 7.4 Longitudinal view of an umbilical cord containing one vein and one artery.
129
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 7.5 Transverse view of a cord tumour containing dense tissue and pseudocysts and corresponding to a cord angiomyxoma.
angiomyxomas or haemangiomas derived from embryonic vessels, teratomas derived from germ cells and vestigial cysts derived from remnants of the allantois or the omphalomesenteric duct.17 A cord angiomyxoma appears sonographically as a heterogeneous mass made of a strong echogenic area, embedding the umbilical vessels12 and surrounded by large echo-poor areas (Fig. 7.5). The prenatal diagnosis of a cord teratoma has rarely been documented but this type of tumour is mainly composed of dense tissue26 and appears echogenic on ultrasound. Conversely, vestigial cysts appear sonographically as a single fluid-filled mass.17 Vestigial cysts and pseudocysts can sometimes be associated with small abdominal wall defects and a precise early prenatal diagnosis can be more difficult to establish.10 These embryonic cysts are usually small but some may exceed 5 cm in size and appear as a poorly reflective round mass adjacent to or within the cord. Colour Doppler shows no blood flow within the mass.17 The prevalence of these cysts is around 3% in the first trimester and is an important differential diagnosis as more than 20% of cases are associated with fetal chromosomal or structural defects, especially when located close to the placental insertion of the cord.25
Secondary Abnormalities Vascular abnormalities
130
Haematomas and thrombosis Spontaneous cord haematomas are occasional perinatal findings and are usually located near the fetal umbilicus.17 Mechanical trauma of the cord such as prolapse, torsion, strangulation or dissecting aneurysm are all potential causes of cord haematoma. At ultrasound examination, the cord appears markedly thickened, sausage-shaped and extremely echogenic. Thrombosis of one or more umbilical cord vessels is a rare complication with an incidence of approximately 0.08% among placentas examined prospectively at delivery.17 Thrombosis of the umbilical vein occurs more frequently than thrombosis of one or both arteries and perinatal morbidity or mortality is more likely with umbilical artery thrombosis than
✩✩✩✩✩✩✩✩✩✩✩ ✩
Vascular abnormalities Abnormal cord position Looping of the cord may occur around the fetal neck, body or shoulder17 and can be diagnosed by sonography. Although in singleton pregnancies looping of the cord around the neck is an uncommon cause of fetal death, in monoamniotic twins a significant portion of the high mortality can be attributed to umbilical cord problems. Short-term fetal complications of the nuchal cord theoretically include variable fetal heart rate decelerations during the first and second stages of labour and lower mean umbilical artery and venous pH at birth. However, because of the small size of these studies the clinical significance of a single nuchal cord remains undetermined. The sensitivity of around 90% for colour Doppler imaging in detecting the presence of a nuchal cord increases with advancing gestation and is always higher than that of grey-scale imaging.11 Colour mapping allows single loops to be differentiated from multiple loops of nuchal cord. However, the sensitivity of the routine ultrasound diagnosis of a nuchal cord is low prior to induction of labour at term.22 Furthermore, a nuchal cord does not appear to increase the risk of caesarean section or poor neonatal outcome. The low ultrasound detection rate of a nuchal cord limits its use in decision making prior to induction of labour in high-risk pregnancies.11,22
Assessment of the placenta and umbilical cord
with umbilical vein thrombosis. Thrombosis of the umbilical vessels may also be secondary to localized increased resistance in the umbilical circulation in cases of torsion, compression and knotting of haematoma. Intense echogenic material within the lumen of the umbilical vessels is the main sonographic finding.17
References 1. Alkazaleh F, Viero S, Simchen M et al. Ultrasound diagnosis of severe thrombotic placental damage in the second trimester: an observational study. Ultrasound Obstet Gynecol 2004;23:472–476 2. Benson CB, Genest DR, Bernstein MR, Soto-Wright V, Goldstein DP, Berkowitz RS. Sonographic appearance of first trimester complete hydatidiform moles. Ultrasound Obstet Gynecol 2000;16:188–191 3. Berkowitz RS, Goldstein DP. Chorionic tumors. N Engl J Med 1996;335:1740–1748 4. Comstock CH, Love JJ Jr, Bronsteen RA et al. Sonographic detection of placenta accreta in the second and third trimesters of pregnancy. Am J Obstet Gynecol 2004;190:1135–1140 5. Deans A, Jauniaux E. Prenatal diagnosis and outcome of subamniotic hematomas. Ultrasound Obstet Gynecol 1998;11:367–377 6. Gielchinsky Y, Rojansky N, Fasouliotis SJ, Ezra Y. Placenta accreta – summary of
10 years: a survey of 310 cases. Placenta 2002;23:210–214 7. Gornall AS, Kurinczuk JJ, Konje JC. Antenatal detection of a single umbilical artery: does it matter? Prenat Diagn 2003;23:117–123 8. Harris RD, Wells WA, Black WC et al. Accuracy of prenatal sonography for detecting circumvallate placenta. Am J Roentgenol 1997;168:1603–1608 9. Jauniaux E, Campbell S. Sonographic assessment of placental abnormalities. Am J Obstet Gynecol 1990;163:1650–1658 10. Jauniaux E, Donner C, Thomas C, Francotte J, Rodesch F, Avni E. Umbilical cord pseudocyst in trisomy 18. Prenat Diagn 1998;8:557–563 11. Jauniaux E, Mawissa C, Peellaerts C, Rodesch F. Nuchal cord in normal third trimester pregnancy: a color Doppler imaging study. Ultrasound Obstet Gynecol 1992;2:417–419
131
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
132
12. Jauniaux E, Moscoso G, Chitty L, Gibb D, Driver M, Campbell S. An angiomyxoma involving the whole length of the umbilical cord: prenatal diagnosis by ultrasonography. J Ultrasound Med 1990;9:419–422 13. Jauniaux E, Nicolaides KH. Early ultrasound diagnosis and follow-up of molar pregnancies. Ultrasound Obstet Gynecol 1997;9:17–21 14. Jauniaux E, Ogle R. Colour Doppler imaging in the diagnosis and management of chorioangiomas. Ultrasound Obstet Gynecol 2000;15:463–467 15. Jauniaux E, Ramsay B, Campbell S. Ultrasonographic investigation of placental morphology and size during the second trimester of pregnancy. Am J Obstet Gynecol 1994;170:130–137 16. Jauniaux E, Toplis PJ, Nicolaides KH. Sonographic diagnosis of a non-praevia placenta accreta. Ultrasound Obstet Gynecol 1996;7:58–60 17. Jauniaux E. The placenta. In: Dewbury K, Meire H, Cosgrove D, Farrant P (eds) Clinical ultrasound. A comprehensive text, 2nd edn, vol 3. Churchill Livingstone, London, 2001: 527–556 18. Jauniaux E. Ultrasound diagnosis and follow-up of gestational trophoblastic disease. Ultrasound Obstet Gynecol 1998;11:367–377 19. Jauniaux E. Partial moles: from postnatal to prenatal diagnosis. Placenta 1999;20:379–388 20. Johns J, Hyett J, Jauniaux E. Obstetric outcome after threatened miscarriage with and without a hematoma on ultrasound. Obstet Gynecol 2003;102:483–487 21. Lazarus E, Hulka CA, Siewert B, Levine D. Sonographic appearance of early complete molar pregnancies. J Ultrasound Med 1999;18:589–593 22. Peregrine E, O'Brien P, Jauniaux E. Ultrasound detection of nuchal cord prior
to labor induction and the risk of cesarean section. Ultraswound Obstet Gynecol 2004;25:160–164 23. Prucka S, Clemens M, Craven C, McPherson E. Single umbilical artery: what does it mean for the fetus? A case-control analysis of pathologically ascertained cases. Genet Med 2004;6:54–57 24. Rembouskos G, Cicero S, Longo D, Sacchini C, Nicolaides KH. Single umbilical artery at 11–14 weeks' gestation: relation to chromosomal defects. Ultrasound Obstet Gynecol 2003;22:567–570 25. Ross JA, Jurkovic D, Zosmer N, Jauniaux R, Hacket E, Nicolaides KH. Umbilical cord cysts in early pregnancy. Obstet Gynecol 1997;89:442–445 26. Satge DC, Laumond MA, Desfarges F, Chenard MP. An umbilical cord teratoma in a 17-week-old fetus. Prenat Diagn 2001;21:284–288 27. Sepulveda W, Rojas I, Robert JA, Schnapp C, Alcalde JL. Prenatal detection of velamentous insertion of the umbilical cord: a prospective color Doppler ultrasound study. Ultrasound Obstet Gynecol 2003;21:564–569 28. Shih JC, Ko TL, Lin MC, Shyu MK, Lee CN, Hsieh FJ. Quantitative three-dimensional power Doppler ultrasound predicts the outcome of placental chorioangioma. Ultrasound Obstet Gynecol 2004;24: 202–206 29. Taipale P, Orden MR, Berg M, Manninen H, Alafuzoff I. Prenatal diagnosis of placenta accreta and percreta with ultrasonography, color Doppler, and magnetic resonante imaging. Obstet Gynecol 2004;104:537–540 30. Zalel Y, Weisz B, Gamzu R, Schiff E, Shalmon B, Achiron R. Chorioangiomas of the placenta: sonographic and Doppler flow characteriztics. J Ultrasound Med 2002;21:909–913
8 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Examining the cervix by transvaginal ultrasound Kjell Å Salvesen Sturla H Eik-Nes
ABSTRACT Transvaginal ultrasound identifies women with high risk of preterm delivery. Cervical funnelling is associated with spontaneous preterm birth. A short cervix is commonly defined as a cervix <25 mm at 20–24 weeks of gestation. Sonographic measurement of the cervical length can help the clinician to distinguish between true and false labour. Of all women with a short cervical length, in only a minority will this be due to cervical incompetence.
Keywords Cervical funnelling, cervical incompetence, cervical length, preterm labour.
Introduction Preterm birth (PTB) is the leading cause of neonatal morbidity and mortality, and is responsible for half of all neonatal deaths. Mortality rises from about 2% for infants born at 32 weeks to more than 90% for those born at 23 weeks.1 Moreover, handicap or disability arises in about 60% of survivors after birth at 26 weeks and 30% in those born at 31 weeks.2 Furthermore, preterm birth is associated with a huge cost to the health service because of the need for neonatal intensive care and the continuing support necessary after discharge from the hospital.3 There are three recognized aetiological categories that result in preterm birth. These include preterm labour (PTL), preterm prelabour rupture of membranes (PPROM) and indicated or iatrogenic preterm delivery (PTD). PTL is defined as uterine activity that leads to cervical effacement and dilation in the absence of PPROM. PPROM is defined as rupture of membranes >1 hour prior to uterine contractions (<37 weeks). Iatrogenic PTD is delivery secondary to maternal
133
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Preterm birth
10%
Multiples
latrogenic deliveries
10%
Fetal anomalies and IUDF
Deliveries
13
Delivery secondary to maternal and fetal complications
80%
13
Preterm labour (PTL)
13
Preterm prelabour rupture of membranes
Spontaneous deliveries
Fig. 8.1 Causes of preterm birth.
and fetal complications of pregnancy. The three aetiological categories are each responsible for around one-third of preterm births in singleton pregnancies without malformation or intrauterine fetal death (Fig. 8.1). The processes that lead to both term and preterm spontaneous labour resemble an inflammatory reaction. Upregulation of inflammatory cytokines and prostaglandins that occurs over a period of several weeks leads to cervical ripening and membrane rupture (PROM). This will again lead to myometrical contractility and labour. Ascending infection is likely to be an aetiological factor. The cervix acts as a barrier to this stimulus, maintaining the distance from the vagina and retaining the cervical mucus plug. Women with a short cervix will be at much greater risk of this cervical barrier being breached. Once inflammation has been stimulated, cervical ripening will occur, which will lead to shortening and funnelling of the cervix. A ‘vicious circle’ will ensue, in which further ascending infection causes increased inflammation.
Transvaginal Ultrasound of the Cervix Predicts Preterm Delivery
134
Transvaginal ultrasound is superior to digital examination and to translabial, transperineal or transabdominal ultrasound in evaluating the uterine cervix. It is well accepted by pregnant women and provides high-quality images of the cervix. Transvaginal ultrasound of the cervix enables us to identify women at high risk of preterm delivery. The shorter the cervical length, the higher is the risk of preterm delivery and vice versa. A screening study at 22–24 weeks has shown that the risk for spontaneous early preterm delivery increases with decreasing cervical length, from about 0.2% at 60 mm to 1.1% at 25 mm, 4.0% at 15 mm and 78% at 5 mm.4 Furthermore, demographic characteristics and obstetric history did not have a substantial additional contribution to that of cervical length in the prediction of preterm delivery.5 Funnelling is the protrusion of membranes into the endocervical canal. Zilanti et al6 suggested that the cervix should be classified according to the shape of the
✩✩✩✩✩✩✩✩✩✩✩ ✩
The process, called funnelling when it occurs in the second and early third trimesters, is actually effacement in progress. It is dynamic, in that the internal os is seen to open and close in the absence of palpable uterine contractions. It is probably normal after 32 weeks.7
Berghella et al8 found that the prevalence of preterm birth before 35 weeks of gestation was significantly higher in women with a short cervical length when funnelling was present. In a logistic regression, controlling for cervical length, funnelling remained associated with spontaneous preterm birth before 35 weeks.8 However, a cervix with funnelling is always short. Thus, the length of the closed cervix has proven to be the single most important measurement in predicting preterm delivery. Funnelling does not seem to add further clinical information.9 Cervical length was normally distributed in 2702 women attending ultrasound at 23 pregnancy weeks at King's College Hospital in London. The median value was 38 mm, and the fifth and first centiles were 23 mm and 11 mm respectively.4,5 The cervical length was <25 mm in 8.1% and <15 mm in 1.6% of women at 23 weeks of pregnancy. Cervical length was significantly shorter in women of AfroCaribbean origin compared to Caucasians, those less than 20 years of age, and those who had previous midtrimester losses or preterm delivery.4,5 A similar distribution of cervical length was found in a study of 2915 US women.10 The mean cervical length at 24 weeks was 34 mm for nulliparous women and 36.1 mm for parous women, and the 10th centile was 26 mm and the fifth centile was 22 mm.10 A Finnish study of 3694 singleton pregnancies between 18 and 22 weeks found a mean cervical length of 40.7 mm and the third
Fig. 8.2 Cervical incompetence with V-shape funnel. Transvaginal scan, 31 weeks.
Examining the cervix by transvaginal ultrasound
funnel, and they suggested the mnemonics T, Y, V, U to denote the relationship of the internal os to the lower segment and cervix. Figure 8.2 demonstrates a V-shaped funnel of cervix in a transvaginal scan at 31 weeks. Iams has suggested that funnelling is nothing but effacement of the cervix:
135
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ centile was 29 mm.11 Based on these studies, a short cervix is commonly defined as <25 mm (10th centile) at 20–24 weeks. A cervix <15 mm will only occur in around 1% of the pregnant population, but the risk of preterm delivery increases exponentially below this length.
Measurement Technique The cervix should be examined with transvaginal ultrasound in a standardized way to allow comparison with results from previous studies and to use the measurements for clinical judgement. The recommended standardized procedure is:
• after patient voiding • no pressure on the cervix • identify the internal and external os in a sagittal view • apply gentle suprapubic or fundal pressure • measure the length of the closed cervix (do not trace) • measure three times – use the minimum. Measurement of the length of the closed cervix is demonstrated schematically in Figure 8.3.
Transvaginal Ultrasound of the Cervix in the Clinical Judgement of Preterm Labour Transvaginal ultrasound of the cervix can be used in clinical judgement of preterm labour. The Oracle II randomized trial enrolled 6295 women in spontaneous preterm labour with intact membranes and without evidence of clinical infection.12 In the placebo group with no treatment (n=1556 women), 85% were undelivered after 7 days. This is in accordance with the clinical experience in most obstetric units. There is an overuse of tocolytic drugs to allow for treatment with cortico steroids for lung maturation. Sonographic measurement of the cervical length can help the clinician to distinguish between true and false labour.
136
Fig. 8.3 Schematic drawing of a measure of cervical length. A straight line is drawn from the internal to the external os.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Treatment of Cervical Incompetence A short cervical length on ultrasound has become synonymous with cervical incompetence. However, any woman who is going to suffer from a spontaneous preterm delivery will develop a short cervix. Thus, a short cervix does not by itself indicate cervical incompetence.15 The critical importance of clinical cervical incompetence lies in differentiating this condition from other causes of early preterm delivery and pregnancy loss. ‘True’ cervical incompetence is believed to be responsible for less than 10% of PTB, but it can be effectively treated by a surgical procedure: cervical cerclage. Figure 8.4 demonstrates an ultrasound picture of an incompetent cervix with a cervical suture ad modum MacDonald.
Fig. 8.4 Cervical incompetence treated with cerclage ad modum MacDonald. Transvaginal scan, 28 weeks. The suture can be seen as white spots within the cervical tissue approximately 1.5 cm above the external os.
Examining the cervix by transvaginal ultrasound
In a study involving 216 women with singleton pregnancies presenting with regular and painful uterine contractions at 24–36 weeks of gestation, spontaneous delivery within 7 days occurred in only 1/173 with cervical length >15 mm, compared to 16/43 (37%) with cervical length <15 mm.13 Thus, if clinicians are in doubt about true or false labour, they can rely on ultrasound measurements of the cervix. This is also true for PPROM. In a study of sonographic measurement of cervical length in PPROM at 24–36 weeks including 101 women with singleton pregnancies, delivery within 7 days of presentation occurred in 58/101 (57%) pregnancies.14 Logistic regression analysis demonstrated that significant independent contribution in the prediction of delivery within 7 days was provided by cervical length (odds ratio 0.91, 95% CI 0.86–0.96), gestational age at presentation (odds ratio 1.35, 95% CI 1.14–1.59) and presence of contractions (odds ratio 3.07, 95% CI 1.05–8.92).14
137
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Randomized clinical cerclage trials in women at high risk of preterm delivery, and even meta-analysis of cerclage trials, present conflicting results.16,17 A possible explanation for these results may be suboptimal patient selection. A more effective way of identifying a high-risk group would be by transvaginal sonographic measurement of cervical length. To et al18 screened cervical length in 47,123 women between 22 and 25 pregnancy weeks. The cervix was 15 mm or less in 470 women. In all, 253 (54%) of these women were randomized to have a cervical cerclage (n=127) or to expectant management (n=126). The proportion of preterm delivery before 33 weeks was similar in both groups, 22% in the cerclage group versus 26% in the control group (relative risk 0.84, 95% CI 0.54–1.31), with no significant differences in perinatal or maternal morbidity or mortality. There is a common misunderstanding that this trial demonstrates that cervical cerclage does not prevent preterm birth in women with short cervix. This is not correct. The trial demonstrates that ultrasound screening for short cervix in lowrisk women, followed by therapeutic cerclage, does not prevent preterm birth. Simcox et al19 advocate caution against extrapolation of the findings of this trial to women with a history of previous midtrimester or preterm delivery. Furthermore, they state that one rationale for the cerclage is to minimize ascending infection by preventing membrane exposure and indicate that inserting a cerclage at a cervical length of 15 mm might be too late.19 To et al, however, argue against decreasing the threshold for cerclage to 20 mm or 25 mm.20 This would result in a threefold and sevenfold increase, respectively, in the screen-positive rate, and subject many women with a very low risk of preterm delivery to a surgical procedure.
Prophylactic Cerclage or Transvaginal Follow-Up of the Cervix
138
One important question is whether women at high risk should be subject to prophylactic cerclage or transvaginal ultrasound follow-up of the cervix. This has not been formally tested in randomized controlled trials, but there is some evidence from observational studies. Groom et al21 performed a matched case–control study of women with a history of preterm birth, second-trimester loss or cervical surgery. Women either received a prophylactic cerclage or were followed up with measurements of cervical length and had therapeutic cerclage, if necessary. A short cervical length was found in 14 of 39 women (36%) in the follow-up group. No differences were found between the groups. Higgins et al22 performed a prospective cohort study of high-risk women. Women were managed according to the obstetric unit to which they were referred. Some of the obstetric units used elective cerclage, and some used therapeutic cerclage after ultrasound follow-up. A short cervix before 24 weeks of gestation was found in 12 of 38 women (32%) in the follow-up group, who were subsequently treated with therapeutic cerclage. Preterm delivery before 30 weeks was significantly more common in the prophylactic cerclage group (19% versus 2.6%, p=0.03).
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prophylactic treatment with progesterone in pregnant women with short cervix Progesterone is a key hormone in the onset of labour in many animal species, but its role in human labour is uncertain. Prophylactic treatment with progesterone to prevent preterm birth is debated. A Cochrane review from 2006 suggests that prophylactic progesterone may halve the incidence of preterm births.23 A randomized controlled trial from 2007 demonstrated that for women with a short cervix (<15 mm) at 23 weeks, prophylactic treatment of 200 mg progesterone per day applied vaginally reduced preterm birth rate before 34 weeks from 34% to 19%.24 A randomized controlled trial of twin pregnancies demonstrated no beneficial effects of prophylactic progesterone injections.25 It is possible that the mechanisms for preterm birth in multiple pregnancies are different from singleton pregnancies. There are reasons to believe that prophylactic use of progesterone will be a future treatment option for women without a history of previous poor obstetric outcome, singleton pregnancy and a short cervix in mid-pregnancy. Women with previous poor obstetric outcome and a short cervix may possibly benefit from therapeutic cerclage. However, it should be pointed out that this treatment strategy needs further support from classical evidence based studies.
Examining the cervix by transvaginal ultrasound
The two studies suggest that therapeutic cerclage after ultrasound follow-up seems to be a better policy than prophylactic cerclage. However, firm conclusions cannot be drawn from observational studies. Randomized controlled trials should be done.
Conclusion Transvaginal ultrasound identifies women at high risk of preterm delivery. Cervical length is related to the risk of preterm delivery. Previous late abortion(s) and/or extreme preterm birth(s) in combination with a short cervix in mid-pregnancy is suggestive of cervical incompetence. These women should be treated by cervical cerclage. Prophylactic use of progesterone may be a future treatment option for women with short cervix and no previous poor obstetric outcome. References 1. Draper ES, Manktelow B, Field DJ, James D. Prediction of survival for preterm births by weight and gestational age: a retrospective population based study. BMJ 1999;319:1093–1097 2. Koppe JG, Verloove-Vanhorick PSP, Ilsen A. Long-term outcome. In: Kurjak A (ed) Textbook of perinatal medicine. Parthenon, Carnforth, 1998: 1362–1374 3. Petrou S. Economic consequences of preterm birth and low birth weight. Br J Obstet Gynaecol 2003;110:17–23
4. Heath VCF, Southall TR, Souka AP, Elisseou A, Nicolaides KH. Cervical length at 23 weeks of gestation: prediction of spontaneous preterm delivery. Ultrasound Obstet Gynecol 1998;12: 312–317 5. Heath VCF, Southall TR, Souka AP, Novakov A, Nicolaides KH. Cervical length at 23 weeks of gestation: relation to demographic characteristics and previous obstetric history. Ultrasound Obstet Gynecol 1998;12:304–311
139
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
140
6. Zilanti M, Azuaga A, Calderon F, Pages G, Mendoza G. Monitoring the effacement of the uterine cervix by transperineal ultrasound. J Ultrasound Med 1995;14:719–724 7. Iams JD. Cervical ultrasonography. Opinion. Ultrasound Obstet Gynecol 1997;10:156–160 8. Berghella V, Pereira L, Gareipa A, Simonazzi G. Prior cone biopsy: prediction of preterm birth by cervical ultrasound. Am J Obstet Gynecol 2004;191:1393–1397 9. To MS, Skentou C, Liao AW, Cacho AM, Nicolaides KH. Cervical length and funneling at 23 weeks of gestation in the prediction of spontaneous early preterm delivery. Ultrasound Obstet Gynecol 2001;18:200–203 10. Iams JD, Goldenberg RL, Meis PJ et al. The length of the cervix and the risk of spontaneous premature delivery. N Engl J Med 1996;334:567–572 11. Taipale P, Hillesmaa V. Sonographic measurement of uterine cervix at 18–22 weeks' gestation and the risk of preterm delivery. Obstet Gynecol 1998;92:902–907 12. Kenyon SL, Taylor DJ, Tarnow-Mordi W and the ORACLE Collaborative Group. Broad-spectrum antibiotics for spontaneous preterm labour: the ORACLE II randomised trial. Lancet 2001;357:989–994 13. Tsoi E, Akmal S, Rane S, Otigbah C, Nicolaides KH. Ultrasound assessment of cervical length in threatened preterm labor. Ultrasound Obstet Gynecol 2003;21:552–555 14. Tsoi E, Fuchs I, Henrich W, Dudenhausen JW, Nicolaides KH. Sonographic measurement of cervical length in preterm prelabor amniorrhexis. Ultrasound Obstet Gynecol 2004;24:550–553 15. Williams M, Iams JD. Cervical length measurement and cervical cerclage to prevent preterm birth. Clin Obstet Gynecol 2004;47:775–783 16. Bachmann LM, Coomarasamy A, Honest H, Khan KS. Elective cervical cerclage for prevention of preterm birth: a systematic
review. Acta Obstet Gynecol Scand 2003;82:398–404 17. Drakeley AJ, Roberts D, Alfirevic Z. Cervical stitch for preventing pregnancy loss in women. Cochrane Database of Systematic Reviews 2003, Issue 1. Art No. CD003253 18. To MS, Alfirevic Z, Heath VCF et al. Cervical cerclage for prevention of preterm delivery in women with short cervix: randomised controlled trial. Lancet 2004;363:1849–1853 19. Simcox R, Bennett PR, Shennan AH. Cervical cerclage for prevention of preterm delivery in women with short cervix. Lancet 2004;364:1934–1935 20. To MS, Alfirevic Z, Williamson PR, Nicolaides KH. Cervical cerclage for prevention of preterm delivery in women with short cervix: randomized controlled trial. Authors' reply. Lancet 2004;364:1935 21. Groom KM, Bennett PR, Golara M et al. Elective cervical cerclage versus serial ultrasound surveillance of cervical length in a population at high risk for preterm delivery. Eur J Obstet Gynecol Reprod Biol 2004;112:158–161 22. Higgins SP, Kornman LH, Bell RJ, Brennecke SP. Cervical surveillance as an alternative to elective cervical cerclage for pregnancy management of suspected cervical incompetence. Aust NZ J Obstet Gynecol 2004;44:228–232 23. Dodd JM, Flenady V, Cincotta R et al. Prenatal administration of progesterone for preventing preterm birth. Cochrane Database Syst Rev 2006; (1): CD004947 24. Fonseca EB, Celik E, Parra M et al. Progesterone and the risk of preterm birth among women with a short cervix. N Engl J Med 2007;357:462–469 25. Rouse DJ, Caritis SN, Peaceman AM et al. A trial of 17 Alpha-hydroxyprogesterone caproate to prevent prematurity in twins. N Engl J Med 2007;357:454–461
9 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Fetal biometry, estimation of gestational age, assessment of fetal growth Domenico Arduini Francesco Giacomello
Abstract The aims of ultrasound fetal biometry are: (1) the estimation of true gestational age, (2) the prediction of day of delivery, (3) the diagnosis of growth disturbances and (4) the diagnosis of malformations. The correct methodology for sonographic measurement of the essential fetal parameters is reported. Basic statistical analysis for defining normal values and nomograms is indicated. Principles for pregnancy dating and limits of the sonographic evaluation of fetal growth disturbances are reported and discussed.
Keywords Fetal biometry, fetal growth restriction, macrosomia, ultrasound.
Principles of Fetal Biometry Aims of Fetal Biometry A significant increase in perinatal morbidity and mortality is recorded for infants born either large or small for their respective age. Fetal biometry has enhanced the ability to detect growth abnormalities, thus directing more intensive antepartum care with potential improvement in perinatal outcome.14,16,22 In addition, routine fetal biometry prior to 20 weeks' gestation provides an accurate dating, allowing more confident diagnoses of growth abnormalities and prediction of neonatal survival in case of premature delivery. Finally, the abnormality of some biometric parameters may indicate the presence of congenital malformations or syndromes. Therefore the aims of fetal biometry are the following: the assessment of true gestational age, the prediction of day of delivery, the diagnosis of fetal growth disturbances, and the diagnosis of fetal malformations and chromosomal syndromes.
141
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
The Reference Values Many tables and nomograms have been published describing the growth of many fetal parameters.2,10 The normal values are defined by measuring the required parameter in fetuses of normal patients with a well-established gestational age (GA).
Patient Selection and Study Design To study the growth of fetal parameters, the date of conception should be certain but this information is available only in cases of treatment for infertility. A well-accepted way of dating the pregnancy is regular cycles, a well-defined last menstrual period (LMP), and a confirmation with early ultrasound. The ideal population should be selected among uncomplicated pregnancies delivered at term.
Longitudinal and Cross-Sectional Studies Data collection could be cross-sectional or longitudinal. In a cross-sectional study the fetus is measured only once during gestation, whereas in a longitudinal study it is measured serially at regular intervals. Cross-sectional studies are usually performed over a shorter period of time with easier collection of data and statistical analysis because each patient needs to be scanned only once. Then the individual growth is missed in favour of a larger population cohort. Common pitfalls for the cross-sectional studies are the occasional inclusion of fetuses with abnormal growth and/or poorly established GA, follow-up problems due to the large number of cases involved, and frequent artefacts concerning values at early and late gestation. An essential rule for cross-sectional studies is that each fetus should be considered only once in the study and that violation of this principle may severely affect the accuracy of the final results. In longitudinal studies one should define GA in early pregnancy and control the established criteria in fewer patients with easy recognition of abnormal growth curves. Such studies require the recruitment of a small number of pregnant women, scanned at regular intervals, and their results are often favoured with mathematical, biological and epidemiological arguments.14
Sample Size The optimal sample size depends on the variability of the parameter under investigation. Small samples preclude the use of polynomial regression whereas very large samples do not decrease the standard deviation significantly but increase the difficulty of follow-up data due to the probability of including data from abnormal cases. The sample should be well distributed throughout gestation with the same number of observations throughout the range of inclusion.14
Displaying Data and Curve Fitting 142
The data collected are represented in graph form, plotting the variable on the y-axis and the GA at which the data were obtained on the x-axis. The resulting
✩✩✩✩✩✩✩✩✩✩✩ ✩
Linear regression analysis In linear regression analysis it is possible to calculate an unknown biometric variable from the following formula: y = a + xb where a is the value of y at the point of intersection with the x-axis and b is the slope of the line. Linear regression is simple to calculate and is appropriate for small samples with a large variability of the parameter whenever the accuracy of the prediction is not crucial, such as in the case of preliminary studies. Curvilinear regression analysis For fetal biometry curvilinear polynomial regression analysis is more appropriate, but more data points are needed. Polynomial equations can be of different orders: first order: a + bx; second order, a + bx + cx2, and third order, a + bx+ cx2 + dx3. The accuracy of the description of the data increases with the order of the polynomial equation but for practical reasons, the lowest order that correlates with the data is usually selected. The coefficients of correlation The coefficient of multiple correlation, R, or the coefficient of determination, R2, indicates the quality of the fit and should be as close as possible to 1. A value of 1 indicates a perfect correlation with all the points in the scattergram located on the regression line, whereas a value of 0 demonstrates no correlation at all. Whenever R2 exceeds 0.90 the correlation is good and the most appropriate curve is the one with the lowest order.
Fetal biometry, estimation of gestational age, assessment of fetal growth
graph is called a scattergram and allows a visual analysis of the data. A correlation is probable if the data are distributed along a line, whereas it is obviously absent in cases of random dispersion of values. Preliminary mathematical analysis consists of: producing for each GA a mean value with standard deviations (SD), fitting a curve to the data passing through the mean of the scattergram, and drawing the variability around this curve. Curve fitting is done by regression analysis that allows the prediction of one variable (biometric value) from the other (GA). The dependent or predicted variable is reported on the x-axis and the independent or observed variable is represented on the y-axis.
The F test To discriminate among equations of different order, the F test, which is a variant of the t-test, is needed. This test is employed to verify the hypothesis that the coefficients (b, c, d …n) of the equations, although very small (since they must be multiplied by x, x2, x3…), are different from 0. A higher order of equation needs more coefficients but these figures will be helpful, increasing the order of the equation and complicating it only if significantly different from 0.
Prediction of Date and Size The obtained equation cannot be used correctly in two senses because a twodirectional reading is a mathematical mistake. Tables used for dating should be
143
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ different from those employed for fetal size assessment. If a biparietal diameter (BPD) of 50 mm corresponds to a determined GA (fetal dating), the reverse is not true because 50 mm will not be necessarily the mean BPD value for that GA (fetal growth assessment). Therefore, a good rule is not to use the same table to determine GA from a parameter and to assess the normality of this parameter against GA.14 In growth curves the biometric value is the dependent variable and GA the independent variable. In dating curves the gestational age is the dependent variable and the biometric value the independent one.
The Confidence Limits The dispersion of values around the mean is the SD and is used to describe the statistical limits of normality. The SD thus measures our degree of uncertainty concerning the biometric value of a random individual from its population. A symmetrical distribution favours the use of SD whereas a skewed distribution suggests the use of percentiles. The interval of variation is also called the confidence limit and is set at the fifth and 95th percentiles (1.66 SD) or at the first and 99th percentiles (2.38 SD). Two SD include 95% of the population, 2.5% being above and 2.5% below the normal limits. Using the fifth and 95th percentiles as reference values, 10% of patients will be outside the normal limits by definition, without necessarily being affected by pathology.14 It is important, for a good predictive value of the equation, that the SD will not change significantly with variation of the observed value and this can be investigated by the Bartlett or Levene test.
Dating Accurate dating or estimation of GA is essential in modern obstetrics for many reasons such as:
• interpretation of biochemical tests early and/or later in pregnancy (double test or triple test)
• planning prenatal diagnostic procedures (chorion villus biopsy, amniocentesis) and therapy (cerclage, fetal transfusions)
• timing of delivery in a high-risk pregnancy • prediction of neonatal viability • reliable diagnosis of growth abnormality • identification of a true postterm pregnancy.
144
Actually, the incidence of fetal growth restriction is as high as 20% when GA is based on menstrual history and as low as 5% when based on ultrasound-derived dates. The incidence of postdate pregnancy is 9% using menstrual dates, but only 3% after ultrasound dating.16 Fetal therapies also require an accurate estimate of the GA. Yet, there is now evidence that ultrasound dating alone is a better predictor of the date of delivery than the LMP within a 14-, 10- or even 7-day margin of error.18
✩✩✩✩✩✩✩✩✩✩✩ ✩
Menstrual, Conceptual and Gestational Age
Errors of Measurements The technical error of a measurement is relatively constant depending on the image selection and caliper positioning. The measurement should be taken at least three times and averaged. Resolution refers to the ability to discriminate between points in the ultrasound beam. Axial resolution describes differentiation of target echoes along the path of a single emitting source of ultrasound. The axial resolution varies directly with the frequency. A 3.5 MHz transducer has an axial resolution of 0.5–0.6 mm. Lateral resolution is the differentiation of two targets that are side by side at a given depth. The time dynamic lateral resolution of diagnostic ultrasound is probably less than 1 mm. The selection of the start and end points for a given measurement has become more difficult with improved sonographic definition of the anatomy. With modern equipment, not only the bony table of the calvarium but also hair, skin and subcutaneous tissue can be identified. It is therefore essential that the starting point of the measurement is set at the calvarium surface and not the scalp surface since the soft tissues of a full-term fetus can easily exceed a thickness of 5–6 mm, producing an overestimation of true BPD greater than 5%.16 The maximum inter- and intraoperator variations for measurements of the long bones are 3 and 2 mm, respectively6 but in some studies deviations of up to 14% were found using different probes.12 The use of millimetres instead of centimetres is recommended by the international system of units.14
Fetal biometry, estimation of gestational age, assessment of fetal growth
The conceptual age is calculated from the assumed time of the ovulation. The menstrual age is calculated from the best knowledge of the first day of the LMP in women with regular cycles. The GA, used in the ultrasound-dated pregnancy, is based on the estimated LMP from the measured ultrasound parameters. The fetal age is expressed in complete gestational weeks and not current weeks. Likewise, maternal age is reported in complete years.
The Accuracy of Dating Ultrasound measurement of the fetus prior to 20 weeks' gestation is thought to be accurate to ±7 days and could be beneficial not only in high-risk pregnancies, since nearly half of fetal growth abnormalities are derived from low-risk patients. Accuracy of ultrasound dating is inversely related to the fetal age. The rate of fetal growth is exponential at the beginning of the pregnancy and linear at late gestation. The influence of individual factors becomes more pronounced as pregnancy advances with a progressive dispersion of biometric values and broadening of the nomogram. Accordingly, the accuracy of fetal biometry is inversely proportional to the GA for almost every parameter measurable by ultrasound.
145
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The optimal method for ultrasound dating varies with GA. From 4 to 5 weeks the gestational sac can be measured, from 6 to 10 weeks the most accurate parameter is crown–rump length (CRL). From 10 to 20 weeks, the most accurate parameter may be the BPD because of the effect that deflection and variable position of the fetus have on the CRL. Fetal long bone measurements become accurate after 14–16 weeks' gestation.6 In late gestation the accuracy of ultrasound dating is increased by serial measurements. Such measurements should be spaced out (2–3 weeks) to ensure that the supposed increase of the biometric value is greater than the measurement error. The slope of fetal growth predicts GA with an accuracy of 7–10 days21 but this method has not been widely accepted in clinical practice.
Biometric Parameters Gestational Sac The gestational sac can be seen transvaginally as early as 4 weeks’ gestation when its greater diameter is 2 mm with corresponding human chorionic gonadotropin (hCG) levels around 1000 mIU/mL (International Reference Preparation or IRP). Its mean diameter bears a linear relationship with GA, and increases 1.0–1.2 mm/ day until the appearance of the fetal pole with its heart beat, at a size of 10 mm, with corresponding hCG levels around 12,000 mIU/mL (IRP).
Crown–Rump Length The CRL is the longest length of the embryo or fetus measurable excluding the limbs and yolk sac.14 The embryo becomes a fetus after 10 gestational weeks (71 completed days based on the LMP). The accuracy of the CRL in dating the pregnancy depends on good correlation between this measurement and fetal age in a period when growth is rapid and minimally influenced by fetal pathology. The CRL is predictive of fetal age with an error of 3 days (90% confidence limits) from 7 to 10 weeks and of 5 days from 10 to 14 weeks' gestation. The CRL grows approximately 10 mm per week from weeks 8 to 12 and a simple rule to obtain GA is the following: GA (week) = CRL (cm) + 6.5.14,22
Head Measures
146
Fetal head size has been one of the most useful and proven measurements to determine GA. The BPD is the most widely used measure, with greatest accuracy between 12 and 22 weeks, declining after this period because of a wider individual variation. The BPD demonstrates linear growth of 3 mm per week from weeks 14 to 28, and 2 mm per week until term.5,22 The measurement is taken at the level of a plane defined by the following intracerebral landmarks: the frontal horns of the lateral ventricle and cavum septum pellucidum anteriorly, the thalami and third ventricle centrally, and the occipital horns of the cerebral ventricle, cisterna
✩✩✩✩✩✩✩✩✩✩✩ ✩
Abdominal Size Abdominal size is assessed by measuring the middle abdominal diameter (MAD) or the abdominal circumference (AC) (Fig. 9.1) at the level of the stomach and the bifurcation of the main portal vein into its right and left branches, taking care to have a section as round as possible, not deformed by the pressure of the probe. The most accurate AC is the smallest obtained since it more closely approximates to a perpendicular plane to the spine at the level of the hepatic vein. Similarly to the calculation of HC, the measurement can be direct (ellipse or trace) or derived from the transverse abdominal diameter and anteroposterior abdominal diameter
Fig. 9.1 Measurement of the fetal upper abdominal circumference (AC). Reproduced by permission of B. Verburg.
Fetal biometry, estimation of gestational age, assessment of fetal growth
venae magnae cerebri and insula posteriorly. The measurement is taken from the outer table of the proximal skull to the outer table of the distal skull with the cranial bones perpendicular to the ultrasound beam.14 The occipitofrontal diameter (OFD) is measured in the same plane as the BPD with the calipers placed on the outer skull table. This parameter can be used to calculate the head circumference (HC) and the cephalic index (CI). Fetal head shape variations (dolichocephaly, brachycephaly) and fetal position can affect the diagnostic accuracy of BPD. In case of an abnormal CI, defined as the ratio of the BPD divided by OFD (normal 0.75–0.85), the HC could be used instead of BPD to avoid this pitfall.22 In fetuses with premature rupture of the membranes, breech presentation or multiple pregnancy, the BPD is not reliable in assessing true GA.19,22 HC is either measured at the same level of BPD directly with trace calipers or indirectly computed by using a formula such as: HC = (BPD + OFD) × 1.57. The direct method systematically overestimates the calculated HC by less than 1.5%. HC grows approximately 14 mm per week between 14 and 17 weeks and 5 mm per week near term.22 Head measurement is a poor screening method for fetal growth abnormalities since it is generally spared until late, both in symmetrical growth restriction and microcephaly.
147
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ (MAD). Due to the irregular shape of the fetal abdomen, the direct method overestimates the indirect one by about 5%; this variation could be relevant in the assessment of fetal weight.24 The AC demonstrates linear growth with a mean of 11–12 mm per week throughout gestation.22 This parameter is the most sensitive in predicting nutritional problems of the fetus, being influenced by the thickness of the abdominal wall and by the amount of the hepatic glycogen stores, and it is used for estimation of fetal weight. For the same reason, the AC should not be used for calculation of a composite GA after the early second trimester.22 Unfortunately, its measurement is affected by the greatest inter- and intra observer variation, accounting for the widely disparate limits of reference values reported by different investigators. Actually, fetal position and breathing movements, probe compression and oligohydramnios could affect the accuracy of this measurement.
Limbs Femur length (FL) can be measured from 10 weeks onwards and it is reproducible from 15 weeks' gestation to term. It represents fetal linear growth, being related to crown–heel length at birth.15 It was originally measured to diagnose limb dwarfism and it is seldom affected by fetal nutritional problems, presentation or oligohydramnios,14,22 being a good parameter for dating the pregnancy. It is measured (Fig. 9.2) from the origin to the distal end of the shaft, from the greater trochanter to the lateral condyle. The femoral head and distal epiphysis are not included in the measurement and the bone should be perpendicular to the ultrasound beam. The femur grows 3 mm per week from 14 to 27 weeks and 1 mm per week in the third trimester.22 Reported accuracy for pregnancy dating ranges from 1 week in the second trimester to 3–4 weeks at term.22 The humerus, tibia, radius and ulna may be measured in the same way as the FL, but they are traditionally not used to date the pregnancy. The tibia and fibula can be differentiated because the fibula is lateral to the tibia. The radius and ulna
148
Fig. 9.2 Measurement of the fetal femur length (FL). Reproduced by permission of B. Verburg.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Other Measurements and Dating Binocular distance should be measured as the smallest diameter between the fetal eyes in a plane including both orbits that must appear symmetrical and equal in size showing its maximal width. It may be useful for dating in cases of occiput-posterior position of the fetus, whenever the measurement of BPD is difficult. This measurement correlates with GA but its growth is non-linear. Variability in predicting GA is 14 days between 14 and 27 weeks and 24 days between 29 and 40 weeks. Binocular distance is important in patients at risk for congenital anomalies and syndromes.14,22 The transverse cerebellar diameter (TCD) measured at the level of the suboccipito-bregmatic plane of the head (Fig. 9.3) has a curvilinear relation with GA and is not much affected by the shape of the head or by growth disturbances.22 Its midpregnancy size in millimetres reflects GA in weeks. The clavicle has a linear growth throughout the second and third trimesters and was proposed as a measurement useful for dating, its length in millimetres being very close to the GA expressed in weeks.14,22 Having an intramembranous ossification instead of endochondral ossification, the clavicle is different from other long bones of the body and is not affected by the same disorders.
Fig. 9.3 Measurement of the fetal transverse cerebellar diameter (TCD). CM, cisterna magna. Reproduced by permission of B. Verburg.
Fetal biometry, estimation of gestational age, assessment of fetal growth
can be well differentiated and measured when the arm is in a supine position because the two bones are lying exactly parallel but in a prone position, the crossing of the two bones requires two different sonar planes to obtain measurements. The ulna appears longer than the radius proximally but distally both bones end at the same level.6 The accuracy of measurement of a long bone is affected by several factors such as the angle of the beam to the long axis of the bone (an angle close to 90 ° should be obtained) and the type of transducer (linear and convex probes are better than sector probes).12 Some researchers have suggested a sort of prenatal ponderal index could be derived from femur length but most likely this calculation adds little information to the other commonly used biometric parameters.14,22
149
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Measurement of the scapula, sacrum, iliac bone and foot have been shown to correlate well with GA.14 Many fetal organs have been measured and related to GA such as kidney, heart, aortic and pulmonary arteries.2,10
Data Report Fetal size is more uniform in early pregnancy than later. Early estimation of the GA (11/0–13/6 week scan) or at the routine fetal examination (16–18 weeks) has been shown to be of considerable value.26 Estimation of day of delivery should not be done later than 22 weeks (BPD 60 mm). The accuracy reduces from 7 days before 16 weeks to 28 days after 28 weeks. If an early scan has been done and a second scan yields a later estimate than the first one, it is not advisable to change the original estimate. The delay is most likely a result of growth restriction. The ultrasonographic composite age is used after the first trimester, obtaining measurements of as many parameters as possible, with the exclusion of AC, to increase the accuracy of estimate. Most authors favour reporting the lower fifth and the upper 95th confidence limits on the prediction of each measurement since this could have legal implications in case of use in management decisions.13 In a multiple pregnancy, most authors agree that the tables used for singleton pregnancies are appropriate for twins, at least in the first and second trimesters. It is advised to base the assessment of GA on the larger twin. The delay of fetal growth in a multiple pregnancy becomes apparent between 25 and 36 weeks of gestation, being more pronounced in triplets compared to twin pregnancies.22
Fetal Weight Estimation
150
Fetal weight estimation may provide the first indication of abnormal fetal growth. Multiple methods of estimating fetal weight have been developed, ranging from a single biometric parameter to the combination of multiple parameters. With the incorporation of multiple parameters, the error is decreased in comparison with results derived from AC alone.16 However, the accuracy of fetal weight estimation depends on several theoretical and practical factors including the variability of fetal volume and density, the technique and skill of the operator, the scanner and the formula used for calculation. The error is reported to vary from 15%9,22 to 21.2%.16 The smallest theoretical error in estimate is achieved when true volume is known with certainty as with water displacement or by direct measurement of physical dimensions and is calculated to be respectively 7.6% and 8.2%. However, when sonographic measurement of the fetus is applied, the error increases to 16.2%.23 However, the greatest error occurs at the extremes of fetal weight, with LGA mostly being underestimated and SGA mostly being overestimated, or in the presence of diabetes or oligohydramnios.22 This inaccuracy can be easily explained since among fetuses with an abnormal growth pattern, variation of density may be even greater than in the normal population, whereas reduced amniotic fluid can determine deformation of the fetus, increasing the error of sonographic measurements.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Biometric Ratios Biometric ratios have been proposed to alert the examiner to the possibility of nutritional or genetic fetal disorders.4 The range is very wide because the increase of different body parts, throughout pregnancy, is not synchronous.22 The HC/AC ratio described by Campbell and Thomas and the FL/AC ratio (0.20–0.24) are applicable only to asymmetrical fetuses but the wide overlap between normal and abnormal values limits their clinical value in the diagnosis of fetal growth disturbances.4 The HC/AC ratio is greater than 1 until 34–36 weeks' gestation and decreases to 1 or less until delivery.22 The FL/BPD ratio (71–87%) is used in the case of suspected skeletal dysplasias or head anomalies.14 Thoracic circumference (TC) is measured at the level of the four-chamber view of the heart. The TC/AC ratio (0.83–0.95) was suggested to predict pulmonary hypoplasia in cases of early, long-lasting oligohydramnios or skeletal dysplasia.14,22
Other Parameters Soft tissue thickness is related to the amount of adipose tissue and has been investigated as a marker of fetal nutritional problems. In particular, the thigh circumference and the cheek-to-cheek diameter14 measured on the coronal view of the face at the level of nostrils and lips have been proposed. The overlap between values belonging to normal fetuses and those with growth disturbances precludes the use of soft tissue parameters in management decisions.11,22
Fetal biometry, estimation of gestational age, assessment of fetal growth
The clinical utility of fetal weight estimation is still debated since it is quite reliable in the case of normality, but often unreliable in the case of pathology, just when legal problems could originate from the association between an ominous fetal outcome and what is wrongly called a ‘diagnostic error’. Therefore most authors agree that the accuracy of fetal weight prediction must be used with caution for management decisions, in particular for fetuses large for gestational age.1,17 The use of three-dimensional ultrasonography in the estimation of fetal weight is under study and was reviewed in 2000.25
Evaluation of Fetal Growth Definition Growth disturbances often represent a progressive disease and sooner or later the affected fetus is supposed to develop an abnormal biometry. Therefore, the final result of growth disturbance can often be diagnosed by a single ultrasound examination with increased sensitivity with advancing gestation. This is particularly true for fetuses with accelerated growth that are commonly delivered at term, whereas most growth-restricted infants are delivered prematurely. In addition, even in the absence of available successful treatment modalities, an early diagnosis of growth restriction is potentially useful to limit fetal and neonatal wastage.
151
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ According to their weight, neonates can be classified at birth as small for GA (SGA), appropriate for GA (AGA) or large for GA (LGA). Prenatal definitions for intrauterine growth retardation (IUGR) have varied widely concerning both the cut-off value (2SD, 2.5th, 3rd, 5th, 6th percentiles) and the parameter considered (AC, its growth in 2–3 weeks, biometric ratios, abnormal growth rate defined by means of individual or personal models). Gardosi et al8 adjusted biometric curves, taking into account physiological factors such as fetal gender, maternal weight and height, ethnic group, parity and size of previous children. Deter & Harrist5 applied a mathematical function to fetal measurements between 15 and 26 weeks' gestation to evaluate the growth potential of the individual fetus, using each fetus as its own control. Both methods have a limited application in current clinical practice. The definition of macrosomia is also imprecise and arbitrary as a variable cutoff is considered for weight at birth (4000, 4200, 4500 g) or for population-based percentile charts (90th, 95th, 97th percentiles). Although defining a pathological condition using the 10th and 90th percentile cut-off is statistically correct, it may not be clinically relevant since abnormal perinatal outcome will generally only be seen in cases of birthweight below the 3rd percentile or untreated gestational diabetes. Actually, growth is a dynamic process and a single sonographic measurement of the fetus is not sufficient to diagnose a growth disorder at its very beginning, when the size of the fetus could be still within normal. On the other hand, the availability of serial biometric observation is rare and the interobserver variability (with two errors in the opposite direction) could heavily influence the slope of the curve. In addition, in cases of overfrequent scanning requested for high-risk pregnancies, the interobserver variation could even exceed the expected fetal growth, leading to unwise management decisions.
Unsolved Problems Many unsolved problems still exist about definition and sonographic evaluation of fetal growth disturbances:
• the widely accepted cut-off value of the 10th and 90th percentile decreases
152
the power of follow-up studies by including normal fetuses since by definition, 10% of normal infants in any population will have birthweights at or below the 10th percentile or at or above the 90th percentile • different definitions preclude a comparison between studies and metaanalysis • the utilization of GA-independent standards, such as ratio or ponderal index, and of soft tissue thickness has been unsatisfactory • the classification in symmetrical or proportioned and asymmetrical or dysproportioned fetuses does not help to define the aetiology and prognosis • the cardiovascular and central nervous function could actually be more relevant than the size of the baby and its sonographic evaluation could be a better target to define fetal well-being.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Screening and Diagnostic Strategies
Fetal Growth Restriction The small size of the fetus is not a diagnosis by itself since it could occur when the infant is actually sick from miscellaneous pathologies such as anatomical anomalies, genetic diseases, viral infections, placental and cord failure. In order to diagnose all these problems, other investigations are needed such as fetal morphology, umbilical Doppler, fetal heart monitoring and biophysical profile supplemented by invasive fetal testing for aneuploidy or viral infection. Oligohydramnios is an important diagnostic and prognostic parameter in fetuses with IUGR but its absence should not detract from the diagnosis. Umbilical Doppler velocimetry is not useful as a screening technique for fetal growth restriction but once the condition is diagnosed, it may reduce interventions and improve fetal outcome. Whenever expectant management is indicated because of normal functional tests, serial ultrasound biometry, 2–3 weeks apart, will allow a correct evaluation of the true fetal growth. An AC growth rate of less than 10 mm/14 days has a sensitivity of 85% and a specificity of 74% for detecting low birthweight.
Fetal biometry, estimation of gestational age, assessment of fetal growth
Repeated ultrasound assessments are not feasible for all pregnant women and a clinical selection of high-risk pregnancies is therefore needed. Accurate risk assessment and dating is therefore the first step before a confident ultrasound diagnosis of fetal growth abnormalities. BPD and FL are rarely affected in growth disturbances and therefore their sensitivity in the detection of growth disturbances is insufficient. For the screening of growth disturbances, most authors rely on measurements of the AC since it reflects hepatic size and the amount of subcutaneous fat. The likelihood of a correct diagnosis increases as the percentile rank decreases below the 10th percentile or increases above the 90th percentile. If normal values are based only on AGA fetuses, the 2.5th percentile is an appropriate cut-off value but if normal values are based on the total population (LGA + AGA + SGA), the 10th percentile is more appropriate.24 The sensitivity is affected by the choice of which percentile is used to define abnormality and by the GA which is good at 34 weeks' gestation and poorer at 29–31 weeks.7 Abnormal values increase the risk of growth disturbances even at a normal fetal weight estimation. For an accurate diagnosis both the AC and estimated fetal weight should be abnormal.24
Macrosomia Risk factors of fetal macrosomia are diabetes, obesity and postdates. Sonographic evaluation often overestimates birthweight, leading to an increase in caesarean section rate, and should therefore be used with caution. However, an estimated fetal weight of over 4200 g in a diabetic pregnancy with a dysproportioned size of AC in comparison to other growth parameters should alert the clinician to consider an elective caesarean section. Such a policy might prevent shoulder dystocia and its consequences without a relevant increase in caesarean section rate.
153
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Macrosomia has been found to be associated with an excessive growth rate of the AC (>12 mm/week), a difference between abdominal diameter and BPD greater than 26 mm and between thoracic diameter and BPD above 14 mm.20 Subcutaneous tissue thickness has been studied as a predictor of macrosomia. The following parameters have been considered: cheek-to-cheek diameter, humeral, shoulder, femoral and abdominal subcutaneous thickness, calculating the most appropriate cut-off value with the ROC curve (from 11 to 13 mm). The application of such measurements in clinical practice is still premature.3
Fetal Biometry, Anomalies and Syndromes The progressive alteration of single biometric values may indicate the presence of fetal malformations as in cases of microcephaly or short-limbed dwarfism. In many instances the diagnosis may not be apparent before the third trimester with progressive alteration of biometric ratios below the first or above the 99th percentile. In such cases the number of SDs below or above the mean value (±3 SD) is more significant to indicate the degree of change in a particular biometric value and the likelihood of a malformation than the percentile. The measurements of some fetal parameters (nuchal translucency, short femur, short humerus) have also been studied in the assessment of the risk of fetal aneuploidy.
Conclusion The careful measurement of selected fetal parameters throughout the pregnancy is the basis for obtaining some of the most important information of the pregnancy, such as the gestational age and expected day of delivery, the size and growth of the fetus and important information for the safe management of the fetus before and after term as well as the delivery and birth. References
154
1. Benacerraf BR, Gelman R, Frigoletto FD. Sonographically estimated fetal weights: accuracy and limitation. Am J Obstet Gynecol 1988;159:1118–1121 2. Bettelheim D, Deutinger J, Bernascheck G. Fetal sonographic biometry. Parthenon, Carnforth, 1997 3. Chauhan SP, West DJ, Scardo JA, Boyd JM, Joyner Y, Hendrix NV. Antepartum detection of macrosomic fetus: clinical versus sonographic, including softtissue measurements. Obstet Gynecol 2000;95:639–642 4. Crang-Svalenius E, Jorgensen C. Normal ultrasonic fetal growth ratios evaluated in cases of fetal disproportion. J Ultrasound Med 1991;10:89–92
5. Deter RL, Harrist RB. Growth standards for anatomic measurements and growth rates derived from longitudinal studies of normal foetal growth. J Clin Ultrasound 1992;20:381–388 6. Exacoustos C, Rosati P, Rizzo G, Arduini D. Ultrasound measurements of fetal limb bones. Ultrasound Obstet Gynecol 1991;1:325–330 7. Ferrazzi E, Nicolini U, Kustermann A, Pardi G. Routine obstetric ultrasound: effectiveness of cross-sectional screening for fetal growth retardation. J Clin Ultrasound 1986;14:17–22 8. Gardosi J, Chang A, Kalyan B, Sahota D, Simmonds EM. Customized antenatal growth charts. Lancet 1992;339:283–287
✩✩✩✩✩✩✩✩✩✩✩ ✩ 18. Mongelli M, Wilcox M, Gardosi J. Estimating the day of confinement: ultrasonographic biometry versus certain menstrual dates. Am J Obstet Gynecol 1996;174:278–281 19. O'Keeffe DF, Garite TJ, Elliott JP, Burns PE. The accuracy of estimated gestational age based on ultrasound measurement of biparietal diameter in preterm premature rupture of the membranes. Am J Obstet Gynecol 1985;151:309–312 20. O' Reilly-Green, Divon M. Sonographic and clinical methods in the diagnosis of macrosomia. Clin Obstet Gynecol 2000;43:309–320 21. Sabbagha RE, Hughey M, Depp R. The assignment of growth-adjusted sonographic age (GASA): a simplified method. Obstet Gynecol 1978;51:383–386 22. Stebbins B, Jaffe R. Fetal biometry and gestational age estimation. In: Jaffe R, Bui TH (eds) Textbook of fetal ultrasound. Parthenon, Carnforth, 1999: 47–57 23. Thompson TE, Manning FA, Morrison I. Determination of fetal volume in utero by an ultrasound method: correlation with neonatal birth weight. J Ultrasound Med 1983;2:113 24. Weiner CP, Robinson D. The sonographic diagnosis of intrauterine growth retrdation using the postnatal ponderal index and the crown–heel length as standards of diagnosis. Am J Perinatol 1989;6:380–383 25. Zelop CM. Prediction of fetal weight with the use of three-dimensional ultrasonography. Clin Obstet Gynecol 2000;43:321–325 26. Tunon K, Eik-Nes SH, Grottum P. A comparison between ultrasound and a reliable menstrual period as predictors of the day of delivery in 15000 examinations. Ultrasound Obstet Gynecol 1996;8: 178–185
Fetal biometry, estimation of gestational age, assessment of fetal growth
9. Hadlock FP, Deter RL, Harrist RB, Park SK. Computer assisted analysis of fetal age in the third trimester using multiple fetal growth parameters. J Clin Ultrasound 1983;11:313–316 10. Hata T, Deter RL. A review of fetal organ measurements obtained with ultrasound: normal growth. J Clin Ultrasound 1992;20:155–174 11. Hill LM, Guzik D, Boyles D, Merolillo C, Ballone A, Ghiter P. Subcutaneous tissue thickness cannot be used to distinguish abnormalities of foetal growth. Obstet Gynecol 1992;80:268–271 12. Jeanty P, Beck GJ, Chevernak FA, Kremkau FW, Hobbins JC. A comparison of sector and linear array scanners for the measurement of the fetal femur. J Ultrasound Med 1985;4:525 13. Jeanty P. A simple reporting system for obstetrical ultrasound examination. J Ultrasound Med 1985;4:591–593 14. Jeanty P. Fetal biometry. In: Fleisher AC, Manning FA, Jeanty P, Romero R (eds) Sonography in obstetrics and gynecology. Principles and practice. Prentice-Hall International, New York, 1996: 131–149 15. Kurniawan YS, Deter RL, Visser GH, Simon NV, van der Weele LT. Prediction of neonatal crown–heel length from femur diaphysis length measurements. J Clin Ultrasound 1994;22:245–252 16. Manning FA. General principles and appli cations of ultrasonography. In: Creasy RK, Resnik R (eds) Maternal-fetal medicine, 4th edn. WB Saunders, Philadelphia, 1999: 169–206 17. Miller JM, Kissling GA, Brown HL, Gabert HA. Estimated fetal weight: applicability to small- and large-forgestational-age fetus. J Clin Ultrasound 1988;16:95–97
155
10 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies Gianluigi Pilu Kypros H Nicolaides Israel Meizner Roberto Romero Waldo Sepulveda
Abstract Congenital anomalies occur in about 2.5% of all births and are the leading cause of infant mortality and probably of long-term handicap. A well-performed ultrasound examination carried out around midgestation allows identification of about 50% of all major anomalies. Ultrasound may also help in identifying aneuploidies at midgestation, although the specific approach remains controversial. The distinctive features of the sonographic diagnosis of anomalies, as well as the clinical implications, are discussed.
Keywords Chromosomal aberrations, congenital anomalies, fetus, prenatal diagnosis, ultrasound.
An Introduction to Congenital Anomalies Detection of fetal anomalies is one of the major reasons motivating the use of ultrasound in pregnancy. Congenital anomalies are the leading cause of infant mortality and probably one of the leading causes of long-term morbidity. Diagnosis of fetal anomalies is far from simple. It demands expertise in obstetrical ultrasound as well as knowledge in many fields including anatomy, embryology, teratology, genetics, paediatrics and cardiology. There is, however, consensus that a wellperformed basic ultrasound scan, including the evaluation of a well-defined set of quantitative and qualitative parameters, can detect the presence of a substantial number of anomalies, thus allowing the patient to undergo a targeted examination in a centre. The elements of the basic evaluation of fetal anatomy have been discussed in a previous chapter. The proportion of anomalies that will be detected by a basic ultrasound survey of fetal anatomy is controversial, as various studies
157
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ have reported very different results, and we will summarize the available experience at the end of this chapter. Our aim is to review the frequency and impact of congenital anomalies and to provide basic concepts useful for ultrasound identification. Diagnosing fetal anomalies is difficult and we refer the interested readers to the many detailed textbooks available on the subject.1–4 A congenital anomaly consists of a departure from the normal anatomical architecture of an organ or system. Anomalies may result from an intrinsically abnormal primordium (malformation) or from a normal primordium that is affected during development by extrinsic forces, such as vascular accidents (disruptions) or mechanical compression (deformations). Although there are several systems used to classify congenital anomalies, a common method is to divide them into major and minor. A major anomaly is one with medical, surgical or cosmetic importance and with impact on morbidity and mortality. A minor anomaly is one that does not have a serious surgical, medical or cosmetic significance, and does not affect normal life expectancy or lifestyle. Obviously, this classification is subjective and arbitrary. There is an overlap between minor anomalies and normal anatomical or phenotypical variants. A phenotypical variant occurs with a frequency of more than 4% in the general population, whereas minor anomalies occur with a rate of less than 4%. Clearly, this is also an arbitrary definition. The precise incidence of congenital anomalies is difficult to determine. Accurate documentation depends on many factors including:
• age at examination (prenatal period, newborn period, infancy or later in life)
• the experience of the observer (e.g. general paediatrician versus dysmorphologist)
• the definition of an anomaly (major, minor, normal phenotypical variation) • the type of examination (body surface examination, extensive examination including evaluation of internal organs)
• ethnic, geographical and social variations in the incidence of individual malformations.
158
There is a general consensus that the prevalence of anomalies detected at birth is in the region of 2.5%, while long-term follow-up studies demonstrate much higher figures, in the range of 14–15%. It is important to remember that even severe anomalies may not be detected at birth; for example, some cardiac abnormalities will only be manifest afterwards. The neurological examination of a newborn infant has many limitations, and severe central nervous system anomalies may be undetected up to 1–3 years of age. Causative factors for congenital malformations may be identified in approximately 40% of cases and are usually divided into four major groups: single gene disorders, chromosome abnormalities, multifactorial conditions (involving both environmental and genetic components), and environmental factors. About 7.5% of all congenital malformations are caused by a single gene
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
mutation.5,6 Autosomal mutations occur when the gene is located in a non-sex chromosome and may be either dominant (e.g. adult polycystic kidney disease, achondroplasia) or recessive (e.g. infantile polycystic kidney disease, achondrogenesis, short-rib polydactyly syndrome). Autosomal dominant conditions have a recurrence risk of 50% for the subsequent offspring, whereas autosomal recessive conditions have a recurrence risk of 25%. The term X-linked disorder is reserved for single gene mutations in the X chromosome (e.g. fragile X syndrome, fetal akinesia syndrome, oto-palato-digital syndrome). In this case, women are asymptomatic carriers and the disease is usually expressed only in males. Chromosomal anomalies are responsible for about 6% of all serious congenital malformations among live-born infants. They may be numerical or structural in nature. Multifactorial conditions are responsible for 20% of malformations in live-born fetuses. Examples of malformations with a multifactorial inheritance include spina bifida, cleft lip/palate and congenital dislocation of the hip. These anomalies are the result of interactions between a relatively large number of genes with similar effects and non-genetic, usually undefined factors. Currently, 2–3% of the spectrum of congenital malformations is attributed to teratogens, with most malformations resulting from exposures during days 18–40 post conception, except for the palate, central nervous system and genital structures that can be affected at later stages of development. Finally, a significant proportion of congenital malformations of unknown aetiology are likely to be polygenic or at least have an important genetic component.5,6 Congenital anomalies are an important determinant of perinatal and infantile death and long-term morbidity. A substantial fall in maternal and infant mortality rates was achieved during the 20th century. Environmental interventions, improvements in nutrition, advances in clinical medicine, wider access to healthcare, increased surveillance and monitoring of disease, better education and higher living standards contributed to this accomplishment. In Scotland, the overall perinatal mortality declined by 75% between the periods 1939– 1941 and 1974–1976, but over the same 37-year time span, the contribution of congenital anomalies to perinatal mortality increased from 10% to 25%.7 From 1915 to 1997, while the United States experienced a 93% drop in infant mortality (from approximately 100/1000 to 7.2/1000 live births),8 the relative contribution of congenital anomalies to the perinatal death rate increased. In 1995, according to the Centers for Disease Control and Prevention, birth defects were the leading cause of infant mortality in the USA.9,10 From 1968 to 1995, the proportion of infant deaths attributable to birth defects increased from 15% to 22%.11,12 Alongside the impact caused by congenital anomalies in perinatal mortality, there is an increased awareness regarding the role of congenital disease in determining morbidity. It has been estimated that at least 1% of all hospital admissions have a genetic basis or genetic contribution to their disease; as many as one of every four hospitalized children is affected by a disease that is at least partially genetically determined and approximately one of every 20 children is affected by a disorder that is completely genetic in origin. Infants with anomalies detected
159
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ within the first year have a significant increase in the risk of death and in all parameters of evaluated postnatal morbidity. Infants with congenital anomalies also impose an economic burden on society and contribute stress to the family nucleus. For example, the incidence of divorce and sibling social maladjustment is greater in families of children with spina bifida than in families of infants without congenital anomalies.
Central Nervous System Anomalies Most cerebral anomalies diagnosable in utero by ultrasound are easily demonstrated by the use of two transverse sections of the fetal head, one obtained at the level of the lateral ventricles (transventricular plane) (Fig. 10.1) and the other at the level of basal ganglia and cerebellum (Fig. 10.2). Recently, magnetic resonance imaging has become a valuable tool in the diagnosis of suspected brain and spine abnormalities.31,32
Mild Ventriculomegaly
Severe
Anterior midline defects
Alobar holoprosencephaly 160
Lobar holoprosencephaly
Agenesis of corpus callosum
Fig. 10.1 Fetal cerebral anomalies detectable with the transventricular plane.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Absent cisterna magna banana sign (spina bifida)
Large cisterna magna cerebellar defect (Dandy–Walker complex)
Prenatal diagnosis of fetal anomalies
Normal cisterna magna
Fig. 10.2 Fetal cerebral anomalies detectable with the transcerebellar view.
Neural Tube Defects These include anencephaly, spina bifida and encephalocele. In anencephaly there is absence of the cranial vault (acrania) with secondary degeneration of the brain. Encephaloceles are cranial defects, usually occipital, with herniated fluid-filled or brain-filled cysts. In spina bifida the neural arch, usually in the lumbosacral region, is incomplete with secondary damage to the exposed nerves. The incidence of neural tube defects is subject to large geographical and temporal variations; in Europe the prevalence is about 1–2 per 1000 births with a peak of 5 per 1000 births. Anencephaly and spina bifida, with an approximately equal prevalence, account for 95% of cases and encephalocele for the remaining 5%. Neural tube defects are multifactorial disorders. Chromosomal abnormalities, single mutant genes and maternal diabetes mellitus or ingestion of teratogens, such as antiepileptic drugs, are implicated in about 10% of cases. When a parent or previous sibling has had a neural tube defect, the risk of recurrence is 5–10%. Periconception supplementation of the maternal diet with folate reduces by about half the risk of developing these defects. The sonographic diagnosis of anencephaly during the second trimester of pregnancy is based on the demonstration of absent cranial vault and cerebral hemispheres. The diagnosis can be made after 11 weeks, when ossification of the skull
161
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
162
normally occurs. Ultrasound reports have demonstrated that there is progression from acrania to exencephaly and finally anencephaly. In the first trimester the pathognomonic feature is acrania, the brain being either entirely normal or with varying degrees of distortion and disruption. Diagnosis of spina bifida requires the systematic examination of each neural arch from the cervical to the sacral region both transversely and longitudinally. In the transverse scan the normal neural arch appears as a closed circle with an intact skin covering, whereas in spina bifida the arch is U-shaped and there is an associated bulging meningocele (thin-walled cyst) or myelomeningocele. The extent of the defect and any associated kyphoscoliosis are best assessed in the longitudinal scan (Fig. 10.3). The diagnosis of spina bifida has been greatly enhanced by the recognition of associated abnormalities in the skull and brain. These abnormalities include frontal bone scalloping (lemon sign) and obliteration of the cisterna magna with either an ‘absent’ cerebellum or abnormal anterior curvature of the cerebellar hemispheres (banana sign). These easily recognizable alterations in skull and brain morphology are often more readily attainable than detailed spinal views.13 A variable degree of ventricular enlargement is present in virtually all cases of open spina bifida at birth, but in only about 70% of cases in the midtrimester. Closed spina bifida may be associated with neurological compromise and the prenatal diagnosis is difficult, because α-fetoprotein is usually within normal limits in both amniotic fluid and maternal serum, there are no cranial signs and the spinal defect may be small and difficult or impossible to identify sonographically. Encephaloceles are recognized as cranial defects with herniated fluid-filled or brain-filled cysts. They are most commonly found in an occipital location (75% of cases) but alternative sites include the frontoethmoidal and parietal regions. Anencephaly is fatal at or within hours of birth. In encephalocele the prognosis is inversely related to the amount of herniated cerebral tissue; overall the
Fig. 10.3 Lumbosacral myelomeningocele in the sagittal (left) and axial (right) view.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Ventriculomegaly The term ventriculomegaly is commonly used to indicate enlargement of the lateral cerebral ventricles. The incidence of this finding is unclear. Severe ventriculomegaly or hydrocephalus is found in less than 1 per 1000 births. Ventriculomegaly may be the consequence of cerebral malformations, chromosomal abnormalities or congenital infection. Genetic factors play an important role. About 25% of severe ventriculomegaly occurring in males is due to X-linked transmission. Fetal ventriculomegaly is diagnosed sonographically, by the demonstration of abnormally dilated lateral cerebral ventricles. A transverse scan of the fetal head at the level of the cavum septum pellucidum will demonstrate the dilated lateral ventricles, defined by an internal diameter of the posterior horn (or atrium) of 10 mm or more.13 The choroid plexuses, which normally fill the lateral ventricles, are surrounded by fluid. A diameter of 10–15 mm indicates mild ventriculomegaly. A diameter greater than 15 mm indicates moderate to severe ventriculomegaly.33 Certainly before 24 weeks and particularly in cases of associated spina bifida, the head circumference may be small rather than large for gestation. Fetal or perinatal death and neurodevelopment in survivors are strongly related to the presence of other malformations and chromosomal defects.34 Isolated severe ventriculomegaly is associated with an increased risk of perinatal death and a 50% chance of neurological sequelae in survivors. Although isolated mild ventriculomegaly (atrial width of 10–15 mm) is generally associated with a good prognosis, it is also the group with the highest incidence of chromosomal abnormalities (often trisomy 21). In addition, in a few cases with apparently isolated mild ventriculomegaly there may be an underlying cerebral maldevelopment (such as lissencephaly) or destructive lesion (such as periventricular leukomalasia). It has been suggested that ventricles of 10–12 mm, which represent the bulk of these cases, tend to have a good prognosis, with neurological compromise in the range of 4%, while those cases in which the measurement is 13–15 mm are associated with a greater probability of handicap, in the range of 12%.
Prenatal diagnosis of fetal anomalies
neonatal mortality is about 40% and more than 80% of survivors are intellectually and neurologically handicapped. In spina bifida, surviving infants are often severely handicapped, with paralysis in the lower limbs and double incontinence; despite the associated hydrocephalus requiring surgery, intelligence may be normal.
Holoprosencephaly This is a spectrum of cerebral abnormalities resulting from incomplete cleavage of the forebrain. There are three types according to the degree of forebrain cleavage. The alobar type, which is the most severe, is characterized by a monoventricular cavity and fusion of the thalami. In the semilobar type there is partial segmentation of the ventricles and cerebral hemispheres posteriorly with incomplete fusion of the thalami. In lobar holoprosencephaly there is normal separation
163
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ of the ventricles and thalami but absence of the septum pellucidum. The first two types are often accompanied by microcephaly and facial abnormalities. Holoprosencephaly is found in about 1 per 10,000 births. Although in many cases the cause is a chromosomal abnormality (usually trisomy 13) or a genetic disorder with an autosomal dominant or recessive mode of transmission, in many cases the aetiology is unknown. For sporadic, non-chromosomal holoprosencephaly, the empirical recurrence risk is 6%. In the standard transverse view of the fetal head for measurement of the biparietal diameter there is a single dilated midline ventricle replacing the two lateral ventricles or partial segmentation of the ventricles. The alobar and semilobar types are often associated with facial defects, such as hypotelorism or cyclopia, facial cleft and nasal hypoplasia or proboscis. Alobar and semilobar holoprosencephaly are lethal. Lobar holoprosencephaly is associated with mental retardation.
Agenesis of the Corpus Callosum The corpus callosum is a bundle of fibres that connects the two cerebral hemispheres. It develops at 12–18 weeks of gestation. Agenesis of the corpus callosum may be either complete or partial (usually affecting the posterior part). Agenesis of the corpus callosum is found in about 5 per 1000 births and may be due to maldevelopment or secondary to a destructive lesion. It is commonly associated with chromosomal abnormalities (usually trisomies 18, 13 and 8) and more than 100 genetic syndromes. The corpus callosum is not visible in the standard transverse views of the brain but agenesis of the corpus callosum may be suspected by the absence of the cavum septum pellucidum. The lateral ventricles usually are mildly enlarged and have a typical ‘teardrop’ configuration. Agenesis of the corpus callosum is demonstrated in the midcoronal and midsagittal views, which may require vaginal sonography. Partial agenesis of the corpus callosum is extremely difficult to diagnose antenatally because the cavum septum pellucidum is present and only a midsagittal view allows demonstration of the condition. The outcome is dependent mostly upon the association with other anomalies. In about 85% of those with apparently isolated agenesis of the corpus callosum, development is normal.
Dandy–Walker Complex
164
The Dandy–Walker complex refers to a spectrum of abnormalities of the cerebellar vermis, cystic dilation of the fourth ventricle and enlargement of the cisterna magna. The condition is classified into (a) Dandy–Walker malformation (complete or partial agenesis of the cerebellar vermis and enlarged posterior fossa), (b) Dandy–Walker variant (partial agenesis of the cerebellar vermis without enlargement of the posterior fossa), and (c) megacisterna magna (normal vermis and fourth ventricle). The Dandy–Walker complex is a non-specific endpoint of chromosomal abnormalities (usually trisomies 18 or 13 and triploidy), more than 50 genetic syndromes, congenital infection or teratogens such as warfarin, but it can also be an isolated finding.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
Ultrasonographically, the contents of the posterior fossa are visualized through a transverse suboccipito-bregmatic section of the fetal head. In the Dandy–Walker malformation there is cystic dilation of the cisterna magna with partial or complete agenesis of the vermis; in more than 50% of cases there is associated hydrocephalus and other extracranial defects. Enlarged cisterna magna is diagnosed if the vertical distance from the vermis to the inner border of the skull is more than 10 mm. Prenatal diagnosis of isolated partial agenesis of the vermis is difficult and a false diagnosis can be made if the angle of insonation is too steep. Classic Dandy–Walker malformation (that is, a large posterior fossa cyst associated with severe ventriculomegaly) is associated with a high postnatal mortality (about 20%) and a high incidence (more than 50%) of impaired intellectual and neurological development. Experience with apparently isolated partial agenesis of the vermis or enlarged cisterna magna is limited and the prognosis for these conditions is uncertain.
Microcephaly Microcephaly means small head and brain. This may result from chromosomal and genetic abnormalities, fetal hypoxia, congenital infection and exposure to radiation or other teratogens, such as maternal anticoagulation with warfarin. It is commonly found in the presence of other brain abnormalities, such as encephalocele or holoprosencephaly. The antenatal diagnosis of microcephaly is limited for many reasons. There is not an absolute cut-off that distinguishes normal fetuses with constitutionally small heads from microcephalics. Furthermore, microcephaly has a variable natural history. In many cases, the head is of normal size until late gestation and even at birth. Fetal microcephaly should be suspected when the head is smaller than −2 standard deviations below the mean. The diagnosis is rapidly established when the head is extremely small (<−4 standard deviations below the mean) or there are associated brain abnormalities, such as holoprosencephaly. In microcephaly there is a typical disproportion between the size of the skull and the face. The brain is small, with the cerebral hemispheres affected to a greater extent than the midbrain and posterior fossa. The prognosis depends largely on the underlying cause and the associated anomalies.
Destructive Cerebral Lesions These lesions include hydranencephaly, porencephaly and schizencephaly. In hydranencephaly there is absence of the cerebral hemispheres with preservation of the midbrain and cerebellum. In porencephaly there are cystic cavities within the brain that usually communicate with the ventricular system, the sub arachnoid space or both. Schizencephaly is associated with clefts in the fetal brain connecting the lateral ventricles with the subarachnoid space. Hydranencephaly is a sporadic abnormality that may result from widespread vascular occlusion in the distribution of the internal carotid arteries, prolonged
165
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ severe hydrocephalus or an overwhelming infection such as toxoplasmosis or cytomegalovirus. Porencephaly may be caused by infarction of the cerebral arteries or haemorrhage into the brain parenchyma. Although schizencephaly is included in this section, it is most likely the consequence of a primary disorder of brain development due to abnormal migration of the neurons from their original location on the walls of the lateral ventricles to the cortical plate. Complete absence of echoes from the anterior and middle fossae distinguishes hydranencephaly from severe hydrocephalus in which a thin rim of remaining cortex and the midline echo can always be identified. In porencephaly there is one or more cystic area in the cerebral cortex, which usually communicates with the ventricle; the differential diagnosis is from intracranial cysts (arachnoid, glyoependymal) that are usually found either within the scissures or in the midline and compress the brain. In schizencephaly there are bilateral clefts extending from the lateral ventricles to the subarachnoid space, and it is usually associated with absence of the cavum septum pellucidum. Hydranencephaly is usually incompatible with survival beyond early infancy. The prognosis in porencephaly is related to the size and location of the lesion and although there is increased risk of impaired neurodevelopment, in some cases development is normal. Bilateral schizencephaly is associated with severe neurodevelopmental delay and seizures. The unilateral form may be manifest only in adulthood with minor neurological symptoms.
Choroid Plexus cysts These cysts, which are usually bilateral, are in the choroid plexuses of the lateral cerebral ventricles. Choroid plexus cysts are found in about 1–2% of fetuses at 20 weeks of gestation but in more than 90% of cases they resolve by 26 weeks. Choroid plexus cysts contain cerebrospinal fluid and cellular debris. They are usually of no pathological significance, but they are associated with an increased risk for trisomy 18 and possibly trisomy 21.35 In the absence of other markers of trisomy 18, the maternal age-related risk is increased by a factor of 1.5.
Craniofacial Anomalies Facial Clefts
166
This term refers to a wide spectrum of clefting defects (unilateral, bilateral, less commonly midline or atypical) usually involving the upper lip, the palate or both. Cleft palate without cleft lip is a distinct disorder. Facial clefts encompass a broad spectrum of severity, ranging from minimal defects, such as a bifid uvula, linear indentation of the lip or submucous cleft of the soft palate, to large deep defects of the facial bones and soft tissues. The typical cleft lip will appear as a linear defect extending from one side of the lip into the nostril. Cleft palate associated with cleft lip may extend through the alveolar ridge and hard palate, reaching the floor of the nasal cavity or even the floor of the orbit. Isolated cleft palate may
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fig. 10.4 Facial clefts demonstrated in an anterior coronal plane of the lips: unilateral cleft lip (left); bilateral cleft lip (middle); median cleft lip (right). This scanning plane does not allow demonstration of whether the defect of the lip extends to the palate.
Prenatal diagnosis of fetal anomalies
include defects of the hard palate, the soft palate or both. Cleft lip and palate is unilateral in about 75% of cases and the left side is more often involved than the right. Facial clefting is found in about 1 per 800 births. In about 50% of cases both the lip and palate are defective, in 25% only the lip and in 25% only the palate is involved. The face is formed by the fusion of four outgrowths of mesenchyme (frontonasal, mandibular and paired maxillary swellings) and facial clefting is usually caused by failure of fusion of these swellings. Cleft lip with or without cleft palate is usually (more than 80% of cases) an isolated condition, but in 20% of cases it is associated with one of more than 100 genetic syndromes. Isolated cleft palate is a different condition and it is more commonly associated with any one of more than 200 genetic syndromes. All forms of inheritance have been described, including autosomal dominant, autosomal recessive, X-linked dominant and X-linked recessive. Associated anomalies are found in about 50% of patients with isolated cleft palate and in about 15% of those with cleft lip and palate. Chromosomal abnormalities (mainly trisomies 13 and 18) are found in 1–2% of cases and exposure to teratogens (such as antiepileptic drugs) in about 5% of cases. Recurrence risks are type specific; if the index case has cleft lip and palate there is no increased risk for isolated cleft palate, and vice versa. Median cleft lip, which accounts for about 0.5% of all cases of cleft lip, is usually associated with holoprosencephaly or the oral-facial-digital syndrome. The sonographic diagnosis of cleft lip depends on demonstration of a groove extending from one of the nostrils to the mouth (Fig. 10.4). Evaluation of the alveolar ridge allows recognition of whether the defect is limited to the lips or involves the hard palate. Both transverse and coronal planes can be used. The diagnosis of isolated cleft palate is difficult and in cases at risk for mendelian syndromes, fetoscopy may be necessary.
167
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
168
Recently, it has been suggested by many authors that three-dimensional ultrasound is particularly useful in making this diagnosis and assessing the severity of the defect. Minimal defects, such as linear indentations of the lips or submucosal cleft of the soft palate, may not require surgical correction. Larger defects cause cosmetic, swallowing and respiratory problems. Recent advances in surgical techniques have produced good cosmetic and functional results. However, prognosis depends primarily on the presence and type of associated anomalies.
Ocular and Orbital Defects In early development the eyes are placed laterally in the primitive face in a fashion similar to that of lower animals with panoramic vision. As gestation progresses, they migrate toward the midline, creating favourable conditions for the development of stereoscopic vision. Hypertelorism (euryopia) is an increased interorbital distance and this can be either an isolated finding or associated with many clinical syndromes or malformations. The most common syndromes with hypertelorism are the median cleft syndrome (hypertelorism, median cleft lip with or without a median cleft of the hard palate and nose, and cranium bifidum occultum), craniosynostoses (including Apert, Crouzon and Carpenter syndromes), agenesis of the corpus callosum and anterior encephaloceles. Hypertelorism per se results only in cosmetic problems and possible impairment of stereoscopic binocular vision. For severe cases, a number of operative procedures, such as canthoplasty, orbitoplasty, surgical positioning of the eyebrows and rhinoplasty, have been proposed. The median cleft face syndrome is usually associated with normal intelligence and life span. However, there is a high likelihood of mental retardation when either an extreme degree of hypertelorism or extracephalic anomalies are found. The severity of the cosmetic disturbance should not be underestimated, because this syndrome may be associated with extremely grotesque features. Hypotelorism (stenopia) indicates decreased interorbital distance and is almost always found in association with other severe anomalies, such as holoprosencephaly, trigonocephaly, microcephaly, Meckel syndrome and chromosomal abnormalities. The prognosis, which depends on the associated anomalies, is usually very poor. Microphthalmia is defined as a decreased size of the eyeball and anophthalmia refers to the absence of the eye; however, the term anophthalmia should be reserved for the pathologist, who must demonstrate absence of not only the eye but also of optic nerves, chiasma and tracts. Microphthalmia/anophthalmia, which is either unilateral or bilateral, is usually associated with one of about 25 genetic syndromes. In Goldenhar syndrome (found in about 1 per 5000 births) there is unilateral anophthalmia, together with ear and facial abnormalities. Prenatal diagnosis is based on the demonstration of decreased ocular diameter and careful examination of the intraorbital anatomy is indicated to identify lens, pupil and optic nerve. Congenital microphthalmia is frequently associated with visual disorders and other anomalies.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Cardiac Anomalies Abnormalities of the heart and great arteries are among the most common congenital abnormalities, with an estimated incidence of 5 per 1000 live births and about 30 per 1000 stillbirths. In general, about half are either severe or require surgery early in life and are generally referred to as major cardiac abnormalities. The aetiology of heart defects is heterogeneous and probably depends on the interplay of multiple genetic and environmental factors, including maternal diabetes mellitus or collagen disease, exposure to drugs such as lithium and viral infections such as rubella. Specific mutant gene defects and chromosomal abnormalities account for less than 5% of cases.36 Heart defects are found in more than 90% of fetuses with trisomy 18 or 13, 50% of trisomy 21, and 40% of those with Turner syndrome, deletions or partial trisomies involving a variety of chromosomes. When a previous sibling has had congenital heart defect, in the absence of a known genetic syndrome, the risk of recurrence is about 2%, and with two affected siblings the risk is 10%. When the father is affected, the risk for the offspring is about 2% and if the mother is affected the risk is about 10%. Echocardiography has been successfully applied to the prenatal assessment of the fetal cardiac function and structure, and has led to the diagnosis of most cardiac abnormalities37,38 (Figs 10.5, 10.6). In many countries, second-trimester ultrasound is used to look for congenital anomalies as part of routine prenatal care.39 Studies from specialist centres report the diagnosis of about 90% of defects. However, the majority of such studies refer to the prenatal diagnosis of moderate to major defects in high-risk populations. Patients at increased risk for fetal cardiac anomalies (the most common indications include familial history, diabetes and ingestion of drugs) should be referred to a specialized centre for a detailed evaluation of the fetal heart. In low-risk patients, evaluation of the four-chamber
Fig. 10.5 Cardiac anomalies diagnosable with the use of the four-chamber view: large muscular septal defect (left); complete atrioventricular septal defect (middle); hypoplastic left heart (right).
Prenatal diagnosis of fetal anomalies
Under normal conditions, the lenses are sonolucent. When the lenses are echogenic, congenital cataract should be suspected. Congenital cataract usually is associated with significant visual impairment and may be a part of many genetic syndromes.
169
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 10.6 Cardiac anomalies demonstrable by the visualization of the outflow tracts. (A) A single arterial trunk arises from the base of the heart, overriding a ventricular septal defect; this is truncus arteriosus communis. (B) Two large vessels arise from the base of the heart in a parallel fashion without crossing; this is transposition of the great arteries (RV, LV, right and left ventricle, respectively).
view is recommended, as it is usually easy to obtain at midgestation and theoretically should demonstrate abnormal findings with many major cardiac defects.14 In reality, studies demonstrate great regional and national variations, with sensitivities ranging between 5% and 60%.15–17 A new approach to fetal echocardiography is the recent introduction of four-dimensional colour Doppler ultrasound using spatiotemporal image correlation technology.40
Atrial and Ventricular Septal Defects Atrial and ventricular septal defects represent about 10% and 30% of all cardiac defects, respectively. In most cases, they involve the septum secundum (the portion above the foramen ovale). Prenatal diagnosis is difficult owing to the physiological presence of the foramen ovale, and is very rarely if ever made. Most ventricular septal defects are small and equally difficult to demonstrate antenatally. As they are usually associated with blood shunting across the septum, colour Doppler may facilitate the diagnosis. Atrial and ventricular septal defects are not a cause of impairment of cardiac function in utero, as a large intracardiac right-to-left shunt is a physiological condition in the fetus. Most affected infants are asymptomatic even in the neonatal period. When the defects are not associated with other cardiac anomalies, the prognosis is excellent. Spontaneous closure is frequent. Primum atrial septal defect is the simplest form of atrioventricular septal defect and will be considered below.
170
Atrioventricular septal defects The core of the heart, that is the apical portion of the atrial septum, the basal portion of the interventricular septum and the medial portion of atrioventricular
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
valves develop from the mesenchymal masses or endocardial cushions. Abnormal development of these structures, commonly referred to as endocardial cushion defects, atrioventricular canal or atrioventricular septal defects, represents about 7% of all cardiac anomalies. In the complete form, persistent common atrioventricular canal, the tricuspid and mitral valve are fused in a large single atrioventricular valve that opens above and bridges the two ventricles. In the complete form of atrioventricular canal, the common atrioventricular valve may be incompetent, and systolic blood regurgitation from the ventricles to the atria may give rise to congestive heart failure. In the partial form, there is a defect in the apical portion of the atrial septum (septum primum defect). There are two separate atrioventricular valves, but they are inserted at the same level on the ventricular septum. Antenatal diagnosis of complete atrioventricular septal defects is usually easy. The four-chamber view reveals an obvious deficiency of the central core structures of the heart. Colour Doppler ultrasound can be useful, in that it facilitates the visualization of the central opening of the single atrioventricular valve. The atria may be dilated as a consequence of atrioventricular insufficiency. In such cases, colour and pulsed Doppler ultrasound allow identification of the regurgitant jet. The incomplete forms are more difficult to recognize. A useful hint is the demonstration that the tricuspid and mitral valves attach at the same level at the crest of the septum. The atrial septal defect is of the ostium primum type (since the septum secundum is not affected) and thus is close to the crest of the interventricular septum. Atrioventricular septal defects do not impair the fetal circulation per se. However, the presence of atrioventricular valve insufficiency may lead to intrauterine heart failure. The prognosis of atrioventricular septal defects is poor when detected in utero, probably because of the high frequency of associated anomalies in antenatal series. Atrioventricular septal defects will usually be encountered either in fetuses with chromosomal aberrations (50% of cases are associated with aneuploidy, 60% being trisomy 21, 25% trisomy 18) or in those with cardiosplenic syndromes. In the former cases, an atrioventricular septal defect is frequently found in association with extracardiac anomalies. In the latter cases, complex cardiac anomalies and abnormal disposition of the abdominal organs are almost the rule. Survival after surgical closure is more than 90% but in about 10% of patients a second operation for atrioventricular valve repair or replacement is necessary. Long-term prognosis is good.
Heterotaxy In heterotaxy, also referred to as cardiosplenic syndromes, the fetus is made of either two left or two right sides. Other terms commonly used include left or right isomerism, asplenia and polysplenia. Unpaired organs (liver, stomach and spleen) may be absent, midline or duplicated. Because of left atrial isomerism (thus absence of right atrium which is the normal location for the pacemaker) and abnormal atrioventricular junctions, atrioventricular blocks are very common. Heterotaxy represents about 2% of all congenital heart defects.
171
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ In polysplenia, the fetus has two left sides (one in normal position and the other as a mirror image); this is called left isomerism. Multiple small spleens (usually too small to be detected by antenatal ultrasound) are found posterior to the stomach. The liver is midline and symmetrical but the stomach and aorta can be on opposite sides. In asplenia, the fetus has two right sides (right isomerism). The liver is generally midline and the stomach right- or left-sided. The aorta and cava are on the same side (either left or right) of the spine. Cardiac malformations are almost invariably present and are usually severe, with a tendency towards a single structure replacing normal paired structures: single atrium, single atrioventricular valve, single ventricle and single great vessel. The main clue for the diagnosis of fetal heterotaxy is the demonstration of complex cardiac anomalies associated with abnormal disposition of the thoracic and/or abdominal organs. In polysplenia, a typical finding is interruption of the inferior vena cava with azygous continuation (there is failure to visualize the inferior vena cava and a large venous vessel, the azygos vein, runs to the left and close to the spine and ascends into the upper thorax). Symmetry of the liver can be sonographically recognized in utero by the abnormal course of the portal circulation that does not display a clearly defined portal sinus bending to the right. The heterogeneous cardiac anomalies found in association with heterotaxy are usually easily seen, but a detailed diagnosis often poses a challenge; in particular, assessment of connection between the pulmonary veins and the atrium (an element that has a major prognostic influence) can be extremely difficult. Associated anomalies include absence of the gallbladder, malrotation of the gut, duodenal atresia and hydrops. The outcome depends on the amount of cardiac anomalies, but it tends to be poor. Atrioventricular insufficiency and severe fetal bradycardia due to atrioventricular block may lead to intrauterine heart failure.
Univentricular Heart
172
This term defines a group of anomalies characterized by the presence of an atrioventricular junction that is entirely connected to only one chamber in the ventricular mass. Therefore, univentricular heart includes both those cases in which two atrial chambers are connected, by either two distinct atrioventricular valves or by a common one, to a main ventricular chamber (double-inlet single ventricle) as well as those cases in which, because of the absence of one atrioventricular connection (tricuspid or mitral atresia), one of the ventricular chambers is either rudimentary or absent. Univentricular heart is rare; it represents about 1.5% of all congenital cardiac defects. Tricuspid atresia is by far the most frequent variety. In double-outlet single ventricle, two separate atrioventricular valves are seen opening into a single ventricular cavity without evidence of the interventricular septum. In tricuspid atresia, there is only one atrioventricular valve connected to a main ventricular chamber. A small rudimentary ventricular chamber lacking atrioventricular connection is a frequent but not constant finding.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Aortic Stenosis Aortic stenosis represents about 3% of all cardiac defects and is commonly divided into supravalvar, valvar and subaortic forms. Supravalvar and subaortic are rare and usually cannot be detected antenatally. The valvar form of aortic stenosis can be due to dysplastic, thickened aortic cusps or fusion of the commissure between the cusps. With severe valvar aortic stenosis the left ventricle may be either hypertrophic or dilated and hypocontractile. The ascending aorta is frequently enlarged. Hyperechogenicity of the aortic valve and pulsed Doppler demonstration of increased peak velocity (usually in excess of 1 m/sec) support the diagnosis. At the colour Doppler examination, high velocity and turbulence usually result in aliasing, with a mosaic of colours within the ascending aorta. Severe aortic stenosis may result in atrioventricular valve insufficiency and intrauterine heart failure. Most cases of mild to moderate aortic stenosis are probably not amenable to early prenatal diagnosis. Asymmetrical septal hypertrophy and hypertrophic cardiomyopathy of fetuses of diabetic mothers resulting in subaortic stenosis have been occasionally diagnosed by demonstrating an unusual thickness of the ventricular septum. Depending upon the severity of the aortic stenosis, the association of left ventricular pressure overload and subendocardial ischaemia, due to decrease in coronary perfusion, may lead to intrauterine impairment of cardiac function. Subvalvar and subaortic forms are not generally manifested in the neonatal period. Conversely, the valvar type can be a cause of congestive heart failure in the newborn and fetus as well. The neonatal outcome depends on the severity of obstruction. If the left ventricular function is adequate, balloon valvoplasty is carried out in the neonatal period and in about 50% of cases surgery is necessary within the first 10 years of life because of aortic insufficiency or residual stenosis. If left ventricular function is inadequate a Norwood type of repair is necessary (see hypoplastic left heart).
Prenatal diagnosis of fetal anomalies
Surgical treatment (the Fontan procedure) involves separation of the systemic circulations by anastomosing the superior and inferior vena cava directly to the pulmonary artery. The survivors from this procedure may develop several complications including arrhythmias, thrombus formation and protein-losing enteropathy. The 5-year survival is about 70%. The long-term outcome is uncertain.
Coarctation, Tubular Hypoplasia and Interruption of the Aortic Arch Coarctation is a localized narrowing of the juxtaductal arch, most commonly between the left subclavian artery and the ductus. Cardiac anomalies are frequently present and include aortic stenosis and insufficiency, ventricular septal defect, atrial septal defect, transposition of the great arteries, truncus and doubleoutlet right ventricle. Non-cardiac anomalies include diaphragmatic hernia and Turner syndrome but not Noonan syndrome. Interrupted aortic arch is typically associated with chromosome 22q.
173
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Coarctation or interruption of the aortic arch should be suspected when the right ventricle is enlarged (right ventricle to left ventricle ratio of more than 1.3). Narrowing of the isthmus or the presence of a shelf is often difficult to demonstrate because in the fetus, the aortic arch and ductal arch are close and difficult to distinguish. In most cases, coarctation can only be suspected in utero and a certain diagnosis must be delayed until after birth. The characteristic finding of an ascending aorta more vertical than usual and the impossibility of demonstrating a connection with the descending aorta suggest the diagnosis. Coarctation/interrupted aortic arch should always be considered when intracardiac lesions diverting blood flow from the left to the right heart are encountered (aortic stenosis and atresia in particular). Critical coarctation and interruption are fatal in the neonatal period after closure of the ductus and therefore prostaglandin therapy is necessary to maintain a patent ductus. Surgery (which involves excision of the coarcted segment and end-to-end anastomosis) is associated with a mortality of about 10% and the incidence of restenosis in survivors (requiring further surgical repair) is about 15%. Interrupted aortic arch should always be considered when intracardiac lesions diverting blood flow from the left to the right heart are encountered (aortic stenosis and atresia in particular). Isolated interruption of the aortic arch is often encountered with enlargement of the right ventricle (right ventricle to left ventricle ratio of more than 1.3). For interrupted aortic arch, recent reports suggest an overall late survival of more than 70% after surgery.
Hypoplastic Left Heart Syndrome
174
Hypoplastic left heart syndrome accounts for 4% of all cardiac anomalies at birth, but it is one of the most frequent cardiac malformations diagnosed antenatally. It is a spectrum of anomalies characterized by a very small left ventricle with mitral and/or aortic atresia or hypoplasia. Blood flow to the head and neck vessels and coronary artery is supplied in a retrograde manner via the ductus arteriosus. Prenatal echocardiographic diagnosis of the syndrome depends on the demonstration of a diminutive left ventricle and ascending aorta. In most cases, the ultrasound appearance is self-explanatory and the diagnosis an easy one. There is, however, a broad spectrum of hypoplasia of the left ventricle and in some cases the ventricular cavity is almost normal in size. As the four-chamber view is almost normal, we anticipate that these cases will certainly be missed in most routine surveys of fetal anatomy. On closer scrutiny, however, the movement of the mitral valve appears severely impaired to non-existent, ventricular contractility is obviously decreased, and the ventricle often displays an internal echogenic lining that is probably due to endocardial fibroelastosis. The definitive diagnosis of the syndrome depends on the demonstration of hypoplasia of the ascending aorta and atresia of the aortic valve. Colour flow mapping is an extremely useful adjunct to the real-time examination, in that it allows the demonstration of retrograde blood flow within the ascending aorta and aortic arch.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
Hypoplastic left heart is well tolerated in utero. The patency of the ductus arteriosus allows adequate perfusion of the head and neck vessels. Intrauterine growth may be normal and the onset of symptoms most frequently occurs after birth. The prognosis for infants with hypoplastic left heart syndrome is extremely poor and this lesion is responsible for 25% of cardiac deaths in the first week of life. Almost all affected infants die within 6 weeks if they are not treated. In the neonatal period prostaglandin therapy is given to maintain ductal patency but still congestive heart failure develops within 24 hours of life. Options for surgery include cardiac transplantation in the neonatal period (with an 80% 5-year survival) and the three-stage Norwood repair. Stage 1 involves anastomosis of the pulmonary artery to the aortic arch for systemic outflow, placement of a systemic-to-pulmonary arterial shunt to provide pulmonary blood flow, and arterial septectomy to ensure unobstructed pulmonary venous return; the survival rate of fetuses diagnosed in utero is in the region of 40%. Stage 2 (which is usually carried out in the sixth month of life) involves anastomosis of the superior vena cava to the pulmonary arteries. Neurodevelopmental abnormalities have been reported in survivors of the Norwood operation.
Pulmonary Stenosis and Pulmonary Atresia Pulmonary stenosis and pulmonary atresia with intact ventricular septum (also known as hypoplastic right ventricle) represent 9% and about 2% of all cardiac anomalies respectively. The most common form of pulmonary stenosis is the valvar type, due to the fusion of the pulmonary leaflets. Haemodynamics is altered proportionally to the degree of the stenosis. The work of the right ventricle is increased, as well as the pressure, leading to hypertrophy of the ventricular walls. The same considerations formulated for the prenatal diagnosis of aortic stenosis are valid for pulmonary stenosis. A handful of cases recognized in utero have been reported in the literature thus far, mostly severe types with enlargement of the right ventricle and/or post-stenotic enlargement or hypoplasia of the pulmonary artery. Pulmonary atresia with intact ventricular septum in infants is usually associated with a hypoplastic right ventricle. However, cases with enlarged right ventricle and atrium have been described with unusual frequency in prenatal series. Enlargement of the ventricle and atrium is probably the consequence of tricuspid insufficiency. Prenatal diagnosis of pulmonary atresia with intact ventricular septum relies on the demonstration of a small pulmonary artery with an atretic pulmonary valve. The considerations previously formulated for the diagnosis of hypoplastic left heart syndrome apply to this condition as well. Patients with mild stenosis are asymptomatic and there is no need for intervention. Patients with severe stenosis and right ventricular overload may experience congestive heart failure and require balloon valvoplasty in the neonatal period with excellent survival and normal long-term prognosis. Fetuses with pulmonary atresia and an enlarged right heart have a very high degree of perinatal mortality. Infants with right ventricular hypoplasia require biventricular surgical repair and the mortality is about 40%.
175
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Conotruncal Malformations
176
Conotruncal malformations are a heterogeneous group of defects that involve two different segments of the heart: the conotruncus and the ventricles. Conotruncal anomalies are relatively frequent. They account for 20–30% of all cardiac anomalies and are the leading cause of symptomatic cyanotic heart disease in the first year of life. Prenatal diagnosis is of interest for several reasons. Given the parallel model of fetal circulation, conotruncal anomalies are well tolerated in utero. The clinical presentation occurs usually hours to days after delivery and is often severe, representing a true emergency and leading to considerable morbidity and mortality. Yet these malformations have a good prognosis when promptly treated. Two ventricles of adequate size and two great vessels are commonly present, giving the premise for biventricular surgical correction. The outcome is indeed much more favourable than with most of the other cardiac defects that are detected antenatally. Unfortunately, the recognition of these anomalies remains difficult. The four-chamber view is frequently unremarkable in these cases. A specific diagnosis requires meticulous scanning and at times may represent a challenge even for experienced sonologists. Transposition of the great arteries is an abnormality in which the aorta arises entirely or in large part from the right ventricle and the pulmonary artery arises from the left ventricle. Associated cardiac lesions are present in about 50% of cases, including ventricular septal defects (which can occur anywhere in the ventricular septum), pulmonary stenosis, unbalanced ventricular size (‘complex transpositions’) and anomalies of the mitral valve, which can be straddling or overriding. Complete transposition is probably one of the most difficult cardiac lesions to recognize in utero. In most cases the four-chamber view is normal and the cardiac cavities and the vessels have normal dimensions. A clue to the diagnosis is the demonstration that the two great vessels do not cross but arise parallel from the base of the heart. The most useful echocardiographic view, however, is the left heart view demonstrating that the vessel connected to the left ventricle has a posterior course and bifurcates into the two pulmonary arteries. Conversely, the vessel connected to the right ventricle has a long upward course and gives rise to the brachiocephalic vessels. Corrected transposition is characterized by a double discordance, at the atrioventricular and ventriculoarterial level. The left atrium is connected to the right ventricle, which is in turn connected to the ascending aorta. Conversely, the right atrium is connected to the right ventricle, which is in turn connected to the ascending aorta. The derangement of the conduction tissue secondary to malalignment of the atrial and ventricular septa may result in dysrhythmias, namely complete atrioventricular block. For diagnostic purposes, the identification of the peculiar difference of ventricular morphology (moderator band, papillary muscles, insertion of the atrioventricular valves) has a prominent role. Demonstration that the pulmonary veins are connected to an atrium, which is in turn connected with a ventricle that has the moderator band at the apex, is an important clue, which is furthermore potentially identifiable even in
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
a simple four-chamber view. Diagnosis requires meticulous scanning to carefully assess all cardiac connections, by using the same views described for the complete form. The presence of atrioventricular block increases the index of suspicion. As anticipated from the parallel model of fetal circulation, complete transposition is uneventful in utero. After birth, survival depends on the amount and size of the mixing of the two otherwise independent circulations. Patients with transposition and an intact ventricular septum present shortly after birth with cyanosis and deteriorate rapidly. When a large ventricular septal defect is present, cyanosis can be mild. Clinical presentation may be delayed up to 2–4 weeks and usually occurs with signs of congestive heart failure. When severe stenosis of the pulmonary artery is associated with a ventricular septal defect, symptoms are similar to those of tetralogy of Fallot. The time and mode of clinical presentation with corrected transposition depend upon the concomitant cardiac defects. Surgery (which involves arterial switch to establish anatomical and physiological correction) is usually carried out within the first 2 weeks of life. Operative mortality is about 10% and 10-year follow-up studies report normal function in the vast majority of cases. The outcome of corrected transposition depends largely upon the associated cardiac defects that are variable. As the systemic ventricle is the right ventricle, there is a high chance of cardiac failure in adulthood. In double-outlet right ventricle (DORV) most of the aorta and pulmonary valve arise completely or almost completely from the right ventricle. The relation between the two vessels may vary, ranging from a Fallot-like to a transposition of the great arteries (TGA)-like situation (the Taussig–Bing anomaly). DORV is not a single malformation from a pathophysiological point of view. The term refers only to the position of the great vessels that is found in association with ventricular septal defects, tetralogy of Fallot, transposition and univentricular hearts. Pulmonary stenosis is very common in all types of DORV but left outflow obstructions, from subaortic stenosis to coarctation and interruption of the aortic arch, can also be seen. Prenatal diagnosis of DORV can be reliably made in the fetus but differentiation from other conotruncal anomalies can be very difficult, especially with tetralogy of Fallot and TGA with ventricular septal defect. The main echocardiographic features include alignment of the two vessels totally or predominantly from the right ventricle and presence in most cases of bilateral coni (subaortic and subpulmonary). The haemodynamics is dependent upon the anatomical type of DORV and the associated anomalies. Since the fetal heart works as a common chamber where the blood is mixed and pumped, DORV is not associated with intrauterine heart failure. However, DORV, in contrast to other conotruncal malformations, is commonly associated with extracardiac anomalies and/or chromosomal defects. Double-outlet right ventricle usually does not interfere with haemodynamics in fetal life. The early operative mortality is about 10%. The essential features of tetralogy of Fallot are a subaortic ventricular septal defect, aorta overriding the ventricular septal defect and infundibular stenosis of the aorta. In about 20% of cases there is atresia of the pulmonary valve,
177
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
178
a condition that is commonly referred to as pulmonary atresia with ventricular septal defect. Tetralogy of Fallot can be associated with other specific cardiac malformations, defining peculiar entities. These include atrioventricular septal defects (found in 4% of cases) and absence of the pulmonary valve (found in less than 2% of cases). Hypertrophy of the right ventricle, one of the classic elements of the tetrad, is always absent in the fetus and only develops after birth. Echocardiographic diagnosis of tetralogy of Fallot relies on the demonstration of a ventricular septal defect in the outlet portion of the septum and an overriding aorta. Colour and pulsed Doppler can be used to identify the patency of the pulmonary valve and exclude pulmonary atresia. Diagnostic problems arise at the extremes of the spectrum of tetralogy of Fallot. In cases with minor forms of right outflow obstruction and aortic overriding, differentiation from a simple ventricular septal defect can be difficult. In those cases in which the pulmonary artery is not imaged, a differential diagnosis between pulmonary atresia with ventricular septal defect and truncus arteriosus communis is similarly difficult. Abnormal enlargement of the right ventricle, main pulmonary trunk and artery suggests absence of the pulmonary valve. Cardiac failure is never seen in fetal life or postnatally. Even in cases of right pulmonary stenosis or atresia, the wide ventricular septal defect provides adequate combined ventricular output, while the pulmonary vascular bed is supplied in a retrograde manner by the ductus. The only exception to this rule is represented by cases with an absent pulmonary valve that may result in massive regurgitation to the right ventricle and atrium. When severe pulmonary stenosis is present, cyanosis tends to develop immediately after birth. With lesser degrees of obstruction to pulmonary blood flow, the onset of cyanosis may not appear until later in the first year of life. When there is pulmonary atresia, rapid and severe deterioration follows ductal constriction. Survival after complete surgical repair (which is usually carried out in the third month of life) is more than 90% and about 80% of survivors have normal exercise tolerance. A single arterial vessel that originates from the heart overrides the ventricular septum and supplies the systemic, pulmonary and coronary circulations, characterized as truncus arteriosus. The single arterial trunk is larger than the normal aortic root and is predominantly connected with the right ventricle in about 40% of cases, with the left ventricle in 20%, and is equally shared in 40%. The truncal valve may have one, two or three cusps and is rarely normal. It can be stenotic or, more frequently, insufficient. A malalignment ventricular septal defect, usually wide, is an essential part of the malformation. There are three types based on the morphology of the pulmonary artery. In type 1, the pulmonary arteries arise from the truncus within a short distance from the valve, as a main pulmonary trunk, which then bifurcates. In type 2, there is no main pulmonary trunk. In type 3, only one pulmonary artery (usually the right) originates from the truncus, while a systemic collateral vessel from the descending aorta supplies the other. Similar to tetralogy of Fallot, and unlike the other conotruncal malformations, truncus is frequently (about 30%) associated with extracardiac malformations.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
Truncus arteriosus can be reliably detected with fetal echocardiography. The main diagnostic criteria are that a single semilunar valve overrides the ventricular septal defect and there is direct continuity between one or two pulmonary arteries and the single arterial trunk. The semilunar valve is often thickened and moves abnormally. Doppler ultrasound is of value in assessing incompetence of the truncal valve. A peculiar problem found in prenatal echocardiography is the demonstration of the absence of pulmonary outflow tract and the concomitant failure to image the pulmonary arteries. In these situations a differentiation between truncus and pulmonary atresia with ventricular septal defect may be impossible. Similar to the other conotruncal anomalies, truncus arteriosus is not associated with alteration of fetal haemodynamics. It is frequently a neonatal emergency. These patients have usually unobstructed pulmonary blood flow and show signs of progressive congestive heart failure with the postnatal fall in pulmonary resistance. Many patients will present with cardiac failure in the first 1–2 weeks of life. Surgical repair (usually before the sixth month of life) involves closure of the ventricular septal defect and creation of a conduit connection between the right ventricle and the pulmonary arteries. Survival from surgery is about 90% but the patients require repeated surgery for replacement of the conduit. Conotruncal anomalies, particularly truncus arteriosus and tetralogy of Fallot, are rather frequently associated with microdeletion of chromosome 22.
Ebstein's Anomaly and Tricuspid Valve Dysplasia Ebstein's anomaly results from a faulty implantation of the tricuspid valve. The posterior and septal leaflets are elongated and tethered below their normal level of attachment on the annulus or displaced apically, away from the annulus, down to the junction between the inlet and trabecular portion of the right ventricle. The anterior leaflet is normally inserted but deformed. The resulting configuration is that of a considerably enlarged right atrium at the expense of the right ventricle. The portion of the right ventricle that is ceded to the right atrium is called the atrialized inlet of the right ventricle. It has a thin wall that may even be membranous and is commonly dilated. The tricuspid valve is usually both incompetent and stenotic. Associated anomalies include atrial septal defect, pulmonary atresia, ventricular septal defect and supraventricular tachycardia. Ebstein's may be associated with trisomy 13 and 21, Turner, de Lange and Marfan syndromes. Maternal ingestion of lithium has also been incriminated as a causal factor. The characteristic echocardiographic finding is that of a massively enlarged right atrium, a small right ventricle and a small pulmonary artery. Doppler can be used to demonstrate regurgitation in the right atrium. About 25% of cases have supraventricular tachycardia (from re-entrant impulse), atrial fibrillation or atrial flutter. Differential diagnosis from pulmonary atresia with intact ventricular septum and a regurgitant tricuspid valve or isolated tricuspid valve insufficiency is difficult and may be impossible antenatally. Although the disease has a variable severity, with some cases discovered only late in life, Ebstein's anomalies detected prenatally have a dismal prognosis, with
179
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
essentially all patients dying. This probably reflects that the prenatal variety is more severe than the one detected in children or adults.
Echogenic Foci Echogenic foci in the heart are found in about 4% of pregnancies and in 12% of fetuses with trisomy 21. Histological studies have shown these foci to be due to mineralization within a papillary muscle. Echogenic foci are detected in the fourchamber view of the heart. In about 95% of cases they are located in the left ventricle and in 5% in the right ventricle; in 98% they are unilateral and 2% bilateral. Ventricular function is normal and the atrioventricular valves are competent. Echogenic foci are usually of no pathological significance and in more than 90% of cases they resolve by the third trimester. However, they are sometimes associated with cardiac defects and chromosomal abnormalities. For isolated hyperechogenic foci, the risk for trisomy 21 may be three times the background maternal age- and gestation-related risk.
Cardiac Dysrhythmias
180
Ectopic heartbeats are common but they are abnormal only when they occur at a frequency of more than 1 in 10 beats. Premature contractions may be of atrial (much more common) or ventricular origin. Immaturity of the conducting system may be the origin. The diagnosis is made by passing an M-mode cursor through one atrium and one ventricle. Premature atrial contractions are spaced closer to the previous contraction than normally and may be transmitted to the ventricle or blocked, resulting in a compensatory pause. Premature ventricular contractions present in the same way but are not accompanied by an atrial contraction and are usually followed by a compensatory pause that is shorter than the one observed with blocked premature atrial contractions. The diagnosis is easily made by obtaining a tracing demonstrating simultaneously atrial and ventricular contractions. This can be obtained by directing the M-mode line across the atrial and ventricular wall or by sampling with pulsed Doppler the atrioventricular valves, hepatic vessels or inferior vena cava, which demonstrate pulsations corresponding to atrial and ventricular contractions. The irregularity of the heart rhythm is the most typical clue to make a diagnosis and to differentiate premature contractions from more severe persistent dysrhythmias. Premature beats tend to disappear spontaneously in utero and only rarely persist after birth. It has been suggested that in some cases there may be progression to tachyarrhythmia, but the risk is small. Tachyarrhythmias are classified according to the origin and the number of beats per minute. In the majority of cases the abnormal electrical impulse originates from the atria. Supraventricular tachycardia is the most common form of tachy arrhythmia. It is characterized by a heart rate of 200–300 bpm, most frequently around 240 bpm. Cardiac malformations are rare. Atrial flutter is associated with an atrial rate of 300–400 bpm. The ventricular response is equal to or less than 2:1.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
A very frequent finding is an atrial rate in the range of 480 with an atrioventricular block of 2:1 and a ventricular response of 240 bpm. Occasionally, atrioventricular blocks of high degree with ventricular bradycardia are seen. Structural anomalies are more common than in supraventricular tachycardia and include Ebstein's anomaly and pulmonary stenosis. Atrial fibrillation is characterized by an atrial rate greater than 400 bpm and completely irregular ventricular rhythm, with constant variation of the distance between systole. The atrial contractions are usually too small to be detected by M-mode. A combination of different atrial arrhythmias may coexist in the same fetus. Ventricular tachycardias are rare and have typically a ventricular frequency of 200 bpm or less. Associated anomalies include atrial septal defect, atrial septal aneurysm, mitral anomalies, endocardial cushion defect, endocardial fibroelastosis, Ebstein's anomaly, cardiac tumours (rhabdomyoma) and anomalies of the conduction system, Coxsackie B infection and cardiomyopathy. Sustained tachycardia with a heart rate exceeding 200/min is associated with suboptimal ventricular filling and decreased cardiac output. This results in atrial overload and congestive failure. Fetuses with supraventricular tachycardia that occasionally convert to sinus rhythm can tolerate the condition well. Sustained tachycardias of greater than 200 bpm frequently result in fetal hydrops. The combination of hydrops and dysrhythmia has a poor prognosis (mortality of 80%) independently of the nature of the tachycardia. Once fetal maturity has been achieved, the fetus should be delivered and treated ex utero. Prenatal treatment is the standard of care for premature fetuses that have sustained tachycardias of more than 200 bpm, particularly if there is associated hydrops and/or polyhydramnios. The treatment depends on the type of tachycardia and the aim is to either decrease the excitability or increase the conduction time to block a re-entrant mechanism. Although a vagal manoeuvre (such as simple compression of the cord) may sometimes suffice, the administration of antiarrhythmic drugs is often necessary. The drugs used include propranolol, verapamil, procainamide, quinidine, flecainide, amiodarone and adenosine; combination of these drugs is also possible but the optimal approach remains uncertain. These drugs are usually administered to the mother but they can also be given directly to the fetus (intraperitoneally, intramuscularly in the thigh or intravascularly through the umbilical cord). The usual response to treatment is conversion to a normal rhythm, followed by shorter episodes of tachycardia that are more interspersed, and finally the presence of ectopic beats alone. Fetuses with normal rhythm but persistent hydrops are still at risk of death. The survival rate of fetuses with tachyarrhythmias treated in utero is more than 90%. In complete atrioventricular block, the atria beat at their own rhythm and none of their impulses is transmitted to the ventricles. The ventricles have a slow rate (40–70 bpm). In 50% of cases structural anomalies are present (mostly cardio splenic syndromes and corrected TGA). In the remaining cases, the condition is almost exclusively caused by the presence of maternal autoantibodies anti-Ro (SS-a) or anti-La (SS-B). Most mothers are asymptomatic but in a few cases connective tissue disease is present (lupus erythematosus, scleroderma, rheumatoid arthritis and Sjögren syndrome). Fetuses with cardiac malformations have
181
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
182
heart block starting from the first trimester. Atrioventricular block secondary to maternal autoantibodies develops slowly throughout gestation; a normal cardiac rhythm may be found in the second trimester. The prognosis depends on the presence of cardiac defects, the ventricular rate and the presence of hydrops; usually, fetuses with a ventricular rate greater than 55 bpm have a normal intrauterine growth and do not develop heart failure. Conversely, hydrops is almost the rule for greater degrees of ventricular bradycardia. Intrauterine treatment by the administration of β-mimetic agents has been used (with the aim of increasing electric excitability of the myocardial cells and thus ventricular rate), but the results have been disappointing. Maternal administration of steroids (dexametasone 4–8 mg/day) has been advocated for complete heart block secondary to maternal autoantibodies, but the value of this treatment remains unproven. Invasive fetal cardiac pacing has been attempted but thus far there have been no survivors.
Thoracic Anomalies Hyperechogenic and Cystic Lungs Fetal hyperechogenic lungs are a recently described entity. The typical finding is that of enlarged, brightly echogenic lungs displacing the mediastinum and causing an inversion of the diaphragm. Most frequently, part of one lung or one entire lung is affected, causing lateral displacement of the heart and mediastinum. Rarely, both lungs are affected, compressing the mediastinum on both sides. The pathophysiology is related to obstruction of the respiratory tree, which causes accumulation of fluid and secretions into the lungs. The effects of respiratory obstruction on the lungs are variable. Accumulation of fluid may lead to lung hyperplasia. Early and long-standing obstruction is probably responsible for the histological alterations that are commonly referred to as cystic adenomatoid malformation of the lungs. The aetiology is variable. Obstruction may result from primary atresia or be the consequence of a mucus plug. A further possibility is pulmonary sequestration. With this condition, part of the lung develops separate from the bronchi and the pulmonary circulation, and is supplied through arteries that arise from the descending aorta. A differential diagnosis between these three conditions is often difficult. With lung sequestration, a specific diagnosis is possible by demonstrating with colour Doppler the abnormal vessels connecting the aorta to the abnormal lung. Spontaneous regression or resolution of the increased echogenicity indicates a mucus plug as the most likely hypothesis. When both lungs are affected, the most likely diagnosis is an obstruction of the upper airways, usually atresia of the trachea. Polyhydramnios and fetal hydrops may occur, particularly with bilateral echogenic lungs and lung sequestration. Lung sequestration may also be associated with cardiac and diaphragmatic defects. In some cases, macroscopic cysts may be associated with the increased echogenicity. Occasionally, large and multiple cysts are the dominant finding. Cystic adenomatoid malformation is usually found at birth in these cases (macrocystic variety). The pathophysiology probably overlaps that of echogenic lungs.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Pleural effusions Fetal pleural effusions may be an isolated finding or may occur in association with generalized oedema and ascites. Irrespective of the underlying cause, infants affected by pleural effusions usually present in the neonatal period with severe and often fatal respiratory insufficiency. This is either a direct result of pulmonary compression caused by the effusions or due to pulmonary hypoplasia secondary to chronic intrathoracic compression. The overall mortality of neonates with pleural effusions is 25%, with a range from 15% in infants with isolated pleural effusions to 95% in those with gross hydrops. The mortality rate in cases of antenatally diagnosed chylothorax is about 50%. Isolated pleural effusions in the fetus may either resolve spontaneously or they can be treated effectively after birth. Nevertheless, in some cases severe and chronic compression of the fetal lungs can result in pulmonary hypoplasia and neonatal death. In others, mediastinal compression leads to the development of hydrops and polyhydramnios, which are associated with a high risk of premature delivery and perinatal death. Attempts at prenatal therapy by repeated thoracocenteses for drainage of pleural effusions have been generally unsuccessful in reversing the hydropic state, because the fluid reaccumulates within 24–48 hours of drainage. A better approach is chronic drainage by the insertion of thoracoamniotic shunts. This is useful for both diagnosis and treatment. First, the diagnosis of an underlying cardiac abnormality or other intrathoracic lesion may become apparent only after effective decompression and return of the mediastinum to its normal position. Second, it can reverse fetal hydrops, resolve polyhydramnios and thereby reduce the risk of preterm delivery, and may prevent pulmonary hypoplasia. Third, it may be useful in the prenatal diagnosis of pulmonary hypoplasia because in such cases the lungs often fail to expand after shunting. Furthermore, it may help distinguish between hydrops due to primary accumulation of pleural effusions, in which case the ascites and skin oedema may resolve after shunting, and other causes of hydrops such as infection, in which drainage of the effusions does not prevent worsening of the hydrops. Survival after thoracoamniotic shunting is more than 90% in fetuses with isolated pleural effusions and about 50% in those with hydrops.
Prenatal diagnosis of fetal anomalies
Unilateral echogenic and/or cystic lungs without other anomalies or hydrops have a very good outcome. The lesions usually decrease in size with gestation and the infants are asymptomatic at birth. Dysplastic lung tissue is, however, usually present and must be surgically removed. Conversely, bilateral lesions or those associated with hydrops usually have a poor outcome. In these cases, drainage or shunting of the cysts may be attempted.
Diaphragmatic Hernia Diaphragmatic hernia is found in about 1 per 4000 births. Development of the diaphragm is usually completed by the ninth week of gestation. In the presence of a defective diaphragm there is herniation of the abdominal viscera into
183
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
184
the thorax at about 10–12 weeks, when the intestines return to the abdominal cavity from the umbilical cord. However, at least in some cases, intrathoracic herniation of viscera may be delayed until the second or third trimester of pregnancy. Diaphragmatic hernia is usually a sporadic abnormality. However, in about 50% of affected fetuses there are associated chromosomal abnormalities (mainly trisomy 18, trisomy 13 and Pallister–Killian syndrome – mosaicism for tetrasomy 12p), other defects (mainly craniospinal defects, including spina bifida, hydrocephaly and the otherwise rare iniencephaly, and cardiac abnormalities) and genetic syndromes (such as Fryns, de Lange and Marfan syndromes). Prenatally, the diaphragm is imaged by ultrasonography as an echo-free space between the thorax and abdomen. However, the integrity of the diaphragm is usually inferred from the normal disposition of the thoracic and abdominal organs. Diaphragmatic hernia can be diagnosed by the ultrasonographic demonstration of stomach, intestines (90% of the cases) or liver (50%) in the thorax and the associated mediastinal shift to the opposite side. Herniated abdominal contents, associated with a left-sided diaphragmatic hernia, are easy to demonstrate because the echo-free fluid-filled stomach and small bowel contrast dramatically with the more echogenic fetal lung. In contrast, a right-sided hernia is more difficult to identify because the echogenicity of the fetal liver is similar to that of the lung and visualization of the gallbladder in the right side of the fetal chest may be the only way of making the diagnosis. Polyhydramnios (usually after 25 weeks) is found in about 75% of cases and this may be the consequence of impaired fetal swallowing due to compression of the oesophagus by the herniated abdominal organs. The main differential diagnosis is from echogenic/cystic lungs. Antenatal prediction of pulmonary hypoplasia remains one of the challenges of prenatal diagnosis because this would be vital in both counselling parents and also in selecting those cases that may benefit from prenatal surgery. Poor prognostic signs are increased nuchal translucency thickness at 10–14 weeks, intrathoracic herniation of abdominal viscera before 20 weeks, severe mediastinal compression suggested by an abnormal ratio in the size of the cardiac ventricles and the development of polyhydramnios. In the human, the bronchial tree is fully developed by the 16th week of gestation at which time the full adult number of airways is established. In diaphragmatic hernia the reduced thoracic space available to the developing lung leads to reduction in airways, alveoli and arteries. Thus, although isolated diaphragmatic hernia is an anatomically simple defect, which is easily correctable, the mortality rate is about 50%. The main cause of death is hypoxaemia due to pulmonary hypertension resulting from the abnormal development of the pulmonary v ascular bed. In a few cases of diaphragmatic hernia, hysterotomy and fetal surgery was carried out but this intervention has now been abandoned in favour of minimally invasive surgery. Animal studies have demonstrated that obstruction of the trachea results in expansion of the fetal lungs by retained pulmonary secretions. Endoscopic occlusion of the fetal trachea has also been carried out in human fetuses with diaphragmatic hernia but the number of cases is too small for useful conclusions to be drawn as to the effectiveness of such treatment.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Anomalies of the Abdominal Wall and Gastrointestinal Tract
Omphalocele, or exomphalos, occurs in about 1 per 4000 births and results from failure of normal embryonic regression of the midgut from the umbilical stalk into the abdominal coeloma. The abdominal contents, including intestines and liver or spleen covered by a sac of parietal peritoneum and amnion, are herniated into the base of the umbilical cord. Less often, there is an upward extension of the defect, associated with a defect in the anterior diaphragm, ectopia cordis and embryonic fold, resulting in the pentalogy of Cantrell. In other cases, the abdominal wall defect may extend inferiorly and associate with exstrophy of the bladder or cloaca, imperforate anus, colonic atresia and sacral vertebral defects. The Beckwith–Wiedemann syndrome (usually sporadic and occasionally familial syndrome with a birth prevalence of about 1 in 14,000) is the combination of omphalocele, macrosomia, organomegaly, macroglossia and severe neonatal hypoglycaemia. In some cases Beckwith–Wiedemann syndrome is associated with mental handicap, which is thought to be secondary to inadequately treated hypoglycaemia. About 5% of affected individuals develop tumours during childhood, most commonly nephroblastoma and hepatoblastoma. The majority of cases of omphalocele are sporadic and the recurrence risk is usually less than 1%. However, in some cases there may be an associated genetic syndrome. Chromosomal abnormalities (mainly trisomy 18 or 13) are found in about 30% of cases at midgestation and in 15% of neonates. Similarly, in Beckwith–Wiedemann syndrome, most cases are sporadic, although autosomal dominant, recessive, X-linked and polygenic patterns of inheritance have been described. The diagnosis of omphalocele is based on the demonstration of the midline anterior abdominal wall defect, the herniated sac with its visceral contents and the umbilical cord insertion at the apex of the sac. The differential diagnosis is mainly with gastroschisis, in which the only herniated abdominal contents are bowel loops, which are not contained by an amnioperitoneal membrane. Omphalocele is a correctable malformation in which survival depends primarily on whether or not other malformations or chromosomal defects are present. For isolated lesions, the survival rate after surgery is about 90%. The mortality is much higher with cephalic fold defects than with lateral and caudal defects. Whether the infants with omphalocele should be delivered by caesarean section to decrease trauma and infection to the herniated abdominal contents is debated.
Prenatal diagnosis of fetal anomalies
Omphalocele
Gastroschisis Gastroschisis is found in about 1 per 4000 births. In gastroschisis the primary body folds and the umbilical ring develop normally and evisceration of the intestine occurs through a small abdominal wall defect located just lateral to and
185
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ usually to the right of an intact umbilical cord. The loops of intestine lie uncovered in the amniotic fluid and become thickened, oedematous and matted. This is a sporadic abnormality. Associated chromosomal abnormalities are rare and although other malformations are found in 10–30% of cases, these are mainly gut atresias, probably due to gut strangulation and infarction in utero. Prenatal diagnosis is based on the demonstration of the normally situated umbilicus and the herniated loops of intestine, which are free floating and widely separated. About 30% of fetuses are growth retarded but the diagnosis can be difficult because gastroschisis as such is associated with a small abdominal circumference. Postoperative survival is about 90%; mortality is usually the consequence of short gut syndrome. Similarly to omphalocele, it is debated whether these infants should be delivered by caesarean section to decrease trauma and infection to the herniated abdominal contents.
Body Stalk Anomaly Body stalk anomaly is an exceedingly rare condition, found in about 1 per 10,000 pregnancies. This abnormality is characterized by the presence of a major abdominal wall defect, severe kyphoscoliosis and a rudimentary umbilical cord. It is a sporadic abnormality. The pathogenesis is uncertain but possible causes include abnormal folding of the trilaminar embryo during the first 4 weeks of development, early amnion rupture with amniotic band syndrome, and early generalized compromise of embryonic blood flow. The ultrasonographic features are a major abdominal wall defect, severe kyphoscoliosis and a short umbilical cord. In the first trimester it is possible to demonstrate that part of the fetal body is in the amniotic cavity and the other part is in the coelomic cavity. The findings suggest that early amnion rupture before obliteration of the coelomic cavity is a possible cause of the syndrome. Body stalk anomaly is invariably lethal.
Bladder Exstrophy and Cloacal Exstrophy
186
Bladder exstrophy is found in 1 per 30,000 births and cloacal exstrophy in about 1 per 200,000 births. Bladder exstrophy is a defect of the caudal fold of the anterior abdominal wall; a small defect may cause epispadias alone whilst a large defect leads to exposure of the posterior bladder wall. In cloacal exstrophy both the urinary and gastrointestinal tracts are involved. Cloacal exstrophy (also referred to as OEIS complex) is the association of an omphalocele, exstrophy of the bladder, imperforate anus and spinal defects such as meningomyelocele. The hemibladders are on either side of the intestines. Bladder exstrophy should be suspected when in the presence of normal amniotic fluid the fetal bladder is not visualized (the filling cycle of the bladder is normally in the region of 15 minutes); an echogenic mass is seen protruding from
✩✩✩✩✩✩✩✩✩✩✩ ✩
Oesophageal Atresia Oesophageal atresia is found in about 1 in 3000 births. It is associated in about 90% of cases with tracheo-oesophageal fistula and results from failure of the primitive foregut to divide into the anterior trachea and posterior oesophagus, which normally occurs during the fourth week of gestation. Oesophageal atresia and tracheo-oesophageal fistula are sporadic abnormalities. Chromosomal abnormalities (mainly trisomy 18 or 21) are found in about 20% of fetuses. Other major defects, mainly cardiac, are found in about 50% of cases. Tracheo-oesophageal fistula may be seen as part of the VATER association (vertebral and ventricular septal defects, anal atresia, tracheo-oesophageal fistula, renal anomalies, radial dysplasia and single umbilical artery). Prenatally the diagnosis of oesophageal atresia is suspected when, in the presence of polyhydramnios (usually after 25 weeks), repeated ultrasonographic examinations fail to demonstrate the fetal stomach or the stomach appears permanently small (<15% of the abdominal circumference); however, gastric secretions may be sufficient to distend the stomach and make it visible. If there is an associated fistula the stomach may look normal. Occasionally (after 25 weeks), the dilated proximal oesophageal pouch can be seen as an elongated upper mediastinal and retrocardiac anechoic structure. Usually, the diagnosis is not made in the second trimester and the condition is only suspected after 28 weeks, when polyhydramnios appears. The differential diagnosis for the combination of absent stomach and polyhydramnios includes intrathoracic compression, by conditions such as diaphragmatic hernia, and musculoskeletal anomalies causing inability of the fetus to swallow. Survival is primarily dependent on gestation at delivery and the presence of other anomalies. Thus, for babies with an isolated tracheo-oesophageal fistula born after 32 weeks, when an early diagnosis is made, avoiding reflux and aspiration pneumonitis, postoperative survival is more than 95%.
Prenatal diagnosis of fetal anomalies
the lower abdominal wall, in close association with the umbilical arteries. In cloacal exstrophy, the findings are similar to bladder exstrophy (large infraumbilical defect that extends to the pelvis) but a posterior anomalous component is present. Other findings include single umbilical artery, ascites, vertebral anomalies, clubfoot and ambiguous genitalia (in boys, the penis is divided and duplicated). With aggressive reconstructive bladder, bowel and genital surgery, survival is more than 80%. Bladder exstrophy is compatible with complete repair although in some cases permanent urinary tract diversion becomes necessary. Cloacal exstrophy is a much more severe disease involving the lower abdominal tract as well, that is associated with significant sequelae.
Duodenal Atresia At 5 weeks of embryonic life the lumen of the duodenum is obliterated by proliferating epithelium. The patency of the lumen is usually restored by the 11th week
187
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ and failure of vacuolization may lead to stenosis or atresia. Duodenal obstruction can also be caused by compression from the surrounding annular pancreas or by peritoneal fibrous bands. Duodenal atresia is found in about 1 per 5000 births. It is a sporadic abnormality, although in some cases there is an autosomal recessive pattern of inheritance. Approximately half of fetuses with duodenal atresia have associated abnormalities, including trisomy 21 (in about 40%) and skeletal defects (vertebral and rib anomalies, sacral agenesis, radial abnormalities and talipes), gastrointestinal abnormalities (oesophageal atresia/tracheo-oesophageal fistula, intestinal malrotation, Meckel diverticulum and anorectal atresia), cardiac and renal defects. Prenatal diagnosis is based on demonstration of the characteristic ‘double bubble’ appearance of the dilated stomach and proximal duodenum, commonly associated with polyhydramnios. However, obstruction due to a central web may result in only a ‘single bubble’ representing the fluid-filled stomach. Continuity of the duodenum with the stomach should be demonstrated to differentiate a distended duodenum from other cystic masses, including choledocal or hepatic cysts. It is usually not diagnosed until after 25 weeks, suggesting that the fetus is unable to swallow sufficient volume of amniotic fluid for bowel dilation to occur before the end of the second trimester of pregnancy. Survival after surgery in cases with isolated duodenal atresia is more than 95%.
Intestinal Obstruction
188
Intestinal obstructions occur in about 1 per 2000 births. In about half the cases there is small bowel obstruction and in the other half anorectal atresia. Small bowel obstruction may derive from primary atresia or stenosis of the bowel, meconium ileus and extrinsic constriction from adhesions. The most frequent site of small bowel obstruction is distal ileus, followed by proximal jejunum. In about 5% of cases obstructions occur in multiple sites. Intestinal obstruction is found in about 1 per 2000 births. Although the condition is usually sporadic, in multiple intestinal atresias, familial cases have been described. Associated abnormalities and chromosomal defects are rare. In contrast with anorectal atresia, associated defects such as genitourinary, vertebral, cardiovascular and gastrointestinal anomalies are found in about 80% of cases. Meconium ileus may be associated with cystic fibrosis. The lumen of the fetal small bowel and colon does not normally exceed 7 mm and 20 mm, respectively. Diagnosis of obstruction is usually made quite late in pregnancy (after 25 weeks), as dilation of the intestinal lumen is slow and progressive. Jejunal and ileal obstructions are imaged as multiple fluid-filled loops of bowel in the abdomen. The abdomen is usually distended and active peristalsis may be observed. If bowel perforation occurs, transient ascites, meconium peritonitis and meconium pseudocysts may ensue. Polyhydramnios (usually after 25 weeks) is common especially with proximal obstructions. Similar bowel appearances and polyhydramnios may be found in fetuses with Hirschsprung
✩✩✩✩✩✩✩✩✩✩✩ ✩
Echogenic Bowel
Prenatal diagnosis of fetal anomalies
disease, the megacystis-microcolon-intestinal hypoperistalsis syndrome and congenital chloride diarrhoea. The differential diagnosis of small bowel obstruction includes renal tract abnormalities and other intra-abdominal cysts such as mesenteric, ovarian or duplication cysts. An important clue specific for bowel obstruction is the presence of peristalsis. In anorectal atresia prenatal diagnosis is usually difficult because the proximal bowel may not demonstrate significant dilation and the amniotic fluid volume is usually normal; occasionally calcified intraluminal meconium in the fetal pelvis may be seen. The prognosis is related to the gestational age at delivery, the presence of associated abnormalities and the site of obstruction. Neonates born after 32 weeks with isolated obstruction requiring resection of only short segments of bowel, survival is more than 95%. Loss of large segments of bowel can lead to short gut syndrome, which is a lethal condition.
The fetal bowel has variable levels of echogenicity. However, when the echogeni city is equal or very similar to that of bone, the risk or associated conditions increases. Such conditions include most chromosomal anomalies, cystic fibrosis and intrauterine growth restriction. Intra-abdominal echogenic foci usually occur in the parenchyma or the capsule of the liver. The vast majority of cases are idiopathic but in a few cases hepatic calcifications have been found in association with congenital infections and chromosomal abnormalities. The prognosis depends on the presence of associated infection or chromosomal defects. Echogenic bowel and isolated foci are of no pathological significance by themselves.
Meconium Peritonitis Meconium peritonitis is found in about 1 in 3000 births. The main aetiology is intrauterine perforation of the bowel which may lead to a local sterile chemical peritonitis, with the development of a dense calcified mass of fibrous tissue sealing off the perforation. Bowel perforation usually occurs proximal to some form of obstruction, although this cannot always be demonstrated. Intestinal stenosis or atresia and meconium ileus account for 65% of cases. Other causes include volvulus and Meckel diverticulum. Meconium ileus is the impaction of abnormally thick and sticky meconium in the distal ileum, and in the majority of cases this is due to cystic fibrosis. The typical sonographic appearance of meconium peritonitis is that of ascites associated with bowel dilation and an area of increased echogenicity in the abdomen. Meconium ileus and hyperechogenic fetal bowel at 16–18 weeks' gestation may be present in 75% of fetuses with cystic fibrosis. The prevalence of cystic fibrosis in fetuses with prenatal diagnosis of intestinal obstruction may be about 10%. Therefore, when other causes of bowel hyperechogenicity have been excluded, DNA studies for cystic fibrosis should be considered. Meconium peritonitis is associated with more than 50% mortality in the neonatal period.
189
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Abdominal Cysts Intra-abdominal cysts are due to a variety of aetiologies and a specific diagnosis with ultrasound is frequently impossible. Cysts arising from the pelvis in female fetuses are most likely ovarian in origin. Cysts in the upper right quadrant of the abdomen may be either choledocal or hepatic cysts. Mesenteric or omental cysts and intestinal duplication are also possible. With fetal abdominal cysts the prognosis is usually good. In cases with rapidly growing cysts, particularly if associated with polyhydramnios, puncture and drainage should be considered.
Anomalies of the Kidneys and Urinary Tract Ultrasound diagnosis of fetal kidney and urinary tract anomalies has been established for many years and large data sets are now available on the impact of this diagnostic technique on fetal outcome.41,42
Renal Agenesis Bilateral renal agenesis is found in 1 per 5000 births, while unilateral disease is found in 1 per 2000 births. Renal agenesis is usually an isolated sporadic abnormality but in a few cases it may be secondary to a chromosomal abnormality or part of a genetic syndrome (such as Fraser syndrome) or a developmental defect (such as VACTERL association). In non-syndromic cases, the risk of recurrence is approximately 3%. However, in about 15% of cases one of the parents has unilateral renal agenesis and in these families the risk of recurrence is increased. Antenatally, the condition is suspected by the combination of anhydramnios and failure to visualize the fetal bladder (Fig. 10.7). Examination of the renal areas is often hampered by the oligohydramnios and the ‘crumpled’ position adopted by these fetuses and care should be taken to avoid the mistaken diagnosis of
190
Fig. 10.7 Renal anomalies demonstrated by a cross-section of the fetal abdomen. (A) There is severe oligohydramnios and the fetal kidneys cannot be visualized; this is bilateral renal agenesis. (B) Cystic enlargement of the renal pelvis and calyceal system; this is hydronephrosis. (C) Cluster of cysts with little interposed tissue replacing one kidney; this is multicystic kidney. (D) Oligohydramnios with enlarged hyperechogenic kidneys; this is autosomal recessive polycystic kidney.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
perirenal fat and large fetal adrenals for the absent kidneys. The differential diagnosis is preterm rupture of membranes, severe uteroplacental insufficiency and obstructive uropathy or bilateral multicystic or polycystic kidneys. Vaginal sonography with a high-frequency, high-resolution probe is useful in these cases. Failure to visualize the renal arteries with colour Doppler is another important clue to the diagnosis in dubious cases, both with bilateral and unilateral agenesis. Prenatal diagnosis of unilateral renal agenesis is difficult because there are no major features, such as anhydramnios and empty bladder, to alert the sonographer to the fact that one of the kidneys is absent. Bilateral renal agenesis is a lethal condition. The presence of amniotic fluid is necessary for the normal development of the lungs up to 22–24 weeks. Early severe oligohydramnios results typically in pulmonary hypoplasia and infants die in the neonatal period of respiratory insufficiency. The prognosis with unilateral agenesis is normal. Unilateral renal agenesis has been recognized in utero as early as the second trimester but the diagnosis is difficult. It has also been suggested that this condition may develop in late pregnancy or after birth, as a consequence of a vascular accident or due to involution of a dysplastic kidney.
Cystic Kidneys Four main categories of cystic dysplastic kidneys are recognized. Two types can be recognized with certainty with antenatal ultrasound: multicystic kidney and cystic dysplasia occurring as a consequence of early and long-standing obstructive uropathy. Multicystic kidneys (see Fig. 10.7) are usually unilateral and appear as a cluster of multiple irregular cysts of variable size with little intervening hyperechogenic stroma. In the majority of cases this is a sporadic abnormality but chromosomal abnormalities (mainly trisomy 18), genetic syndromes and other defects (mainly cardiac) are present in about 50% of cases. Isolated unilateral multicystic kidneys have a good prognosis.43 Early and persistent obstruction of the lower urinary tract is associated with secondary cystic dysplasia of the kidneys that appear hyperechogenic, increased in size and present small cysts spread in the parenchyma. In these cases the diagnosis is made by the simultaneous demonstration of obstructive uropathy (distended bladder, convoluted ureters, pyelectasia, oligohydramnios). The prognosis is poor. Autosomal recessive cystic kidneys (also referred to as infantile polycystic kidneys) are characterized by markedly enlarged kidneys filled with numerous cortical cysts and dilated collecting ducts. Sonographically, the kidneys are enlarged on both sides and hyperechogenic (see Fig. 10.7). These sonographic appearances may, however, be manifest only in late gestation. Prognosis is variable. Cases appearing early in gestation are associated with oligohydramnios since the second trimester and are usually lethal due to a combination of renal failure and pulmonary hypoplasia. In other cases, the onset of the disease occurs later in gestation or after birth and there is a variable progression towards renal failure. The infantile
191
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
192
and juvenile types result in chronic renal failure, hepatic fibrosis and portal hypertension; many survive into their teens and require renal transplantation. Autosomal dominant cystic kidneys, one of the most common genetic diseases, are usually asymptomatic until the third or fourth decade of life. Usually, sonography will not demonstrate abnormalities prior to the second or third decade. In a handful of cases, however, affected fetuses have demonstrated findings similar to the autosomal recessive variety: enlarged and echogenic kidneys. It is clear that this disease covers a wide spectrum. The experience with prenatal diagnosis is limited. It would not seem, however, that intrauterine presentation is necessarily associated with a poor prognosis. Cystic kidneys are also found with many mendelian disorders such as tuberous sclerosis, Jeune, Sturge–Weber, Zellweger, Lawrence–Moon–Biedl and Meckel– Gruber syndromes.
Urinary Tract Enlargement Urinary tract enlargement occurs, usually albeit not exclusively, as the consequence of obstruction. When the obstruction is complete and occurs early in fetal life, cystic renal dysplasia ensues. On the other hand, where intermittent obstruction allows for normal renal development or when it occurs in the second half of pregnancy, hydronephrosis will result and the severity of the renal damage will depend on the degree and duration of the obstruction. Different entities with variable findings and clinical implications exist depending upon the location and severity of the dilation.44 Hydronephrosis refers to dilation of the renal pelvis (see Fig. 10.7). Mild hydronephrosis or pyelectasia is defined by the presence of an anteroposterior diameter of the pelvis of >4 mm at 20–29 weeks and >9 mm at 30–40 weeks, and/or dilation of the renal calyces. Transient hydronephrosis may be due to relaxation of smooth muscle of the urinary tract by the high levels of circulating maternal hormones, or maternal/fetal overhydration. In the majority of cases the condition remains stable or resolves in the neonatal period. In about 20% of cases there may be an underlying pathology that requires postnatal follow-up and possible surgery. Those cases in which the anteroposterior pelvic diameter is <10 mm at 30 weeks or beyond have a very low risk of a renal anomaly, and at present no follow-up is suggested. An anteroposterior pelvic diameter of more than 10 mm is almost invariably associated with calyceal dilation, is usually progressive and in about 30% of cases requires surgery during the first 2 years of life. Detailed postnatal follow-up is therefore certainly recommended in these cases. Sonographically, it may be difficult at times to distinguish severe hydronephrosis with significant calyceal enlargement from multicystic kidney. A scan oriented along the coronal plane of the kidney is required to demonstrate the radial projection of the calyces around the enlarged pelvis. Sections oriented in different planes may create the false impression of multiple cysts separated by parenchymal tissue that are typical of multicystic kidney. Hydronephrosis is usually the consequence of either ureteropelvic junction obstruction or vesicoureteric reflux.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
These are sporadic conditions and although in some cases there is an anatomical cause, in most instances the underlying cause is thought to be functional. In 80% of cases, the condition is unilateral. Associated anomalies are very rarely found, although a slightly increased risk of chromosomal aberrations has been suggested. Independently from the degree or progression of hydronephrosis, the prognosis is generally good. The presence of a normal amount of amniotic fluid is reassuring with regard to renal function and no modification of standard obstetric care is required. Hydroureteronephrosis is the combination of hydronephrosis and enlarged ureter. Of course, these findings are generally present with megacystis. However, the following discussion refers to hydroureteronephrosis with a normal bladder, which may result from either ureterovesical reflux or ureterovesical junction obstruction. Under normal conditions, the small ureter cannot be visualized with antenatal ultrasound. The dilated ureter appears as a tortuous fluid-filled tubular structure interposed between the renal pelvis, which is variably dilated, and the bladder. Very rarely, a primary megaureter will be present, with a normal renal pelvis. The outcome and management principles are similar to those outlined for hydronephrosis. Megacystis is defined as an abnormal enlargement of the urinary bladder and is most frequently the consequence of urethral obstruction. Typically, it is seen in the early midtrimester and has been visualized as early as 11 weeks' gestation. The bladder is usually greatly enlarged, occupying most of the abdomen and distending it. Urethral obstruction can be caused by urethral agenesis, persistence of the cloaca, urethral stricture or posterior urethral valves. Posterior urethral valves occur only in males and are the commonest cause of bladder outlet obstruction. The condition is sporadic and is found in about 1 in 3000 male fetuses. With posterior urethral valves, there is usually incomplete or intermittent obstruction of the urethra, resulting in an enlarged and hypertrophied bladder with varying degrees of hydroureters, hydronephrosis, a spectrum of renal hypoplasia and dysplasia, oligohydramnios and pulmonary hypoplasia. In some cases, there is associated urinary ascites from rupture of the bladder or transudation of urine into the peritoneal cavity. When megacystis is found in association with either normal or increased amounts of amniotic fluid, the possibility of megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS) should be considered. This is a sporadic abnormality characterized by a massively dilated bladder and hydronephrosis in the presence of normal or increased amniotic fluid; the fetuses are usually female. There is associated shortening and dilation of the proximal small bowel and microcolon with absent or ineffective peristalsis. The condition is usually lethal due to bowel and renal dysfunction. The outcome of urethral obstruction depends upon how severe and early this occurs. Complete persistent obstruction occurring in the early midtrimester (e.g. urethral atresia, early posterior urethral valves) results in massive distension of the bladder and abdominal wall (prune-belly abdomen), severe oligohydramnios, dysplastic kidneys and pulmonary hypoplasia. Obstruction occurring in late
193
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ gestation may be associated with oligohydramnios and hydronephrosis, but does not result in pulmonary hypoplasia and dysplastic kidneys. Management of earlyappearing megacystis is debated. Shunting the fetal bladder is feasible, although there is not conclusive evidence that such intervention improves renal or pulmonary function beyond what can be achieved by postnatal surgery. Antenatal evaluation of renal function relies on a combination of ultrasonographic findings and analysis of fetal urine obtained by puncture of the bladder or renal pelvis. An attempt to assess the severity of renal compromise should, however, be done before embarking upon fetal therapy. Poor prognostic signs are the presence of bilateral multicystic or severely hydronephrotic kidneys with echogenic kidneys, suggestive of renal dysplasia, anhydramnios implying complete urethral obstruction, and high urinary sodium, calcium and β2-microglobulin levels. In these cases, there is little chance of the infant surviving. Conversely, potential candidates for intrauterine surgery are fetuses with bilateral moderately severe pelvicalyceal dilation and normal cortical echogenicity, severe megacystis and oligohydramnios, and normal levels of urinary sodium, calcium and β2-microglobulin.
Skeletal Anomalies
194
Skeletal dysplasia is found in about 1 per 4000 births; about 25% of affected fetuses are stillborn and about 30% die in the neonatal period. The existing nomenclature for skeletal dysplasias is complicated. There is a wide range of rare skeletal dyplasias, each with a specific recurrence risk, dysmorphic expression and implications for neonatal survival and quality of life. Our knowledge of the in utero expression of these syndromes is based on a few case reports and, therefore, in attempting to perform prenatal diagnosis of individual conditions in at-risk families, extrapolation of findings from the perinatal period is often necessary. The incidental discovery of a skeletal dysplasia on routine ultrasound screening in a pregnancy not known to be at risk of a specific syndrome necessitates a systematic examination to arrive at the correct diagnosis. All limbs must be evaluated as to their length, shape, mineralization and movement, and associated abnormalities in other systems, particularly the head, thorax and spine, should be sought. Rather frequently, sonography will not allow a specific diagnosis, given the complexity of findings, the rarity of the conditions and the frequently overlapping features. Radiography may be utilized but its value is limited in antenatal studies. The specific gene defect has been identified for many anomalies, and DNA analysis is now available for many anomalies. Wherever available, genetic tests should be offered to couples at risk either because of a previous affected child or because of abnormal sonographic findings. The interested reader is referred to specific textbooks for a detailed discussion on the antenatal diagnosis of fetal skeletal dysplasias. We present here a brief description of the most frequent anomalies. Thanatophoric dysplasia is the most common skeletal dysplasia with a birth prevalence of about 1 in 10,000. It is invariably lethal (the term derives from the Greek, meaning death bearing). The characteristic features are severe shortening
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
of the limbs, narrow thorax and large head with prominent forehead. The trunk has a normal trunk length. In type I, which is sporadic, the femurs are curved (‘telephone receiver’) and in type II, which is autosomal recessive, the femurs are straight and the skull is cloverleaf shaped. Usually, it is not a problem to diagnose thanatophoric dysplasia early in gestation, because the length of the femur will fall well below normal limits as early as 15 weeks. Genetic analysis is, however, available for a specific diagnosis. Achondroplasia is the second most common skeletal dysplasia encountered at birth (1 in 26,000 births). It has autosomal dominant transmission but the majority of cases represent new mutations. The characteristic features of heterozygous achondroplasia include short limbs, lumbar lordosis, short hands and fingers, macrocephaly with frontal bossing and depressed nasal bridge. Intelligence and life expectancy are normal. Prenatally, limb shortening usually becomes apparent only after 22 weeks of gestation. In the homozygous state, which is a lethal condition, short limbs are associated with a narrow thorax. Achondroplasia is due to a specific mutation within the fibroblast growth factor receptor type 3 gene (FGFR3) and can now be diagnosed by DNA analysis of fetal blood or amniotic fluid obtained in cases of suspicious sonographic findings. In cases where both parents have achondroplasia there is a 25% chance that the fetus is affected by the lethal type and the diagnosis can be made by first-trimester chorionic villous sampling. Achondrogenesis is a lethal skeletal dysplasia with a birth prevalence of about 1 in 40,000. The characteristic features are severe shortening of the limbs, narrow thorax and large head. Compared with thanatophoric dysplasia, the trunk is much shorter. Many classifications of achondrogenesis have been proposed but the one most commonly used recognizes two main types. In achondrogenesis type I, which is autosomal recessive, there is poor mineralization of the skull and vertebral bodies as well as rib fractures. In type II, which is sporadic (new autosomal dominant mutations), there is hypomineralization of the vertebral bodies but normal mineralization of the skull, and there are no rib fractures. In type I the femurs are extremely shortened, while in type II this occurs to a variable degree. Osteogenesis imperfecta is a genetically heterogeneous group of disorders presenting with fragility of bones, blue sclerae, loose joints and growth deficiency. There are four clinical subtypes. Prenatal diagnosis is certainly possible only for type II, a lethal disorder with a birth prevalence of about 1 in 60,000. Most cases represent new dominant mutations (recurrence is about 6%). Sonographically there is early prenatal onset of severe bone shortening and bowing due to multiple fractures affecting all long bones and ribs, and poor mineralization of the skull. Type III is a progressively deforming condition characterized by multiple fractures, usually present at birth, resulting in scoliosis and very short stature. Both autosomal dominant and recessive modes of inheritance have been reported. Prenatal diagnosis has been reported by the demonstration of either fracture or bowing of long bones, femur and tibia in particular. Type I and type II usually are asymptomatic at birth and cannot be recognized by antenatal ultrasound.
195
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
196
A group of skeletal dysplasias with autosomal recessive transmission is characterized by a narrow thorax and polydactyly. The prenatal findings and postnatal outcome are similar. Asphyxiating thoracic dysplasia (Jeune syndrome) is an autosomal recessive condition with a birth prevalence of about 1 in 70,000. The characteristic features are narrow chest and rhizomelic limb shortening. There is a variable phenotypical expression and consequently the prognosis varies from neonatal death, due to pulmonary hypoplasia, to normal survival. Limb shortening is mild to moderate and this may not become apparent until after 24 weeks of gestation. Chondroectodermal dysplasia (Ellis–Van Creveld syndrome) is a rare, autosomal recessive condition characterized by acromelic and mesomelic shortness of limbs, postaxial polydactyly, small chest, ectodermal dysplasia, and congenital heart defects in more than 50% of cases. Short limb polydactyly syndromes are a group of lethal disorders characterized by short limbs, narrow thorax and postaxial polydactyly. Associated anomalies are frequently found, including congenital heart disease, polycystic kidneys and intestinal atresia. Four different types have been recognized. Type I (Saldino–Noonan) has narrow metaphyses; type II (Majewski) has cleft lip and palate and disproportionally shortened tibiae; type III (Naumoff) has wide metaphyses with spurs; type IV (Beemer– Langer) is characterized by median cleft lip, small chest with extremely short ribs, protuberant abdomen with umbilical hernia and ambiguous genitalia in some 46,XY individuals. Absence of an extremity or a segment of an extremity is referred to as limb deficiency or congenital amputation. The prevalence of limb reduction deformities is about 1 per 20,000 births. In about 50% of cases there are simple transverse reduction deficiencies of one forearm or hand without associated anomalies. In the other 50% there are multiple amputations and there may be additional anomalies of the internal organs or craniofacial structures. In general, an isolated limb deficiency of the upper extremity is an isolated anomaly, whereas congenital amputation of the leg or bilateral amputations or reductions of all limbs are usually part of a genetic syndrome. Isolated amputation of an extremity can be due to amniotic band syndrome, exposure to a teratogen or a vascular accident. There is an association between chorionic villus sampling before 10 weeks of gestation and transverse limb defects. Fetal akinesia deformation sequence is a heterogeneous group of conditions with a birth prevalence of about 1 in 3000. Neurological, muscular, connective tissue and skeletal abnormalities result in multiple joint contractures, including bilateral talipes and fixed flexion or extension deformities of the hips, knees, elbows and wrists. This sequence includes congenital lethal arthrogryposis, multiple pterygium and Pena–Shokeir syndromes. The deformities are usually symmetrical and in most cases all four limbs are involved. The severity of the deformities increases distally in the involved limb, with the hands and feet typically being the most severely affected. The condition is commonly associated with polyhydramnios (usually after 25 weeks), narrow chest, micrognathia and nuchal oedema (or increased nuchal translucency at 10–14 weeks). The diagnosis is made by demonstrating absence of fetal movements, contractures and polyhydramnios.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fetal Tumours Prenatal diagnosis of fetal anomalies
Fetal tumours are rare but they have important implications for the health of both the fetus and the mother. The natural history and prognosis of most fetal tumours is well known. Once a fetal tumour has been detected, close surveillance by a multidisciplinary team of doctors is mandatory, with anticipation and early recognition of problems during pregnancy, labour and immediate postnatal life. When the sonographic diagnosis is uncertain, fetal tissue biopsy may be necessary to obtain a histological diagnosis. In rare cases, intrauterine treatment may be possible. Some fetal tumours may be malignant and could metastasize to other fetal organs and the placenta; maternal metastases in such cases are unknown. In contrast, on rare occasions maternal malignancies (melanoma, leukaemia and breast cancer) can metastasize to the placenta; in about half of such cases, mostly with malignant melanoma, the tumour can metastasize to fetal viscera. Intracranial tumours include a variety of conditions. The most frequent entity is intracranial teratoma, which usually is diagnosed only in the third trimester and is indicated by macrocrania, a complex (partly cystic, partly solid) intracranial lesion with a mass effect, distorting intracranial anatomy and occasionally the face. Prognosis depends on a number of factors, including the histological type and the size and location of the lesion. Large tumours are usually fatal. Epignathus is a very rare teratoma arising from the oral cavity or pharynx. Prenatal diagnosis is suggested by the demonstration of a solid mass arising from the oral cavity. Calcifications and cystic components may also be present. Polyhydramnios (due to pharyngeal compression) is usually present. A careful examination of the brain is important because the tumour may grow intracranially. The outlook depends on the size of the lesion and the involvement of vital structures. Lesions detected antenatally have been very large. Polyhydramnios has been associated with poor prognosis. The major cause of neonatal death is asphyxia due to airway obstruction. Surgical resection and normal postoperative course are possible. Cervical teratoma appears on ultrasound as a well-demarcated, partly solid and cystic or multiloculated mass, arising from the anterior neck of the fetus and typically causing severe hyperextension of the fetal head. Polyhydramnios due to oesophageal obstruction is frequent. The prognosis is very poor and the intrauterine or neonatal mortality (due to airway obstruction) is about 80%. Survival after surgery is more than 80% but since these tumours tend to be large, extensive neck dissection and multiple additional procedures are necessary to achieve complete resection of the tumour with acceptable functional and cosmetic results. Primary hepatic tumours include haemangioma, mesenchymal hamartoma, hepatoblastoma and adenoma. They have similar sonographic features: either a defined lesion (cystic or solid) is present or hepatomegaly exists. Calcifications may appear and both oligohydramnios and polyhydramnios have been observed. Colour and pulsed Doppler may reveal in these cases increased and aberrant vascular supply to the lesion. Haemangiomas are histologically benign and regress spontaneously after infancy. However, occasionally, they are associated with arteriovenous shunting, congestive heart failure and hydrops, resulting in intrauterine or neonatal death.
197
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Neuroblastoma is one of the most common tumours of infancy and is found in about 1 per 20,000 births. It arises from undifferentiated neural tissue of the adrenal medulla or sympathetic ganglia in the abdomen, thorax, pelvis or head and neck. Usually, the lesion is isolated but occasional metastasis before birth may occur. Sonographically, the tumour appears as a cystic, solid or complex mass in the region of the adrenal gland (directly above the level of the kidney and under the diaphragm). Occasionally, calcifications are present. The differential diagnosis includes adrenal haemorrhage and subdiaphragmatic lung sequestration. The prognosis is excellent if the diagnosis is made in utero or in the first year of life (survival more than 90%), but for those diagnosed after the first year survival is less than 20%. Mesoblastic nephroma (renal hamartoma) is the most frequent renal tumour, while Wilms tumour (nephroblastoma) is extremely rare. The sonographic picture in both tumours is of a solitary mass replacing the normal architecture of the kidney, and in most cases there is associated polyhydramnios. Cystic areas may appear in both tumours. Mesoblastic nephromas are benign and nephrectomy is curative in the majority of cases. Wilms tumour is a genetically heterogeneous group of malignant tumours and up to 60% of affected cases are associated with genetic syndromes (such as Beckwith–Wiedeman syndrome). Treatment of the tumour requires surgery, chemotherapy and sometimes radiotherapy. Sacrococcygeal teratoma is the most frequent fetal tumour, occurring in about 1 per 40,000 births. It appears on ultrasound as a solid, complex or fluid-filled lesion that protrudes to a variable degree from the perineal area. The main clue to the diagnosis is the relationship of the mass to the anterior sacrum. Distinguishing a teratoma with predominant abdominal development from another tumour may, however, be difficult. Most teratomas are extremely vascular, which is easily shown using colour Doppler ultrasound. The tumours may be entirely external, partly internal and partly external or mainly internal. Polyhydramnios is frequent and this may be due to direct transudation into the amniotic fluid and to fetal polyuria, secondary to the hyperdynamic circulation, which is the consequence of arteriovenous shunting. Similarly, high-output heart failure leading to hepatomegaly, placentomegaly and hydrops fetalis can occur. Sacrococcygeal teratoma is associated with a high perinatal mortality (about 50%), mainly due to the preterm delivery (the consequence of polyhydramnios) of a hydropic infant requiring major neonatal surgery. Difficult surgery, especially with tumours that extend in the pelvis and abdomen, can result in nerve injury and incompetence. The tumour is almost invariably benign in the neonatal period but delayed surgery or incomplete excision can result in malignant transformation (about 10% before 2 months of age to about 80% by 4 months).
Hydrops Fetalis
198
Hydrops is defined by abnormal accumulation of serous fluid in skin (oedema) and body cavities (pericardial, pleural or ascitic effusions). It is found in about 1 per 2000 births. Hydrops is a non-specific finding in a wide variety of fetal and maternal disorders, including haematological, chromosomal, cardiovascular,
✩✩✩✩✩✩✩✩✩✩✩ ✩
Prenatal diagnosis of fetal anomalies
renal, pulmonary, gastrointestinal, hepatic and metabolic abnormalities, congenital infection, neoplasms and malformations of the placenta or umbilical cord. Hydrops is classically divided into immune (due to maternal haemolytic antibodies) and non-immune (due to all other aetiologies). With the widespread introduction of immunoprophylaxis and the successful treatment of rhesus disease by fetal blood transfusions, non-immune causes have become responsible for at least 75% of cases and make a greater contribution to perinatal mortality. While in many instances the underlying cause may be determined by maternal antibody and infection screening, fetal ultrasound scanning, including echocardiography and Doppler studies, and fetal blood sampling, quite often the abnormality remains unexplained even after expert postmortem examination. Although isolated ascites, in both fetuses and neonates, may be transitory, the spontaneous resolution of hydrops has not been reported and the overall mortality for this condition is about 80%. Fetal therapy is possible with some aetiologies. Immune hydrops can be successfully treated by blood transfusions to the fetus. Such treatment often results in reversal of hydrops and the survival rate is about 80%. Fetal therapy can also successfully reverse some types of non-immune hydrops, such as fetal tachy arrhythmias (by transplacental or direct fetal administration of antiarrhythmic drugs), pleural effusions (by pleuroamniotic shunting), urinary ascites (by vesico amniotic or peritoneo-amniotic shunting), parvovirus B19 infection or severe fetomaternal haemorrhage (by fetal blood transfusions), diaphragmatic hernia, cystic adenomatoid malformation of the lungs and sacrococcygeal teratoma (by open fetal surgery), and the recipient fetus in twin-to-twin transfusion syndrome (by endoscopic laser coagulation of the communicating placental vessels).
Chromosomal Defects Ultrasound Findings with Chromosomal Aberrations The commonest chromosomal defects are trisomies 21, 18 or 13, Turner syndrome (45X), 47,XXX, 47,XXY, 47,XYY and triploidy. In the first trimester, a common feature of many chromosomal defects is increased nuchal translucency thickness at 11–14 weeks. In later pregnancy each chromosomal defect has its own syndromic pattern of abnormalities. Trisomy 21 is associated with a tendency to brachycephaly, hypoplastic nasal bone, mild ventriculomegaly, flattening of the face, nuchal oedema, atrioventricular septal defects, duodenal atresia and echogenic bowel, mild hydronephrosis, shortening of the limbs, sandal gap and clinodactyly or midphalanx hypoplasia of the fifth finger. Trisomy 18 is associated with strawberry-shaped head, choroid plexus cysts, absent corpus callosum, enlarged cisterna magna, facial cleft, micrognathia, nuchal oedema, heart defects, diaphragmatic hernia, oesophageal atresia, exomphalos, renal defects, myelomeningocele, growth retardation and shortening of the limbs, radial aplasia, overlapping fingers and talipes or rocker bottom feet.
199
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ In trisomy 13 common defects include holoprosencephaly and associated facial abnormalities, microcephaly, cardiac and renal abnormalities (often enlarged and echogenic kidneys), exomphalos and postaxial polydactyly. Triploidy, in which the extra set of chromosomes is paternally derived, is associated with a molar placenta and the pregnancy rarely persists beyond 20 weeks. When there is a double maternal chromosome contribution, the pregnancy may persist into the third trimester. The placenta is of normal consistency and the fetus demonstrates severe asymmetrical growth retardation. Commonly there is mild ventriculomegaly, micrognathia, cardiac abnormalities, myelomeningocele, syndactyly and ‘hitch-hiker’ toe deformity. There are two types of Turner syndrome: lethal and non-lethal. The rate of intrauterine lethality between 12 and 40 weeks is about 75%. The lethal type of Turner syndrome presents with large nuchal cystic hygroma, generalized oedema, mild pleural effusions and ascites, and cardiac abnormalities. The non-lethal type usually does not demonstrate any ultrasonographic abnormalities. The main sex chromosome abnormalities, other than Turner syndrome, are 47,XXX, 47,XXY and 47,XYY. These are not associated with an increased prevalence of sonographically detectable defects. Table 10.1 shows the common chromosomal abnormalities in the presence of various sonographically detected defects.
Table 10.1 Common chromosomal abnormalities in fetuses with sonographic defects Trisomy 21
Trisomy 18
Trisomy 13
Triploidy
Turner
Strawberry-shaped head
−
+
−
−
−
Brachycephaly
+
+
+
−
+
Microcephaly
−
−
+
−
+
Ventriculomegaly
+
+
−
+
−
Holoprosencephaly
−
−
+
−
−
Choroid plexus cysts
+
+
−
−
−
Absent corpus callosum
−
+
−
−
−
Posterior fossa cyst
+
+
+
−
−
Enlarged cisterna magna
+
+
+
−
−
Facial cleft
−
+
+
−
−
Micrognathia
−
+
−
+
−
Nuchal oedema
+
+
+
−
−
Cystic hygromata
−
−
−
−
+
Diaphragmatic hernia
−
+
+
−
−
Cardiac abnormality
+
+
+
+
+
Skull/brain
Face/neck
Chest
200
✩✩✩✩✩✩✩✩✩✩✩ ✩
Abdomen −
+
+
−
−
Duodenal atresia
+
−
−
−
−
Collapsed stomach
+
+
−
−
−
Mild hydronephrosis
+
+
+
−
+
Other renal abnormalities
+
+
+
+
−
Hydrops
+
−
−
−
+
Small for gestational age
−
+
−
+
+
Relatively short femur
+
+
−
+
+
Other
Clinodactyly
+
−
−
−
−
Overlapping fingers
−
+
−
−
−
Polydactyly
−
−
+
−
−
Syndactyly
−
−
−
+
−
Talipes
−
+
+
+
−
Prenatal diagnosis of fetal anomalies
Exomphalos
Ultrasound studies have demonstrated that major chromosomal defects are often associated with multiple fetal abnormalities. The overall risk for chromosomal defects increases with the total number of abnormalities that are identified. It is therefore recommended that when an abnormality/marker is detected at routine ultrasound examination, a thorough check is made for the other features of the chromosomal defect(s) known to be associated with that marker; should additional abnormalities be identified, the risk is dramatically increased.
Individual Risk Assessment of Chromosomal Aberrations by the use of Midtrimester Ultrasound It is commonly accepted that in the second trimester ultrasound does not provide a specific diagnosis of chromosomal aberrations, and has in general a low sensitivity in pregnancies at low risk. However, a detailed assessment of fetal anatomy may offer at times important clues. Documentation of abnormal findings may lead to the offer of karyotyping to an otherwise low-risk patient. Conversely, a negative sonogram may lower the a priori high risk of a patient, thus avoiding the need for invasive testing. Both issues are debated at present and there is no general consensus. In general, if the midtrimester scan demonstrates major defects it is advisable to offer fetal karyotyping even if these defects are apparently isolated. The prevalence of these defects is low and therefore the cost implications are small. If the defects are either lethal or they are associated with severe handicap, fetal karyotyping constitutes one of a series of investigations to determine the possible cause
201
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
202
and therefore the risk of recurrence. Examples of these defects include hydrocephalus, holoprosencephaly, multicystic renal dysplasia and severe hydrops. In the case of isolated neural tube defects there is controversy as to whether the risk for chromosomal defects is increased. Similarly, for skeletal dysplasias where the likely diagnosis is obvious by ultrasonography, it would probably be unnecessary to perform karyotyping. If the defect is potentially correctable by intrauterine or postnatal surgery, it may be logical to exclude an underlying chromosomal abnormality, especially because for many of these conditions the usual abnormality is trisomy 18 or 13. Examples include facial cleft, diaphragmatic hernia, oesophageal atresia, exomphalos and many of the cardiac defects. In the case of isolated gastroschisis or small bowel obstruction, there is no evidence of increased risk of trisomies. Recently, the association of fetal chromosomal aberrations with fetal variants of normal anatomy that do not represent clear-cut malformations, also referred to as soft markers (e.g. hypoplastic nasal bone, choroid plexus cysts, thick nuchal fold, mild hydronephrosis, short femur), has been reported in many studies. Establishing a general policy with regard to this finding is impossible at present. Reports from different institutions demonstrate large differences in the frequency of such findings and in the incidence of associated chromosomal defects. It is therefore uncertain whether in such cases karyotyping should be undertaken, especially for those abnormalities that have a high prevalence in the general population and for which the prognosis in the absence of a chromosomal defect is good. Since the incidence of chromosomal defects is associated with maternal age, it is possible that the wide range of results reported in the various studies is the mere consequence of differences in the maternal age distribution of the populations examined. In addition, since chromosomal abnormalities are associated with a high rate of intrauterine death, differences may arise from the fact that studies were undertaken at different stages of pregnancy. The risk for trisomies increases with maternal age and decreases with gestation; the rate of intrauterine lethality between 12 and 40 weeks is about 30% for trisomy 21, and 80% for trisomies 18 and 13 (Table 10.2). Turner syndrome is usually due to loss of the paternal X chromosome and consequently the frequency of conception of 45,X embryos, unlike that of trisomies, is unrelated to maternal age. The prevalence is about 1 per 1500 at 12 weeks, 1 per 3000 at 20 weeks and 1 per 4000 at 40 weeks. For the other sex chromosome abnormalities (47,XXX, 47,XXY and 47,XYY) there is no significant change with maternal age and since the rate of intrauterine lethality is not higher than in chromosomally normal fetuses the overall prevalence (about 1 per 500) does not decrease with gestation. Polyploidy affects about 2% of recognized conceptions but it is highly lethal and is very rarely observed in live births; the prevalence at 12 and 20 weeks is about 1 per 2000 and 1 per 250,000 respectively. The available experience suggests that screening for trisomy 21 and other chromosomal aberrations with nuchal translucency measurement and biochemistry at 11–14 weeks is accurate. Second-trimester biochemistry is equally feasible
✩✩✩✩✩✩✩✩✩✩✩ ✩
Trisomy 21 Maternal age (yrs)
Trisomy 18
20 weeks
40 weeks
20 weeks
40 weeks
20
1/1295
1/1527
1/4897
25
1/1147
1/1352
1/4336
30
1/759
1/895
31
1/658
1/776
32
1/559
33 34
Trisomy 13 20 weeks
40 weeks
1/18013
1/14656
1/42,423
1/15951
1/12978
1/137,567
1/2869
1/10554
1/8587
1/24,856
1/2490
1/9160
1/7453
1/21,573
1/659
1/2490
1/7775
1/6326
1/18,311
1/464
1/547
1/1755
1/6458
1/5254
1/15,209
1/378
1/446
1/1429
1/5256
1/4277
1/12,380
35
1/302
1/356
1/1142
1/4202
1/3419
1/9876
36
1/238
1/280
1/899
1/3307
1/2691
1/7788
37
1/185
1/218
1/698
1/2569
1/2090
1/6050
38
1/142
1/167
1/537
1/1974
1/1606
1/4650
39
1/108
1/128
1/409
1/1505
1/1224
1/3544
40
1/82
1/97
1/310
1/1139
1/927
1/2683
41
1/62
1/73
1/233
1/858
1/698
1/2020
42
1/46
1/55
1/175
1/644
1/524
1/1516
43
1/35
1/41
1/131
1/481
−
−
Prenatal diagnosis of fetal anomalies
Table 10.2 Risk of autosomal trisomies in relation to maternal age and gestation (data derived from Snijders RJM et al. Ultrasound Obstet Gynecol 1999;13:167–170 and Snijders RJM et al. Fetal Diagn Ther 1995;10:356–367)
although less accurate. There are much less solid data for the use of second-trimester soft markers. However, if a decision is made to use soft markers to modify the individual risk of chromosomal anomalies for a given patient, the best approach would be to multiply the background (maternal age- and gestation-related) risk (see Table 10.2) by a factor depending on the specific defect. For the following conditions there are sufficient data in the literature to estimate the risk factors. Absent or hypoplastic nasal bone (<2.5 mm) This may be the most significant marker of trisomy 21; it is found in less than 1% of euploid Caucasian fetuses and in 60% of trisomy 21 fetuses, resulting in about a 50-fold increase of the baseline risk. This finding is less valuable in AfroCaribbean fetuses as it is identified in about 8% of normal fetuses. Nuchal oedema or fold more than 6 mm This is the second-trimester form of nuchal translucency. It is found in about 0.5% of fetuses and may be of no pathological significance. However, it is sometimes associated with chromosomal defects, cardiac anomalies, infection or genetic syndromes. For isolated nuchal oedema the risk for trisomy 21 may be 10 times the background.
203
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Hyperechogenic bowel This is found in about 0.5% of fetuses and is usually of no pathological significance. The commonest cause is intra-amniotic bleeding but occasionally it may be a marker of cystic fibrosis or chromosomal defects. For isolated hyperechogenic bowel the risk for trisomy 21 may be seven times the background. Short femur If the femur is below the fifth centile and all other measurements are normal, the baby is likely to be normal but rather short. Rarely this is a sign of dwarfism. Occasionally it may be a marker of chromosomal defects. On the basis of existing studies, short femur is found four times as commonly in trisomy 21 fetuses compared to normal fetuses. However, there is some evidence that isolated short femur may not be more common in trisomic than normal fetuses. Echogenic foci in the heart These are found in about 4% of pregnancies and they are usually of no pathological significance. However, they are sometimes associated with cardiac defects and chromosomal abnormalities. For isolated hyperechogenic foci the risk for trisomy 21 may be three times the background. Choroid plexus cysts These are found in about 1–2% of pregnancies and they are usually of no pathological significance. When other defects are present there is a high risk of chromosomal defects, usually trisomy 18 but occasionally trisomy 21. For isolated choroid plexus cysts the risk for trisomy 18 and trisomy 21 is 1.5 times the background. Mild hydronephrosis This is found in about 1–2% of pregnancies and is usually of no pathological significance. When other abnormalities are present there is a high risk of chromosomal defects, usually trisomy 21. For isolated mild hydronephrosis the risk for trisomy 21 is 1.5 times the background.
Accuracy of Ultrasound in the Detection of Fetal Anomalies
204
In the 1980s, there were great expectations that the systematic use of ultrasound would allow recognition of most fetal anomalies. In most European countries, an obstetric sonogram at midgestation rapidly became the standard of care. However, the results of the available studies18–27 demonstrate great national and regional variations (Table 10.3). The disappointing sensitivities of some studies were probably the consequence of inadequate expertise of the operators and it is reassuring to note a progressive improvement throughout the years. Most of the studies published in the late 1990s described sensitivities in excess of 50%. A word of caution is, however, necessary. Some of the series with the best results had an unusually low prevalence of anomalies at birth, in the region of 1%. These low
✩✩✩✩✩✩✩✩✩✩✩ ✩ Table 10.3 Studies documenting the results of routine obstetric ultrasound for the detection of fetal anomalies
Cases
Sensitivity
Specificity
Anomalies detected per 1000 pregnancies
Rosendahl 198925
9012
1.03
0.39
0.999
4
Saari-Kemppainen 199023
4691
0.43
0.47
0.998
2
Chitty 199119
8785
1.5
0.74
0.999
11
15,654
2.3
0.21
1.00
4
Shirley 199226
6412
1.4
0.60
0.999
8
Luck 1992
8844
1.9
0.85
0.999
16
Ewigmann
7617
2.46
0.17
9392
2.45
0.41
0.999
9
33,376
2.17
0.55
0.995
11
1.4
0.81
0.999
8
Levi 1992 22
Levi 1995
21
Boyd 199818 Whitlow 199927
6443
−
4
figures may be the consequence of incomplete postnatal ascertainment, which of course would lead to overestimation of the real sensitivity of antenatal studies. At the time of writing, the accuracy of ultrasound in detecting fetal anomalies remains a subject of debate in the literature. Fetal ultrasound is clearly the combination of sophisticated technology and skilled medical craftsmanship, strictly intertwined. The ability to detect fetal anatomical defects depends largely upon the operator's skills and expertise. It is clear that despite the quality of instrumentation and the ability of the operator, a reasonable proportion of fetal anomalies will be missed. The remarkable results of pilot studies performed in referral centres are largely due to the selection of patients. Such studies include large numbers of pregnancies in which either a fetal anomaly had been previously suspected during a basic scan or there was a family history of anomalies amenable to ultrasound diagnosis. Independently from the expertise of the operator or the equipment used, some fetal anomalies will not be detectable in utero or in early gestation due to either late development or limitations of current ultrasound technology. Examples of the former group of lesions include persistence of the fetal circulation, disruptions (porencephaly, migrational disorders), tumours, intestinal obstructions, urinary tract dilation and many types of skeletal dysplasias. Examples of the latter group include ventricular and atrial septal defects. Given the heterogeneity of congenital anomalies, in many cases it remains difficult to establish whether a specific condition can be recognized in early gestation or not. Indeed, even within the same centre indicated sonograms result in a much greater sensitivity than screening examination performed on low-risk patients.28 One important problem that is surfacing and that needs to be addressed when establishing a program of ultrasound screening in pregnancy is the issue of the so-called soft markers. This term is commonly employed to define an ultrasound
Prenatal diagnosis of fetal anomalies
Study
Prevalence of anomalies at birth (%)
205
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ finding that is not abnormal per se but increases the likelihood of a fetal anomaly, most frequently a chromosomal aberration. An increased nuchal fold or a choroid plexus cyst represents a typical example. The surveys on the systematic use of ultrasound in pregnant patients in the 1980s and early 1990s were at variance in the sensitivity, but luckily specificity was invariably high in all studies, no matter the type of population scanned or the ultrasonographic expertise of those performing the examinations. False positives occurred in less than 1 case in 1000 patients. It was reassuring to know that although anomalies could be missed, they were very rarely overdiagnosed. While a false-negative diagnosis may leave the family with the emotional, medical, social and economic burdens imposed by a child born with a congenital anomaly, false-positive diagnoses may be ominous as well since they may lead to termination of a normal fetus. In one recent study, soft markers were responsible for a false-positive rate greater than 1 in 200.18 Although it is debatable whether a soft marker should be considered a false positive or more simply a risk factor for further investigation, there is no doubt that they can cause a great deal of parental anxiety. The available experience on soft markers is conflicting. Different researchers have reported different results, many different markers have been described, and some of them have subjective definitions (e.g. hyperechogenic bowel). A review of the literature suggested that the use of soft markers in low-risk patients allows detection of some fetal anomalies, but at the same time results in severe anxiety for a number of couples and increases the number of invasive tests.29 In the study previously quoted, soft markers increased the sensitivity of the midtrimester sonogram from 51% to 55% but at the same time they increased 12-fold the false-positive rate, from 1 in 2332 to 1 in 188.18 At present there is a lack of consensus on whether soft markers should be employed in low-risk patients, and if so, which soft markers should be used and how the patients should be counselled.30 As this is likely to become one of the most critical issues in the future of obstetric ultrasound, every ultrasound laboratory should establish its own policy. The most important variables to consider in establishing such a policy include the expectations of the population that is undergoing the ultrasound examination, the experience of the operators, the availability of other screening programmes such as nuchal translucency at 11–14 weeks’ scan and maternal biochemistry that has been demonstrated to be more reproducible.
Conclusion
206
A careful ultrasound examination of the midtrimester fetus, performed with current ultrasound technology by an expert examiner, allows the detection of many anomalies, probably in the range of 50% of those that can be identified at birth. The systematic use of a well-defined set of qualitative as well as quantitative parameters is critical for the good result of the examination. Some areas of fetal anatomy remain difficult to evaluate, the most remarkable example being the heart. It is expected that advances in the technology of diagnostic ultrasound, better training and increasing awareness of the operators will further improve the current standards.
✩✩✩✩✩✩✩✩✩✩✩ ✩
References 1. Romero R, Pilu G, Jeanty P, Ghidini A, Hobbins JC. Prenatal diagnosis of congenital anomalies. Appleton and Lange, Norwalk, CT, 1988 2. Nyberg D, Mahony BS, Pretorius D. Diagnostic ultrasound of fetal anomalies: text and atlas. Year Book Medical Publishers, Chicago, 1990 3. Pilu G, Nicolaides KH. Diagnosis of fetal abnormalities. The 18–23 week scan. Parthenon Publishing, London, 1999 4. Nyberg D, McGahan J, Pretorius D, Pilu G. Diagnostic ultrasound of fetal anomalies. Lippincott, Williams and Wilkins, Philadelphia, 2001 5. Kalter H, Warkany J. Medical progress. Congenital malformations: etiologic factors and their role in prevention (first of two parts). N Engl J Med 1983;308:24–31 6. Kalter H, Warkany J. Congenital malformations (second of two parts). N Engl J Med 1983;308:91–97 7. Leck I. Fetal malformations. In: Barron SL, Thomson AM (eds) Obstetrical epidemiology. Academic Press, London, 1983: 263–318 8. CDC. Achievements in public health, 1900–1999: healthier mothers and babies. MMWR 1999;48(38):849–857 9. CDC. Contribution of birth defects to infant mortality – United States, 1986. MMWR 1989;38:633 10. Anderson RN, Kochanek KD, Murphy SL. Report of the final mortality statistics, 1995. US Department of Health and Human Services, CDC, National Center for Health Statistics, Hyattsville, MD, 1997 11. Ventura SJ, Martin JA, Curtin SC, Mathews TJ. Report of final natality statistics, 1995. US Department of Health and Human Services, CDC, National Center for Health Statistics, Hyattsville, MD, 1997 12. National Center for Health Statistics. Vital statistics of the United States, 1968, vol II, mortality, part A. US Department of Health, Education and Welfare, Public Health Service, CDC, Rockville, MD, 1972 13. Filly RA, Cardoza JD, Goldstein RB, Barkovich AJ. Detection of fetal central nervous system anomalies: a practical level of effort for a routine sonogram. Radiology 1989;172(2):403–408
14. Copel JA, Pilu G, Green J, Hobbins JC, Kleinman CS. Fetal echocardiographic screening for congenital heart disease: the importance of the four-chamber view. Am J Obstet Gynecol 1987;157(3):648–655 15. Buskens E, Grobbee DE, Frohn-Mulder IM et al. Efficacy of routine fetal ultrasound screening for congenital heart disease in normal pregnancy. Circulation 1996;94(1):67–72 16. Tegnander E, Williams W, Johansen OJ, Blaas HJ, Eik-Nes SH. Prenatal detection of heart defects in a non-selected population of 30,149 fetuses – detection rates and outcome. Ultrasound Obstet Gynecol 2006;27:252–265 17. Allan L, Benacerraf B, Copel JA et al. Isolated major congenital heart disease. Ultrasound Obstet Gynecol 2001;17(5):370–379 18. Boyd PA, Chamberlain P, Hicks NR. 6-year experience of prenatal diagnosis in an unselected population in Oxford, UK. Lancet 1998;352(9140):1577–1581 19. Chitty LS, Hunt GH, Moore J, Lobb MO. Effectiveness of routine ultrasonography in detecting fetal structural abnormalities in a low risk population. BMJ 1991;303(6811):1165–1169 20. Levi S, Hyjazi Y, Schaaps JP, Deffoort P, Coulon R, Bueckens P. Sensitivity and specificity of routine antenatal screening for congenital anomalies by ultrasound: the Belgian Multicentric Study. Ultrasound Obstet Gynecol 1991;1(2):102–110 21. Levi S, Schaaps JP, De Havay P, Coulon R, Defoort P. End-result of routine ultrasound screening for congenital anomalies: the Belgian Multicentric Study 1984–92. Ultrasound Obstet Gynecol 1995;5(6): 366–371 22. Luck CA. Value of routine ultrasound scanning at 19 weeks: a four year study of 8849 deliveries. BMJ 1992;304(6840):1474–1478 23. Saari-Kemppainen A, Karjalainen O, Ylostalo P, Heinonen OP. Ultrasound screening and perinatal mortality: controlled trial of systematic one-stage screening in pregnancy. The Helsinki Ultrasound Trial. Lancet 1990;336(8712):387–391
Prenatal diagnosis of fetal anomalies
Note Further images relating to this chapter are found on the CD accompanying this book.
207
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
208
24. Saari-Kemppainen A, Karjalainen O, Ylostalo P, Heinonen OP. Fetal anomalies in a controlled one-stage ultrasound screening trial. A report from the Helsinki Ultrasound Trial. J Perinat Med 1994;22(4):279–289 25. Rosendahl H, Kivenen S. Antenatal detection of congenital malformations by routine ultrasonography. Obstet Gynecol 1989;73(6):947–951 26. Shirley IM, Bottomley F, Robinson VP. Routine radiographer screening for fetal abnormalities by ultrasound in an unselected low risk population. Br J Radiol 1992;65(775):564–569 27. Whitlow BJ, Chatzipapas IK, Lazanakis ML, Kadir RA, Economides DL. The value of sonography in early pregnancy for the detection of fetal abnormalities in an unselected population. Br J Obstet Gynaecol 1999;106(9):929–936 28. Van Dorsten JP, Hulsey TC, Newman RB, Menard MK. Fetal anomaly detection by second-trimester ultrasonography in a tertiary center. Am J Obstet Gynecol 1998;178(4):742–749 29. Smith-Bindman R, Hosmer W, Feldstein VA, Deeks JJ, Goldberg JD. Secondtrimester ultrasound to detect fetuses with Down syndrome: a meta-analysis. JAMA 2001;285(8):1044–1055 30. MacLachlan N, Iskaros J, Chitty L. Ultrasound markers of fetal chromosomal abnormality: a survey of policies and practices in UK maternity ultrasound departments. Ultrasound Obstet Gynecol 2000;15(5):387–390 31. Whitby EH, Paley MN, Sprigg A et al. Comparison of ultrasound and magnetic resonance imaging in 100 singleton pregnancies with suspected brain abnormalities. Br J Obstet Gynaecol 2004;111:784–792 32. Von Koch CS, Glenn OA, Goldstein RB, Barkorich AJ. Fetal magnetic resonance imaging enhances detection of spinal cord anomalies in patients with sonographically detected bony anomalies of the spine. J Ultrasound Med 2005;24:781–789 33. Goldstein I, Copel JA, Makhoul IR. Mild cerebral ventriculomegaly in foetuses: characteristicts and outcome. Fetal Diagn Ther 2005;20:281–284
34. Gaglioti P, Danelon D, Bontempo S et al. Fetal cerebral ventriculomegaly: outcome in 176 cases. Ultrasound Obstet Gynecol 2005;25:372–377 35. Bernier FP, Crawford SG, Dewey D. Developmental outcome of children who had choroid plexus cysts detected prenatally. Prenat Diagn 2005;25:322–326 36. Pajkrt E, Weisz B, Firth HV, Chitty LS. Fetal cardiac anomalies and genetic syndromes. Prenat Diagn 2004;24:1104–1115 37. Allan L, Benacerraf B, Cope L JA et al. Isolated major congenital heart disease. Ultrasound Obstet Gynecol 2001;17:370–379 38. Mohan UR, Kleinman CS, Kern JH. Fetal echocardiography and its evolving impact 1992 to 2002. Am J Cardiol 2005;96: 134–136 39. Sharland G. Routine fetal cardiac screening: what are we doing and what should we do? Prenal Diagn 2004;24:1123–1129 40. Goncalves LF, Lee W, Chaiworaponga T et al. Four-dimensional ultrasonography of the fetal heart with spatiotemporal image correlation. Am J Obstet Gynecol 2003;189:1792–1802 41. Wiesel A, Queisser-Luft A, Clementi M, Bianca S, Stoll C, Euroscan Study Group. Prenatal detection of congenital renal malformations by fetal ultrasonographic examination: an analysis of 709,030 births in 12 European countries. Eur J Med Gen 2005;48:131–144 42. Damen-Elias HA, De Jong TP, Stigter RH, Visser GH, Stoutenback PH. Congenital renal tract anomalies: outcome and follow up of 402 cases detected antenatal between 1986 and 2001. Ultrasound Obstet Gynecol 2005;25:134–143 43. Van Eijk L, Cohen-Overbeek TE, den Hollander NS, Nijman JM, Wladimiroff JW. Unilateral multicystic kidney: a combined pre- and postnatal assessment ultrasound. Obstet Gynecol 2002;19:180–183 44. Cohen-Overbeek TE, Wijngaard-Boom P, Ursem NT, Hop WC, Wladimiroff JM, Wolffenbuttel KP. Mild renal pyelectasis in the second trimester: determination of cutoff levels for postnatal referral ultrasound. Obstet Gynecol 2005;25:375–383
11 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Evaluation of fetal and uteroplacental blood flow Annegret Geipel Ulrich Gembruch
ABSTRACT Doppler application in modern obstetric practice has been expanded widely. Flow velocity waveforms of maternal and fetal vessels provide important diagnostic and prognostic information with respect to a variety of pregnancy complications. Impaired placentation, as depicted by uterine Doppler sonography, is associated with an increased risk for the development of pre-eclampsia and/or growth restriction. Doppler information of fetal systemic vessels helps the obstetrician in managing pregnancies complicated by intrauterine growth restriction. Longitudinal observations of fetal Doppler changes in growth-restricted fetuses demonstrate progressive deterioration of umbilical artery blood flow, followed by middle cerebral artery velocimetry and finally ductus venosus blood flow. Doppler signal characteristics aid in the decision on when to time the delivery. Further, the rate and degree of deteriorating Doppler signals are closely related to the risks for adverse perinatal outcome. The Doppler assessment of middle cerebral artery peak systolic velocity is increasingly used in the surveillance of fetuses at risk for anaemia, thus avoiding the need for invasive procedures. Doppler is also an invaluable contributor in managing pregnancies complicated by heart disease or twin–twin transfusion syndrome.
Keywords Ductus venosus, fetal anaemia, fetal Doppler, fetal growth restriction, middle cerebral artery, pre-eclampsia, twin–twin transfusion syndrome, umbilical artery, uteroplacental blood flow, venous Doppler.
Introduction Doppler ultrasound assessment of the placental and fetal circulations plays an important role in modern antenatal care. Uterine Doppler investigation is a
209
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ screening tool for impaired placentation and its complications of pre-eclampsia, fetal growth restriction and placental abruption. Doppler ultrasonography of fetal vessels (umbilical artery, middle cerebral artery, ductus venosus) helps in the diagnosis and management of a wide range of pathological conditions, such as fetal growth restriction (FGR), fetal anaemia, twin–twin transfusion syndrome (TTTS) and fetal cardiac disease. Table 11.1 summarizes important topics of Doppler application in pregnancy. As illustrated there, fetomaternal Doppler evaluation is part of first- and second-trimester screening programmes in low- and highrisk pregnancies, the latter defined by history and by diagnosis of anatomical or growth abnormalities in these examinations. In clinical practice, arterial flow velocity waveforms are quantified by the use of indices. The advantage of indices compared to absolute velocities is that they
Table 11.1 Indications for Doppler application in pregnancy Indication
Gestational age
Vessel
Parameter
Detailed first trimester screening – advanced maternal age – increased nuchal translucency
12–14 weeks
DV
a-wave (positive/ negative)
History of – pre-eclampsia/PIH/ placental abruption – IUFD/ severe FGR
18–22 weeks
uterine artery
notching, PI/RI
Maternal vascular disease – lupus erythematodes/ antiphospholipid/ antibodies/thrombophilia – hypertension – diabetes mellitus
18–22 weeks
uterine artery
notching, PI/RI
Abnormal fetal growth – small for dates/FGR – proved FGR
2nd/3rd trimester
uterine artery UA (1st), MCA (2nd) UA, MCA, DV
notching, PI/RI PI/RI PI/RI, PVIV/PIV
Risk of fetal anaemia 2nd/3rd trimester – red cell alloimmunization – parvovirus infection
MCA
PSV
Twin pregnancy – discordant growth – TTTS/TRAP sequence
2nd/3rd trimester
uterine artery UA (1st), MCA (2nd) UA, MCA, DV
notching, PI/RI PI/RI PI/RI, MCA PSV, PVIV/PIV
Fetal abnormality – cardiac disease/ arrhythmia – fetal hydrops
2nd/3rd trimester
UA, MCA, DV fetal echocardiography
PI/RI, MCA PSV, PVIV/PIV
DV, ductus venosus; FGR, fetal growth restriction; IUFD, intrauterine fetal death; MCA, middle cerebral artery; PIH, pregnancy-induced hypertension, PI, pulsatility index; PIV, pulsatility index for veins; PSV, peak systolic velocity, PVIV, peak velocity index for veins, RI, resistance index; TRAP, twin reversed arterial perfusion; TTTS, twin–twin transfusion syndrome; UA, umbilical artery.
210
✩✩✩✩✩✩✩✩✩✩✩ ✩
• pulsatility index (PI) • resistance index (RI) • S/D ratio. The calculation of these indices is demonstrated in Figure 11.1. The use of the PI has the advantage of a wider spectrum of values in cases with no end-diastolic flow component. In addition to the various indices, blood flow can be categorized according to a particular waveform pattern, such as the presence or absence of an end-diastolic component or of an end-diastolic notch. In general, a low-pulsatility waveform represents a low distal resistance (e.g. normal uterine artery Doppler) and
A Arterial Doppler (umbilical artery) Pulsatility Index (PI) PI =
S−D TAMX
PI =
30 − 9 = 1.2 17
RI =
30 − 9 = 0.7 30
Evaluation of fetal and uteroplacental blood flow
are angle independent. For the assessment of true velocities, an angle of insonation close to 0 ° is desired, as otherwise with increasing angle the blood velocity is progressively underestimated or increasingly incorrect if the function of angle correction is used. Commonly used downstream indices that represent mainly the impedance of the distal vascular bed are:
Resistance Index (RI) RI =
S−D S
Systolic/ Diastolic Ratio S/ D Ratio =
S D
S/ D =
30 = 3.3 9
B Venous Doppler (ductus venosus)
Peak Velocity Index for Veins (PVIV) PVIV =
S−A D
PVIV =
65 − 34 = 0.49 63
Pulsatility Index for Veins (PIV) PIV =
S−A TAMX
PIV =
65 − 34 = 0.59 52
Figure 11.1 Calculation of commonly used Doppler indices. (A) Arterial Doppler (umbilical artery). (B) Venous Doppler (ductus venosus).
211
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
212
a high-pulsatility waveform indicates high peripheral resistance (e.g. normal middle cerebral Doppler). Impedance to flow of the ductus venosus, the venae cavae or the hepatic veins can be calculated by the following indices (see Fig. 11.1):
• pulsatility index for veins (PIV) • peak velocity index for veins (PVIV). Uterine Artery Doppler The impedance to flow in the uterine arteries decreases with advancing gestation in normal pregnancies, reflecting the trophoblastic invasion of the spiral arteries. This process is complete by about 18 weeks' gestation. In pregnancies with impaired placentation, high uterine vascular resistance will persist after this time (Fig. 11.2). Uterine Doppler screening is commonly performed around 20 weeks of gestation, as a part of the fetal anomaly scan.39 A transabdominal or transvaginal approach is possible. Colour Doppler assists in the quick visualization of the uterine artery at its crossing with the external iliac artery. Pulsed-wave Doppler is used to obtain 3–5 similar consecutive waveforms from both sides. The waveform can be analysed by calculating indices (PI, RI) or by assessing the presence or absence of an end-diastolic notch. Impedance of the uterine artery on the placental side is usually lower. In most studies, the mean indices from both vessels are calculated. Cut-off values at 23 weeks' gestation are a mean PI above 1.5–1.61,38 or a mean RI above 0.57–0.58. 17,28 The persistence of bilateral notches after 24 weeks' gestation also represents high uterine resistance and is considered abnormal. Bilateral notches are found in about 25–30% of pregnancies at 12 weeks, 10–15% at 20 weeks and 5% at 24 weeks. Notch quantification has been suggested, but is rarely used in daily clinical practice. In the case of a laterally located placenta, blood flow on the placental side is more important. While a notch on the non-placental side is of reduced significance, the presence of an ipsilateral notch is of high importance. Over the last 25 years a number of Doppler studies on the uteroplacental perfusion have demonstrated that high impedance to flow in the second trimester is associated with a higher risk of pre-eclampsia, FGR or placental abruption. The optimum gestational age for uterine screening studies is considered to be 20– 24 weeks of gestation, providing the best sensitivity/specificity trade-off. Increased impedance to flow in the uterine arteries will identify about 40–50% of the pregnancies that will subsequently develop pre-eclampsia and approximately 30% of those that will develop FGR. More importantly, abnormal uterine Doppler waveforms perform better in predicting severe, early-onset complications. The sensitivity of uterine Doppler screening for pre-eclampsia and FGR requiring delivery before 34 weeks' gestation is about 80% and 60–70%, respectively (Table 11.2). Another important finding of those studies is the high negative predictive value of 98–99% for pre-eclampsia and 93–95% for FGR. This finding might aid in stratifying a more risk-orientated antenatal care approach. Women with normal uterine Doppler findings are unlikely to develop early pre-eclampsia or FGR and
✩✩✩✩✩✩✩✩✩✩✩ ✩
Evaluation of fetal and uteroplacental blood flow
Figure 11.2 Uterine artery Doppler. (A) Normal impedance to flow at 22 weeks' gestation. (B) Increased impedance to flow with end-diastolic notching at 24 weeks.
213
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Table 11.2 Sensitivity of second-trimester uterine artery Doppler screening studies in predicting pre-eclampsia and FGR Sensitivity Total study group Study
Abnormal test result
Delivery <34 weeks
Screen +
Pre-eclampsia
FGR <10th cent.
Preec FGR lampsia <10th cent
Harrington et al 199623
Bilateral notch (19–21 weeks)
9.1%
55%
22%
81%
58%
Albaiges et al 20001
PI 1.45 (23 weeks)
5.1%
35%
21%
80%
70%
Papageorghiou et al 200138
PI 1.63 (23 weeks)
5.1 %
41%
16%
81%
64%
therefore do not need serial monitoring as suggested for those with abnormal Doppler results.1,23,28,39 The combination of uterine artery Doppler studies with maternal history and biochemical markers, such as plasma-protein A, inhibin-A, vascular endothelial growth factor or soluble fms-like tyrosine kinase 1 may further increase the accuracy of risk assessment.2,40,41,46 A significant negative correlation exists between birthweight and first-trimester uterine Doppler flow patterns. The value of first-trimester uterine artery Doppler as a prognostic screening tool, either in isolation or in conjunction with maternal biochemistry, remains to be determined.27 In women with increased uterine artery impedance to flow at 20–24 weeks, follow-up is recommended at 26–28 weeks. If the uterine artery resistance has normalized at this time, the patient will receive regular antenatal care. However, even if late normalization occurs, birthweight is significantly lower compared to those with normal uterine artery Doppler at 20 weeks.13 If high uterine resistance or notching maintains, 3–4-week monitoring intervals are advised. Increased uterine artery vascular impedance in third-trimester pregnancies is associated with a higher risk for developing fetal distress and the need for delivery by caesarean section.30,44
Umbilical Artery Doppler
214
The umbilical artery was the first vessel studied by obstetric Doppler examination. Flow velocity waveforms from the umbilical artery represent the downstream or placental resistance to flow. Umbilical artery resistance decreases progressively throughout gestation, reflecting the increase and dilation in villous vascularization. In normal pregnancies, end-diastolic blood flow is usually seen in almost all fetuses from 14 weeks of gestation onwards. Absent or reduced end-diastolic blood flow in the mid-second or third trimester may be related to incorrect measurement techniques, by too large insonation angle, use of too high high-pass
✩✩✩✩✩✩✩✩✩✩✩ ✩
Evaluation of fetal and uteroplacental blood flow
filter setting, low transducer frequency, and marked fetal breathing movements. The location of the Doppler sampling site along the umbilical cord also affects the Doppler waveform, as resistance progressively declines from the fetal to the placental end of the cord. Significant reduction of the villous exchange area due to decreased numbers and maldevelopment of peripheral villi results in increased fetoplacental resistance, causing a reduction of umbilical artery end-diastolic flow. Local intraplacental stem vessel vasoconstriction and a low cardiac output are additional mechanisms that may contribute to increased umbilical artery pulsatility. In the small-for-date fetus, umbilical artery Doppler distinguishes between the fetus with true growth restriction due to uteroplacental dysfunction and the fetus that is just constitutionally small. The combination of FGR and increased umbilical artery resistance should also warrant detailed anatomical examination, as some of these fetuses will have associated malformations and/or aneuploidy. The latter is especially true for fetuses with distinct FGR and increased amount of amniotic fluid in the late second and third trimester and/or structural anomalies and/or normal uterine Doppler flow velocity waveforms. Doppler velocimetry of the umbilical artery has been the subject of multiple clinical studies, but results have been inconsistent due to heterogeneity in methodologies and studied populations. A meta-analysis of 11 studies involving nearly 7000 women reported an improvement in obstetric care in selected high-risk pregnancies, characterized by suspected impaired fetal growth and/or pre-eclampsia.35 Compared to pregnancies with no Doppler ultrasound evaluation, the use of Doppler surveillance resulted in fewer admissions to hospital (odds ratio 0.56, 95% CI 0.43–0.72) and fewer inductions of labour (odds ratio 0.83, 95% CI 0.74–0.93). A promising trend towards reduction in perinatal death was also noted (odds ratio 0.71, 95% CI 0.5–1.0). No difference was found for intrapartum fetal distress and caesarean delivery. A separate analysis of umbilical Doppler in low-risk patients concluded that there was no evidence for any benefit.35 In terms of monitoring pregnancies with FGR, reduction of umbilical artery end-diastolic flow is an early sign of fetal impairment. FGR pathologies are known to follow an abnormal pulsatility in the umbilical artery by many weeks at an early gestational age.9 Progressively decreasing umbilical artery end-diastolic blood flow in early growth restriction should alert the obstetrician to the need for appropriate referral, administration of steroids and detailed maternal evaluation to exclude associated maternal pathology. The differentiation of fetal well-being in cases with increased umbilical resistance requires intensified monitoring, using additional Doppler information from systemic vessels (middle cerebral artery, ductus venosus) and the biophysical profile.22 Progressive increase in placental blood flow resistance is mirrored by worsened umbilical artery Doppler waveforms, as absent end-diastolic flow (AEDF) or even reversed end-diastolic flow (REDF) (Fig. 11.3). REDF represents the extreme end of the whole spectrum and the majority of fetuses will have an estimated weight below the 10th percentile. If this flow pattern occurs,
215
216
Ultrasound in obstetrics and gynaecology
D
C
E
Figure 11.3 (A) Umbilical artery: reversed end-diastolic blood flow in a second-trimester growth-restricted fetus. (B) Severe fetal growth restriction at 27 weeks of gestation; absent end-diastolic umbilical artery blood flow. (C) Brain-sparing effect. (D) Increased ductus venosus pulsatility. (E) Tricuspid regurgitation.
✩ ✩✩✩✩✩✩✩✩✩✩✩
B
A
✩✩✩✩✩✩✩✩✩✩✩ ✩
Evaluation of fetal and uteroplacental blood flow
a significant number of fetuses will additionally have abnormal flow waveforms in the cerebral and venous circulation. Fetuses with AEDF or REDF constitute a group with increased perinatal mortality and a high risk for developing fetal distress in labour, with lower Apgar scores and blood gases. In a multicentre study involving high-risk patients, perinatal mortality in fetuses with AEDF and REDF compared to fetuses with positive end-diastolic flow was increased 4.0-fold and 10.6-fold, respectively.29 The majority of those fetuses were delivered by caesarean section with variable prematurity and the possible consequences thereof, such as respiratory distress, intraventricular haemorrhage, necrotizing enterocolitis and subsequently prolonged stay at the neonatal intensive care unit.5,8,37 However, in recent years a number of research groups have noticed that the umbilical artery is not the ultimate determinant of adverse outcome, especially not in the early and most severe forms of FGR. Doppler changes of the cerebral and venous circulation are more predictive for fetal outcome.6,8,12,16,25 Therefore, preterm delivery based on results of umbilical artery Doppler alone seems no longer appropriate. Growth restriction in the third-trimester fetus might present differently. Many fetuses with mild restriction will maintain normal or only slightly altered umbilical blood flow.30,44 Therefore, increased umbilical artery resistance identifies the fetus at risk, but a normal umbilical Doppler does not necessarily exclude the fetus from being at risk. For this group of fetuses, Doppler evaluation of the middle cerebral and uterine arteries will provide more valuable information. When both vessels have normal waveforms, the chances of distress are small.30,44
Middle Cerebral Artery Doppler To perform Doppler studies of the middle cerebral artery (MCA), a transverse view of the fetal brain at the level of the biparietal diameter is obtained. The transducer is then moved towards the base of the fetal skull. By colour Doppler imaging, the circle of Willis is easily visualized. The MCA is a short vessel, running along the sphenoid wing in an anterolateral direction. The sampling site is the internal third of the vessel with a preferred insonation angle of less than 10°. To measure peak systolic velocities (PSV), the image of the circle of Willis should be enlarged to 50% of the screen. Measurement is repeated at least three times, the highest PSV being recorded. Because of its favourable course, measurements taken from this vessel are highly reproducible when performed by experienced sonographers. Impedance to flow decreases and maximum blood velocity increases with advancing gestation. Close to term, increased end-diastolic blood flow is recognized in a certain number of fetuses, without being associated with fetal compromise. Fetal head compression should be generally avoided as it can artificially lead to decreased diastolic flow in the MCA. In clinical practice, there are two major applications for Doppler studies of the MCA. The first is the monitoring of IUGR fetuses, especially those with increased impedance to flow in the umbilical artery. The second is to evaluate peak systolic flow in fetuses at risk for anaemia.
217
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
MCA in Fetal Growth Restriction As a consequence of progressing placental insufficiency, the growth-restricted fetus shifts its blood flow towards the vital organs, namely the brain, the heart and the adrenal glands. The increase in blood supply for the brain is called brain sparing and this redistribution can be assessed by MCA Doppler sonography. In fetuses with brain-sparing effect, hypoxia-induced cerebrovascular dilation increases end-diastolic blood flow and therefore the impedance decreases (see Fig 11.3B). This is in contrast to fetuses with normal growth pattern, where the resistance of the MCA is usually higher than in the umbilical artery. Within a certain range, changes in the impedance in peripheral arterial vascular beds represent intact autoregulation and normal hormonal and vegetatively mediated vascular response important for nutrition supply, fetal activities, continued growth and normal pH.6 In FGR fetuses delivered before 32 weeks of gestation, Hecher et al reported progressively abnormal MCA PI towards delivery. However, in fetuses delivered after 32 weeks of gestation, a trend towards normalization of MCA resistance was seen. This finding was thought to be attributed to the physiological decrease in cerebrovascular resistance with advancing gestational age. Fetal heart rate (FHR) abnormalities were preceded by approximately 3 weeks by the occurrence of abnormal MCA velocity.25 Improved prediction of outcome in small for gestational age fetuses by incorporating cerebral Doppler findings, including the cerebroplacental ratio (CPR), was noted by Bahado-Singh et al. 3 The CPR has the potential advantage of summarizing information regarding redistribution of blood flow of two different vascular beds. Both, increasing placental resistance as well as decreasing cerebral vascular resistance might affect the ratio, therefore fetal response to placental insufficiency might be detected earlier. MCA Doppler is a useful tool to monitor the third-trimester growthrestricted fetus, as redistribution may occur in the presence of normal umbilical Doppler. Abnormal middle cerebral Doppler findings are associated with an increased risk of caesarean section delivery and need for neonatal admission.26,44 The information conveyed by MCA Doppler investigation of the preterm growth-restricted fetus allows further specification of clinical management. While maintenance of normal MCA values is suggestive of fetal circulatory compensation, decreasing MCA resistance indicates the need for tertiary fetal monitoring, including venous Doppler studies and biophysical profile scoring.22 When growth restriction becomes terminal, cardiac output might no longer be sufficient to support optimal blood flow to the brain and other vital organs throughout the entire cardiac cycle. The concomitant drop in the diastolic portion of the flow signal may then result in so-called ‘pseudo-normalization’ of MCA flow, which represents an ominous sign.47
MCA in Fetal Anaemia 218
The use of MCA PSV is nowadays the standard of care in tertiary referral centres in managing pregnancies at risk for fetal anaemia.32 The discovery of a negative correlation
✩✩✩✩✩✩✩✩✩✩✩ ✩
MCA-PSV (cm/s)
15 17 19 21 23 25 27 29 31 33 35 37 39 Gestational age (weeks)
Figure 11.4 Peak velocity of systolic blood flow in the middle cerebral artery (MCA) with advancing gestation. The curves indicate the median (below) and 1.5 multiples of the median (MoM) (above) peak systolic velocity (PSV) in the MCA. (Reprinted from G. Mari et al. N Engl J Med 2000;342:9–14, with permission. Copyright © 2000 Massachusetts Medical Society.)
between fetal haemoglobin and MCA PSV has led to a more than 70% reduction in the need for invasive tests, such as amniocentesis or cordocentesis. Normative data have been published by the group of Mari et al (Fig. 11.4). In this study, all fetuses with moderate or severe anaemia had peak systolic values above 1.5 times the median.31 A prospective multicentre study on an intention to treat basis confirmed MCA PSV as an accurate method of monitoring pregnancies complicated by red cell antibodies. The overall sensitivity to detect moderate to severe anaemia below 35 weeks was 88% and the negative predictive value was 98%. This study also demonstrated that the false-positive rate increases following 35 weeks' gestation.51 A recent comprehensive multicentre study by Oepkes et al in which MCA PSV and amniocentesis were performed prior to cordocentesis reported that MCA PSV is superior to amniocentesis in detecting fetal anaemia in red cell alloimmunization cases and can be safely used for the timing of cordocentesis and/or intrauterine transfusion.36 Intrauterine transfusion is associated with a significant decrease in the MCA PSV, which is proportional to the increase in fetal haematocrit (Fig. 11.5). Measurement of MCA PSV is also applicable in monitoring cases of Kell alloimmunization, parvovirus infection, fetomaternal haemorrhage or TTTS. Understandably, MCA PSV serves as a major diagnostic tool in the differential diagnosis of fetal hydrops.
Evaluation of fetal and uteroplacental blood flow
120 110 100 90 80 70 60 50 40 30 20 10
Ductus Venosus The ductus venosus connects the intra-abdominal portion of the umbilical vein with the inferior vena cava at its inlet to the right atrium. The shunt plays a critical role in the delivery of well-oxygenated blood predominantly towards the left side of the fetal heart and thus to the coronary and cerebral circulation. The small vessel can be visualized by the use of colour Doppler imaging in either a midsagittal longitudinal section or a transverse view through the upper abdomen. Due to the narrow diameter of the ductus venosus, colour Doppler indicates the presence of characteristically higher flow velocities compared to other praecordial veins, and with a low Nyquist limit this produces an aliasing effect that aids its identification. The preferred sample site is the inlet, where the highest velocities are recorded.
219
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Figure 11.5 Middle cerebral artery Doppler. (A) Fetal anaemia secondary to red blood cell alloimmunization prior to intrauterine transfusion at 30 weeks, Hb 8.2 g/dL. (B) The same fetus on day 1 after intrauterine transfusion (50 mL of packed erythrocytes); Hb 13.6 g/dL.
220
The typical waveform of the ductus venosus is triphasic, reflecting the pressure differences between the venous system and the heart throughout the cardiac cycle. Blood flow velocities are highest during ventricular systole (S). Early diastole (D) represents the second peak of forward flow. The nadir is seen with atrial contraction (a-wave) in late diastole (see Fig. 11.1). In contrast to the inferior vena cava and the hepatic veins, with absence or reversal of flow during atrial contraction, blood flow in the ductus venosus is usually forward in physiological conditions. In the first trimester (11–14 weeks), a negative a-wave may be recorded in about 3% of normal fetuses. The absolute blood flow velocities increase, whereas the pulsatility (PIV, PVIV) decreases with advancing gestation, reflecting decreasing cardiac afterload and maturation of diastolic ventricular function. Reference ranges have been established in the past.24 Pathological conditions which may alter ductus venosus flow pattern include myocardial failure, increase in cardiac afterload or increase in cardiac preload. When right atrial and central venous pressure increases progressively, decreasing velocity during atrial contraction results, escalating to reversal of flow during a-wave in most severe fetal compromise (see Fig. 11.3; Fig. 11.6). In growth-restricted fetuses, abnormal ductus venosus flows are frequently associated with fetal acidaemia and the highest perinatal mortality compared to those where flow abnormalities are confined to the umbilical or middle
A
B
C
D
E
F
✩✩✩✩✩✩✩✩✩✩✩ ✩
Figure 11.6 Ductus venosus blood flow in fetal disease. Ductus venosus in a fetus with Uhls anomaly: progressing cardiac dysfunction due to right ventricular failure at 28 weeks (A) and 31 weeks (B). Recipient in TTTS: marked cardiomegaly and AV valve regurgitation (C), increased ductus venosus pulsatility (D). Cardiomegaly in Ebstein anomaly (E) and corresponding ductus venosus flow profile with reduced forward flow during systole (F).
Evaluation of fetal and uteroplacental blood flow
221
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Table 11.3 Outcome parameters in fetal growth restriction (n=328) according to Doppler assessment
222
UA abnormal only (n=109)
MCA abnormal (n=87)
DV abnormal (n=132)
pH <7.20
15.4%
21.0%
39.4%*
5 min Apgar score <7
4.7%
1.2%
11.4%*
Intrauterine death
1.8%
2.3%
15.2%*
Neonatal death
2.9%
4.9%
16.5%*
Perinatal mortality
4.6%
6.9%
28.8%*
DV, ductus venosus; MCA, middle cerebral artery; UA, umbilical artery. * p<0.05 compared to fetuses with abnormal umbilical artery only and to fetuses with brain sparing. Data from reference 8.
cerebral artery (Table 11.3).5,6,8,12,16,25 In fetal growth restriction <32 weeks of gestation, progressive increase in ductus venosus pulsatility was accompanied by a mirror-like decrease of short time variation of the fetal heart rate pattern and both became abnormal on average only a few days before delivery.12,25 Similar observations have been made for the biophysical scoring index and venous Doppler signal deterioration; these two parameters were the last to drop.6 A recent review by Baschat summarized eight studies which evaluated relationships between venous Doppler parameters and various perinatal outcomes. In fetuses with normal venous Doppler studies, neonatal deaths accounted for most of the perinatal mortality, while in fetuses with elevated venous Doppler indices, stillbirth and neonatal mortality were equal contributors to an overall increased perinatal mortality. With the exception of necrotizing enterocolitis, the frequency of all postpartum complications was significantly increased in fetuses with abnormal venous Doppler findings.7 While it is evident that ductus venosus deterioration correlates well with adverse fetal outcome, the question remains whether the risk of fetal damage that has already occurred by the time of detection of pathological venous changes or the risk of prematurity by timing the delivery before these changes is higher. Randomized management trials are necessary to verify this issue including the impact of gestational age at delivery. Assessment of ductus venosus flow velocity waveforms may also provide useful information in fetuses with cardiac disease and non-immune fetal hydrops (see Fig. 11.6). In the latter, alterations in ductus venosus blood flow may be seen in fetuses with AV malformations, indicating high cardiac output failure. Persistent arteriovenous (AV) fetal tachyarrhythmia above a critical frequency of 210–220 bpm causes marked reversal of ductus venosus blood flow during entire diastole, indicating an abrupt increase in central venous pressure. Although ductus venosus pulsatility is not reliable in terms of screening for cardiac defects in the third or second trimester,19 it does characterize the specific haemodynamic situation in certain groups of heart disease. In a study comprising fetuses with right-sided cardiac lesions
✩✩✩✩✩✩✩✩✩✩✩ ✩
Umbilical Vein
Evaluation of fetal and uteroplacental blood flow
with obstructions of the inflow or outflow with intact ventricular septum, abnormal high pulsatilities in the ductus venosus were found, without being necessarily associated with cardiac failure or hypoxaemia.11 However, in some cases with severe AV regurgitation, progressive increase in right atrial and central venous pressure occurs, resulting in hydrops and poor prognosis.11 Heart compression by pericardial effusion also increases ductus venosus pulsatility. Impairment of systolic forward flow with subsequent decrease in peak velocity may occasionally be found in fetuses with severe tricuspid regurgitation (e.g. Ebstein's anomaly) (see Fig. 11.6C).45 Recently, ductus venosus Doppler evaluation has been integrated into detailed first-trimester screening studies in selected high-risk groups. In conjunction with increased nuchal translucency, reversed velocity during atrial contraction improves the predictive capacity for an underlying chromosomal abnormality and/or a major cardiac defect.15,34 However, the application of ductus venosus Doppler studies as a reliable screening tool in true low-risk patients has not been clarified yet. A second critical issue is that accurate examination of the ductus venosus is more time consuming and requires highly trained operators, as currently available at specialist centres only.
In first-trimester pregnancies, umbilical venous pulsations are frequently seen but progressively disappear until 14 weeks of gestation. The normal flow profile of the umbilical vein in the second and third trimester is continuous forward flow. Mild pulsations or sinusoidal waveforms might be seen during fetal breathing movements. Severe, biphasic or triphasic pulsations, mimicking systemic venous flow patterns, have been described in fetal compromise, such as terminal growth restriction and fetal right heart decompensation.4 Umbilical venous pulsations in the context of fetal pathology are considered an ominous sign, associated with intrauterine demise and neonatal complications. An exception to this rule is fetal tachyarrhythmia, where umbilical venous pulsations are already seen in the early stage of the disease. In severe growth-restricted fetuses, Doppler examination of venous blood flow volume demonstrated a significant increase in the shunting of umbilical vein blood flow through the ductus venosus, providing preferential blood flow to the heart and brain at the expense of fetal hepatic perfusion.10
Doppler in Twin Pregnancies Compared to singletons, twin pregnancies are at increased risk for a range of pregnancy complications including preterm delivery, pre-eclampsia, fetal growth restriction and subsequent birthweight discordance. In monochorionic pregnancies, the risks of early fetal loss, severe preterm delivery and intrauterine death are even higher, mainly attributed to the complications of TTTS.
223
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
224
Therefore, Doppler ultrasound evaluation in multiple pregnancies may be of use for selected conditions. Investigation of the uteroplacental circulation by uterine Doppler velocimetry in midgestation demonstrated lower mean artery resistance in twins compared to singletons. This may reflect the larger placental implantation area. Compared to screening efficacy in singletons, prediction of pre-eclampsia and FGR in twins was lower (sensitivity of about 30% and 20%, respectively).18,50 However, since the prevalence of complications is increased in multiple pregnancies, although sensitivity is lower, the positive predictive value of an abnormal test is higher.50 Several Doppler studies have examined flow velocity waveforms of various vessels in twins. In uncomplicated twin pregnancies, there are no differences in the umbilical artery and middle cerebral artery resistances compared to singleton pregnancies. In the presence of growth restriction and/or weight discordance, Doppler of the umbilical artery has been reported to be a valuable adjunct.14 A recent prospective randomized controlled multicentre trial investigated the performance of umbilical artery Doppler added to standard ultrasound biometry in the management of twin pregnancies.20 In this study, close surveillance resulted in a lower than expected fetal mortality in both the non-Doppler and Doppler groups. There were no differences between the two groups with respect to antenatal and postnatal outcomes. However, a major concern in this study is that it does not address the issue of chorionicity.20 Currently, Doppler plays a critical role in the management of monochorionic pregnancies complicated by TTTS and is incorporated into a widely used staging system.42,43 The association of increased nuchal translucency with abnormal flow pattern in the ductus venosus in first-trimester monochorionic twins may be an early manifestation of a haemodynamic imbalance between a donor and a recipient, thus predicting manifestation of TTTS.33 Colour Doppler sonography may also help in the identification and differentiation of the communicating placental vessels prior to endoscopic laser surgery. Doppler detection of artery-to-artery anastomosis carries a decreased risk of TTTS and improves stage-independent survival.48 Fetal Doppler findings in manifest TTTS do reflect circulatory changes due to hypovolaemia in the donor and congestive heart failure following cardiac overload in the recipient (see Fig. 11.6B). Successful laser ablation of intertwin anastomosis may lead to resolution of the disease and the concomitant Doppler changes. Return of donor umbilical artery end-diastolic blood flow and reappearance of positive flow during atrial contraction in the recipient ductus venosus can be found after therapy as well as transient increase in venous pulsatility in the donor fetus.21 Twin reversed arterial perfusion (TRAP) sequence is a rare complication in monochorionic twins. It is characterized by artery-to-artery anastomosis with the feature of reversed umbilical perfusion from the donor fetus to the acardiac twin and may result in cardiac failure of the donor. Serial echocardiographic and venous Doppler ultrasound examinations are most helpful in monitoring these pregnancies and discriminating between those suitable for conservative management and others that will benefit from cord occlusion.49
✩✩✩✩✩✩✩✩✩✩✩ ✩ References 11. Berg C, Kremer C, Geipel A, Kohl T, Germer U, Gembruch U. Ductus venous blood flow alterations in fetuses with obstructive lesions of the right heart. Ultrasound Obstet Gynecol 2006;28:137–142 12. Bilardo CM, Wolf H, Stigter RH et al. Relationship between monitoring parameters and perinatal outcome in severe, early intrauterine growth restriction. Ultrasound Obstet Gynecol 2004;23:119–125 13. Campbell S, Black RS, Lees CC, Armstrong V, Peacock JL. Doppler ultrasound of the maternal uterine arteries: disappearance of abnormal waveforms and relation to birthweight and pregnancy outcome. Acta Obstet Gynecol Scand 2000;79:631–634 14. Chittacharoen A, Leelapattana P, Rangsiprakarn R. Prediction of discordant twins by real-time ultrasonography combined with umbilical artery velocimetry. Ultrasound Obstet Gynecol 2000;15: 118–121 15. Favre R, Cherif Y, Kohler M et al. The role of fetal nuchal translucency and ductus venosus Doppler at 11–14 weeks of gestation in the detection of major congenital heart defects. Ultrasound Obstet Gynecol 2003;21:239–243 16. Ferrazzi E, Bozzo M, Rigano S et al. Temporal sequence of abnormal Doppler changes in the peripheral and central circulatory systems of the severely growthrestricted fetus. Ultrasound Obstet Gynecol 2002;19:140–146 17. Frusca T, Soregaroli M, Valcamonico A, Guandalini F, Danti L. Doppler velocimetry of the uterine arteries in nulliparous women. Early Hum Dev 1997;48:177–185 18. Geipel A, Berg C, Germer U et al. Doppler assessment of the uterine circulation in the second trimester in twin pregnancies: prediction of pre-eclampsia, fetal growth restriction and birth weight discordance. Ultrasound Obstet Gynecol 2002;20:541–545 19. Gembruch U, Meise C, Germer U, Berg C, Geipel A. Venous Doppler ultrasound in 146 fetuses with congenital heart disease. Ultrasound Obstet Gynecol 2003;22:345–350. 20. Giles W, Bisits A, O'Callaghan S, Gill A, for the DAMP Study Group. The Doppler Assessment in Multiple Pregnancy randomised controlled trial of ultrasound biometry versus umbilical artery Doppler ultrasound and biometry in twin pregnancy. Br J Obstet Gynaecol 2003;110:593–597
Evaluation of fetal and uteroplacental blood flow
1. Albaiges G, Missfelder-Lobos H, Lees C, Parra M, Nicolaides KH. One-stage screening for pregnancy complications by color Doppler assessment of the uterine arteries at 23 weeks' gestation. Obstet Gynecol 2000;96:559–564 2. Aquilina J, Thompson O, Thilaganathan B, Harrington K. Improved early prediction of pre-eclampsia by combining secondtrimester maternal serum inhibin-A and uterine artery Doppler. Ultrasound Obstet Gynecol 2001;17:477–484 3. Bahado-Singh RO, Kovanci E, Jeffres A et al. The Doppler cerebroplacental ratio and perinatal outcome in intrauterine growth restriction. Am J Obstet Gynecol 1999;180:750–756 4. Baschat AA, Gembruch U. Triphasic umbilical venous blood flow with prolonged survival in severe intrauterine growth retardation: a case report. Ultrasound Obstet Gynecol 1996;8:201–205 5. Baschat AA, Gembruch U, Reiss I, Gortner L, Weiner CP, Harman CR. Relationship between arterial and venous Doppler and perinatal outcome in fetal growth restriction. Ultrasound Obstet Gynecol 2000;16:407–413 6. Baschat AA, Gembruch U, Harman CR. The sequence of changes in Doppler and biophysical parameters as severe fetal growth restriction worsens. Ultrasound Obstet Gynecol 2001;18:571–577 7. Baschat AA. Doppler application in the delivery timing of the preterm growthrestricted fetus: another step in the right direction. Ultrasound Obstet Gynecol 2004;23:111–118 8. Baschat AA, Galan HL, Bhide A et al. Doppler and biophysical assessment in growth restricted fetuses: distribution of test results. Ultrasound Obstet Gynecol 2006;27:41–47 9. Bekedam DJ, Visser GH, van der Zee AG, Snijders RJ, Poelmann-Weesjes G. Abnormal velocity waveforms of the umbilical artery in growth retarded fetuses: relationship to antepartum late heart rate decelerations and outcome. Early Hum Dev 1990;24:79–89 10. Bellotti M, Pennati G, De Caspari C, Bozzo M, Battaglia FC, Ferrazzi E. Simultaneous measurements of umbilical venous, fetal hepatic, and ductus venosus blood flow in growth-restricted human fetuses. Am J Obstet Gynecol 2004;190:1347–1358
225
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
226
21. Gratacós E, Van Schoubroeck D, Carreras E et al. Impact of laser coagulation in severe twin–twin transfusion syndrome on fetal Doppler indices and venous blood flow volume. Ultrasound Obstet Gynecol 2002;20:125–130 22. Harman CR, Baschat AA. Comprehensive assessment of fetal wellbeing: which Doppler tests should be performed? Curr Opin Obstet Gynecol 2003;15:147–157 23. Harrington K, Cooper D, Lees C, Hecher K, Campbell S. Doppler ultrasound of the uterine arteries: the importance of bilateral notching in the prediction of pre-eclampsia, placental abruption or delivery of a smallfor-gestational-age baby. Ultrasound Obstet Gynecol 1996;7:182–188 24. Hecher K, Campbell S, Snijders R, Nicolaides K. Reference ranges for fetal venous and atrioventricular blood flow parameters. Ultrasound Obstet Gynecol 1994;4:381–390 25. Hecher K, Bilardo CM, Stigter RH, Ville Y, Hackelöer BJ, Kok HJ. Monitoring of fetuses with intrauterine growth restriction: a longitudinal study. Ultrasound Obstet Gynecol 2001;18:564–570 26. Hershkovitz R, Kingdom JC, Geary M, Rodeck CH. Fetal cerebral blood flow redistribution in late gestation: identification of compromise in small fetuses with normal umbilical artery Doppler. Ultrasound Obstet Gynecol 2000;15:209–212 27. Hollis B, Prefumo F, Bhide A, Rao S, Thilaganathan B. First-trimester uterine artery blood flow and birth weight. Ultrasound Obstet Gynecol 2003;22:373–376 28. Irion O, Masse J, Forest JC, Moutquin JM. Prediction of pre-eclampsia, low birthweight for gestation and prematurity by uterine artery blood flow velocity waveforms analysis in low risk nulliparous women. Br J Obstet Gynaecol 1998;106:88–89 29. Karsdorp VH, van Vugt JM, van Geijn HP et al. Clinical significance of absent or reversed end diastolic velocity waveforms in umbilical arterey. Lancet 1994;344:1664–1668 30. Li H, Gudnason H, Olofsson P, Dubiel M, Gudmundsson S. Increased uterine artery vascular impedance is related to adverse outcome of pregnancy but is present in only one-third of late third-trimester preeclamptic women. Ultrasound Obstet Gynecol 2005;25:459–463 31. Mari G, Deter RL, Carpenter RL et al. Noninvasive diagnosis by Doppler
ultrasonography of fetal anemia due to maternal red-cell alloimmunization. Collaborative Group for Doppler Assessment of the Blood Velocity in Anemic Fetuses. N Engl J Med 2000;342:9–14 32. Mari G. Middle cerebral artery peak systolic velocity for the diagnosis of fetal anemia: the untold story. Ultrasound Obstet Gynecol 2005;25:323–330 33. Matias A, Montenegro N, Areias JC. Anticipating twin–twin transfusion syndrome in monochorionic twin pregnancy. Is there a role for nuchal translucency and ductus venosus blood flow evaluation at 11–14 weeks? Twin Res 2000;3:65–70 34. Mavrides E, Sairam S, Hollis B, Thilaganathan B. Screening for aneuploidy in the first trimester by assessment of blood flow in the ductus venosus. Br J Obstet Gynaecol 2002;109:1015–1019 35. Neilson JP, Alfirevic Z. Doppler ultrasound for fetal assessment in high risk pregnancies. Cochrane Database Syst Rev 2000; issue 2; D000073 36. Oepkes D, Seaward G, Vandenbussche F et al for the Diamond Study Group. Doppler ultrasonography versus amniocentesis to predict fetal anemia. N Engl J Med 2006;355:156–164 37. Ozcan T, Sbracia M, d'Ancona RL, Copel JA, Mari G. Arterial and venous Doppler velocimetry in the severely growthrestricted fetus and associations with adverse perinatal outcome Ultrasound Obstet Gynecol 1998;12:39–44 38. Papageorghiou AT, Yu CK, Bindra R, Pandis G, Nicolaides KH for the Fetal Medicine Foundation Second Trimester Screening Group. Multicenter screening for pre-eclampsia and fetal growth restriction by transvaginal uterine artery Doppler at 23 weeks of gestation. Ultrasound Obstet Gynecol 2001;18:441–449 39. Papageorghiou AT, Yu CK, Cicero S, Bower S, Nicolaides KH. Secondtrimester uterine artery Doppler screening in unselected populations: a review. J Matern Fetal Neonatal Med 2002;12:78–88 40. Papageorghiou AT, Yu CK, Erasmus IE, Cuckle HS, Nicolaides KH. Assessment of risk for the development of pre-eclampsia by maternal characteristics and uterine artery Doppler. Br J Obstet Gynaecol 2005;112:703–709
✩✩✩✩✩✩✩✩✩✩✩ ✩ fetuses with breakdown of the brain-sparing effect diagnosed by spectral Doppler. J Matern Fetal Med 2001;10:122–126 48. Tan TY, Taylor MJ, Wee LY, Vanderheyden T, Wimalasundera R, Fisk NM. Doppler for artery–artery anastomosis and stage-independent survival in twin– twin transfusion. Obstet Gynecol 2004;103:1174–1180 49. Weisz B, Peltz R, Chayen B et al. Tailored management of twin reversed arterial perfusion (TRAP) sequence. Ultrasound Obstet Gynecol 2004;23:451–455 50. Yu CK, Papageorghiou AT, Boli A, Cacho AM, Nicolaides KH. Screening for pre-eclampsia and fetal growth restriction in twin pregnancies at 23 weeks of gestation by transvaginal uterine artery Doppler. Ultrasound Obstet Gynecol 2002;20: 532–534 51. Zimmerman R, Carpenter RJ Jr, Durig P, Mari G. Longitudinal measurement of peak systolic velocity in the fetal middle cerebral artery for monitoring pregnancies complicated by red cell alloimmunisation: a prospective multicentre trial with intention-to-treat. Br J Obstet Gynaecol 2002;109:746–752
Evaluation of fetal and uteroplacental blood flow
41. Papageorghiou AT, Roberts N. Uterine artery Doppler screening for adverse pregnancy outcome. Obstet Gynecol 2005;17:584–590 42. Quintero RA, Morales WJ, Allen MH, Bornick PW, Johnson PK, Kruger M. Staging of twin–twin transfusion syndrome. J Perinatol 1999;19:550–555 43. Quintero RA, Dickinson JE, Morales WJ et al. Stage-based treatment of twin–twin transfusion syndrome. Am J Obstet Gynecol 2003;188:1333–1340 44. Severi FM, Bocchi C, Visentin A et al. Uterine and fetal cerebral Doppler predict the outcome of third-trimester smallfor-gestational-age fetuses with normal umbilical artery Doppler. Ultrasound Obstet Gynecol 2002;19:225–228 45. Smrcek JM, Krapp M, Axt-Fliedner R et al. Atypical ductus venosus blood flow pattern in fetuses with severe tricuspid valve regurgitation. Ultrasound Obstet Gynecol 2005;26:180–182 46. Spencer K, Yu CKH, Cowans NJ, Otigbah C, Nicolaides KH. Prediction of pregnancy complications by first-trimester maternal serum PAPP-A and free ß-hCG and with second-trimester uterine artery Doppler. Prenat Diagn 2005;25:949–953 47. Takahashi Y, Kawabata I, Tamaya T. Characterization of growth-restricted
227
12 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Invasive procedures in obstetrics Yves Ville
ABSTRACT The main focus in fetal invasive testing is fetal karyotyping, although increasingly molecular studies on fetal material are being carried out. Invasive techniques include chorion villus sampling and fetal blood sampling as the sources of fetal tissue. The technique and safety of these procedures are presented. Intrauterine fetal blood transfusion is indicated in severe fetal anaemia such as in red cell alloimmunization, fetomaternal haemorrhage and parvovirus B19 infection with fetal hydrops. Fetal shunting is limited to very selective fetal diseases following careful evaluation, i.e. obstructive uropathy, macrocystic congenital malformation of the lungs (CCAM) or pleural effusions associated with fetal hydrops. Ultrasound plays a pivotal role in selective fetocide performed in higher-order multiple pregnancies.
Keywords Amniocentesis, chorion villus sampling, fetal blood sampling, fetal shunting, selective fetocide.
Introduction The introduction of a needle through the maternal abdomen under ultrasound guidance is the basis for invasive prenatal diagnosis and fetal therapy to treat a critically ill fetus. All intrauterine invasive procedures in obstetrics should be carried out under continuous real-time ultrasound control. These procedures carry a risk of fetal loss and/or preterm delivery or intrauterine death. The most common reason for fetal invasive testing is karyotyping and there are three main techniques used to obtain fetal tissue: chorion villus sampling (CVS), amniocentesis (AC) and fetal blood sampling (FBS). All three have been credited with various risks and it is important to critically appraise the indications for each
229
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
15%
2% 1% 5wks 11wks 16wks
40wks
Fig. 12.1 Spontaneous fetal loss rate throughout gestation. (Reproduced with permission from Hook EB. Down syndrome live births and spontaneous abortions of unknown karyotype. Prog Clin Biol Res 1985;163C:21–24.)
of these procedures. It is vital to understand that the risk of spontaneous miscarriage is present throughout the pregnancy, even though it decreases with increased gestation: from 15% at 5 weeks down to 1% at 16 weeks of gestation (Fig. 12.1). Non-specific risks involve fetal loss which may be idiopathic or may occur as a result of direct fetal injury with subsequent exsanguination or infection. Preterm delivery, intra-amniotic haemorrhage and chorioamnionitis also contribute to the morbidity of invasive procedures. Adequate methodology should include registration of the outcome of all pregnancies without excluding any complication from a causal relationship with the procedure performed.
Counselling Genetic counselling will not be discussed in detail in this chapter. However, a few guidelines will be mentioned, since counselling is an essential factor in all invasive procedures. Counselling involves helping the individual and her family to understand the indication, the expected results, the failure rate and the procedurerelated risks as well as available alternatives. Counselling should take place before the procedure is carried out. It should be done in a place where privacy, confidentiality and autonomy are guaranteed. It should not be done on an examination couch but outside the procedure room. Counselling requires time, patience and skills to convey the information in understandable language considering the individual's education and ethical beliefs. The counselling should be documented in writing and should included the time(s) and the nature of the counselling as well as what was discussed. The documentation may be needed for future reference, possibly in connection with medico-legal claims. Written consent prior to an invasive procedure does not substitute for documented information about counselling.
Training 230
Training in invasive procedures is not easy and should always be supervised by a competent senior operator. Although programmes for training of junior doctors
✩✩✩✩✩✩✩✩✩✩✩ ✩
Invasive procedures in obstetrics
in obstetric ultrasound are now well established, the opportunity to acquire the specific skills necessary to perform FBS is currently available in only a few major fetal medicine centres where training is carried out with active supervision of the trainee. The technique described below allows for control of every step of the procedure and anticipation of the next one through full visualization of the needle path and that of the target. Supervision can therefore be timely and explicit without increasing the anxiety already felt by the patient as a result of the uncertainty over the outcome of the pregnancy. The use of phantoms helps the inexperienced operator to master basic technique and also reduces uncertainty. It is recommended that the first 100 procedures be performed with such a set-up. There are several types of phantoms described in the literature.1,2 Some are even home-made.2 They all use anechoic gel in which the target is placed. The particular aim of the training is to be able to direct a needle transabdominally towards a target in the fetoplacental unit under complete operator control and continuous visualization of both the target and the needle. In our experience, invasive procedures may be performed with a free-hand technique by a single operator. We use a curvilinear transducer, visualizing clearly the abdominal wall and placing the target in the centre of the screen. The needle should be visualized from its entry through the skin and the zoom should not be used until the needle is approaching the target. The transducer is ideally held in the left hand of a righthanded operator. The needle may be inserted 3 cm away from the transducer at an angle of 45° with the horizontal probe (Fig. 12.2).
Right angle to the table 33cm cm
3 cm, 45° 45°
Long axis
of the uterus
Table plane Fig. 12.2 Operative plan of any invasive procedure showing the position of the transducer, the target on the screen and the angle at which the needle should be introduced.
231
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Some of the most difficult aspects of the procedure are:
• visualizing the cord longitudinally at either the placental or umbilical insertion
• maintaining the transducer in the proper position throughout the procedure
• introducing the needle through the skin at the correct angle and distance from the transducer
• advancing the needle under full vision towards and into the cord • introducing the needle into the umbilical vein through the Wharton's jelly surrounding the cord
• finding the target again and repositioning the needle in the same alignment if the target has moved.
The Procedures Each of the invasive procedures is presented below, starting with chorion villous sampling (CVS) which, in the chronology of the pregnancy, is the first invasive test which can performed safely and reliably. The basic technique and equipment for each procedure are described, along with known complications, safety aspects and any special considerations regarding multiple gestations.
Asepsis Common to all the procedures is asepsis. The site is cleaned with an antiseptic solution (usually chlorhexidine 0.5% in spirit or iodine solution) and the mother's lower abdomen is draped with sterile towels. The ultrasound probe may be placed in a sterile plastic bag. Iodine ensures good contact between the wrapped probe and the skin; sterile Vaseline may also be used. The operator wears sterile gloves.
Chorionic Villous Sampling The aim of chorionic villous sampling (CVS) is to insert a sampling device, either a needle or a biopsy forceps, inside and parallel to the great axis of the chorion frondosum in order to sample an adequate amount of trophoblast (Fig. 12.3). Several techniques have been developed over the last 10 years for CVS either transabdominally or transcervically using catheters, needles or biopsy forceps.3
• CVS should be done after 10 completed weeks of gestation. This timing is
232
derived from the analysis of cases of severe transverse limb abnormalities or oromandibular-limb hypogenesis syndrome reported after CVS performed prior to 66 days of gestation.20 CVS may be performed up to 14–15 weeks but some may prefer it as a first-line technique up to term. The question remains whether CVS sampling after 10 weeks has the potential to cause more subtle defects but most centres performing CVS after 10 weeks have not seen an increase in limb defects.4
✩✩✩✩✩✩✩✩✩✩✩ ✩ 1. Anterior Insertion
2. Fundal Insertion
L
1. Posterior Insertion
Invasive procedures in obstetrics
l L
Fig. 12.3 The CVS needle must be inserted in the longitudinal axis of the trophoblast to allow sufficient course for the needle to be moved back and fore.
• A transabdominal approach is preferable since the infection-related risk of
fetal loss seems to be higher when the transcervical technique is used. Three techniques for transabdominal sampling are mainly used. In the single-needle approach, a 12–15 cm 20 gauge spinal needle is used.5 Aspiration is usually achieved by connecting a catheter to the hub of the needle and to a 20 mL syringe together with hand grip while the operator is moving the needle to and fro within the trophoblast 10–15 times, following a straight 4–5 cm course under continuous ultrasound guidance. The double-needle technique uses an outer guide needle introduced down through the skin and myometrium at the edge of the chorion frondosum. This can be either an 18 gauge thin-walled needle or a standard 16–17 gauge spinal needle. A smaller, usually 20 gauge, sampling needle is then passed through and used for the direct sampling as described above. The advantage of the double-needle technique is that it allows for quantitative and qualitative assessment of the sample while the first needle is still in the uterus and the procedure can be completed if necessary without the need for a repuncture. Some prefer that local anaesthesia be given down to the myometrium along the needle path. • A variation of the latter is the use of a biopsy forceps passed down a 16–18 gauge needle. Chorionic villus sampling in multiple gestations The best and, in fact only, screening test for fetal aneuploidy in the first trimester in twin pregnancies is nuchal translucency thickness (NT) measurement, although a recent study suggests that false-positive rates and invasive diagnostic procedures
233
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ are reduced when first-trimester biochemistry is added.21 In dichorionic twins NT is measured above the 95th centile in 5% of the twins; in monochorionic pregnancies these figures are reported to be up to 9% and 13% respectively. If selective termination is an option in an aneuploid dichorionic twin, it should be noted that the outcome is dependent upon the timing of reduction with a sharp increase in the fetal loss rate after 16 weeks.22 CVS performed at 11–14 weeks has therefore become a real alternative to amniocentesis in twins. Precise determination of chorionicity is an absolute prerequisite and is easy to ascertain at 11–14 weeks of gestation. This will help to determine the necessity of sampling only one or both trophoblasts. Indeed, in monochorionic gestations, heterokaryotic twins are an anecdotal phenomenon and sampling of the trophoblast close to the high-risk twin should lead to identical karyotype in both fetuses. When the sampling of both twins is indicated, as in non-chromosomic genetic or biochemical testing, two needle insertions are necessary in order to provide the best approach to the trophoblast of each dichorionic twin. One should consider the risk of two needle insertions at this stage as compared to a single needle insertion to perform an amniocentesis at 15 weeks. This should be carefully evaluated, taking into account the risk of finding an affected pregnancy as compared to that of fetal loss. Safety There are several large studies reporting on the safety of CVS,6 including more than 200,000 procedures, suggesting that CVS is associated with a low pregnancy loss, comparable to second-trimester amniocentesis.7
Amniocentesis
234
Cytogenetic analysis and diagnosis of intra-amniotic infection are the main diagnostic indications. Drainage of polyhydramnios and medical treatment of fetal disorders are rare therapeutic indications. Amniocentesis can be performed from 15–16 completed weeks of gestation onwards. This restriction appears reasonable, since several randomized studies8,9 have clearly demonstrated that amniocentesis carries a higher fetal loss and morbidity rate when performed before 14 completed weeks as compared to later amniocentesis, and to CVS performed at the same gestational age. This is likely to be due to the presence of the extracoelomic space. Even when it has become virtual, the amniotic membrane can remain incompletely fused to the uterine wall until up to 14–15 weeks. Dry taps may then occur since the amniotic membrane will be tented by the needle and not perforated. The so-called ‘early amniocentesis’ should therefore be abandoned for safety reasons. A site of puncture is chosen to avoid placental tissue and umbilical cord in the needle path. Isoimmunization is likely to be increased by a transplancental approach, but there is little evidence to suggest this would be more deleterious in terms of intra-amniotic bleeding or fetal loss.9,10 Indeed, a transplacental approach in the late first trimester could well decrease the risk of membrane tenting when the extraamniotic space has virtually disappeared but the amnion is not yet attached.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Safety Fetal loss rates for mid-trimester amniocentesis are best expressed through a randomized clinical trial of genetic amniocentesis involving 4606 low-risk women who were randomized to have either an amniocentesis or an ultrasound examination.8 All procedures were performed by five physicians at the same institution using a 20 gauge needle. The study group had a higher rate of spontaneous abortion compared with the control group (1.7% vs 0.7%; OR 95% 2.3(1.3–4.0); p<0.01). The authors also underlined that 1% might be an underestimation of the actual procedure-related risk since termination of the affected pregnancies in the study group and not in the control group may have artificially decreased the spontaneous fetal loss rate. Risk factors included high maternal serum α-fetoprotein (AFP), perforation of the placenta and discoloured (brown- and green-stained) amniotic fluid. Technical difficulties and multiple needle insertions have also been implicated as causes for an increased rate of pregnancy loss.10,11
Invasive procedures in obstetrics
In the vast majority of cases, a regular 20 gauge needle with a length of 12–15 cm excluding the hub will be chosen. This offers a good combination of length and rigidity and may even be inserted through thick abdominal walls followed by a rapid fluid withdrawal. There is no strong evidence that the use of smaller bore needles decreases the procedure's complication rate.
Amniocentesis in multiple gestations Amniocentesis in twin pregnancies has traditionally involved puncture of the first sac, withdrawal of amniotic fluid, injection of a dye and then a new needle insertion to puncture the second sac. When the second sac was sampled, the fluid was then supposed to be free of dye. The disadvantage is that two punctures of the skin and of the uterus are necessary, potentially increasing the procedure-related risk. In addition, with the injection of dyes, a foreign substance is introduced into the amniotic cavity of one of the fetuses, and neonatal occlusion of the intestinal tract has been reported after injection of methylene blue. We therefore recommend a single-needle insertion technique. The site of the needle insertion is determined mainly by the position of the membrane separating the two sacs. After entry into the first sac and aspiration of amniotic fluid, the stylet is replaced in the needle which is then advanced sharply through the dividing membrane into the second sac. To avoid contamination of the second sample with any amniotic fluid from the first sac still in the needle, the first 1 mL of fluid is discarded.12
Fetal Blood Sampling Ultrasound-guided fetal blood sampling (FBS) or cordocentesis or funipuncture has developed since its introduction by Daffos et al in 1983.13 In low-risk pregnancies FBS can be performed from 20 weeks onwards when the size of the umbilical vein allows for the procedure to be safely performed. FBS shares the same diagnostic indications as amniocentesis or CVS when this is done after 20 weeks of gestation. FBS has specific therapeutic indications
235
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
such as intrauterine fetal blood or platelet transfusions in severe fetal anaemia or alloimmune fetal thrombocytopenia respectively. Technique The aim is to puncture the cord at the placental cord insertion. All procedures can be planned as access to either an anterior placenta, with a direct transplacental access to the umbilical vein, or to a posterior placenta with a transamniotic access to the vein. Ultrasound examination should therefore carefully assess the entire placental surface to plan the procedure. Local anaesthetic is not necessary for diagnostic procedures but it is a useful adjunct in intrauterine blood transfusions.
• An anterior placenta makes cord insertion technically easier; the umbilical
vein insertion on the placenta should be visualized in the ultrasound plane (Fig. 12.4A) with an angle which allows the needle to be directed to the vein. • Posterior placenta and cord insertion requires a transamniotic approach to the cord insertion. The needle should puncture the umbilical vein at an angle as close to 90° as possible; indeed, the smaller the angle, the higher the risk of hurting the cord and lacerating the vessels (Fig. 12.4B). Indenting the cord under gentle needle pressure should precede a sharp and controlled puncture. • When the cord insertion is not accessible, for example in cases with a posterior placenta when the fetus is lying on the insertion, the needle can be directed towards the intrahepatic umbilical vein. A transverse view of the fetal abdomen should be obtained with the fetus lying on its back or side. A Catheterization of the vein
YES
B
NO
Free loop stuck on the placenta YES
90° to the insertion
Insertion unattainable
NO
236
Fig. 12.4 Ultrasound-guided funipuncture in an anterior placenta (A) and a posterior placenta (B).
✩✩✩✩✩✩✩✩✩✩✩ ✩
• One should avoid aiming at a free loop. The target is mobile and therefore
When FBS is undertaken after 28 weeks, it should ideally be performed after a course of steroids for fetal lung maturation. The procedure should be attempted in an operative theatre to allow an emergency caesarean section if fetal distress occurs. This should be discussed with the parents prior to the procedure. A total volume of 2–5 mL of blood is sampled in 1 mL syringes; this may contain a small amount of heparin or citrate, depending on the investigations to be performed. The sample should be immediately placed in the appropriate containers and the purity of blood assessed by the haematology lab. This will generally involve comparisons of mean corpuscular volumes (MCV) in fetal and maternal blood samples. Depending on the indication, determination of white blood cell count, differential cell evaluation, blood and Rh grouping, anti-I and anti-I antigen, Kleihauer–Betke test, concentration of β-human chorionic gonadotropin, factors IX and VIIC, and AFP levels in maternal and fetal blood may be necessary.
Invasive procedures in obstetrics
the cord puncture is uncertain; it can lacerate the cord and the vessel to be punctured cannot be chosen, thus increasing the risk of arterial puncture. When this situation cannot be avoided, the loop should be pushed onto the placental surface and then punctured sharply.
Complications The overall fetal loss rate due to cordocentesis is estimated to be 1% in a low-risk population.14 However, there is great variation in the series published, with rates ranging from 0% to 12%.14 There is a negative correlation between fetal loss rate and the size of the series published. Furthermore, several authors have pointed out that there is a distinct learning curve for the performance of cordocentesis.16 The first 100 procedures are critical regarding maximal loss rate and the procedure should be regularly practised.15 The presumed causes of pregnancy losses following cordocentesis are: chorio amnionitis, premature rupture of the membranes, fetal exsanguination, severe bradycardia and cord haematoma. The duration and difficulty of the procedure are major risk factors. These complications are more prone to occur when the cord is punctured through a transamniotic approach, especially in a free loop. Bleeding occurs in 60–70% of these cases and lasts for less than 1 minute in the vast majority of cases. Bradycardia below 100 beats/min occurs in 10–20% of arterial punctures, usually as a result of a vasospasm. The mother should be placed on her left side and breathe oxygen; 0.5 mg of atropine can be used occasionally. A rare but serious cause of bradycardia is cord haematoma; this can arise as a consequence of cord laceration in difficult procedures and can lead to cord tamponade.
Intrauterine Fetal Blood Transfusion16 The technique of fetal blood transfusion has a lot in common with that of cordo centesis. However, preparation should allow for a good catheterization of the umbilical vein by inserting the needle in alignment with the cord insertion. Initial sampling will serve to establish the starting haemoglobin and/or platelet count.
237
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The former will be quickly established using a proper analyser in the operative room. In intravascular blood transfusion, either top-up or exchange transfusions can be used with no clear advantage of one technique over the other. In most centres the top-up technique is used. The main indications for intrauterine fetal blood transfusions in severe (<9 g/dL) fetal anaemia are red cell alloimmunization, fetomaternal haemorrhage and parvovirus B19 infection with fetal hydrops. The volume of blood to be transfused (V) depends upon several factors: V = Vf(H2−H1)/Ht where H1 = preoperative fetal Hb concentration (g/dL), H2 = fetal Hb concentration expected at the end of the procedure, Ht = Hb concentration in the donor blood, optimally around 70–80% and Vf = fetal blood volume (80 mL/kg). The final haemoglobin concentration should roughly be 14 g/dL in the presence of hydrops and 16 g/dL in the absence of hydrops. In severe fetal anaemia before 18–19 weeks, intraperitoneal blood transfusion is an alternative which can be life saving. Very rarely, in cases of fetal terminal anaemia with bradycardia, intracardiac blood transfusion can be given in the left ventricle of the heart.23 In severe fetal alloimmune thrombocytopenia (<50,000 platelets/dL), intravascular platelet transfusion may be indicated and should be repeated weekly if gestational age is still remote from term. One platelet unit of 10 mL usually brings fetal platelet count up to 100,000 platelets/dL. However, this is usually a second-line treatment given only when maternal administration of corticosteroids and nonspecific immunoglobulins has failed to improve fetal platelet count in 6–8 weeks. Complications The complications are similar to those of FBS. However, cord haematoma/tamponade is more frequent in transfusions, especially with fetal movements and needle displacements in the absence of curarization. Fetal bradycardia is more frequent in arterial transfusion. Specific complications due to administration of blood products can be overcome by selection of blood negative for CMV, hepatitis and HIV. Twenty-fiveGy irradiation of the blood will prevent graft vs host immunization, and separation of blood cells will allow for concentrated blood or platelet units to be prepared. Prevention and early recognition of these complications involve checking the fetal heart rate and contractility during the procedure as well as the direct flow of the blood transfused in the umbilical vessel. The procedure should be discontinued when bradycardia or a decrease in ventricular contraction arises or when the needle placement is uncertain or when an echogenic area develops within the cord.
Fetal Shunts 238
Recognition of fetal obstructive diseases by prenatal ultrasound examination has made it possible to envisage in utero derivation of the obstructed cavity/organ
✩✩✩✩✩✩✩✩✩✩✩ ✩
Techniques Extensive counselling by an experienced operator and consultation with a neonatologist and most often a paediatric surgeon are essential prerequisites for shunting.
Invasive procedures in obstetrics
into the amniotic cavity. Fetal shunting should be contemplated only for conditions frequently associated with significant mortality and morbidity since there is sufficient evidence from both animal and human data that the natural development can be altered by the procedure. Fetal shunting has been performed for a variety of conditions including obstructive uropathies, hydrocephalus, pleural effusion, pulmonary cysts and ascites. To date, however, only three diseases still leave some scope for antenatal shunting in carefully evaluated cases: obstructive uropathy, macrocystic congenital cystic malformations (CCAM) of the lungs or compressive pleural effusions when complicated by fetal hydrops. Permanent irreversible renal damage can only arise from bilateral urethral obstruction or low obstruction such as in posterior urethral valves or urethral atresia. The only condition whereby unilateral obstruction could indicate invasive renal assessment including drainage is in severe pyeloureteral junction obstruction with contralateral renal agenesis. In these situations, an ultrasound assessment alone has a low sensitivity which can be increased by the analysis of urine concentrations of calcium and sodium which have the best sensitivity and specificity, respectively. β2-microglobulin concentration in the fetal plasma is another useful marker in obstructive uropathies. Urine biochemistry cannot be assessed by a single evaluation and this should be repeated at 1–2 week intervals.17 This should precede indications for bladder shunting. Fetuses with persistent megacystis who have ultrasound-based and biochemical evidence of adequate renal function are the most likely group to benefit from shunting. However, close follow-up of this group should be done in order to redefine indications for shunting fetuses with obstructive uropathy, mainly when the obstruction is severe and biochemically assessed renal function is normal at a gestation still remote from term. Complete drainage of the fetal bladder might be unsuccessful at obtaining resolution of hydronephrosis or ureteral dilation; this is usually due to a bladder wall hypertrophy responsible for subsequent low bilateral ureteral obstruction, massive reflux, ureterocele or a combination of these. Thoracoamniotic shunting in CCAM or in pleural effusions should only be attempted in severely compressive conditions. The fetus would therefore be hydropic and signs of thoracic compression should be present with at least one of the following: polyhydramnios, severe mediastinal shift, eversion of the diaphragm and venous and cardiac compression as documented by a reverse flow in the ductus venosus Doppler waveform during atrial contraction. Shunting should result in immediate and nearly complete drainage. Incomplete drainage with failure of the lungs to expand and fill the chest following pleuro amniotic shunting, although technically satisfactory, should raise the suspicion of pulmonary hypoplasia.
239
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The shunting can be performed as an outpatient procedure with a mild maternal sedation (diazepam or Rohypnol 10 mg) given orally as well as prophylactic tocolysis with indometacin (50 mg suppository) and antibiotics can be recommended for maternal and operator comfort although there is no strong evidence that they have a significant impact on the outcome. Fetal analgesia may be given (sufentanyl 0.5 μg/kg) in the umbilical circulation and pancuronium may also be administered for fetal paralysis (10 μg/kg). This involves performing a cordocentesis as described above. The most widely used catheter in Europe is the Rocket (Rocket of London Ltd, Watford, UK) developed by Rodeck et al in 1982.18 It is a double-pigtail silastic catheter with an external diameter of 2.1 mm, with radio-opaque stainless steel inserts at each end and lateral holes around the coils which are preformed at right angles to each other. This makes dislodgement less likely. The catheter is introduced through a cannula loaded with a sharp triangular-shaped trocar mounted on a handle. The external diameter of the 18 cm long trocar is 2.5 mm (Fig. 12.5). The best transverse section of the fetal target is obtained without magnification and the expected site of entry in the fetus is placed in the centre of the screen. Local anaesthetic is administered as previously described. If there is oligohydramnios, a 20 gauge needle is first passed into the amniotic cavity and an amnioinfusion given with 150–200 mL of warmed normal saline. This may improve the image and allow the anomaly scan to be completed, but its main purpose is to facilitate the deposition of the intra-amniotic end of the catheter.
A
B
C
240
Fig. 12.5 Shunting instruments. (A) Cannula. (B) Trocar. (C) Double-pigtail catheter.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Invasive procedures in obstetrics
The trocar and cannula are introduced into the amniotic cavity and then inserted through the fetal cavity to be drained. After checking that the cannula is in the correct position, the trocar is removed and the end of the catheter is blocked with the operator's finger. The fetal catheter is straightened out on its wire and inserted into the cannula. The guidewire is removed and the shorter obturator pushes half the catheter out and this coils up inside the fetus in the fluid. The cannula is carefully drawn back into the amniotic cavity where the other half of the catheter is deposited by the longer obturator. This requires fluid in the amniotic cavity. In bladder shunting, the shunt should be inserted suprapubicly and away from the midline. In thoracic shunting, the shunt should be inserted in the midthoracic region below the scapula and posterior to the axillary midline in order to minimize the risk of catheter dislodgement by the fetus. If drainage from the contralateral region is also needed, fetal curarization will usually allow rotation of the fetal body with the tip of the cannula once the trocar has been removed. Complications The fetal loss or premature delivery rate can be roughly estimated to range between 5% and 15%, often preceded by rupture of the membranes and/or chorioamnionitis, depending on the operator’s experience and the gestational age at which this is performed. Other complications are more frequent, such as inadequate drainage (20%) or shunt dislodgement. Dislodgement can happen either spontaneously or by the fetus itself in up to 25% of cases. Most dislodgements will cause externalization of the catheter in the amniotic fluid which must be checked at the time of delivery; however, some catheters are occasionally displaced into the cavity they were meant to drain and they should be surgically removed postnatally. Some complications are rare but could cause technical and clinical management dilemmas. Urinary ascites is usually associated with vesicoamniotic shunt dislodgement and can indicate peritoneo-amniotic drainage. Amniotic fluid leakage to the maternal peritoneal cavity can occur through the path of the trocar, causing painful maternal chemical peritonitis; this often requires morphine administration but will resolve spontaneously within hours. Delivery and shunt removal Mode of delivery should not be influenced by the presence of the shunt. However, an experienced neonatologist should be present at delivery. A vesical shunt should be left in situ and be used for postnatal drainage until surgical correction of the problem. There is no consensus with regard to pleural shunts; however, immediate clamping is a reasonable option, followed by gentle ablation once respiratory assistance has been started. The main risk is for a pneumothorax to develop. When the shunt cannot be found at birth, both the neonate and the mother should undergo x-ray to locate the radio-opaque steel tips of the shunts.
241
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
242
Outcome Selection of cases of obstructive uropathies is a difficult process and there are no randomized trials or detailed long-term studies that assess the benefit of vesicoamniotic shunting. A major worry is the transformation of a group of neonates who would have died without a shunt into a group of severely chronically ill survivors. There seems to be a strong incentive to drain early in the obstructive process which could be picked up in the late first trimester. However, such a policy would require the creation of adapted instruments; it would also be necessary to randomize the cases for future evaluation. Shunting for thoracic fluid is less controversial when the cases are selected on the presence of hydrops due to thoracic compression and the benefit can be assessed in utero and soon after birth.
Diagnostic and Operative Fetoscopy19 Embryo-fetoscopy is a relatively old technique that allows the direct endoscopic visualization of the embryo or the fetus by introducing an endoscope through the cervix or through the maternal abdomen and the uterine wall. This was also the first manner of guidance for performing fetal blood sampling through an operative channel of the scope. The development of high-resolution ultrasonography made the technique obsolete in the late 1980s. However, technical development has also enabled the construction of new endoscopes with a diameter less than 3 mm. The field of view in these endoscopes is rather limited and all of them must be introduced and moved inside the amniotic cavity under ultrasound guidance. At present there are hardly any indications for embryoscopy between 11 and 14 weeks. With high-resolution transvaginal ultrasound, one can do a thorough work-up of the fetal anatomy. The only established indication for operative fetoscopy to date is for fetoplacental surgery in the severe complications affecting monochorionic multiple pregnancies. Such complications mainly represent the severe twin-to-twin transfusion syndrome (TTTS), acardiac twinning and discordant anomalies in monochorionic twins when the abnormality is not lethal and/or has a threatening effect on the whole pregnancy, i.e. polyhydramnios in the sac of an anencephalic fetus. The target of the fetoscopically assisted procedure is then either the placental surface such as in TTTS or the umbilical cord of a monochorionic twin to be selectively coagulated. The technique involves percutaneous introduction of a trocar which will carry the fetoscope, as well as a 400–600 µm Nd:YAG or diode laser fibre, under ultrasound guidance after local analgesia has been given, as previously described. One should avoid penetrating the placenta. When the placental surface must be explored, the trocar is introduced away from the stuck donor twin and at right angles to it, in order to maximize the chances of being able to follow the insertion of the intertwin membrane which usually runs close and parallel to the long axis of the donor twin in an oligohydramniotic sac. Identification of the vessels to coagulate and the technique of coagulation are described elsewhere.19
✩✩✩✩✩✩✩✩✩✩✩ ✩
Pregnancy Reduction in Multifetal Pregnancies
Technique Although transabdominal and transvaginal techniques are equally effective, a transabdominal approach should be used whenever possible since it will preserve fetuses closer to the cervix and therefore potentially decrease the risk of preterm premature rupture of the membranes and/or infection. Asepsis should be obtained as described for any invasive procedure. A transverse view of the thorax of the fetus(es) to be reduced is placed in the middle of the screen and the needle should be introduced so that the sac of embryos which are meant to remain alive is not perforated. Local anaesthetic is given down to the myometrium. A 20 gauge needle is directed in the fetal thorax and 1–2 mL of a mixture of fentanyl and potassium chloride is injected into the fetal heart/ thorax. The needle is left in place for 15–30 seconds after the heart has stopped beating to confirm fetal death. When another embryo is to be reduced, the needle is then pushed through the dividing membranes sharply to avoid tenting and the
Invasive procedures in obstetrics
In the absence of fetal abnormalities, embryo reduction is medically justified in quadruplet and higher-order pregnancies resulting in a significantly better outcome for the reduced pregnancies.24 In twins, very few indications would be accepted by most operators beyond selective fetocide for fetal abnormality. The optimal number of fetuses to be left alive is now widely accepted to be two as an ideal compromise to allow for a good neonatal outcome of the survivors and an acceptable procedure-related fetal loss rate. Indeed, the neonatal outcome improves as the number of live fetuses decreases, but the fetal loss rate increases inversely. Preoperative counselling should discuss the 6–15% fetal loss rate before 24 weeks of gestation, mainly between 2 and 8 weeks after the procedure.24 The optimal gestational age at which reduction should be performed is still debated but is focused at around 11 weeks. Indeed, the spontaneous fetal loss rate decreases from 15% to less than 2% between 5 and 11 weeks of gestation. The NT measurement as well as an early examination of the fetal anatomy can therefore be performed to help select the fetuses to be reduced. When the fetuses cannot be selected on this basis, fetocide will be targeted to the fetuses which are most easily accessible, therefore closer to the fundus of the uterus when the procedure is performed transabdominally. Multifetal pregnancy reduction can only be contemplated in dichorionic fetuses. If the multifetal pregnancy includes a set of monochorionic twins, both should preferentially be reduced, since reducing one fetus could precipitate acute haemodynamic changes in its co-twin and lead to the development of severe sequelae. Monochorionic twins can also develop TTTS in up to 14% of cases. Careful and precise mapping of the fetuses and the trophoblasts should be done prior to the procedure in cases where the heart would only stop temporarily, there would be a high risk of abnormal fetal development and the procedure should therefore be completed.
243
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
procedure is repeated on the second fetus. Amniocentesis/amniodrainage of the sac of the reduced fetus is unnecessary and potentially deleterious.
Selective Fetocide for Fetal Abnormality This represents an indication for fetocide to be performed in a twin or higherorder multifetal pregnancy. The same technique applies to these cases. The risk of miscarriage roughly doubles after 16 weeks. Therefore, in order to obtain early information of the karyotype, first-trimester screening by NT measurement and CVS is advisable in multiple pregnancies when one fetus is at high risk of fetal abnormality or aneuploidy. In late gestation (>20 weeks), sufentanyl followed by KCl can be injected in the umbilical vein using the same technique as that described for intrauterine transfusion. This avoids the potentially painful and often difficult intracardiac injection at this gestation. Abortions later than weeks 22 or 24 are accepted in only a few countries. The same goes for fetocide. In monochorionic multiple gestations, KCl injection cannot be used for selective fetocide. Indeed, this would precipitate an acute hypotensive episode in the surviving twin through bleeding into the dead co-twin through the placental anastomoses still present on the placental surface. This would occur irrespective of the histological nature of the vessels. The alternative is to coagulate the umbilical cord. This can be achieved using Nd:YAG laser technology when the cord is still small in diameter; however, the technique may not be used after 20 weeks of gestation. Alternatively, a bipolar forceps of 2–3 mm has been developed that can be passed down a cannula under ultrasound guidance and grasp the cord to coagulate. This is done under continuous ultrasound/colour Doppler control. This efficient technique is still under evaluation. The subsequent risk of preterm premature rupture of the membranes is not precisely known, but could be as high as 20–30%.
Conclusion
244
Ultrasound-guided invasive procedures represent the foundation for fetal medicine. They can be learned as variations of the same technical approach, implying the use of both hands of one operator which would shorten the learning curve and improve the safety of the most frequently performed procedures, such as amniocentesis and CVS. There is rarely such a thing as a difficult procedure when done by a well-trained operator who performs a high number of invasive procedures. In addition, it is important to plan the procedure well by following the simple rules mentioned in this chapter. Ultrasound examination prior to performing the procedure is therefore a key element. Visualizing the target and the entry point on the maternal abdomen ensures a straightforward path without interposition of any fetal structures in the path of the needle.
✩✩✩✩✩✩✩✩✩✩✩ ✩ References pregnancies. In: Santoyala-Forgas J, Lemery D (eds) Interventional ultrasound in obstetrics, gynecology and the breast. Blackwell, Oxford, 1998: 146–150 13. Daffos F, Capella-Pavlowsky M, Forestier F. A new procedure for fetal blood sampling in utero: preliminary results of 53 cases. Am J Obstet Gynecol 1983;146:985–998 14. Ghidini A, Sepulveda W, Lockwood C, Romero R. Complications of fetal blood sampling. Am J Obstet Gynecol 1993;168:1339–1344 15. Perry KG, Hess LW, Roberts WE et al. Cordocentesis by maternal fetal fellows: the learning curve. Fetal Diagn Ther 1991;157:858–859 16. Moise KJ. Intrauterine transfusion with red cells and platelets. West J Med 1993;159:318–324 17. Evans MI, Sacks AJ, Johnson MP, Robichaux AG, May M, Moghissi KS. Sequential invasive assessment of fetal renal function and intrauterine treatment of fetal obstructive uropathies. Obstet Gynecol 1991;77:54–55 18. Rodeck CH, Nicolaides KH. Ultrasound guided invasive procedures in obstetrics. Clin Obstet Gynecol 1983;10:515–540 19. Yamamoto M, El Murr L, Robyr l, Leleu F, Takahashi Y, Ville Y. Incidence and impact of perioperative complications in 175 fetoscopy-guided laser coagulations of chorionic plate anastomoses in fetofetal transfusion syndrome before 26 weeks of gestation. Am J Obstet Gynecol 2005;193:1110–1116 20. Firth H. Chorion villus sampling and limb deficiency – cause or coincidence? Prenat Diagn 1997;17:1313–1330 21. Gonce A, Borrel A, Fortuny A et al. First-trimester screening for trisomy 21 in twin pregnancy: does the addition of biochemistry make an improvement? Prenat Diagn 2005;25:1156–1161 22. Stewart KS, Johnson MP, Quintero RA, Evans MI. Congenital abnormalities in twins: selective termination. Cur Opin Obstet Gynecol 1997;9:136–139 23. Westgren M, Selbing A, Stangenberg M. Fetal intracardiac transfusions in patients with rhesus isoimmuniation. BMJ 1988;296:885–886 24. Evans MI, Ciorca D, Britt DW, Fletcher JC. Update on selective reduction. Prenat Diagn 2005;25:807–813
Invasive procedures in obstetrics
1. Ville Y, Cooper M, Revel A, Frydman R, Nicolaides KH. Development of a training model for ultrasound-guided invasive procedures in fetal medicine. Ultrasound Obstet Gynecol 1995;5:180–183 2. Timor-Tritsch IE, Yeh MN. In vitro training model for diagnostic and therapeutic fetal intravascular needle puncture. Am J Obstet Gynecol 1987;157:858–859 3. Wapner R. Chorionic villous sampling. In: Santoyala-Forgas J, Lemery D (eds) Interventional ultrasound in obstetrics, gynecology and the breast. Blackwell, Oxford, 1998:45–59 4. Jackson L, Wapner R, Barr-Jackson M. Chorionic villus sampling (CVS) is not associated with an increased incidence of limb reduction defects. Abstract for the American Society of Human Genetics 43rd Meeting, New Orleans, LA, October 1993 5. Brambati B, Oldrini A, Lanzani A. Transabdominal chorionic villus sampling: a freehand ultrasound guided technique. Am J Obstet Gynecol 1987;157:134–142 6. MRC Working Party on the Evaluation of Chorionic Villus Sampling. MRC European trial of chorionic villus sampling. Lancet 1991;337:726–741 7. Canadian Collaborative CVSAmniocentesis. Clinical trial of chorionic villous sampling and amniocentesis. Lancet 1991;337:1491–1509 8. Tabor A, Madsen M, Obel EB, Philip J, Bang J, Noorgard Pedersen B. Randomised controlled trial of genetic amniocentesis in 4606 low-risk women. Lancet 1986;i:1287 9. Nicolaides KH, Brizet ML, Patel F, Snijders R. Comparison of chorion villus sampling and early amniocentesis for karyotyping in 1,492 singleton pregnancies. Fetal Diagn Ther 1996;11:9–15 10. Kappel B, Nielsen J, Brogaard Hansen K, Mikkelsen M, Therkelsen AAJ. Spontaneous abortion following midtrimester amniocentesis. Clinical significance of placental perforation and blood-stained amniotic fluid. Br J Obstet Gynaecol 1987;94:50 11. Andreasen E, Kristoffersen T. Incidence of spontaneous abortion after amniocentesis: influence of placental localisation and past obstetric and gynecologic history. Am J Perinatol 1989;6:268 12. Ville Y, Nicolaides KH. Prenatal diagnosis and therapeutic techniques in twin
245
13 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Multiple pregnancies Kurt Hecher Werner Diehl
ABSTRACT Detection of the number of fetuses, chorionicity and amnionicity should be achieved during the first-trimester scan. Invasive diagnostic techniques such as chorion villous sampling and amniocentesis may be used to obtain karyotypes of all fetuses and this should be discussed individually with the couple, taking into account the risk to benefit ratio, i.e. the procedure-related risk of a miscarriage and the individual risk for chromosomal abnormalities. Fetal growth impairment in dichorionic twins will more often reflect uteroplacental insufficiency as compared to singleton pregnancies and fetal surveillance including Doppler ultrasound should be intensified. In monochorionic twins, one should be aware of the risk for the development of twin–twin transfusion syndrome, and amniotic fluid volumes and their relation to bladder filling of both twins should be monitored from the early stages of gestation onwards. Monoamniotic twins, occurring in 5% of monochorionic gestations, show the highest risk for structural anomalities and poor outcome. The assessment of monoamniotic pregnancies implies close fetal monitoring and detection of cord implications. Conjoined twins represent the most severe form of splitting disorders in monozygotic twins. They occur in 1% of monochorionic pregnancies, and their outcome depends mainly on the site of conjoining and the organs involved.
Keywords Amnionicity, chorionicity, early risk assessment, fetal surveillance, multiple pregnancy, zygocity.
Introduction Perinatal mortality and morbidity rates are increased three to seven times in twin pregnancies,8 as compared to singleton gestations. Although twin pregnancies
247
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ account only for 2.5% of the population, they are responsible for up to 12.6% of the overall perinatal mortality rate.28 Additionally, assisted reproduction techniques have led to an increase in the incidence of twinning with almost 50% of the twins resulting from infertility treatment.22 The application of such techniques has also contributed to an increase in the incidence of multiple pregnancies of a higher grade (e.g. triplets, quadruplets). The fact that this population also shows a higher number with women at an advanced age, with an increased age-related risk for chromosomal abnormalities and for impairment of the uteroplacental perfusion, also contributes to the high risk in this collective. Approximately two-thirds of twin pregnancies are dizygotic and therefore dichorionic and diamniotic. One-third is monozygotic; of these, one-third is dichorionic (splitting occurring at less than 4 days after conception) and the other twothirds are monochorionic and diamniotic (splitting occurring from days 4 to 8 after conception). A later splitting (9–13 days) leads to the occurrence of monoamniotic twins, and a division beyond the 14th day to conjoined twins. It is known that mortality and morbidity rates are higher in monochorionic twins.16,17,32 Conditions unique to them, such as twin–twin transfusion syndrome (TTTS), reverse twin arterial perfusion sequence and monoamniotic pregnancies, are responsible for an increased risk of adverse perinatal outcome. Therefore, early assessment of chorionicity and amnionicity plays an important role in the risk stratification of multiple pregnancies and has practical consequences for the management of those pregnancies. Due to the high-risk nature of multiple pregnancies fetal surveillance should be undertaken in appropriate intervals.
First-Trimester Ultrasound Pregnancy Dating The crown–rump length (CRL) of the fetuses is the most important ultrasound parameter for dating of the pregnancy and, if necessary, to correct the gestational age in cases with a non-reliable menstrual history. The onset of early growth retardation in one of the fetuses may indicate a higher risk for chromosomal abnormalities. Normally, the CRLs correlate between co-twins, although some degree of variability has been observed in multifetal pregnancies.19,34 Measurement of the CRL can easily be done at the time of the first-trimester scan (11–14 weeks of gestation). Later in pregnancy, correction of gestational age should be avoided, since growth curves in multiple pregnancies differ from those in singleton pregnancies beyond the second trimester.
Number of Fetuses
248
The currently widespread availability of transvaginal ultrasound enables early detection of multiple pregnancies and their localization. Additionally, it allows precise assessment of chorionicity and amnionicity. The diagnosis of twins with
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fig. 13.1 Assessment of chorionicity. (A) Transverse view of the uterus at 12 weeks of gestation, showing two separate amniotic cavities with two placentae (dichorionicity) and two fetuses. (B) Intertwin membranes in trichorionic triplets at 20 weeks of gestation showing the lambda signs at the placental base. (C) The confluence of the intertwin membranes in a trichorionic triplets pregnancy at 12 weeks of gestation. (D) Pentachorionic quintuplets pregnancy at 10 weeks of gestation.
Multiple pregnancies
the observation of two embryos may be confusing for the parents, if there is subsequent disappearance of one of them during further examinations (vanishing twin phenomenon). The spontaneous incidence of this phenomenon in multiple pregnancies has been reported to be between 21%21 and 50% in triplets23 and occurs most frequently during the first 7 weeks of pregnancy and never beyond 14 weeks. Some authors consider monochorionic twinning as a risk factor for neurological abnormalities in the surviving twin after disappearance of one embryo, since this form of placentation may predispose to vascular events in early fetal life.6 After 10 weeks of gestation a reliable identification of the number of fetuses and their chorionicity may be expected even with transabdominal ultrasound (Fig. 13.1).
249
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Chorionicity and Amnionicity
250
For reasons of risk stratification in multiple pregnancies, one of the most important goals of early ultrasound in this population is the determination of chorionicity and amnionicity.35–37 Early in gestation (6–9 weeks), the presence of two separate gestational sacs indicates dichorionicity. From 10–14 weeks onwards, a thick septum and a triangular tissue projection at the placental base of the separating membrane (lambda sign) predict dichorionicity27 (see Fig. 13.1; Fig. 13.2). This is due to four layers of the intertwin membrane: amniotic and chorionic layers of fetus 1 and chorionic and amniotic layers of fetus 2. Monochorionic twins show a very thin intertwin membrane (only two amniotic layers) and no lambda sign, since there are no chorionic layers between the two amniotic layers of the membrane (see Fig. 13.2). Misdiagnosis of monoamniotic twins due to visualization of a single gestational sac may occur, if identification of the thin separating membrane is difficult. Later during pregnancy, identification of fetal
Fig. 13.2 The lambda sign. (A,C) The lambda sign (arrows) at the placental base of the intertwin membrane in dichorionic pregnancies at 15 weeks (A) and 10 weeks (C) of gestation. (B,D) Absence of the lambda sign (arrows) in monochorionic diamniotic twin pregnancies at 16 weeks (B) and 20 weeks (D) of gestation. Note the thin intertwin membrane (M) and the common anterior placenta (PL).
✩✩✩✩✩✩✩✩✩✩✩ ✩
Nuchal Translucency
Multiple pregnancies
gender may also be helpful in the assessment of chorionicity, although overall two-thirds of twins are of the same sex: one-third consists of all monochorionic twins and the other one of 50% of all dichorionic twins. Discordant sex indicates dichorionicity. Regarding amnionicity, the lack of an intertwin membrane, despite careful scanning of the whole amniotic cavity, leads to the diagnosis of monoamniotic twinning.25 The presence of a unique yolk sac also indicates monoamnionicity.7
Between 10 and 14 weeks of gestation, it is possible to assess the woman's individual risk for chromosomal abnormalities combining the measurement of the nuchal translucency (NT) and maternal age.29 However, in multiple pregnancies, this risk calculation has to take into account several aspects.38,39 In dizygotic twins, the risk for a chromosomal abnormality is calculated individually for each twin in the same fashion as for singleton fetuses. However, the risk that at least one fetus of this pregnancy is affected is the summation of the two individual risks, which is twice as high as in a singleton pregnancy if the individual risks are almost the same. Squaring the singleton risk derives from the risk that both fetuses are affected. In monozygotic twins, the risk for a chromosomal abnormality is the same as that of a singleton pregnancy, but in cases of an abnormal karyotype both fetuses are affected. A higher false-positive rate for risk calculations of chromosomal defects in monochorionic twins can be explained due to an early manifestation of a twin–twin transfusion syndrome (TTTS), where an increased NT in at least one fetus has been shown as a marker for prediction of TTTS.26 Increased NT in the recipient fetus as a consequence of hypervolaemia is considered as an early sign for TTTS and the risk for the development of the syndrome is increased almost fourfold. The nature of the estimation of a likelihood, the options of invasive diagnostic procedures for the assessment of the fetal karyotype and the possible consequences of an abnormal result have to be explained in detail during the counselling. The knowledge of chorionicity is paramount for risk estimation, the decision regarding the technique of invasive testing and its consequences.
Invasive Diagnostic Procedures Chorionic villous sampling (CVS) can be done as early as 10–12 weeks of gestation and has then a risk for a procedure-related pregnancy loss of about 1%. In another 1% of cases the results may be unclear, for instance due to the presence of mosaicism in the chorionic tissue. However, studies have established comparable risks to those of second-trimester amniocentesis, if performed by experienced operators.20 In dichorionic twins these risks may increase, if double sampling has to be performed to assure obtaining a result for both fetuses. Thus, sampling has optimally
251
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ to be performed below the umbilical cord insertions of the respective twins. The possibility of cross-contamination of the sample, when single puncture is performed, is about 0.6%. Maternal contamination is another problem of CVS, as well as sampling the same fetus twice, but these problems occur in less than 1% of procedures, as reported in recent studies.1,31 The advantage of this procedure, which can be performed earlier than amniocentesis, is that in case of a chromosomal defect of one of the fetuses, an earlier selective fetocide with a lower procedure-related risk for fetal loss (5% versus 16% at 15 weeks or later) may be performed.9 If the individual risk for chromosomal abnormalities, calculated by maternal age and NT, in at least one of the fetuses is greater than 1 in 50, it may be preferable to perform a CVS for fetal karyotyping. For pregnancies with a lower combined risk calculation, an amniocentesis after 15 weeks of gestation may be more appropriate.24 Also, with amniocentesis in dichorionic twins, obtaining a result for both fetuses has to be guaranteed. This can be achieved by either puncturing each amniotic sac separately with two needle insertions or with only one uterine needle insertion by crossing the intertwin membrane and sampling amniotic fluid separately from each sac under ultrasound guidance. In structurally normal monochorionic twins, single sampling may be sufficient, since monozygotic fetuses can be expected to be genetically identical.
Growth Discrepancy and Fetal Monitoring
252
The longitudinal assessment of fetal growth in both twins gives valuable information about their intrauterine well-being. In dichorionic twins biometry should be performed at monthly intervals,28 keeping in mind the higher risk for intrauterine growth retardation, as compared to singleton pregnancies. Beyond the 20th week of gestation even normal twin fetuses may show smaller biometric measurements than singletons and, therefore, specially adapted growth curves should be used.15 If the growth curve of one of the fetuses shows the tendency to approach the 5th percentile for gestational age, control intervals should be shortened to every second week. In small-for-gestational age fetuses, the benefits of Doppler ultrasound should be used. Serial ultrasound examinations from the second trimester onwards, including Doppler velocimetry if necessary, represent the most reasonable antenatal assessment of twin pregnancies.11 However, in monochorionic twins, due to the existence of placental vascular anastomoses which continuously allow interfetal blood flow, ultrasound examinations should be performed at shorter intervals, every 2–3 weeks. Attention should be drawn to the amounts of amniotic fluid in each amniotic cavity and the bladder filling of each fetus. An early TTTS can be recognized following these criteria. The development of growth restriction of one fetus may result as a consequence of TTTS, but also as a consequence of placental insufficiency.16 Doppler assessment of the fetal circulation may help to distinguish between these two conditions.33
✩✩✩✩✩✩✩✩✩✩✩ ✩
Malformations and Fetal Demise Multiple pregnancies
In general, the risk for malformations in twin pregnancies is elevated. It is increased in monochorionic twins and in monoamniotic twins it is reported to be as high as 38%,4,25,40 where the inherent mechanism for the malformation may be related to the process of splitting itself. The risk for fetal loss in dichorionic twins after selective fetocide, due to the presence of a chromosomal abnormality in one of the fetuses, is about 10%. Spontaneous intrauterine death of one twin usually does not affect the co-twin, because there are no vascular anastomoses in dichorionic placentae. However, the situation is completely different in monochorionic twins. After a single intrauterine death there is a high risk for damage of the co-twin, due to the presence of placental vascular anastomoses.3 As a consequence of an acute loss of blood towards the dying fetus or immediately after its death, a hypotensive and anaemic episode may occur in the co-twin and subsequently lead to its death or to neurological damage (in 20–30%). This has also to be taken into account if one of the fetuses of a monochorionic twin pregnancy shows structural anomalies and selective termination is considered. More recently, invasive techniques have been developed to occlude completely the umbilical vessels by laser or bipolar coagulation of the umbilical cord, to avoid acute haemodynamic imbalance in the co-twin.10
Twin–Twin Transfusion Syndrome In 10–15% of monochorionic pregnancies, severe midtrimester TTTS develops, which is associated with a mortality rate of 80–90% if left untreated.41–43 The underlying cause for the development of the syndrome is the presence of vascular anastomoses in all monochorionic placentae. As a consequence of the different types of anastomoses (arteriovenous, arterioarterial and venovenous) and the blood flow direction in the arteriovenous anastomoses, a net imbalance in intertwin blood flow may ensue. The recipient fetus becomes hypervolaemic and polyuric, leading to polyhydramnios, and may develop congestive heart failure due to cardiac overload. The donor fetus becomes hypovolaemic and anuric, leading to severe oligo- and anhydramnios. Premature rupture of membranes, owing to the extreme polyhydramnios, miscarriage and extremely premature delivery, as well as intrauterine death, are the main complications contributing to the high perinatal mortality. The diagnostic ultrasound criteria for TTTS are the observation of a single monochorionic placenta, the presence of polyhydramnios in the amniotic cavity of the recipient fetus, who shows also a distended bladder (Fig. 13.3), and severe oligo- or anhydramnios in the amniotic cavity of the donor fetus, who shows only a weak or no bladder filling at all. Due to the absence of amniotic fluid in the donor's amniotic sac, the intertwin membrane may not be visible as it is adherent to the fetus who is pressed against the uterine wall or the placenta (stuck twin) (Fig. 13.4). The absence of a visible intertwin membrane may lead to the misdiagnosis of monoamniotic twins. TTTS may develop in the early second trimester (at 16 or 17 weeks of gestation) and within a short period of time (1 or 2 weeks).
253
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 13.3 Twin–twin transfusion syndrome. Note the distended (polyuric) bladder of the recipient twin and the massive polyhydramnios (gestational age 21+5 weeks; deepest vertical pool was 14 cm).
Fig. 13.4 Twin–twin transfusion syndrome. The ‘stuck twin’ phenomenon: due to anhydramnios the donor twin (circle) is stuck to the uterine wall.
254
Doppler assessment of blood flow in the umbilical arteries and the ductus venosus of both twins provides valuable information about the fetal cardiovascular condition. In the recipient fetus, signs of congestive heart failure, such as abnormal ductus venosus flow, tricuspid and mitral regurgitation, fetal hydrops (ascites, pleural effusions, skin oedema), reduce the probability of survival. In the donor fetus, an increased placental resistance with absent or reversed enddiastolic flow in the umbilical artery is associated with a lower survival rate.33 As fetal viability is not yet achieved during the second trimester of pregnancy, delivery is not a realistic option for the management of these cases. There are two options for therapy: serial amniodrainages and percutaneous fetoscopic laser coagulation of the placental vascular anastomoses. The latter offers a causal therapeutic approach and an overall survival rate of 68% and 81% of pregnancies with
✩✩✩✩✩✩✩✩✩✩✩ ✩
Multiple pregnancies
at least one survivor can be achieved.18 During laser surgery a mean of 5–6 anastomoses can be identified and coagulated. In all cases arteriovenous anastomoses from donor to recipient are present, with the majority of cases also showing anastomoses shunting in the opposite direction, and arterioarterial anastomoses are present in about one-third of pregnancies with TTTS.12 After laser therapy, follow-up scans are performed at weekly intervals first and then every second week, as normally done for fetal surveillance in monochorionic twins, drawing attention to the amounts of amniotic fluid, bladder fillings, growth patterns and Doppler flow velocity waveforms of both fetuses.
Twin Reversed Arterial Perfusion The prevalence of twin reversed arterial perfusion (TRAP) or acardiac twins is about 1 in 35,000 pregnancies. The presence of an arterioarterial and a venovenous anastomosis between both cord insertions in monochorionic twins may lead to a reversed perfusion of one fetus, if one pulse wave predominates over the other early in gestation. In the reversely perfused fetus there is no cardiac development at all or only a rudimentary heart tube can be detected. The development of the upper part of the body is also severely impaired and most of the acardiac fetuses also show acrania and severe hydrops. This condition represents a high risk for heart failure and intrauterine demise or preterm delivery of the pumping twin. The typical ultrasound appearance of the acardiac twin is a hydropic mass without a heartbeat or only with a rudimentary pulsatile cardiac structure. Colour Doppler sonography reveals the reversed perfusion via the single umbilical artery (Fig. 13.5). These ultrasound features are unique to this disorder and may be detected in the first trimester of pregnancy. Treatment strategies range from vessel obliteration by intracardiac application of alcohol to fetoscopic ligation and bipolar or laser coagulation of the umbilical cord of the acardiac twin.
Fig. 13.5 Twin reversed arterial perfusion (TRAP sequence). (A) The hydropic acardiac twin with multiple malformations at 20 weeks of gestation. (B) Colour Doppler depicts the reversed arterial perfusion (blue) to the acardiac twin and the returning blood flow via the umbilical vein (red) to the pumping twin.
255
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Monoamniotic Twins Monoamniotic twinning occurs in 5% of monochorionic twins (1% of all twins), and the most severe form of splitting disorders in monozygotic twins is conjoined twins. At the 10–14-week scan, the criteria for monoamnionicity are the absence of the intertwin amniotic membrane and the presence of only one yolk sac7 and it should be suspected if the placental cord insertions are close to each other and an unusual intrauterine position of both fetuses, in close proximity to each other, is seen.25 Monoamniotic twins show a significantly increased risk for structural anomalies and for poor perinatal outcome, even in the absence of an intertwin discordance. In both structurally normal and abnormal twins, cord entanglement, which has been reported to be present as early as the first trimester,2 has been responsible for the demise of one or both fetuses in the majority of cases. The aim of fetal surveillance should be to reach at least 32 weeks of gestation and delivery by elective caesarean section should be performed to avoid acute cord complications during delivery. Cord entanglement may be detected by colour Doppler ultrasound. However, its consequences remain controversial, because the incidence of loose entanglement seems to be high, but fetal jeopardy occurs only if this leads to compression of the cords, which may be an acute event. The primary ultrasound feature of conjoined twins is the fact that they are always close to each other with common movement patterns and without separation from each other if observed over a certain period of time. The chance for survival depends on the site of conjoining and the organs involved, and overall about 50% are stillborn. One third of the live-born twins have defects, which are impossible to correct surgically, and in those cases where surgery is attempted, a survival rate of about 60% of babies is achieved.30
Higher-Order Multiple Pregnancies Recently the incidence for multiples of a higher order has increased due to the use of different techniques in assisted reproduction. The use of transvaginal and transabdominal ultrasound to assess the number of fetuses and their chorioni city is fundamental in the early diagnosis and management of these pregnancies. With the measurement of the nuchal translucency, the individual fetal risk for chromosomal abnormalities and other maldevelopments can be calculated and a selective reduction can be performed under ultrasound guidance to reduce the perinatal risk associated with multiples of higher order than twins or triplets. Multifetal reduction has been reported to reduce triplets to twins5 and the risk for fetal loss after the procedure has been continuously diminishing during recent years, as more experience in this technique has been gained. In general, the higher the starting number of fetuses, the poorer is the outcome after reduction, with fetal loss rates reported to range from 15.4% to 4.5% according to starting numbers ranging from six to three fetuses, respectively.13,14 256
✩✩✩✩✩✩✩✩✩✩✩ ✩ References 13. Evans MI, Goldberg JD, Horenstein J et al. Selective termination for structural, chromosomal, and mendelian anomalies: international experience. Am J Obstet Gynecol 1999;181:893–897 14. Evans MI, Berkowitz RL, Wapner RJ et al. Improvement in outcomes of multifetal pregnancy reduction with increased experience. Am J Obstet Gynecol 2001;184:97–103 15. Farina A, Vesce F, Garutti P, Jorizzo G, Bianciotto A. Evaluation of intrauterine growth pattern of twins by linear discriminant analysis of the values of biparietal diameter, femur length and abdominal circumference. Gynecol Obstet Invest 1999;48:14–17 16. Gaziano EP, De Lia JE, Kuhlmann RS. Diamniotic monochorionic twin gestations: an overview. J Matern Fetal Med 2000;9:89–96 17. Hatkar PA, Bhide AG. Perinatal outcome of twins in relation to chorionicity. J Postgrad Med 1999;45:33–37 18. Hecher K, Diehl W, Zikulnig L, Vetter M, Hackelöer BJ. Endoscopic laser coagulation of placental vascular anastomoses in 200 pregnancies with severe mid-trimester twinto-twin transfusion syndrome. Eur J Obstet Gynecol Reprod Biol 2000;92:135–139 19. Isada NB, Sorokin Y, Drugan A, Johnson MP, Zador I, Evans MI. First trimester interfetal size variation in well-dated multifetal pregnancies. Fetal Diagn Ther 1992;7:82–86 20. Jenkins TM, Wapner RJ. First trimester prenatal diagnosis: chorionic villous sampling. Semin Perinatol 1999;23:403–413 21. Landy HJ, Weiner S, Corson SL, Batzer FR, Bolognese RJ. The ‘vanishing twin’: ultrasonographic assessment of fetal disappearance in the first trimester. Am J Obstet Gynecol 1986;155:14–19 22. Loos R, Demron C, Vlietinick R, Demron R. The East Flanders prospective twin survey (Belgium): a population-based register. Twin Res 1998;1:167–178 23. Manzur A, Goldsman MP, Stone SC, Frederick JL, Balmaceda JP, Asch RH. Outcome of triplet pregnancies after assisted reproductive techniques: how frequent are the vanishing embryos? Fertil Steril 1995;63:252–257 24. Pandya P. Ultrasound and multiple pregnancies. Front Fetal Health 2001;3: 89–91
Multiple pregnancies
1. Appleman Z, Vinkler C, Caspi B. Chorionic villous sampling in multiple pregnancies. Eur J Obstet Gynecol Reprod Biol 1999;85:979 2. Arabin B, Laurini RN, van Eyck J. Early prenatal diagnosis of cord entanglement in monoamniotic multiple pregnancies. Ultrasound Obstet Gynecol 1999;13: 181–186 3. Bajoria R, Wee LY, Anwar S, Ward S. Outcome of twin pregnancies complicated by single intrauterine death in relation to vascular anatomy of the monochorionic placenta. Hum Reprod 1999;14:2124–2130 4. Baldwin VJ. The pathology of monochorionic monozygocity. In: Baldwin VJ (ed) Pathology of multiple pregnancy. Springer Verlag, New York, 1994: 199–214 5. Boulot P, Vignal J, Vergnes C, Dechaud H, Faure JM, Hedon B. Multifetal reduction of triplets to twins: a prospective comparison of pregnancy outcome. Hum Reprod 2000;15:1619–1623 6. Brodtkorb E, Myhr G, Gimse R. Is monochorionic twinning a risk factor for focal cortical dysgenesis? Acta Neurol Scand 2000;102:53–59 7. Bromley B, Benacerraf B. Using the number of yolk sacs to determine amnionicity in early first trimester monochorionic twins. J Ultrasound Med 1995;14:415–419 8. Chitrit Y, Filidori M, Pons JC, Duyme M, Papiernik E. Perinatal mortality in twin pregnancies: a 3-year analysis in Seine Saint-Denis (France). Eur J Obstet Gynecol Reprod Biol 1999;86:23–28 9. De Catte L, Liebaers I, Foulon W. Outcome of twin gestations after first trimester chorionic villous sampling. Obstet Gynecol 2000;96:714–720 10. Deprest JA, Audibert F, Van Schoubroeck D, Hecher K, Mahieu-Caputo D. Bipolar coagulation of the umbilical cord in complicated monochorionic twin pregnancy. Am J Obstet Gynecol 2000;182:340–345 11. Devoe LD, Ware DJ. Antenatal assessment of twin gestation. Semin Perinatol 1995;19:413–423 12. Diehl W, Hecher K, Zikulnig L, Vetter M, Hackelöer BJ. Placental vascular anastomoses visualised during fetoscopic laser surgery in severe mid-trimester twin–twin transfusion syndrome. Placenta 2001;22:876–881
257
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
258
25. Sebire NJ, Souka A, Skentou H, Geerts L, Nicolaides KH. First trimester diagnosis of monoamniotic twin pregnancies. Ultrasound Obstet Gynecol 2000;16:223–225 26. Sebire NJ, Souka A, Skentou H, Geerts L, Nicolaides KH. Early prediction of severe twin-to-twin transfusion syndrome. Hum Reprod 2000;15:2008–2010 27. Sepulveda W, Sebire NJ, Hughes K, Odibo A, Nicolaides KH. The lambda sign at 10-14 weeks of gestation as a predictor of chorionicity in twin pregnancies. Ultrasound Obstet Gynecol 1996;7:421–423 28. Sherer DM. Is less intensive fetal surveillance of dichorionic twin gestations justified? Editorial. Ultrasound Obstet Gynecol 2000;15:167–173 29. Snijders RJM, Noble P, Sebire NJ, Souka AP, Nicolaides KH. UK multicentre project on assessment of risk for trisomy 21 by maternal age and fetal nuchal translucency at 10–14 weeks of gestation. Fetal Medicine Foundation First Trimester Screening Group. Lancet 1998;352: 343–346 30. Spitz L. Conjoined twins. Br J Surg 1996;83:1028–1030 31. van den Berg C, Braat AP, Van Opstal D et al. Amniocentesis or chorionic villous sampling in multiple gestations? Experience with 500 cases. Prenat Diagn 1999;19: 234–244 32. Victoria A, Mora G, Arias F. Perinatal outcome, placental pathology, and severity of discordance in monochorionic and dichorionic twins. Obstet Gynecol 2001;97:310–355 33. Zikulnig L, Hecher K, Bregenzer T, Bäz E, Hackelöer BJ. Prognostic factors in severe twin–twin transfusion syndrome treated by endoscopic laser surgery. Ultrasound Obstet Gynecol 1999;14:380–387
34. Kalish RB, Gupta M, Perni SC, Berman S, Chasen ST. Clinical significance of first trimester crown–rump length disparity in dichorionic twin gestation. Am J Obstet Gynecol 2004;191:1437–1440 35. Machin GA. Why is it important to diagnose chorionicity and how do we do it? Best Pract Res Clin Obstet Gynecol 2004;18:515–530 36. Menon DK. A retrospective study of the accuracy of sonographic chorionicity determination in twin pregnancies. Twin Res Hum Genet 2005;8:259–261 37. Geipel A, Berg C, Katalinic A et al. Prenatal diagnosis and obstetric outcomes in triplet pregnancies in relation to chorionicity. Br J Obstet Gynaecol 2005;112:554–558 38. Van der Cruys, Faiola S, Auer M, Sebire N, Nicolaides KH. Screening for trisomy 21 in monochorionic twins by measurement of fetal nuchal translucency thickness. Ultrasound Obstet Gynecol 2005;25: 551–553 39. Wald NJ, Rish S, Hackshaw AK. Combining nuchal translucency and serum markers in prenatal sceening for Down syndrome in twin pregnancies. Prenat Diagn 2003;23:588–592 40. Garne E, Andersen HJ. The impact of multiple pregnancies and malformations on perinatal mortality. J Perinat Med 2004;32:215–219 41. Huber A, Hecher K. How can we diagnose and manage twin-twin transfusion syndrome? Best Pract Res Clin Obstet Gynaecol 2004;18:543–556 42. Fisk NM, Tan TY, Taylor MJ. Stagesaved treatment of twin-twin transfusion syndrome. Am J Obstet Gynecol 2004;190:1491–1492 43. Robyz R, Quarello E, Ville Y. Management of fetofetal transfusion syndrome. Prenat Diagn 2005;25:786–795
14 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis Rabih Chaoui Bernard Benoit
Abstract Three-dimensional ultrasound has been the most rapidly evolving technique in fetal imaging in recent years and is mainly known for the demonstration of the face or other fetal surface structures. The potential of this technique in prenatal diagnosis is, however, greater, based on the possibility of acquiring a volume data set of a region of interest which can then be displayed in different ways. This chapter will emphasize these display modes as the demonstrations of reconstructed two-dimensional images either as orthogonal or parallel crosssection planes (tomographic mode) or the rendering of the three-dimensional/ four-dimensional information. Rendering includes the surface mode, the maximum, minimum and inversion modes, as well as glass body mode when combined with colour or power Doppler acquisition. Spatial and temporal image correlation technology enables the acquisition of fetal heart data and the display of one single cardiac cycle in different modes. The chapter supports the idea that we are now moving from the era of ‘sonography in two-dimensional planes’ to ‘volume ultrasound’.
Keywords Inversion mode, maximum mode, minimum mode, prenatal diagnosis, spatial and temporal image correlation, three-dimensional ultrasound, tomographic imaging, volume ultrasound.
Introduction Three-dimensional (3D) ultrasound has become the most rapidly evolving technique in fetal imaging, but some examiners are still using 3D and fourdimensional (4D) techniques only to demonstrate the fetal face to the parents,
259
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ which has made this new technique very popular with them as well. However, the concept of ‘volume ultrasound’ introduced a few years ago enabled a more comprehensive medical and clinical application of 3D technology to prenatal diagnosis.1 A volume data set of the region of interest is acquired digitally, and the information stored can be displayed in different ways to highlight the spatial arrangement of a specific structure in the region of interest. Many colleagues may still be unfamiliar with all of these features, which are now well established in targeted prenatal diagnosis for ruling out or clearly demonstrating fetal malformations. In this chapter we will review the potential of volume ultrasound and the application of some display modes in clinical work.
Volume Acquisition A volume data set can be acquired in different ways. The acquisition can be achieved as a:
• static 3D • real-time 3D or 4D • spatial and temporal image correlation for heart and vessels. Static 3D This is the 3D used in most fetal studies (face, hands, etc.) and consists of a single volume data set. The volume quality is defined by the choice of the acquisition time. Static 3D can also be combined with colour Doppler, power Doppler, high-definition (HD) flow, and B-flow, depending on the question of interest.
Real-Time 3D or 4D Ultrasound Real-time 3D or 4D is achieved today mainly by a mechanical 3D transducer with a rapid acquisition from 1.5 to 40 volumes/sec. A few matrix transducers provide electronic 3D information but their use in obstetric ultrasound is still limited. The advantage of a 4D examination is its ease of use. The direct result on the screen enables online manipulation to acquire the best image by changing the gain and the contrast depending on the mode used. Furthermore, it allows the transducer to be moved depending on the insonation angle. The technique is ideal for studying fetal movements and behaviour throughout pregnancy (smiling, yawning, grimacing, etc.). It can also be used for fetal echocardiography but this requires a great deal of experience.
Spatial and Temporal Image Correlation
260
Spatial and temporal image correlation (STIC) is a software application providing an acquisition of a fetal heart volume data set over a period of few seconds (i.e. 7.5–15 sec). It allows the acquisition of numerous planes including
✩✩✩✩✩✩✩✩✩✩✩ ✩
Volume Data Display Single Plane of Choice, Multiplanar Orthogonal Planes or Multiple Tomographic Parallel Slices From a digitally stored 3D/4D data set, cross-sectional views can be obtained at any desired orientation (a so-called ‘anyplane’), direction and depth. It must be borne in mind that the acquisition (A-) plane provides the best information, whereas the reconstructed planes (B-, C- or others) are of lesser quality. This should be considered during the volume acquisition. The 2D image analysis from a volume can be achieved from a 3D, 4D or STIC data set. The display format is either a single-plane view or a multiplanar view showing three planes which are perpendicular to each other (Fig. 14.1). In the lateral view the intersection of the three planes is a dot and by moving the position of this dot, the examiner can navigate through the volume (see Fig. 14.1). The recent introduction of multislice analysis known as tomographic ultrasound imaging (TUI) is similar to the tomographic assessment known from computed tomography (CT) and magnetic resonance (MR) workstations (Figs 14.2, 14.3). The examiner can define the slice thickness and the number of planes demonstrated. The multiplanar mode can be used to acquire a plane not directly seen on cross-section 2D during live examination, mainly in cases with non-optimal fetal position, so as to demonstrate the corpus callosum, a fetal profile, a limb or the aortic arch. It can be used to visualize exact midline planes after making adjustments in the two other orthogonal planes (for nasal bone assessment). One of the major advantages of a 3D data set is the potential for offline examination of a few volumes at a remote station.4 One of the future potential uses of this mode could be the transfer of data via the Internet to a remote site to get a second opinion or a complete offline evaluation without examining the patient.5 However, since the quality of reconstructed images depends mainly on the original acquisition, the examiner should consider this aspect when acquiring volumes for future studies.
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
additional information from an entire cardiac cycle. The software calculates the mean heart rate acquired and the images in the volume are rearranged according to their temporal event within the heart cycle. The displayed volume then includes a single ‘hypothetical’ heart cycle, which is reconstructed from single selected images of the A-plane (acquisition plane) in the different phases of the heart cycle, whereas the B- and C-planes are reconstructed digitally.2 STIC can be used with grey-scale fetal echocardiography but can also be combined with colour Doppler, power Doppler, HD flow, B-flow, etc.3 Once the acquisition of a volume is achieved, the information can be visualized as either single or multiple 2D images regenerated from the volume and selected by the examiner or as a volume spatial information called 3D rendering, allowing the application of different modes. Some of the actual display modes will be emphasized and illustrated in this chapter.
261
Ultrasound in obstetrics and gynaecology 262
Fig. 14.1 Volume data set of a fetal face shown with the ‘multiplanar mode’ with three orthogonal planes. The dot is the intersection of all three planes and can be used to achieve the best position for assessing the profile. In the C-plane (lower panel) the dot is on the nasal bone. In the lower panel in another fetus the volume information of the face was used to achieve a plane of the soft palate after offline processing.
Fig. 14.3 In this fetal thorax, the cross-section volume acquisition in anterior–posterior tomographic mode is used to demonstrate the slices of the heart, lungs, stomach, diaphragm, etc. In the lower middle panel the bifurcation of the trachea is well seen.
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Fig. 14.2 Tomographic ultrasound imaging (TUI) of the brain demonstrating all important brain structures including the lateral ventricles, the cerebellum, the cavum septum pellucidum and insula.
263
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 14.4 TUI can be used for the heart combined with STIC. Within one image mainly moving structures can be seen.
Once a volume data set of a fetal region is stored, the examiner can scroll through the volume to get the plane of interest independent from the insonation angle. In a STIC volume the reconstructed cardiac volume can be displayed in the multiplanar or tomographic modes (Fig. 14.4), and played in slow motion or stopped at any time for detailed analysis of specific phases of the cardiac cycle. When combined with colour Doppler, events within the cardiac cycle during systole and diastole can be very well demonstrated.
Surface Mode Rendering
264
The image rendering of the fetal surface is the best known and most commonly used display modality in 3D and 4D. From the volume acquired, the skin is primarily demonstrated (surface) and not the organs inside the body. It is used to visualize the surface of a structure which is best achieved in the interlay between fluid and surface, such as the face of a fetus in amniotic fluid or the valves within the heart. The main advantage of the technique is its ease of use and its impact on patients and doctors due to the lifelike image (Fig. 14.5), and comparison with the postnatal appearance. Clinical applications include demonstration of the whole fetus in the first trimester up to 12 weeks' gestation (see Fig. 14.5), and demonstration of the face (Fig. 14.6), limbs, etc. in order to rule out or confirm anomalies involving the skin as well as facial anomalies, spina bifida, limb anomalies and others. It is best demonstrated using 3D as well as 4D, whereas the latter
✩✩✩✩✩✩✩✩✩✩✩ ✩
Fig. 14.6 With surface mode, maturation of the face and changes occurring during pregnancy are well recognized. Three fetuses at 14 weeks (left), 26 weeks (middle) and 31 weeks (right).
can be used to analyse behaviour such as fetal movements, grimacing, yawning or eye opening. Surface rendering can be applied to the fetal heart to visualize cardiac cavities and valves (Fig. 14.7). It can be used in the brain to demonstrate cavities such as the lateral ventricles, especially in the presence of brain anomalies.
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Fig. 14.5 Surface mode demonstrating two fetuses at 10 weeks (left) and at 13 weeks.
Maximum Mode Rendering This mode is used to highlight the maximal echo information of a volume data set and is an ideal tool for the 3D reconstruction of bony structures (Fig. 14.8).6 In general, cranial bones, the ribs and other curvilinear bones cannot be clearly seen in a single 2D plane and are therefore better assessed in a maximum mode projection. This technique has been applied in the demonstration of spine and limb abnormalities but was recently used in the assessment of the nasal bones, the cranial bones and corresponding sutures in normal and abnormal conditions.7–11 This technique delivers a picture similar to an x-ray of the bony skeleton in the fetus.
265
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 14.7 Acquisition with STIC and surface mode rendering can be used at the level of the heart to visualize the spatial appearance of the heart cavities.
Fig. 14.8 Maximum mode rendering is used to visualize the fetal skeleton; here the bony face with the nasal bones and the metopic suture (left), the skull from the side with skull sutures (middle), and the fetal spine with the scapulae, long bones and pelvis (right).
Minimum Mode Rendering
266
This mode is used to highlight the hypoechoic structures in the volume of interest and to demonstrate a 3D projection of vessels, cysts, bladders and others that appear black against a surrounding of more echogenic tissue (Fig. 14.9). It is preferable to make the rendering box narrow in order to focus on the region of interest. Within the box, the presence of amniotic fluid should be avoided as it casts a large black shadow. Images produced with this technique are similar to x-ray projection. Regions of interest are mainly the stomach (see Fig.14.9 right), the bladder, the brain ventricles and the heart with the corresponding vessels.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Inversion Mode Rendering This display mode inverts the colour of the anechoic information (similar to negative/positive film), thus presenting the hypoechoic structures as echogenic solids.12,13 It blackens most of the surrounding tissue information (Fig. 14.10). By changing certain preset parameters, the image can be improved. This technique was also called negative surface display and it was discovered that the images produced were similar to postmortem casting. Artifacts may result from rib shadowing or from amniotic fluid, etc., but can be eliminated using the electronic scalpel during offline volume manipulation.
Fig. 14.10 Inversion mode in different fetal conditions. (Left top) A dilated ventricle on 2D in a longitudinal view in a fetus with spina bifida. (Left bottom) Inversion mode demonstrating the shape of the dilated ventricles in the same fetus. The black areas are the lack of information of the choroid plexus. (Middle) A fetal bladder with dilated ureter and hydronephrosis. (Right) Inversion mode demonstrating the heart and the crossing of the great vessels.
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Fig. 14.9 Minimum mode rendering demonstrating in the left and middle images the abdomen with bladder (BL), gallbladder (GB), umbilical vein (UV), stomach (ST), inferior vena cava (VCI) and aorta (AO). On the right, as comparison, a double bubble sign observed at 24 weeks in duodenal atresia.
267
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ The role of this technique has been analysed in visualizing cardiac and extra cardiac fluid-filled structures in the fetus. Application fields are not only the heart and vessels (see Fig. 14.10 right) but also kidneys in hydronephrosis (see Fig. 14.10 middle), brain ventricles (see Fig. 14.10 left) and other hypoechoic cystic structures. Regions of interest in the fetus could be the fluid-filled structures as the stomach, the urinary bladder or gallbladder. The shape of the stomach and duodenum in the presence of a double bubble in duodenal atresia could be a clinically important application. The kidneys can mainly be demonstrated in anteroposterior longitudinal projection and clinical benefit can be found in multicystic kidneys and hydronephrosis. Intracranial brain structures, especially the lateral ventricles in early pregnancy, can be clearly demonstrated and malformations with disturbed anatomy of the lateral ventricles can be seen with inversion mode. One of the major fields of interest with inversion mode is the cardiovascular system. The examiner can visualize the heart and vessels in a manner similar to 3D power Doppler ultrasound at a better resolution and with a more rapid acquisition rate. Particularly easily demonstrated is the crossing of the vessels of the heart or the relationship of the ventricles and their size. The main advantage of this technique is that the image is similar to the one acquired by power Doppler but without the difficulties encountered in adjusting the image. The volume can be acquired in grey scale as 3D static or as a STIC, at a high frame rate and resolution, whereas volumes with power Doppler information are at low frame rates and subject to movement artifacts. Thus, the image quality with inversion mode is superior to the quality obtained by power Doppler; however, it lacks the information of neighbouring tissue demonstrated in the glass body mode. Since inversion mode can also be used for volume calculation, it could be more easily used to calculate volumes of structures with irregular shape than with the VOCAL technique.
Glass Body Mode Rendering This mode is used to demonstrate a volume with grey scale and colour or power Doppler information simultaneously. The acquisition can either be achieved as static 3D or as a STIC. Volume data can be displayed in three ways: the colour information alone, the grey-scale information alone or a combination of both as a so-called ‘glass body’ mode (Fig. 14.11). A prerequisite for a good volume is the optimal presetting of the colour during 2D scan before acquiring a volume. One of the main application fields of this mode is the demonstration of the cardiac chambers and the great vessels14 (see Fig. 14.11). Peripheral vessels such as the umbilical cord (see Fig. 14.11), intra-abdominal, thoracic and brain vessels can be well demonstrated.
Volume Calculation
268
Biometry is an integral part of the antenatal ultrasound examination and has been achieved for years by measuring distances, circumferences and areas. The acquisition of a 3D volume data set allows easy reconstruction of a selected 2D plane to
✩✩✩✩✩✩✩✩✩✩✩ ✩
perform well-known measurements such as nuchal translucency, biparietal diameter or femur length, but also offers the potential to accurately calculate the volume of a selected region of interest. Volume measurements can be achieved using either the multiplanar mode or the VOCAL™ software (VOlume CALculation). Recently, another possibility has been developed for liquid-filled structures involving the threshold principle in combination with the inversion mode. Volume measurements are still time-consuming and thus limited to research purposes. Volume measurements and charts were reported for the placenta, the amniotic cavity, the first trimester fetus, the fetal brain, liver and arm, but there was a special interest in measuring fetal lung volume.15,16 Fields of interest in these measurements focused chiefly on the detection of difference in volume in pregnancies complicated by chromosomal anomalies, diabetes, intrauterine growth restriction and congenital diaphragmatic hernia.
Conclusion Three-dimensional ultrasound application in prenatal diagnosis should not be limited to the demonstration of the fetal face to please the parents. The concept of volume ultrasound demonstrated in this chapter enables the acquisition of a digital volume data set and the display of the information in different ways. The different display modes available can be used for the demonstration of the spatial appearance of surface structures as well as the projection of bony structures for a better understanding of skeletal and other findings. The multiplanar mode and tomographic imaging allow the reconstruction of planes not directly seen on the screen and offer new insight into fetal anatomy similar to images now demonstrated by MRI for brain structures. The numerous enthusiastic articles on 3D written in recent years confirm that we are rapidly moving from the era of ‘sonography in 2D planes’ to ‘volume ultrasound’. New rendering modes and clinical features will appear in the near future and the development of faster processors in computer technology will enable the advent of matrix transducers with the possible instant application of these techniques.
Three-dimensional and four-dimensional ultrasound application in prenatal diagnosis
Fig. 14.11 Glass body mode. On the left, a longitudinal view of the brain with vessels (pericallosal artery and ramifications). In the middle, the heart and the great vessels from a STIC volume. On the right, the posterior placenta demonstrating the central insertion of the umbilical vessels.
269
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
References
270
1. Chaoui R, Heling KS. Three-dimensional ultrasound in prenatal diagnosis. Curr Opin Obstet Gynecol 2006;18:292–302 2. Devore GR, Falkensammer P, Sklansky MS, Platt LD. Spatio-temporal image correlation (STIC): new technology for evaluation of the fetal heart. Ultrasound Obstet Gynecol 2003;22:480–487 3. Chaoui R, Heling KS. New developments in fetal heart scanning: three- and fourdimensional fetal echocardiography. Semin Fetal Neonatal Med 2005;10:567–577 4. Benacerraf BR, Shipp TD, Bromley B. How sonographic tomography will change the face of obstetric sonography: a pilot study. J Ultrasound Med 2005;24:371–378 5. Vinals F, Mandujano L, Vargas G, Giuliano A. Prenatal diagnosis of congenital heart disease using four-dimensional spatio-temporal image correlation (STIC) telemedicine via an Internet link: a pilot study. Ultrasound Obstet Gynecol 2005;25:15–31 6. Benoit B. The value of three-dimensional ultrasonography in the screening of the fetal skeleton. Child's Nerv Syst 2003;19 (7–8):403–409 7. Dikkeboom CM, Roelfsema NM, Van Adrichem LN, Wladimiroff JW. The role of three-dimensional ultrasound in visualizing the fetal cranial sutures and fontanels during the second half of pregnancy. Ultrasound Obstet Gynecol 2004;24:412–416 8. Benoit B, Chaoui R. Three-dimensional ultrasound with maximal mode rendering: a novel technique for the diagnosis of bilateral or unilateral absence or hypoplasia of nasal bones in second-trimester screening for Down syndrome. Ultrasound Obstet Gynecol 2005;25:19–24
9. Chaoui R, Levaillant JM, Benoit B, Faro C, Wegrzyn P, Nicolaides KH. Threedimensional sonographic description of abnormal metopic suture in second- and third-trimester fetuses. Ultrasound Obstet Gynecol 2005;26:761–764 10. Faro C, Chaoui R, Wegrzyn P, Levaillant JM, Benoit B, Nicolaides KH. Metopic suture in fetuses with Apert syndrome at 22–27 weeks of gestation. Ultrasound Obstet Gynecol 2006;27:18–33 11. Faro C, Wegrzyn P, Benoit B, Chaoui R, Nicolaides KH. Metopic suture in fetuses with holoprosencephaly at 11 + 0 to 13 + 6 weeks of gestation. Ultrasound Obstet Gynecol 2006;27(2):162–166 12. Lee W, Goncalves LF, Espinoza J, Romero R. Inversion mode: a new volume analysis tool for 3-dimensional ultrasonography. J Ultrasound Med 2005;24:201–207 13. Benacerraf BR. Inversion mode display of 3D sonography: applications in obstetric and gynecologic imaging. Am J Roentgenol 2006;187(9):965–971 14. Chaoui R, Schneider MBE, Kalache KD. Right aortic arch with vascular ring and aberrant left subclavian artery: prenatal diagnosis assisted by three-dimensional power Doppler ultrasound. Ultrasound Obstet Gynecol 2003;22:661–663 15. Moeglin D, Talmant C, Duyme M, Lopez AC. Fetal lung volumetry using two- and threedimensional ultrasound. Ultrasound Obstet Gynecol 2005;25:219–227 16. Peralta CF, Cavoretto P, Csapo B, Falcon O, Nicolaides KH. Lung and heart volumes by three-dimensional ultrasound in normal fetuses at 12–32 weeks' gestation. Ultrasound Obstet Gynecol 2006;27(2):128–133
15 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Fetal movement patterns and behavioural states Gerard H A Visser Eduard J H Mulder
Abstract Fetal movements appear early in pregnancy, are from their inception specific and closely resemble movements after birth. This makes them candidates for diagnostic purposes. In this chapter the normal development of fetal motor patterns and of behavioural states is discussed and clinical implications of altered behaviour are emphasized.
Keywords Fetal behaviour, fetal monitoring, fetal movements, maternal diseases, medication.
Introduction Ultrasound in obstetrics focuses on morphology and Doppler waveform patterns of fetal and maternal vessels. Fetal motility usually gets less attention. However, some knowledge regarding incidence, quality and periodicity of fetal movement patterns is necessary in order to:
• obtain insight into normal developmental aspects of nervous system
functioning (and related phenomena such as fetal heart rate patterns, Doppler flow profiles and fetal micturition) • identify situations with a negative impact on nervous system development and • identify individual fetuses with abnormal brain or neuromuscular functioning. In this chapter the normal development of fetal motor patterns and of fetal sleep or behavioural states is discussed and clinical implications of altered behaviour are emphasized.
271
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Methodology
272
Observation of fetal movements can best be done by using a real-time linear array transducer with a long probe (>9 cm) or a curved array transducer, with a high frame rate (>30 pictures per second). One transducer is sufficient until about 20 weeks of gestation, but thereafter two transducers are necessary if it is intended to observe all movement patterns. Also, for the recording of fetal behavioural states, two transducers are necessary: one for the observation of body movements and one for eye movements. Due to the episodic occurrence of the different movement patterns and the development of fetal behavioural states, it is necessary to make relatively long observations (0.5–2 h). With a recording of 1 hour's duration and a spatial peak temporal average of the equipment of 0.4 mw/cm2, the product of intensity and exposure time is 1.4 J/cm2, which is far below the accepted 50 J/cm2.
The Emergence of Fetal Movement Patterns Endogenously generated (i.e. spontaneous) fetal movements can first be observed after 7 weeks postmenstrual age (i.e. 5 weeks after conception).8 At this early age these movements are difficult to classify because of the small size of the embryo (1–2 cm) and the limited resolution of the ultrasound equipment. All types of movements emerging after 8 weeks are, however, specific and easily recognizable. Surprisingly, all these early emerging movements closely resemble those observed in preterm and full-term newborn infants, which makes it possible to classify them accordingly.8,32 There is an early emergence of different movement patterns and at 15 weeks of gestation 12 distinct patterns can already be distinguished (startle, general movements, hiccup, breathing, isolated arm or leg movement, isolated retroflexion/rotation and anteflexion of the head, jaw movements, sucking and swallowing, hand–face contact, stretch, yawn, body rotation). The developmental profile of these movements plotted according to their first appearance in a group of 12 normal fetuses is shown in Figure 15.1. In addition, slow eye movements can be observed from 18 weeks onwards, while rapid eye movements emerge somewhat later.5,15 These movements, once observed, remain present during the course of pregnancy and their appearance hardly changes. All these data were obtained in the early 1980s with the equipment available at that time, but are still unchallenged. This early emergence of highly organized, specific movement patterns, long before birth, seems surprising, even more so when the minimal development of the nervous system at that age is taken into account. Studies on the ultrastructure of the nervous system of the young fetus are still scarce. The available data suggest, however, that movements commence as soon as the first connective structures are formed.8 The reason why the different movement patterns emerge so early is still unclear. Certain movement patterns have an adaptive effect on the survival or development of the fetus. Frequent and active changes of the intrauterine
✩✩✩✩✩✩✩✩✩✩✩ ✩
Just discern. mov.
General mov. Hiccup Isol. arm mov. Isol. leg mov. Head retroflexion Head rotation Hand–face contact Breathing mov. Jaw opening Stretch Head anteflexion Yawn Sucking+swallow. 7
8
9
10
11
12
13
14
15
16
17
18
19
20 weeks
Fetal movement patterns and behavioural states
Startle
Fig. 15.1 Timetable of emergence of specific movement patterns in a longitudinal study of 12 fetuses. Each dot indicates the first observation of a particular pattern in an individual from the weekly observation. Postmenstrual age is given in weeks and days (reproduced from reference 1, with permission).
position may prevent adhesions and local stasis of the circulation of the skin. Individual movements may prevent the occurrence of contractures, as can be found after prolonged oligohydramnios following leakage of amniotic fluid. Sucking and swallowing movements are necessary for the regulation of the amount of amniotic fluid. Another reason for the early emergence of fetal movements is anticipation of postnatal functions. Some motor patterns emerge during early prenatal development and are regularly performed spontaneously long before they fulfil a meaningful task as part of a complex adaptive function. For example, fetal breathing movements are already present at 10 weeks. These movements might also have a profound influence on lung growth, as in animal experiments spinal cord transection results in fetal lung hypoplasia;18 however, this link is still unclear in the human. The frequent occurrence of many specific movements during the first trimester of pregnancy can be depicted in a complex actogram, as is shown in an example of a 1-hour recording at 13 weeks (Fig. 15.2). At all ages there are large interindividual differences in the incidence of the various types of movements.9 There are, however, specific developmental trends in the quantity (incidence) of the various types of movements. For example, the incidence of general movements increases rapidly until a plateau is reached at 10 weeks (about 12% of recording time), with a slight fall towards term age. The incidence of startles and hiccups declines
273
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
13 weeks Startle General mov. Hiccup Breathing mov. Isol. arm mov. Isol. leg mov. Head retroflexion Head rotation Head anteflexion Jaw opening Sucking+swallow. Hand–face contact Stretch Yawn Minutes 0 30 60 Fig. 15.2 Compiled actogram of 1 h observation of a fetus at 13 weeks of gestation. Note the periodicities and the multitude of specific movement patterns (data extracted from references 1 and 6, with permission).
after 12 weeks of gestation, while breathing movements gradually increase until 30 weeks; at the latter age breathing movements are on average present during 30% of recording time.9,36
Body Movements in Normal Pregnancy
274
Several authors have reported on the incidence of fetal body movements. However, because of the absence of a uniform definition and differences in study design and data analysis, the reported mean/median values and ranges of normality differ greatly among the various studies. Figure 15.3 shows nomograms of four incidence parameters of fetal body movements from 24 weeks till term. These data are from a longitudinal study in 29 normal fetuses. Fetal movements were recorded serially for 60 minutes at fortnightly intervals between 24 weeks and 36 weeks of gestation and for 120 minutes weekly from 36 weeks until delivery. Body movements which
✩✩✩✩✩✩✩✩✩✩✩ ✩ A
B 45 Number of fetal movements per hour
Percentage of fetal movements
35 30 25 20 15 10
250 200 150 100 50
5 0
0 24
28
30
32
34
36
38
40
42
D
10
45
8
40
7 6 5 4 3 2 1
24
26
28
24
26
28
30
32
34
36
38
40
42
30 32 34 36 Gestational age (weeks)
38
40
42
50
9 Median interval duration (sec)
Mean duration of fetal movements (sec)
C
26
35 30 25 20 15 10
Fetal movement patterns and behavioural states
40
300
5
0
0 24
26
28
30 32 34 36 Gestational age (weeks)
38
40
42
Fig. 15.3 Nomograms of the four incidence parameters of fetal body movements. Presented are the median (solid line), 2.5th and 97.5th centiles (dashed lines), and individually measured values in relation to gestational age for (A) the percentage of time spent making body movements, (B) the number of body movements per hour, (C) their mean duration, and (D) the median onset–onset interval (reproduced from reference 8, with permission).
occurred within 1 second apart were considered as a single burst of movement. The duration of individual fetal body movements remained stable with gestation whereas the onset–onset interval increased, resulting in a gradual decline in the number of movements per hour. The median percentage incidence of fetal body movements decreased from 17% at 24 weeks to about 7% near term. This overall decline in incidence appears to be a developmental phenomenon, rather than the result of developing sleep states, since the declining trends are similar during ‘active’ and ‘quiet’ sleep.40 There is some degree of intrafetal consistency in the incidence of body movements, but intra- (and inter-) fetal variances are generally high, for instance much higher than those for fetal heart rate and its variation. The incidence of fetal body movements is the same for boys and girls.35 Maternal meals do not affect the incidence of body movements. During the second half of gestation there is a diurnal variation in the incidence of general movements, with peak values occurring around midnight.34 This diurnal rhythm as well as those in fetal heart rate variation is related to maternal adrenal activity (cortisol).44
275
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Fetal Breathing in Normal Pregnancy
276
Fetal breathing movements are characterized by a fluent downward movement of the diaphragm, outward displacement of the abdomen and inward displacement of the thorax. Apnoea is defined as an interval between two consecutive breaths of more than 6 seconds. The incidence of fetal breathing increases up to about 30 weeks of gestation. At 20 weeks, breathing is on average present during 5% of recording time and at 30 weeks during 30%. Fetal breathing movements are affected by maternal meals and plasma glucose concentrations, especially during the third trimester of pregnancy. The highest incidence occurs 1.5–2 hours after a meal and 1 hour after the highest blood glucose value. There is also an increase in breathing incidence at night, but this is related to a circadian rhythm and not to glucose concentrations.30
Normal Development of Fetal Behavioural States During early gestation movements are scattered over time, but in the course of pregnancy a progressive clustering occurs in rest/activity cycles and later in behavioural states. These behavioural states develop during the third trimester of pregnancy. They are distinct and discontinuous modes of neural activity and, although defined by a different set of variables, are homologous to the states in the newborn.28 Each state is defined by a specific combination of the parameters of three selected variables: fetal heart rate pattern, body and eye movements. Such a combination is relatively stable, i.e. it is maintained uninterrupted over longer periods and transitions from one state to another are characterized by the almost simultaneous change of state variables. In the healthy fetus behavioural states are fully developed from about 36 weeks onwards, an age at which behavioural states are also present in low-risk preterm newborn infants. In the near-term human fetus four behavioural states have been identified: 1F–4F (F stands for fetal).28 State 1F is characterized by a stable heart rate with a small oscillation bandwidth (FHR pattern A) and absence of eye and generalized body movements. In state 2F, eye movements and periodic body movements are present; fetal heart rate has a wide oscillation bandwidth between frequent accelerations (FHR pattern B). In state 3F body movements are absent, eye movements are present and fetal heart rate has a wide oscillation bandwidth without accelerations (FHR pattern C). In state 4F there are prolonged accelerations (FHR pattern D), numerous body movements and presence of eye movements. If a stable association of the three state parameters exists for at least 3 minutes and if transitions from one state to another do not last more than 3 minutes, the presence of fetal behavioural states is accepted. The fetal states correspond to state 1 to state 4 in the full-term newborn infant, and in the neonate they may also be classified as quiet sleep, REM sleep, quiet awake and active awake, respectively. An example of a fetal behavioural state recording is shown in Figure 15.4. Fetal behavioural states develop gradually and from 28 weeks onwards there is a significant association between the state variables.48 This development results
✩✩✩✩✩✩✩✩✩✩✩ ✩
FHR
180 120
EM
FHRP GM EM
D C B A
+ − + −
C 2F
STATE
C 1F
C 2F
C 1F
C 2F
2F 1F
0
30
60
90
120
150
180 Minutes
Fig. 15.4 Example of a 3-h recording of a healthy fetus at 38 weeks of gestation. It shows from above downwards: (1) the fetal heart rate tracing (FHR) and the occurrence of general movements (GM) and eye movements (EM). Three periods of high heart rate variation (pattern B) were interrupted by two periods of low variation (pattern A); during the former both general movements and eye movements were present (coincidence 2F), but absent during pattern A (coincidence 1F); (2) profiles of the three state variables and the resulting episodes of coincidence 1F and 2F; (3) presence of behavioural states 1F and 2F (transitions <3 min).
in a decrease in the occurrence of no coincidence, i.e. of the percentage of time during which state criteria are not met.2,28 In the near-term fetus state 1F is on average present for about 35% of the time and state 2F for 50%; states 3F and 4F or episodes of no coincidence account for the remaining 15%. The mean duration of an enclosed epoch of state 2F is 65 minutes and that of state 1F approximately 25 minutes, which results in a complete sleep cycle of about 90 minutes. Near term, an episode of state 1F may last for up to 45 minutes. Fetal behavioural states are associated with other physiological phenomena. For instance, it has been shown that the fetal micturition cycle is related to states, with voiding occurring at or after a change from low to high heart rate variation.45 Fetal blood flow velocity waveforms, indicative of vascular resistance, are also related to states and during 2F a lower resistance in the descending aorta and internal carotid artery has been found.42 This implies that in relation to these measurements, fetal behavioural states must be taken into account. The latter also holds true for fetal heart rate monitoring: episodes of low heart rate variation may be indicative of a poor fetal condition, but may also be physiological and part of state 1F. Behavioural state organization in the human fetus is not easily influenced by maternal or environmental factors. Hitherto, it has been found that in normal pregnancy, state 1F is not influenced by Braxton Hicks contractions25 and uterine contractions during labour13 nor by induced maternal emotions,41 shaking the maternal abdomen49 and transabdominal sound stimulation.37 These findings are in line with the fact that it is difficult to wake up a newborn infant when in state 1. The fetus may benefit from this inaccessibility as it guarantees a more or less undisturbed endogenous development. However, fetuses do react to
Fetal movement patterns and behavioural states
GM
277
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ vibroacoustic stimulation using an electronic artificial larynx and during the past 5 years, numerous papers on the use of this device have been published. The most important rationale for stimulation is to differentiate between poor and good fetal health in cases of suspect FHR patterns, e.g. low heart rate variation. This kind of stimulus induces excessive fetal movements, a prolonged tachycardia and disorganized behavioural states.47 Therefore, it seems better not to use this device, especially as it induces intrauterine sound levels exceeding 125 dB.29
Abnormal Conditions Affecting Fetal Movement Patterns (Table 15.1) Altered Brain or Muscular Development Abnormal movement patterns, indicative of altered brain or muscular development, have been described in fetuses with chromosome abnormalities,7 in anencephalic fetuses,46 in fetuses with other cerebral malformations, in growthretarded fetuses3 and in fetuses suffering from prolonged oligohydramnios.38 Common features in all these cases are the qualitative changes in the execution of movement patterns, which are abrupt and forceful, with large amplitude, in the majority of fetuses with a chromosome or central nervous system defect and slow, with small amplitude, in the others. Fetal seizures have been described in association with severe brain abnormalities.1 It should be emphasized that movement abnormalities associated with central nervous system dysfunction are mainly qualitative and not quantitative in nature. In preterm babies with brain lesions, assessment of the quality of movements appears to be a much better predictor of neurological outcome than the number of movements.31 In anencephalic fetuses movements tend to be numerous, forceful, jerky in character and of
Table 15.1 Alterations in fetal behaviour in cases of fetal (central nervous system) anomalies, growth retardation and maternal diabetes or induced by exogenous teratogens and stimulation Fetal movements Emergence
Quality
Congential malformations
+
Maternal diabetes
+
+
+
Intrauterine growth retardation
+
+
+
Alcohol
+
+
Caffeine
+
Cocaine
278
Quantity
+
+
+
Corticosteroids
+
Maternal stress
+
Vibroacoustic stimulation
+
+
Sleep states
✩✩✩✩✩✩✩✩✩✩✩ ✩
Intrauterine Growth Retardation (IUGR) In IUGR fetuses movements are slow with a small amplitude.3 The development of fetal behavioural states is delayed and/or altered, in such a way that the percentage of no coincidence is increased with a ‘redistribution’ of coincidence 2F to coincidence 1F, i.e. towards an increase of a less active state.2,12 These changes precede the occurrence of fetal heart rate abnormalities and, therefore, of fetal hypoxaemia. Brain dysfunction in these fetuses is therefore more likely the result of chronic malnutrition in utero than due to hypoxaemia. Changes in the quantity of fetal movements are rather late signs of impairment and occur after the onset of fetal heart rate abnormalities. This has been found both for the components of the biophysical profile score14 and in longitudinal ultrasound observations (Fig. 15.5): fetal body movements decline in incidence at FHR variation
3
General movements
Fetal movement patterns and behavioural states
a large amplitude.46 This indicates that only minimal neural structures are necessary for movements to be generated. On the other hand, these data indicate that already in the first half of pregnancy a normal nervous system, although only partly developed, is necessary for movements to be executed normally. Prospective studies of behavioural development in fetuses affected by neuromuscular disorders or restrictive dermopathy are scarce.19,22 The existing evidence shows that absence or low levels of fetal body and limb movements, breathing activity and mouth movements (sucking and swallowing) usually lead to the almost simultaneous occurrence of joint contractures, pulmonary hypoplasia, and facial anomalies and polyhydramnios, respectively. This phenomenon is known as the fetal akinesia deformation sequence (FADS). Data on abnormal behaviour in individual fetuses with abnormal brain functioning are still rare. Prenatal prediction of neurological outcome on the basis of altered fetal behaviour is likely to remain difficult and requires extensive knowledge of normal movements and different diagnostic approaches.
Breathing movements
2
1
0
Time (weeks) Fig. 15.5 Time-related changes in fetal general movements, breathing movements and fetal heart rate (FHR) variation with progressive deterioration of the fetal condition. The dashed line represents the lower limit of the normal range for the biophysical variables studied (data extracted from reference 35, with permission).
279
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ or after the occurrence of fetal hypoxaemia and this is most likely due to adaptation.33 With further deterioration there is usually a rapid decline in heart rate variation and in body and breathing movements, associated with poor fetal condition (acidaemia).
Maternal Diabetes In women with type 1 diabetes, embryonic movements emerge during the first trimester of pregnancy about 1 week later than in control fetuses, apart from fetal breathing which starts earlier.26 During the third trimester fetal behavioural states are less well organized, indicating a delayed or disturbed development of nervous system functioning.24 The percentage of no coincidence is related to the degree of (early) embryonic growth delay during the first trimester27 and these data stress the importance of the effects of early disturbances in development on nervous system functioning at the end of pregnancy. These data are consistent with those of Bloch Petersen et al,6 who found a relationship between early embryonic growth delay and impaired development at 4 years of age.
Preterm Contractions and/or Rupture of Membranes The presence of fetal breathing movements in women admitted with preterm contractions and intact membranes is a reassuring sign and less than 10% of them will have delivered within a week (positive predictive value 93%: Table 15.2).4,11 The negative predictive value is considerably lower (±67%). In other words, the presence of fetal breathing movements is one of the best markers of low risk for preterm delivery in women being admitted with contractions. This may be explained by the fact that fetal breathing movements usually disappear during labour, most likely because of increased prostaglandin levels. The negative predictive value of breathing movements is lower and this is due to the episodic character of breathing movements. The predictive value of fetal breathing movements in cases of preterm rupture of membranes (PROM) is considerably lower (see Table 15.2). The risk of intrauterine infection in cases of PROM is generally low if fetal breathing is present (±15%) and high in the absence of breathing (±55%). Table 15.2 Presence of fetal breathing movements (FBM) as a predictor of preterm delivery in cases admitted because of preterm contractions with intact membranes (n= 219, 5 studies) or rupture of membranes (n= 41, 3 studies) Intact membranes (5 studies)
FBM(+)
280
Rupture of membranes (3 studies)
Continued ≥2 days
Delivered <2 days
n
Continued ≥2 days
Delivered <2 days
n
166
10
176
9
6
15
FBM(−)
11
32
43
0
26
26
n
177
42
219
9
32
41
n
177
42
219
9
32
41
✩✩✩✩✩✩✩✩✩✩✩ ✩
Drugs, Medication, Stress and Fetal Stimulation Fetal movement patterns and behavioural states
By studying the fetal behaviour, effects of exogenous behavioural teratogens may be identified. Some investigators think that observation of fetal reactions to (repetitive) stimuli may give insight into fetal brain integrity. In a carefully controlled study, we found that two glasses of white wine temporarily suppress fetal breathing movements and disturb fetal state cycling, the latter being mainly due to suppression of fetal eye movements.21 REM sleep is important for normal brain development and these data may shed some light on behavioural abnormalities observed in infants whose mothers consumed more than two glasses of alcohol per day during pregnancy. A study like this one, demonstrating direct effects of alcohol on the fetus, may discourage pregnant women from drinking. Maternal caffeine intake causes considerable increases in fetal body movements and in the percentage of fetal heart rate variability pattern D, indicating that the fetus spends more time ‘awake’.39 Induced maternal emotions do not affect fetal state cycling, but there is a positive correlation between the level of maternal stress and the incidence of fetal body movements.41 Active fetuses also tend to have a high activity level after birth and one may speculate whether this is due to prenatal effects of high maternal anxiety or to genetic differences. The relationship between maternal stress and fetal and neonatal behaviour is complex, given the large variety of stressors and differences in ‘coping’ with stress. Moreover, maternal stress and cortisol do not show a clear relationship. Exogenous corticosteroids induce a temporary reduction in fetal movements and fetal activity is inversely correlated to the maternal diurnal cortisol rhythm.10,34,44 Thus, this important topic still needs further exploration. Betametasone, administered to the mother to enhance fetal lung maturation in case of threatened preterm delivery, results in a 50% reduction of body movements and in an almost complete cessation of fetal breathing on days 2 and 3 after the first administration.10 Also heart rate variation is temporarily reduced and due account of this phenomenon has to be taken when monitoring the fetus. These effects are not due to fetal hypoxaemia, but most likely to binding of this corticosteroid to receptors in the brainstem. There is evidence that the reductions in movements and heart rate variation are caused by a temporary abolishment of the diurnal rhythm.16 Dexametasone has a less dramatic effect on fetal behaviour, but there is evidence that the beneficial effects of this drug are less than those of betametasone.20 Numerous investigators have studied the effects of repeated fetal stimulation mainly by using vibroacoustic stimulators (electro larynx, electric toothbrush or other sound or vibratory sources). They looked at habituation, defined as the progressive decrease in response when the fetus is stimulated repeatedly. This process is considered a simple form of learning and is supposed to reflect normal brain functioning. However, the importance of habituation in distinguishing between normal and abnormal fetuses is still controversial, mainly because there
281
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ is no generally accepted standard procedure. Methodological differences among the studies are abundant and include a multitude of sound sources, varying definitions as to habituation, absence of appropriate control episodes during which no stimulation occurred, and neglect of the state dependency of fetal responses to stimulation.17,23,43
Conclusion Fetal movements appear early, are specific from their inception and closely resemble movements after birth. This makes them candidates for diagnostic purposes. Knowledge of normal fetal motor development and of fetal behavioural states is important for the interpretation of other clinical measurements, such as fetal heart rate records and Doppler velocity waveform patterns. Disturbances in embryonic and fetal central nervous system development can be investigated by studying the timetable of appearance of movement patterns, the quality of specific movements and the development of fetal behavioural states. Abnormal development can be found in many endogenous malfunctions and in disturbances caused by maternal diseases and exogenous behavioural teratogens. It remains questionable whether fetal behavioural studies will prove to be specific enough to identify the individual fetus with impaired brain functioning, except in isolated cases. References
282
1. Abrams LA, Balducci J. Fetal seizures: a case study. Obstet Gynecol 1996;88:661–662 2. Arduini D, Rizzo G, Caforio L, Boccolini MR, Romanini C, Mancuso S. Behavioural state transitions in healthy and growth retarded fetuses. Early Hum Dev 1989;19;155–165 3. Bekedam DJ, Visser GHA, de Vries JJ, Prechtl HFR. Motor behaviour in the growth retarded fetus. Early Hum Dev 1985;12:155–165 4. Besinger RE, Compton AA, Hayaski RH. The presence or absence of fetal breathing movements as a predictor of outcome in preterm labor. Am J Obstet Gynecol 1987;157:753–757 5. Birnholz JC. The development of human fetal eye movement patterns. Science 1981;213:679–681 6. Bloch Petersen M, Pedersen SA, Greisen G, Pedersen JF, Molsted-Pedersen L. Early growth delay in diabetic pregnancy: relation to psychomotor development at age 4. BMJ 1988;296:598–600 7. Boué J, Vignal P, Aubry MC, Alees JM. Ultrasound movement patterns of fetuses with chromosome anomalies. Prenat Diagn 1982;2:61–65
8. de Vries JIP, Visser GHA, Prechtl HFR. The emergence of fetal behaviour. I. Qualitative aspects. Early Hum Dev 1982;7:301–322 9. de Vries JIP, Visser GHA, Prechtl HFR. The emergence of fetal behaviour. II. Quantitative aspects. Early Hum Dev 1985;12:99–120 10. Derks JB, Mulder EJH, Visser GHA. The effects of maternal betamethasone administration on the fetus. Br J Obstet Gynaecol 1995;102:40–46 11. Devoe LD, Youssef EA, Croom CS, Watson J. Can fetal biophysical observations anticipate outcome in preterm labor or preterm rupture of membranes? Obstet Gynecol 1994;84:432–438 12. Gazzolo D, Visser GHA, Sauti F et al. Behavioural development and Doppler velocimetry in relation to perinatal outcome in small for dates fetuses. Early Hum Dev 1995;43:185–195 13. Griffin RL, Caron FJM, van Geijn HP. Behavioural states in the human fetus during labour. Am J Obstet Gynecol 1985;152:828–833 14. Harman CR, Meuticoglou SM, Manning FA, Morrison IS. Fetal biophysical variables and fetal states. In: Maulik D (ed) Asphyxia and
✩✩✩✩✩✩✩✩✩✩✩ ✩ on diabetic pregnancy. Early Hum Dev 1992;31:91–95 28. Nijhuis JG, Prechtl HFR, Martin CB Jr, Bots RSGM. Are there behavioural states in the human fetus? Early Hum Dev 1982;6: 177–195 29. Nyman M, Arulkumaran S, Hsu TS, Ratman SS, Till O, Westgren M. Vibroacoustic stimulation and intrauterine pressure levels. Obstet Gynecol 1991;78:803–806 30. Patrick J, Campbell K, Carmichael L, Natale R, Richardson B. Patterns of human fetal breathing during the last 10 weeks of pregnancy. Obstet Gynecol 1980;56:24–30 31. Prechtl HFR. Editorial: qualitative changes of spontaneous movements in fetus and preterm infant are a marker of neurological dysfunction. Early Hum Dev 1990;23: 151–158 32. Prechtl HFR. The neurological examination of the full-term newborn infant. Clin Dev Med 1977;63:65 33. Ribbert LSM, Visser GHA, Mulder EJH, Zonneveld MF, Morssink LP. Changes with time in fetal heart rate variation, movement incidences and haemodynamics in intrauterine growth retarded fetuses; a longitudinal approach to the assessment of fetal wellbeing. Early Hum Dev 1993;31:195–208 34. Roberts AB, Little D, Cooper D, Campbell S. Normal patterns of fetal activity in the third trimester. Br J Obstet Gynaecol 1979;86:4–9 35. Robles de Medina PG, Visser GHA, Huizink AC, Buitelaar JK, Mulder EJH. Fetal behaviour does not differ between boys and girls. Early Hum Dev 2003;73:17–26 36. Roodenburg PJ, Wladimiroff JW, van Es A, Prechtl HFR. Classification and quantitative aspects of fetal movements during the second half of normal gestation. Early Hum Dev 1991;25:19–36 37. Schmidt W, Boos R, Gnirs J, Auer L, Schulze S. Fetal behavioural states and controlled sound stimulation. Early Hum Dev 1985;12:145–153 38. Sival DA, Visser GHA, Prechtl HFR. Does reduction of amniotic fluid affect fetal movements? Early Hum Dev 1990;23: 233–246 39. Tegaldo L, Mulder EJH, Visser GHA, Bruschettini PL. The effects of maternal caffeine intake on the near term human fetus (abstract). Prenat Neonat Med 1998;3(suppl 1):30 40. ten Hof J, Nijhuis IJM, Mulder EJH et al. Longitudinal study of fetal body movements: nomograms, intrafetal
Fetal movement patterns and behavioural states
fetal brain damage. Wiley-Liss, New York, 1998: 279–320 15. Inoue M, Koyanagi T, Nakahare H, Hara K, Hori E, Nakano H. Functional development of human eye movement in utero assessed quantitatively with real-time ultrasound. Am J Obstet Gynecol 1986;155:170–174 16. Koenen SV, Mulder EJH. Wijnberger DE, Visser GHA. Transient loss of the diurnal rhythms of fetal breathing movements, body movements, and heart rate and its variation, after maternal betamethasone administration. Pediatr Res 2005;57:1–6 17. Leader LR, Baillie P, Martin B, Vermeulen E. Fetal habituation in high-risk pregnancies. Br J Obstet Gynaecol 1982;89:441–446 18. Liggins GC, Vilos GA, Kitterman JA, Lee CH. The effect of spinal cord transection on lung development in the fetal sheep. J Dev Physiol 1981;3:267–274 19. Mulder EJH, Beemer FA, Stoutenbeek P. Restrictive dermopathy and fetal behaviour. Prenat Diagn 2001;21:581–585 20. Mulder EJH, Derks JB, Visser GHA. Antenatal corticosteroid therapy and fetal behaviour: a randomised study of the effects of betamethasone and dexamethasone. Br J Obstet Gynaecol 1997;104:1239–1247 21. Mulder EJH, Morssink LP, Benschop T, Visser GHA. Acute maternal alcohol consumption disrupts behavioural state organization in the near term fetus. Pediatr Res 1998;44:774–779 22. Mulder EJH, Nikkels PGJ, Visser GHA. Fetal akinesia deformation sequence: behavioural development in a case of congenital myopathy. Ultrasound Obstet Gynecol 2001;18:253–257 23. Mulder EJH, Robles de Medina PG, Beekhuijzen MEW, Wijnberger DE, Visser GHA. Fetal stimulation and activity state. Lancet 2001;357:478–479 24. Mulder EJH, Visser GHA, Bekedam DJ, Prechtl HFR. Emergence of behavioural states in fetuses of type-1 diabetic women. Early Hum Dev 1987;15:231–252 25. Mulder EJH, Visser GHA. Braxton Hicks contractions and motor behaviour in the near-term human fetus. Am J Obstet Gynecol 1987;156:543–549 26. Mulder EJH, Visser GHA. Growth and motor development in fetuses of women with type-1 diabetes. II. Emergence of specific movement patterns. Early Hum Dev 1991;25:107–115 27. Mulder EJH, Visser GHA. Impact of early growth delay on subsequent fetal growth and functional development: a study
283
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
284
consistency and relationship with fetal heart rate patterns A and B. Pediatr Res 2002;52:568–575 41. van den Bergh BRH, Mulder EJH, Visser GHA, Poelmann-Weesjes G, Bekedam DJ, Prechtl HFR. The effect of (induced) maternal emotions on fetal behaviour: a controlled study. Early Hum Dev 1989;19:9–19 42. van Eyck J, Wladimiroff JW, van de Wijngaard JAGW, Noordam MJ, Prechtl FHR. The blood flow velocity waveform in the fetal internal carotid and umbilical artery; its relationship to fetal behavioural states in normal pregnancy at 37–38 weeks of gestation. Br J Obstet Gynaecol 1987;94:736–741 43. van Heteren CF, Boekkooi PF, Jongsma HW, Nijhuis JG. Fetal learning and memory. Lancet 2000;356:1169–1170 44. Visser GHA, Goodman JDS, Levine DH, Dawes GH. Diurnal and other cyclic varia tions in human fetal heart rate near term. Am J Obstet Gynecol 1982;142:535–544
45. Visser GHA, Goodman JDS, Levine DH, Dawes GS. Micturition and the heart period cycle in the human fetus. Br J Obstet Gynaecol 1981;88:803–805 46. Visser GHA, Laurini RN, de Vries JIP, Bekedam DJ, Prechtl HFR. Abnormal motor behaviour in anencephalic fetuses. Early Hum Dev 1985;12:173–183 47. Visser GHA, Mulder HH, Wit HP, Mulder EJH, Prechtl HFR. Vibro-acoustic stimulation of the human fetus: effect on behavioural state organization. Early Hum Dev 1989;19:285–296 48. Visser GHA, Poelmann-Weesjes G, Cohen TMN, Bekedam DJ. Fetal behaviour at 30 to 32 weeks gestation. Pediatr Res 1987;22:655–658 49. Visser GHA, Zeelenberg HJ, de Vries JIP, Dawes GS. External physical stimulation of the human fetus during episodes of low heart rate variation. Am J Obstet Gynecol 1983;145:579–584
16 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal gynaecological anatomy (uterus, tubes, ovaries) Lil Valentin Povilas Sladkevicius
Abstract Ultrasound examination of the uterus and ovaries is best performed transvaginally. The ultrasound morphology and size of the uterus and ovaries change during the menstrual cycle. In menopausal transition the ovaries are smaller and contain fewer follicles than during the reproductive years. They continue to shrink after the menopause, when the uterus also becomes smaller. A small amount of fluid in the pouch of Douglas is normal in women of fertile age but abnormal after the menopause. Normal tubes can only be seen if they float freely in fluid in the pouch of Douglas. On saline infusion sonography a normal uterine cavity is regular and outlined by a smooth endometrium. Hystero-contrast salpingosonography is used to assess tubal patency. If one can observe moving contrast in the interstitial part of the tube for 10 seconds, and if no hydrosalpinx is seen, the tube is probably patent, even if free spill of contrast around the ovary is not clearly seen.
Keywords Hydrosonography, hystero-contrast salpingosonography, menstrual cycle, postmenopause, ultrasonography.
Introduction Even though an ultrasound examination of the uterus and ovaries can be carried out transabdominally, transvaginal ultrasound examination is preferable, because it can be performed using higher ultrasound frequencies and this means better resolution, which in turn means that very fine details can be seen. If transvaginal ultrasound examination is impossible, transrectal ultrasound is an alternative. The anterior–posterior diameter of the uterus should be measured from a sagittal view of the uterus, where it appears to be at its thickest, and the width of the
285
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ uterus should be measured from a transverse view of the uterus, where it appears to be at its widest. There is no consensus about how to measure uterine length, i.e. whether to measure it as a straight line from the outer cervical os to the fundus uteri or whether to take separate measurements of the length of the cervix and the uterine corpus and then to add the two, the results of the two measurement techniques being different if the uterus is flexed. Endometrial thickness is measured from a sagittal view of the uterus, where it appears to be at its thickest.1 Ovarian volume (mL) can be calculated by measuring three orthogonal diameters of the ovary and then using the formula: length (cm) × depth (cm) × width (cm) × 0.5.
Normal Ultrasound Morphology of the Cervix Uteri An ultrasound examination of the uterus should always start with examination of the cervix. The cervical canal should be identified and followed towards the corpus uteri so that it can be seen to join the endometrium. This examination technique ensures that it is indeed the uterus and the endometrium that have been identified. The myometrium of a normal cervix is homogeneous. In the late proliferative phase of the menstrual cycle, clear fluid, corresponding to the ovulatory cervical mucus, can be seen in the cervix. The finding of many and even large retention cysts in the cervix is normal. Ultrasound images of a normal cervix are shown in Figure 16.1.
Normal Ultrasound Morphology of the Uterus in Women of Fertile Age The myometrium of a normal uterus is homogeneous. The ultrasound morphology of the endometrium changes during the menstrual cycle.2,3 In the beginning of the menstrual cycle, the uterus is at its smallest and the endometrium is thin. During the follicular phase, the uterus increases in size and the endometrium becomes thicker and manifests a ‘triple-layer’ appearance. It is thought that the central echogenic line represents direct contact of the anterior and posterior B
A
FHRP
286
Fig. 16.1 A normal cervix (A) at the time of ovulation containing fluid corresponding to ovulatory cervical mucus and (B) containing two retention cysts.
✩✩✩✩✩✩✩✩✩✩✩ ✩
A
B
C
D
Normal gynaecological anatomy (uterus, tubes, ovaries)
endometrial layers, and that the two outer hyperechogenic lines represent the endometrial–myometrial junction. After ovulation the ‘triple-layer’ appearance of the endometrium disappears and the endometrium becomes homogeneously hyperechoic. Echo enhancement is often seen behind a secretory endometrium. These endometrial changes are illustrated in Figure 16.2. On a transverse or longi tudinal section through a uterus, the outer layers of the myometrium may be seen to contain small circular hypoechoic (black) spaces. These correspond to blood vessels (see Fig. 16.2) and are often seen both in women of fertile age and in postmenopausal women. In a nulliparous woman, a normal uterus measures approximately 7 cm in length, 3 cm in anterior–posterior diameter and 4 cm in width; in a parous woman it measures approximately 8 cm in length, 4 cm in anterior–posterior diameter and 4.5 cm in width. In a woman who has given birth to two or more children, the uterus may even be slightly larger.4 Endometrial thickness changes
E
Fig. 16.2 Endometrial ultrasound morphology changes during a normal menstrual cycle. (A) On cycle days 2–4 the endometrium is thin and hyperechoic; ‘pencil-line’ appearance. (B) In the late proliferative phase the endometrium becomes thicker and exhibits ‘triplelayer’ appearance. (C) In the secretory phase the endometrium is thick and homogeneously hyperechogenic. (D) Echo enhancement (arrows) is often seen behind the secretory endometrium. (E) Uterus with vessels in its periphery (arrows).
287
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ throughout the menstrual cycle, the endometrium being at its thinnest at the end of menstruation (3–5 mm). During the follicular phase it increases in thickness until ovulation when it is about 10 mm thick, and then it remains virtually unchanged in thickness throughout the secretory phase.5
Normal Ultrasound Morphology of the Ovaries in Women of Fertile Age Ovarian ultrasound morphology also changes during the menstrual cycle.3,6 In the beginning of the menstrual cycle both ovaries usually contain 6–7 follicles of <10 mm in diameter.6 The non-dominant ovary retains this appearance throughout the menstrual cycle.6 In the early follicular phase, it is not possible to determine which ovary is going to become the dominant one, i.e. the one carrying the follicle destined to ovulate. The dominant ovary can usually be identified 9–6 days (mean 7 days) before the LH surge, i.e. between cycle days 5 and 12 (mean cycle day 8), the dominant ovary being the ovary carrying a follicle larger than any of the other follicles and with a diameter of the largest follicle, >10 mm.6 The dominant follicle displays a linear growth rate of 1.4–2.2 mm (mean 1.7) per day.6 At the time of the LH surge the leading follicle has a diameter of 18–22 mm.6 After ovulation the follicle becomes a corpus luteum. The corpus luteum is usually smaller than the dominant follicle, its wall is thicker, and with high-resolution ultrasound systems it is possible to see the crenellated appearance of its wall. Bleeding into the corpus luteum explains the presence of echoes in the corpus luteum at ultrasound examination.3 The corpus luteum is well vascularized and therefore it is surrounded by a ‘colour ring’ on colour or power Doppler ultrasound examination7,8 (see also below). On the third day of menstruation the corpus luteum of the previous cycle is no longer distinguishable, not even using colour Doppler ultrasound.9 Changes in the ultrasound appearance of the ovaries during a normal menstrual cycle are illustrated in Figure 16.3. Ovarian size changes during the menstrual cycle. The volume of the nondominant ovary is approximately 7–8 mL and remains unchanged throughout the menstrual cycle, while the volume of the dominant ovary increases from 7–8 mL in the early follicular phase to approximately 20 mL on the day before ovulation. After ovulation, it decreases slightly and is approximately 15 mL in the luteal phase.8
Normal Ultrasound Morphology of the Uterus and Ovaries in Postmenopausal Women
288
The uterus and ovaries are smaller in postmenopausal women than in women of fertile age.4 A normal uterus in a woman who is more than 5 years postmenopausal may measure 5–6 cm in length, 2.5 cm in anterior–posterior diameter and 3 cm in width, and a normal ovary may have a volume of 1–4 mL.4,10 The endometrium has uniform ultrasound morphology because there are no cyclical hormonal changes. It is thin (usually no more than 5 mm thick) and hyperechoic.4,10
✩✩✩✩✩✩✩✩✩✩✩ ✩ A
D
E
Normal gynaecological anatomy (uterus, tubes, ovaries)
C
B
Fig. 16.3 Changes in ovarian ultrasound morphology during a normal menstrual cycle. (A) Normal ovary in the early follicular phase; at this stage both ovaries look similar, they usually contain 6–7 follicles <10 mm in diameter, and the non-dominant ovary retains this appearance throughout the menstrual cycle. (B) A normal dominant ovary with one follicle larger than any of the other follicles and with a diameter of >10 mm. (C) A normal dominant ovary in the luteal phase, where the corpus luteum has a crenellated appearance and echogenic contents. (D) A normal dominant ovary in the luteal phase, where the corpus luteum has anechoic contents. (E) A normal dominant ovary in the luteal phase with a haemorrhagic corpus luteum.
Calcified blood vessels in the periphery of the myometrium are common in postmenopausal women and are seen as bright echoes in the periphery of the uterus (see Fig. 16.3). In a postmenopausal woman the ovaries contain no follicles but one or more inclusion cysts up to 10 mm in diameter are common and normal ultrasound findings in postmenopausal women.10,11 Ultrasound images of normal postmenopausal uteri and ovaries are shown in Figures 16.4 and 16.5.
289
✩ ✩✩✩✩✩✩✩✩✩✩✩ B
Ultrasound in obstetrics and gynaecology
A
C
Fig. 16.4 Ultrasound images of a normal postmenopausal uterus. (A) Longitudinal view; the endometrium is thin and hyperechogenic. (B) Transverse view. (C) Calcifications of vessels appearing as echogenic spots in the periphery of a normal postmenopausal uterus. B A
Fig. 16.5 Ultrasound images of normal postmenopausal ovaries. (A) Small ovary without visible follicles. (B) Ovary with a follicle-like cystic structure, in all likelihood an inclusion cyst.
Normal Ultrasound Morphology of the Uterus and Ovaries in Menopausal Transition
290
Menopausal transition starts with the beginning of the first menstrual irregularity and ends with the final menstrual period (menopause). The menopausal transition period precedes the final menses by 2–8 years. In one of our own studies24 we examined women longitudinally from 2 years before to 2 years after their menopause. As early as 2 years before menopause, the ovaries were smaller (largest ovary approximately 6 mL) than in normo-ovulatory women of fertile age where
✩✩✩✩✩✩✩✩✩✩✩ ✩
Normal Uterine and Ovarian Vascularization as Assessed by Doppler Ultrasound Technique Uterine and ovarian vascularization can be studied non-invasively using twodimensional or three-dimensional Doppler ultrasound technique. Both uterine and ovarian vascularization change throughout the menstrual cycle.7–9,13 There is indirect evidence that the uterus and endometrium are better perfused in the late follicular and luteal phase than in the early follicular phase. Blood flow velocities are higher and the pulsatility index is lower in the main uterine arteries and subendometrial arteries, and blood flow indices in endometrial and subendometrial volumes obtained at three-dimensional power Doppler ultrasound examination are higher in the late follicular and luteal phase than in the early follicular phase.7,13 The same is true of the dominant ovary,7,8 where changes in vascularization are obvious to the naked eye: the ovary bearing the dominant follicle (and especially the wall of the dominant follicle) becomes successively more intensely coloured on colour Doppler ultrasound examination from 1 to 2 days before ovulation, and the ovary harbouring the corpus luteum is more intensely coloured than the same ovary before ovulation and than the contralateral ovary.7 These changes are illustrated in Figure 16.6. Even though a corpus luteum can usually be distinguished A
Normal gynaecological anatomy (uterus, tubes, ovaries)
the volume of the non-dominant ovary is about 8 mL (see above).8 Moreover, in the women in menopausal transition the ovaries usually contained only one or two follicles versus the reported six to seven in women of reproductive age.6 The greyscale ultrasound findings in women in menopausal transition were clearly different from those in women of fertile age, not only because the number of follicles was much lower but also because in 70% of the examinations performed during menopausal transition, it was impossible to determine the phase of the menstrual cycle, the endometrium not manifesting the features typical of proliferation or secretion and there being no dominant follicle or corpus luteum. This is in agreement with the findings of Landgren et al, who reported that 62% of menstrual cycles examined during the last 10 years before menopause were anovulatory.12
B
Fig. 16.6 Ultrasound images illustrating the difference in vascularization between the dominant follicle and the corpus luteum. (A) Power Doppler image of the dominant follicle; only a thin line of colour surrounds a small part of the follicle. (B) Power Doppler image of the corpus luteum; a thick line of colour surrounds a large part of the corpus luteum.
291
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ from a follicle on the basis of the grey-scale ultrasound image alone (thicker wall, more irregular wall, crenellated wall, echogenic contents), the thick and intense colour ring surrounding a corpus luteum may help confirm its presence.
The Tubes The interstitial part of the tube can be seen on a transverse section through the uterus. It is important to identify this part of the tube at hystero-contrast salpingosonography (see below). The more distal parts of a normal tube cannot be seen at ultrasound examination, unless the tube is floating freely in fluid in the pouch of Douglas or in ascites (Fig. 16.7).
The Pouch of Douglas In women of fertile age, fluid is almost always seen in the pouch of Douglas, at least in the late follicular phase and in the early secretory phase of the menstrual cycle3 (Fig. 16.8). In the early secretory phase, the pouch of Douglas normally contains 15–25 mL fluid.3 It is not possible to give an exact cut-off in millimetres of a normal amount of pelvic fluid in a woman of fertile age, but fluid outside the pouch of Douglas, e.g. in the space between the uterus and the bladder, is extremely unusual and should be regarded as abnormal. An ultrasound finding of fluid in the pouch of Douglas in a postmenopausal woman is not normal. Follow-up is needed to exclude disease explaining the fluid.
Fig. 16.7 Ultrasound image of a normal tube floating in free fluid.
292
Fig. 16.8 Normal amount of fluid in the pouch of Douglas in a woman of fertile age.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Hydrosonography Normal gynaecological anatomy (uterus, tubes, ovaries)
Hydrosonography, i.e. infusion of sterile saline into the uterine cavity during transvaginal scanning, makes it possible to detect focal lesions (e.g. endometrial polyps or submucuous myomas) in the uterine cavity.14 Hydrosonography is carried out by inserting a thin sterile plastic catheter (e.g. a baby feeding tube or an insemination catheter) connected to a sterile syringe containing sterile saline into the uterine cavity through the cervical canal. A balloon catheter is not needed; it is expensive and inflation of the balloon causes the woman unnecessary pain. Insertion of the catheter is usually easy in women of fertile age but may be difficult in postmenopausal women, who often have a stenotic cervix. In these women it may be necessary to use both a tenaculum and a small uterine sound before the catheter can pass into the uterus. When the catheter is in place, the vaginal transducer is introduced into the vagina and the uterine cavity is scanned while saline is being infused into the cavity. Sometimes only a few millilitres of saline is needed to expand the cavity. If there is backflow, more than 20 mL may be required. One should strictly avoid introducing air into the uterine cavity, because air obscures the view. Some have used hydroxyethylcellulose gel containing anaesthetic and antiseptic agents instead of saline, the alleged advantages being less fluid leakage and less pain.15 A normal uterine cavity in the follicular phase of the menstrual cycle or in a postmenopausal woman is smooth and contains no focal lesions. Possibly, a thick secretory endometrium or an otherwise hormonally influenced endometrium may be folded, and such folds could potentially be confused with focal lesions. However, because of the possibility of the presence of an early pregnancy, hydrosonography should not be carried out in the secretory phase of the menstrual cycle. To the best of our knowledge, the normal appearance of a secretory endometrium at hydrosonography is not known. Hydrosonography images are shown in Figure 16.9. We have found no scientific studies that have examined whether or not cleansing of the vagina or prophylactic antibiotics should be recommended before hydrosono graphy. In our ultrasound unit, we do not clean the vagina before hydrosonography and we do not give prophylactic antibiotics.
Hystero-Contrast Salpingosonography (HyCoSy) Traditionally, tubal patency has been assessed by hysterosalpingography. This examination can be replaced by hystero-contrast salpingosonography (HyCoSy), where the flow of a contrast medium from the uterine cavity into the fallopian tubes is observed using ultrasound technique.16 The late preovulatory phase of the menstrual cycle (days 8–12) is the optimal time to perform this examination. It should not be carried out in the secretory phase because of the possibility of the presence of an early pregnancy. HyCoSy is usually immediately preceded by hydrosonography to assess the uterine cavity (see above) and is performed by inserting a sterile balloon catheter
293
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
A
B
C D
Fig. 16.9 Normal ultrasound findings at hydrosonography, i.e. the endometrium outlining the cavity is smooth and there are no focal lesions. (A) Transverse view of the uterus from a woman in the proliferative phase of the menstrual cycle. (B) Transverse view of the uterus from a woman in the secretory phase of the menstrual cycle. Hydrosonography should not be carried out in the secretory phase of the menstrual cycle but this examination was performed under exceptional circumstances. The endometrium is thick and slightly folded. (C) Longitudinal view of the uterus in a postmenopausal woman. (D) Transverse view of the uterus from a woman with a thick and folded hormonally influenced endometrium; the folds could potentially be confused with focal lesions.
294
connected to a sterile syringe containing a sterile contrast medium into the uterine cavity through the cervical canal. There are dedicated commercial contrast media but air in saline can also be used.17,18 A balloon catheter, or some other catheter that prevents backflow through the cervix, is needed to force the contrast medium into the tubes. The balloon can be inflated either in the cervix or in the uterine cavity. Both procedures may be painful. When the catheter with its inflated balloon is in place, the vaginal transducer is introduced into the vagina and the uterine cavity is scanned while the contrast medium is slowly being injected. When starting the contrast infusion, it is good to have a sagittal view of the uterus on the screen. When the contrast is seen to arrive at the upper part of the uterine cavity, one changes to a transverse view of the fundus uteri with the interstitial part of one of the tubes in view, so that the passage of contrast medium through the interstitial part of the tube can be seen. By manipulating the probe, the contrast can be followed from the interstitial part of the tube to its fimbrial end, where free spill
✩✩✩✩✩✩✩✩✩✩✩ ✩
A
B
C
D
E
F
Normal gynaecological anatomy (uterus, tubes, ovaries)
can be observed. Observing free spill may be difficult, because the contrast agent has the same echogenicity as the surrounding bowel. On the other hand, the proximal end of the tube filled with running contrast medium is almost always visible. If one can observe moving contrast in the interstitial part of the tube for 10 seconds, and if no hydrosalpinx is seen, the fallopian tube is almost certainly patent, even if free spill of contrast is not clearly seen.19 It is only possible to assess the patency of one tube at a time. If at least one tube is patent, there should be free contrast in the pouch of Douglas at the end of the procedure. Ultrasound images from a HyCoSy procedure are shown in Figure 16.10. We have found no scientific studies that have examined whether or not cleansing of the vagina or prophylactic antibiotics should be recommended before HyCoSy. A Cochrane meta-analysis is being planned (‘Prophylactic antibiotics for transcervical intrauterine procedures’, J Thinkhamrop, M Laopaiboon, P Lumbiganon; www. cochrane.org/) that might shed light on this issue in the future. In our unit we clean the vagina with chlorhexidine 2 mg/mL and we do use prophylactic antibiotics. We also give prophylactic painkillers 1 hour before the procedure to reduce pain.
G
Fig. 16.10 Ultrasound images obtained during hystero contrast salpingosonography (HyCoSy). (A) The contrast is seen to approach the fundus uteri on a sagittal view of the uterus. (B) The contrast is seen to have entered the interstitial part of the right tube on a transverse section through the uterus. (C) The contrast has entered the interstitial part of both tubes. (D) Contrast in the right tube. (E) Contrast in the left tube. (F) Free contrast in the pouch of Douglas; a normal result requires quick passage of contrast through the interstitial part of the tube during at least 10 seconds and confirmation of contrast spreading freely around the ovaries. (G) No passage of contrast into the free part of the tube, only the interstitial part is filled with contrast. This is abnormal and suggests a blocked tube; alternatively, tubal spasm could explain the finding.
295
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
296
It is important to realize that there is no true gold standard for methods used to assess tubal patency. The only thing one can do is to compare the results of various methods, none of which can provide us with the truth, e.g. compare the results of HyCoSy with those of hysterosalpingography or with laparoscopy with chromopertubation. Overall, agreement between these methods has been reported to be good.20–23
Acknowledgements This work was supported by the Swedish Medical Research Council (grants nos K2001-72X-11605-06A, K2002-72X-11605-07B and K2004-73X-11605-09A), two governmental grants (Landstingsfinansierad regional forskning, Region Skåne and ALF-medel), and funds administered by Malmö University Hospital. References 1. Sladkevicius P, Valentin L, Marsal K. Endometrial thickness and Doppler velocimetry of the uterine arteries as discriminators of endometrial status in women with postmenopausal bleeding: a comparative study. Am J Obstet Gynecol 1994;171(3):722–728 2. Forrest TS, Elyaderani MK, Muilenburg MI, Bewtra C, Kable WT, Sullivan P. Cyclic endometrial changes: US assessment with histologic correlation. Radiology 1988;167(1):233–237 3. Ritchie WG. Sonographic evaluation of normal and induced ovulation. Radiology 1986;161(1):1–10 4. Merz E, Miric-Tesanic D, Bahlmann F, Weber G, Wellek S. Sonographic size of uterus and ovaries in pre- and postmenopausal women. Ultrasound Obstet Gynecol 1996;7(1):38–42 5. Raine-Fenning NJ, Campbell BK, Clewes JS, Kendall NR, Johnson IR. Defining endometrial growth during the menstrual cycle with three-dimensional ultrasound. Br J Obstet Gynaecol 2004;111(9):944–949 6. Pache TD, Wladimiroff JW, de Jong FH, Hop WC, Fauser BC. Growth patterns of nondominant ovarian follicles during the normal menstrual cycle. Fertil Steril 1990;54(4):638–642 7. Sladkevicius P, Valentin L, Marsal K. Blood flow velocity in the uterine and ovarian arteries during the normal menstrual cycle. Ultrasound Obstet Gynecol 1993;3(3): 199–208 8. Jokubkiene L, Sladkevicius P, Rovas L, Valentin L. Assessment of changes in volume and vascularity of the ovaries during
the normal menstrual cycle using threedimensional power Doppler ultrasound. Hum Reprod 2006;21(10):2661–2668 9. Sladkevicius P, Valentin L, Marsal K. Blood flow velocity in the uterine and ovarian arteries during menstruation. Ultrasound Obstet Gynecol 1994;4(5):421–427 10. Sladkevicius P, Valentin L, Marsal K. Transvaginal gray-scale and Doppler ultrasound examinations of the uterus and ovaries in healthy postmenopausal women. Ultrasound Obstet Gynecol 1995;6(2):81–90 11. Valentin L, Akrawi D. The natural history of adnexal cysts incidentally detected at transvaginal ultrasound examination in postmenopausal women. Ultrasound Obstet Gynecol 2002;20(2):174–180 12. Landgren BM, Collins A, Csemiczky G, Burger HG, Baksheev L, Robertson DM. Menopause transition: annual changes in serum hormonal patterns over the menstrual cycle in women during a nineyear period prior to menopause. J Clin Endocrinol Metab 2004;89(6):2763–2769 13. Jokubkiene L, Sladkevicius P, Rovas L, Valentin L. Assessment of changes in endometrial and subendometrial volume and vascularity during the normal menstrual cycle using three-dimensional power Doppler ultrasound. Ultrasound Obstet Gynecol 2006;27(6):672–679 14. Parsons AK, Lense JJ. Sonohysterography for endometrial abnormalities: preliminary results. J Clin Ultrasound 1993;21(2):87–95 15. Exalto N, Stappers C, van Raamsdonk LA, Emanuel MH. Gel instillation sono hysterography: first experience with a new technique. Fertil Steril 2007;87(1):152–155
✩✩✩✩✩✩✩✩✩✩✩ ✩ (HyCoSy) for infertility. J Obstet Gynaecol 2005;25(3):275–278 21. Cimen G, Trak B, Elpek G, Simsek T, Erman O. The efficiency of hysterosalpingocontrast sonography (HyCoSy) in the evaluation of tubal patency. J Obstet Gynaecol 1999;19(5):516–518 22. Dijkman AB, Mol BW, van der Veen F, Bossuyt PM, Hogerzeil HV. Can hysterosalpingocontrast-sonography replace hysterosalpingography in the assessment of tubal subfertility? Eur J Radiol 2000;35(1):44–48 23. Holz K, Becker R, Schurmann R. Ultrasound in the investigation of tubal patency. A meta-analysis of three comparative studies of Echovist-200 including 1007 women. Zentralbl Gynakol 1997;119(8):366–373 24. Sokalska A, Valentin L. Changes in ultrasound morphology of the uterus and ovaries during the menopausal transition and early postmenopause: a 4-year longitudinal ultrasound study. Ultrasound Obstet Gynecol 2008;31:210–217
Normal gynaecological anatomy (uterus, tubes, ovaries)
16. Campbell S, Bourne TH, Tan SL, Collins WP. Hysterosalpingo contrast sonography (HyCoSy) and its future role within the investigation of infertility in Europe. Ultra sound Obstet Gynecol 1994;4(3):245–253 17. Chenia F, Hofmeyr GJ, Moolla S, Oratis P. Sonographic hydrotubation using agitated saline: a new technique for improving fallopian tube visualization. Br J Radiol 1997;70(836):833–836 18. Heikkinen H, Tekay A, Volpi E, Martikainen H, Jouppila P. Transvaginal salpingosonography for the assessment of tubal patency in infertile women: methodological and clinical experiences. Fertil Steril 1995;64(2):293–298 19. Ayida G, Harris P, Kennedy S, Seif M, Barlow D, Chamberlain P. Hysterosalpingocontrast sonography (HyCoSy) using Echovist-200 in the outpatient investigation of infertility patients. Br J Radiol 1996;69(826):910–913 20. Shahid N, Ahluwalia A, Briggs S, Gupta S. An audit of patients investigated by hysterosalpingo-contrast-sonography
297
17 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: the uterus Rehan Salim Davor Jurkovic
abstract Uterine pathology includes congenital uterine anomalies, uterine fibroids, uterine sarcoma, adenomyosis, endometrial polyps, endometrial hyperplasia and malignancy. The impact of two-dimensional and three-dimensional ultrasound on the clinical management of uterine pathology is discussed.
Keywords Adenomyosis, fibroids, hyperplasia, malignancy, polyps, sarcoma, uterine anomalies.
Introduction The use of ultrasound in the examination of the uterus has evolved over the last few decades. Initially, ultrasound was mostly used to raise a suspicion of a possible uterine abnormality, whilst more invasive techniques, such as laparoscopy or hysteroscopy, were used to establish the final diagnosis of uterine lesions. Improvements in ultrasound technology, and in particular the use of high-frequency transvaginal probes, have helped to transform the role of ultrasound from a general screening tool to a definitive diagnostic test for most pathological conditions affecting the uterus. In this chapter we will review the use of ultrasound in the diagnosis of uterine pathology.
Congenital Uterine Anomalies These morphological anomalies of the uterus, which arise during organogenesis, have been a source of much debate regarding their significance. Traditionally, they have been associated with poor reproductive outcomes, specifically
299
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
300
recurrent early pregnancy loss and preterm labour. However, clear evidence regarding their prevalence and benefit of treatment has always been lacking. The major factor underlying this has been the need for invasive diagnostic methods, such as hysterosalpingography or hysteroscopy and laparoscopy, to make a diagnosis; these invasive tests are not applicable to all women, thus making comprehensive screening difficult. The advent of three-dimensional (3D) ultrasound in gynaecological practice has significantly enhanced our ability to detect uterine abnormalities. This technology collates a set of ultrasound data, which can then be manipulated and viewed at any arbitrary angle and plane. In the context of uterine assessment, it allows the operator to view the coronal plane of the uterus, which is often unobtainable on the conventional B-mode two-dimensional (2D) transvaginal ultrasound examination, as it is lying perpendicularly to the ultrasound beam. The importance of this plane is that it allows for the differentiation between the most common duplication anomalies including the arcuate, subseptate and bicornuate uterus (Figs 17.1, 17.2). This is important as each of these anomalies carries different reproductive implications and they have very different management strategies, i.e. an attempt to resect a septum in a bicornuate uterus could lead to perforation of the fundus. Two early studies examined the diagnostic accuracy of 2D and 3D ultrasonography for the diagnosis of congenital uterine anomalies, using hysterosalpingography as the gold standard.1,2 They both showed a good agreement between 3D ultrasound and hysterosalpingography in classifying the uterus as abnormal or normal. This result was superior to that of 2D ultrasound, which did identify all cases of abnormal uterus but also gave a number of false-positive findings. The reproducibility of 3D ultrasound diagnosis of uterine anomalies has also been tested using a modified American Fertility Society classification of congenital uterine anomalies3 (Table 17.1). A good intra- and interobserver agreement has been reported with only occasional differences between the operators, mainly in cases of arcuate and subseptate uteri.4 Three-dimensional ultrasound is at present the only imaging technique which has been systematically assessed for the reproducibility of the diagnosis of congenital uterine anomalies. Using 3D ultrasound, a large-scale screening study of women at low risk for the presence of congenital uterine anomalies was done by Jurkovic et al.5 The reported prevalence of major anomalies was 2.3%, which was similar to the results of previous studies that used more invasive methods to diagnose uterine defects.6 Subsequently, the reproductive impact of anomalies in the low-risk group was reported by Woelfer et al, who used 3D ultrasonography to screen 1089 women who presented for pelvic imaging for indications unrelated to their past reproductive performance.7 The study showed that even in women with an incidental finding of uterine anomaly, the risk of first-trimester miscarriage was significantly increased in those diagnosed with a subseptate uterus compared to women with normal uteri. There was also a slightly higher risk of second-trimester miscarriage and preterm delivery in women with arcuate uteri.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: the uterus Fig. 17.1 Three-dimensional image of an arcuate uterus in the coronal plane demonstrating a normal outer contour and a deep fundal indentation of the uterine cavity.
Another comparative study of low-risk women and those with a history of recurrent miscarriage showed a four times higher prevalence of anomalies in those who suffered repeated pregnancy losses.8 In addition, the study showed that uterine anomalies in women with recurrent pregnancy loss tend to be more severe compared to the anomalies which were diagnosed incidentally on screening.
301
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 17.2 A coronal view of a subseptate uterus showing a deep septum extending down two-thirds the length of the uterine cavity.
Table 17.1 Three-dimensional ultrasound classification of congenital uterine anomalies
302
Uterine morphology
Fundal contour
External contour
Normal
Straight or convex
Uniformly convex or with indentation <10 mm
Arcuate
Concave fundal indentation with central point of indentation at obtuse angle (>90°)
Uniformly convex or with indentation <10 mm
Subseptate
Presence of septum, which does not extend to cervix, with central point of septum at an acute angle (<90°)
Uniformly convex or with indentation <10 mm
Bicornuate
Two well-formed uterine cornua – fundal contour convex in each
Fundal indentation >10 mm dividing the two cornua
✩✩✩✩✩✩✩✩✩✩✩ ✩
Uterine Fibroids Uterine fibroids are the most common uterine abnormality encountered in women of reproductive age, being present in at least 40% of women over the age of 40. Clinically, they often present with menstrual problems, classically menorrhagia and dysmenorrhoea; however, they may also cause pressure symptoms on the bladder, leading to urinary frequency. Uterine fibroids can also be found during investigations for infertility, where they are associated with a reduced chance of successful assisted reproduction treatment. The ultrasound appearance of fibroids is variable but most commonly they appear as well-defined, echo-dense single or multiple myometrial tumours (Fig. 17.3). Histologically, fibroids are composed of densely packed whorls of smooth muscle and connective tissue, which cause reflection of the ultrasound beam and
Fig. 17.3 A transverse view of the uterus showing a large posterior intramural fibroid.
Gynaecological pathology: the uterus
These studies provide strong objective evidence to support the widely held view that congenital uterine anomalies have a significant detrimental effect on women's reproductive performance. However, it is still not clear what benefits, if any, surgical correction of uterine anomalies may have on women's future reproductive performance. The ability to perform a detailed non-invasive assessment of uterine anomalies, including measurement of uterine cavity dimensions before and after surgery, may help to improve selection of patients and to provide an objective measure of the success of anatomical reconstruction of the uterine cavity.
303
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
304
acoustic shadowing. Occasionally, fibroids may undergo degeneration or they may contain areas of calcification, which may alter their ultrasound appearance quite significantly. These changes often occur in pregnancy when the trophic action of increased circulating oestrogens stimulates fibroids to grow fast. The rapidly enlarging fibroid may quickly outgrow its blood supply, leading to infarction and degeneration. Clinically, degeneration of fibroids can be the cause of significant pain in pregnancy. The degenerated fibroid is located at the site of maximal tenderness and usually has a cystic core, which may be filled with hypoechoic fluid and septa of the remnants of the necrotic myometrium. These appearances can be alarming and may be mistaken for more significant pathology, such as a sarcoma or an ovarian mass. The differentiation is generally easy as an ovarian mass is separate from the uterus and sarcoma is exceedingly rare in premenopausal women. Similar ultrasound appearances occur in uterine fibroids following embolization. This iatrogenic method of causing vascular occlusion and degeneration usually results in cystic necrosis similar to that found in pregnancy. However, over time fibroids that have undergone embolization may become calcified and appear hyperechoic on ultrasound scan.9 Although uterine fibroids are easily diagnosed on ultrasonography, it is their location, rather than their presence, which is often the most significant factor in determining their clinical significance and management options. Intramural fibroids are predominantly located within the myometrium and they rarely lead to significant clinical problems unless they are large (i.e. >5 cm), when they may cause pressure effects on surrounding organs, specifically the urinary bladder, leading to symptoms including urinary frequency. Subserous fibroids project from the uterine serosa and they too are only problematic when large and indenting surrounding organs. Occasionally, subserous fibroids may be entirely extrauterine and connected to the uterus by a small pedicle. These are classified as pedunculated fibroids, which may sometimes undergo torsion and present with an acute abdomen. Occasionally, they may be mistaken for an ovarian tumour; however, this is overcome by identifying an ipsilateral normal ovary and the stalk connecting the fibroid to the uterus using Doppler. Identifying and describing the location of all fibroids on ultrasound examination is of importance as it enables the clinician to make a more complete assessment regarding the contribution of uterine fibroids to the clinical symptomatology. It also helps to plan further management, selection of the appropriate procedure and the chances of success of removal. Therefore, a small intramural fibroid on the posterior wall of the uterus is unlikely to be the cause of any significant menstrual irregularities. However, the knowledge that the uterine cavity is morphologically normal would enable the patient who is suffering from heavy dysfunctional uterine bleeding to consider either endometrial ablation or an intrauterine progestogen-releasing device to control the symptoms. Clinically, the most important uterine fibroids are submucous fibroids, which account for only 5% of all uterine fibroids. These are the cause of the most classic symptoms associated with uterine fibroids – dysmenorrhoea and menorrhagia. Submucous fibroids protrude into the uterine cavity to varying degrees, with
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: the uterus
Fig. 17.4 A longitudinal view of the uterus showing a submucous fibroid, which is almost completely protruding into the uterine cavity.
some causing only a minor indent whilst some are entirely within the endometrial cavity, i.e a fibroid polyp (Fig. 17.4). It is important to attempt to provide an estimate of the degree of protrusion of a fibroid into the uterine cavity as fibroids that are predominantly within the cavity may be amenable to hysteroscopic resection. A classification system for this is already in use by hysteroscopic surgeons who define submucous fibroids as type 0 (polyps), which are entirely within the cavity, type 1, which have <50% of the total fibroid within the myometrium, and type 2 which have >50% of the total fibroid within the myometrium.10 The type 2 fibroid may be unsuitable for hysteroscopic resection or may require a twostage procedure. In either case this classification system is aimed at improved patient selection for hysteroscopic resection and this is conventionally done by a diagnostic hysteroscopy. However, it is still uncertain whether hysteroscopy should be the imaging modality to select those fibroids that are amenable to hysteroscopic resection. Vercellini et al reported that only 69% of submucous fibroids deemed amenable to hysteroscopic resection were actually successfully removed at operative hysteroscopy.11 This suggests that preoperative assessment by hysteroscopy may not be accurate in predicting the success of fibroid resection. Ultrasound has the advantage of being a widely available outpatient imaging modality with the ability to measure and assess the depth of fibroid involvement into the myometrium more accurately than any other imaging technique. However, conventional B-mode transvaginal ultrasound is not accurate enough for the detection of intracavitary pathology or for the measurement of extension of fibroids into the uterine cavity.11 A refinement, saline infusion sonohysterography,
305
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ allows a clearer view of the uterine cavity by providing an acoustic contrast within the uterine cavity. This enables more accurate detection of focal pathology in the uterine cavity, including submucous fibroids, with results comparable to diagnostic hysteroscopy.12 Three-dimensional ultrasound may further facilitate the assessment of the relationship of submucous fibroids and the uterine cavity. Preliminary data indicate that 3D is a reproducible method for the assessment of uterine fibroids, which may provide a more effective alternative to diagnostic hysteroscopy for preoperative assessment of submucous fibroids.13 Submucous fibroids may be a cause of infertility in some women as conception rates are improved following fibroid removal. Eldar-Geva et al reported a 33.8% miscarriage rate in women with submucous fibroids compared to 16.8% in controls.14 Bernard et al reported that removal of even solitary submucous fibroids improves live-birth rates.15 Although these results are encouraging, there are no prospective randomized controlled studies to assess the true impact of these interventions. The significance of intramural fibroids in women complaining of infertility remains uncertain. However, a study by Hart et al investigated the impact of small (<5 cm) intramural fibroids on conception rates in 112 women, using conventional B-mode ultrasound.16 They reported that the presence of small intramural fibroids reduced the chances of conception by 50%. These findings are of some concern and it remains to be seen whether they will be confirmed in future studies.
Uterine Sarcoma
306
This rare tumour of the uterine myometrium is usually diagnosed after hysterectomy. The clinical presentation is usually of a rapidly enlarging uterus in a postmenopausal woman. Although pain is generally not a feature, the rapid growth of the tumour may cause it to outgrow its blood supply, leading to necrosis and subsequent pain. The condition is rare and thought to complicate around 0.03% of benign fibroids, although this figure is highly speculative. The natural history of sarcoma uteri remains unknown and there is no clear evidence to link benign uterine fibroids with subsequent malignant transformation into sarcoma. Preoperative detection has been problematic as the rarity of the tumour has not enabled collation of morphological data from significant numbers of women. The ultrasound features are non-specific and the most useful finding is the presence of wide areas of tumour necrosis. Only limited data regarding ultrasound features of sarcomata are available. On Doppler examination, sarcomas may display increased vascularity. Hata et al compared blood flow indices between five uterine sarcomata and 41 uterine fibroids.17 They reported that using a cut-off of 41 cm/s for peak systolic velocity, on colour Doppler, the detection rate for sarcoma was 80% with a false-positive rate of 2.4% with no significant difference in resistance index between the two groups. Szabo et al reported on the comparison of 12 women with sarcomas and 117 women with benign fibroids.18 In contrast to the former study, in this group there was a reduction in the resistance index with an increase in blood velocity within sarcomas. This study also reported that subjective assessment of vascularity demonstrated irregular blood vessel patterns within
✩✩✩✩✩✩✩✩✩✩✩ ✩ uterine sarcoma. The differences between the two studies highlight the difficulties in obtaining a correct preoperative ultrasound diagnosis of uterine sarcomata.
Adenomyosis is a common condition, which is associated with a range of symptoms including pelvic pain, dysmenorrhoea and menorrhagia. As these symptoms are also commonly encountered in other gynaecological conditions, the reported accuracy of clinical diagnosis of adenomyosis ranges from 2.6% to 26%.19 Adenomyosis may be found in up to 20% of hysterectomy specimens; however, it is asymptomatic in around 30% of these cases. It is more common in older multiparous women and those who have had previous uterine surgery, especially curettage and caesarean section. Advances in endometrial ablation have reduced the need for hysterectomy in many women; however, if adenomyosis is present then the risk of subsequent hysterectomy is increased. Preoperative screening for adenomyosis may play a role in the improved triage of women who are likely to benefit from endometrial ablation. On clinical examination, there may be diffuse uterine enlargement, although the posterior uterine wall may be disproportionately larger, which is usually more pronounced in the premenstrual phase. Diagnosis with ultrasound is difficult as there are no characteristic features. Early studies used transabdominal ultrasound and described the myometrium as having a ‘focal honeycomb’ appearance with irregular 5–7 mm cystic spaces; these findings confirmed adenomyosis in four out of nine subjects (Fig. 17.5).20 Subsequently, Bohlman et al diagnosed adenomyosis on the basis of
Fig. 17.5 A logitudinal view of the uterus showing a thick and hyperechoic posterior uterine wall, which is typical of adenomyosis.
Gynaecological pathology: the uterus
Adenomyosis
307
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ hypoechogenicity of the myometrium, posterior uterine wall thickening and anterior displacement of the endometrial cavity.21 However, these findings were confirmed at histology in only 50% of cases. Siedler et al used similar criteria and reported a sensitivity of only 63% but a specificity of 97% with a positive predictive value of 71%.22 Transvaginal ultrasound with its improved resolution enables evaluation of more subtle features that may be suggestive of adenomyosis. Several features have been reported that would be suggestive of adenomyosis, including uterine enlargement not explained by leiomyomas, asymmetrical thickening of the anterior or posterior uterine walls, lack of contour or abnormality effect, heterogeneous and poorly circumscribed areas in the myometrium, increased echotexture of the myometrium and anechoic cysts or lacunae within the myometrium.23,24 In isolation, however, none of these features is either sensitive nor specific.25 Diagnostic difficulties may arise in differentiating adenomyosis from fibroids, which may also co-exist in up to 60% of women. Several features have been proposed that would be more suggestive of adenomyosis, including poorly defined hypoechogenic area, minimal mass effect on the serosa or endometrium relative to the size of the lesion, lack of edge shadowing, echogenic nodules and linear striations radiating out from the myometrium and into the endometrium, and absence of circular blood flow in the periphery on colour Doppler examination.26
Endometrial Polyps
308
The ultrasound features of endometrial polyps are well recognized, being focal hyperechoic lesions within the endometrium; this appearance remains constant throughout the menstrual cycle as benign endometrial polyps are not responsive to ovarian steroid hormones. Detailed inspection of the polyp may also reveal small hypoechoic spaces within it, these being small pockets of glandular endometrial secretions. They are best visualized in the proliferative phase of the menstrual cycle as at this time they contrast against the relatively hypoechoic endometrium. Endometrial polyps should be differentiated from fibroid polyps as the latter are hypoechoic and cast acoustic shadows as a characteristic of being fibroids. Endometrial polyps usually present in women after the age of 35. However, their significance differs according to age group as in younger women, they are more likely to be benign and present with intermenstrual bleeding, dysmenorrhoea or subfertility. In the older, perimenopausal woman, they are usually detected during screening for endometrial pathology due to irregular or postmenopausal bleeding. In these women, polyps may be either seen as focal lesions or be detected as thickened endometrium. Detection is important as, although only a minority of polyps are malignant or hyperplastic, the standard management is hysteroscopic removal rather than endometrial biopsy. Detection may be improved by the addition of saline into the endometrial cavity – saline infusion sonohysterography. However, this technique, although being comparable to diagnostic hysteroscopy, is associated with pain, infection and the risks of intraperitoneal spillage of malignant endometrial cells. Timmerman et al have recently described the ‘pedicle sign’ which refers to the colour Doppler detection of a feeding vessel that enters the body of a polyp
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: the uterus
Fig. 17.6 An image of a large endometrial polyp with a prominent vascular pedicle.
through its stalk (Fig. 17.6).27 They prospectively assessed 3099 women and found that the pedicle sign had a sensitivity of 76.4% and specificity of 95.3% for detection of endometrial polyps. The positive predictive and negative predictive values were 81.3% and 93.8% respectively. The positive predictive value for any intracavitary pathology was 94.2%. Given the high positive predictive value for the detection of intracavitary pathology, the authors conclude that the pedicle sign has the potential to replace second-line diagnostic tests such as saline infusion sonohysterography and hysteroscopy.
Endometrial Hyperplasia and Malignancy Ultrasound measurement of endometrial thickness has become the fundamental step in screening for pathology in women presenting with abnormal bleeding during the peri- and postmenopausal decades. In these women, 10% will have significant endometrial pathology. The aim of ultrasound, therefore, is to screen out the 90% who do not require further intervention and allow selection of appropriate intervention in the remainder. The meta-analysis of Smith-Bindman et al, of 6000 women, forms the basis for most strategies, namely that an endometrial thickness less than 4 mm, including both leaves of endometrium, is highly unlikely to harbour any significant pathology and the chances of malignancy are <1%.28 In the remainder of women, i.e. those with an endometrial thickness greater than 5 mm, the next step is usually either endometrial biopsy or hysteroscopy. Both are invasive to varying degrees. In an attempt to obviate the need for further tests and proceed directly to treatment, several refinements on ultrasound endometrial assessment have been proposed. Saline contrast sonohysterography allows not only detection of focal pathology but
309
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 17.7 An example of a large malignant polyp with an irregular surface.
also an assessment of the morphological features. Benign endometrial polyps are likely to have smooth surfaces whereas malignant polyps are likely to have irregular surfaces and may have necrotic cores and are associated with a haematometra (Fig. 17.7). Doppler examination of the endometrium has been suggested to help differentiate between benign and malignant endometrial lesions; however, authors have reported a significant overlap and the usefulness of this modality has been questioned. Power Doppler, on the other hand, with its ability to sensitively detect small irregular vessels and with less interference from background noise, may have potential in this context. In a study by Epstein et al, endometrial vascularization was assessed subjectively by the operator and objectively using various Doppler vascularization indices.29 Both were reasonably accurate in detecting endometrial cancer with sensitivities of 75% and 88% and specificities of 96% and 81% respectively. Although the Doppler tests performed well in women with endometrial thickness between 5 and 15 mm, subjective assessment of endometrial morphology was a better diagnostic test in women with endometrial thickness >15 mm.
Conclusion
310
Transvaginal ultrasound has been accepted as the most effective method for the diagnosis of various uterine abnormalities. In recent years it has also been playing an increasingly important role in the selection of women for different conservative and surgical management options. The introduction of 3D ultrasound has significantly improved the accuracy of ultrasound diagnosis of congenital uterine anomalies and submucous fibroids, which may help to improve our understanding of the clinical significance of these conditions and facilitate the development of more effective strategies for their management.
✩✩✩✩✩✩✩✩✩✩✩ ✩ References ultrasonography, sonohysterography and hysteroscopy for the investigation of abnormal uterine bleeding in premenopausal women. Acta Obstet Gynecol Scand 2003;82:493–504 13. Salim R, Lee C, Davies A, Jolaoso B, Ofuasia E, Jurkovic D. A comparative study of threedimensional saline infusion sonohysterography and diagnostic hysteroscopy for the classification of submucous fibroids. Hum Reprod 2005;20:253–257 14. Eldar-Geva T, Meagher S, Healy DL, MacLachlan V, Breheny S, Wood C. Effect of intramural, subserosal, and submucosal uterine fibroids on the outcome of assisted reproductive technology treatment. Fertil Steril 1998;70:687–691 15. Bernard G, Darai E, Poncelet C, Benifla JL, Madelenat P. Fertility after hysteroscopic myomectomy: effect of intramural myomas associated. Eur J Obstet Gynecol Reprod Biol 2000;88:85–90 16. Hart R, Khalaf Y, Yeong CT, Seed P, Taylor A, Braude P. A prospective controlled study of the effect of intramural uterine fibroids on the outcome of assisted conception. Hum Reprod 2001:16:2411–2417 17. Hata K, Hata T, Maruyama R, Hirai M. Uterine sarcoma: can it be differentiated from uterine leiomyoma with Doppler ultrsonography? A preliminary report. Ultrasound Obstet Gynecol 1997;9:101–104 18. Szabo I, Szantho A, Papp Z. Uterine sarcoma: diagnosis with multiparameter sonographic analysis. Ultrasound Obstet Gynecol 1997;10:220–225 19. Reinhold C, Tafazoli F, Wang L. Imaging features of adenomyosis. Hum Reprod Update 1998;4:337–349 20. Walsh JW, Taylor KJ, Rosenfield AT. Gray scale ultrasonography in the diagnosis of endometriosis and adenomyosis. Am J Roentgenol 1979;132:87–90 21. Bohlman ME, Ensor RE, Sanders RC. Sonographic findings in adenomyosis of the uterus. Am J Roentgenol 1987;148: 765–766 22. Siedler D, Laing FC, Jeffrey RB Jr, Wing VW. Uterine adenomyosis. A difficult sonographic diagnosis. J Ultrasound Med 1987;6:345–349 23. Reinhold C, Atri M, Mehio A, Zakarian R, Aldis AE, Bret PM. Diffuse uterine adenomyosis: morphologic criteria and diagnostic accuracy of endovaginal sonography. Radiology 1995;197:609–614
Gynaecological pathology: the uterus
1. Jurkovic D, Geipel A, Gruboeck K et al. Three-dimensional ultrasound for the assessment of uterine anatomy and detection of congenital anomalies: a comparison with hysterosalpingography and two-dimensional sonography. Ultra sound Obstet Gynecol 1995;5:233–237 2. Raga F, Bonilla-Musoles F, Blanes J, Osborne NG. Congenital Mullerian anomalies: diagnostic accuracy of three-dimensional ultrasound. Fertil Steril 1996;65:523–528 3. Buttram VC, Gibbons WE. Mullerian anomalies: a proposed classification (an analysis of 144 cases). Fertil Steril 1979;32:40–46 4. Salim R, Woelfer B, Backos M, Regan L, Jurkovic D. Reproducibility of threedimensional ultrasound diagnosis of congenital uterine anomalies. Ultrasound Obstet Gynecol 2003;21:578–582 5. Jurkovic D, Gruboeck K, Tailor A, Nicolaides KH. Ultrasound screening for congenital uterine anomalies. Br J Obstet Gynaecol 1997;104:1320–1321 6. Simon C, Martinez L, Prado F. Mullerian defects in women with normal reproductive outcome. Fertil Steril 1991;56:1192–1193 7. Woelfer B, Salim R, Banerjee S et al. Reproductive outcomes in women with congenital uterine anomalies detected by three-dimensional ultrasound screening. Obstet Gynecol 2001;98:1099–1103 8. Salim R, Regan L, Woelfer B et al. A comparative study of the morphology of congenital uterine anomalies in women with and without a history of recurrent first trimester miscarriage. Hum Reprod 2003;1:162–166 9. Mueller GC, Gemmete JJ, Carlos RC. Diagnostic imaging and vascular embolization for uterine leiomyomas. Semin Reprod Med 2004;22:131–142 10. Wamsteker K, Emanuel MH, de Kruif JH. Transcervical hysteroscopic resection of submucous fibroids for abnormal uterine bleeding: results regarding the degree of intramural extension. Obstet Gynecol 1993;82:736–740 11. Vercellini P, Cortesi I, Oldani S, Moschetta M, De Giorgi O, Giorgio Crosignani P. The role of transvaginal ultrasonography and outpatient diagnostic hysteroscopy in the evaluation of patients with menorrhagia. Hum Reprod 1997;12:1768–1771 12. Farquhar C, Ekeroma A, Furness S, Arroll B. A systematic review of transvaginal
311
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
312
24. Hirai M, Shibata K, Sagai H, Sekiya S, Goldberg BB. Transvaginal pulsed and color Doppler sonography for the evaluation of adenomyosis. J Ultrasound Med 1995;14:529–532 25. Brosens JJ, Barker FG. The role of myometrial needle biopsies in the diagnosis of adenomyosis. Fertil Steril 1995;63: 1347–1349 26. Devlieger R, D'Hooghe T, Timmerman D. Uterine adenomyosis in the infertility clinic. Hum Reprod Update 2003;9:139–147 27. Timmerman D, Verguts J, Konstantinovic ML et al. The pedicle artery sign based on sonography with color Doppler imaging
can replace second-stage tests in women with abnormal vaginal bleeding. Ultrasound Obstet Gynecol 2003;22:166–171 28. Smith-Bindman R, Kerlikowaske K, Feldstein VA et al. Endovaginal ultrasound to exclude endometrial cancer and other endometrial abnormalities. JAMA 1998;280:1510–1517 29. Epstein E, Skoog L, Isberg PE et al. An algorithm including results of gray-scale and power Doppler ultrasound examination to predict endometrial malignancy in women with postmenopausal bleeding. Ultrasound Obstet Gynecol 2002;20:370–376
18 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: tubes and ovaries Rüdiger Osmers
ABSTRACT Size and structure of adnexal tumours are presented, with emphasis on twodimensional ultrasound. Benign tumours include dysfunctional ovarian cysts and endometriosis. Malignant tumours include epithelial ovarian tumours. Other tumours discussed in this chapter are fibromas, fibrothecomas and ovarian germ cell tumours. In a separate section, the sonographic features of adnexal torsion are presented. Tubal pathology includes tubal pregnancy, tubal carcinoma, hydrosalpinx and pyosalpinx.
Keywords Adnexal torsion, cyst, endometriosis, fallopian tubes, hydrosalpinx, ovaries, pyosalpinx, tubal pregnancy, tumour.
Ovaries Benign and Malignant Ovarian Cysts: General Considerations Refinements in ultrasound technology have been dramatic during the last few decades and since the introduction of transvaginal ultrasound, assessment of the female lower pelvis has been improved. High-resolution images contribute to a better understanding of ovarian function. On the other hand, the diagnosis of ovarian cysts has become an increasingly more common phenomenon. This is true especially for hitherto clinically undetected ovarian cysts. However, the enormous histological diversity of adnexal masses as well as physiological changes of the normal ovary co-exist with a variety of sonographic findings. Therefore a particular challenge, especially in premenopausal women, is avoiding unnecessary operations on functional tumours and,
313
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
314
on the other hand, correctly identifying true neoplasms and applying suitable therapy. The importance of sonography in the differential diagnosis of adnexal masses is unquestionable and the main indications can be highlighted as follows:
• screening for adnexal tumours in asymptomatic women • diagnostic clarification of women with clinical symptoms of disease • morphological description and differential diagnosis of adnexal tumours • diagnostic exploration of the abdomen in cases of suspected malignancy (liver, omentum, kidney, ascites).
The significance of sonography as a screening method in the detection of ovarian tumours has been subject to controversy. As the prognosis of advanced carcinoma is poor, the aim of every screening programme must be the detection of early stages of disease, including tumours of low malignant potential. It has been questioned, however, whether these early stages as a whole really contribute to the rapidly growing group of ovarian carcinomas, which develop widespread peritoneal metastasis. In a survey of 1601 women with family risk of ovarian cancer, Bourne et al2 found one ovarian carcinoma stage Ia, one stage III and three tumours of low malignant potential. However, out of those women with an inconspicuous scan, five developed advanced stages of carcinoma within a time period of 24–44 months. The incidence of malignant ovarian tumours increases with patient age and the menopausal status has to be considered.21 In a literature review of 8000 asymptomatic women, who had been scanned by means of abdominal or vaginal sonography, an ovarian carcinoma was detected in 10 cases.14 Due to these limitations it has been recommended to further evaluate the significance of screening programmes. In order to increase the predictive value, screening should be restricted to specific risk groups such as women with a family history of ovarian cancer, postmenopausal status, nulliparae and women who have never taken oral contraceptives (low ovulatory age). The assessment and management of ovarian cysts are largely influenced by patient age but the size of the ovary itself varies due to the alterations in the endocrine environment. Between the second and fourth decade benign ovarian tumours occur 10 times more often than malignant neoplasms. Dermoid cysts predominate before the age of 40; later these are mucinous and serous cystomas. In the postmenopause there is a marked increase in the incidence of malignant tumours. As functional and inflammatory aspects change and endometriosis ceases to be of importance, the likelihood of malignancy is higher in every sonographically detected tumour. Different sonographic scoring systems have been introduced in an attempt to identify criteria to differentiate benign from malignant adnexal tumours.22–24 These tumour scoring systems are all based on descriptive sonomorphological findings and most of them include the following items:
• tumour size • tumour structure
✩✩✩✩✩✩✩✩✩✩✩ ✩
papillary projections • presence or absence of solid parts within the tumour • thickness of cyst wall and septal wall • echo-dense foci and acoustic shadowing • echogenicity of the lesion: hyperechoic, hypoechoic, anechoic • colour Doppler sonography: identification of blood vessels within the cyst wall and septa, within solid components and papillary projections. Assessment of the flow profile including flow velocity, resistance and pulsatility indices, identification of arteriovenous shunting.
Tumour Size The size of cystic ovarian lesions is one of the most important characteristics. The risk of malignancy rises with increasing tumour size and this is true in both pre- and postmenopausal women.5 Although the prevalence of malignancy related to the tumour size varies in different studies, there is general agreement that tumours over 10 cm in diameter should be removed.4,18 The limited depth of penetration of the vaginal probes makes a reliable ultrasound evaluation of the entire cyst questionable and the probability of malignancy is too high to justify conservative management.
Gynaecological pathology: tubes and ovaries
• number of cysts and locules • inner and outer surface of the cyst: smooth surface or existence of
Tumour Structure Complexity is a major feature of ovarian tumours in estimating the risk of malignancy.10 So-called ‘simple’ ovarian cysts are unilocular with no irregularities. As long as these simple cysts are small (less than 3 cm) the risk of being malignant is low.6 In contrast, the term ‘complex’ cyst has been introduced to describe multiloculated or multicystic tumours with or without papillary projections and solid components. A loculated cyst is characterized by septa, which create compartments within a single cyst, whereas in multicystic tumours separate cysts exist apart from each other. Papillary projections originating from cyst wall or septa must be interpreted as localized epithelial overgrowth and strongly correlate with an increased risk of malignancy.5 Colour Doppler can identify blood vessels within papillary irregularities and solid tumour components but the absence of detectable blood flow in a small papillary projection should not influence clinical decisions unless the differential diagnosis of adherent fibrin or blood clots has to be excluded. As a rule, the likelihood of malignancy increases with increasing complexity of an ovarian tumour and this is true especially for the finding of papillary projections.
Cyst Wall and Septal Wall Thickness The significance of cyst wall and septal wall thickness in evaluating ovarian tumours has been subject to debate. Thin and smooth cyst walls more likely correlate with benign conditions whereas thick and irregular walls are preferentially found in
315
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ malignant neoplasms.12 However, there are inherent methodological difficulties as to how to standardize the measurement and how to define a cut-off value when a marked overlap of false-positive and false-negative results can be expected. Certain benign cysts such as endometriomas and benign teratomas frequently accompany thick walls or septa whereas on the other hand, early stages of ovarian cancer may have rather thin walls. Therefore, this criterion should not be overestimated and should be interpreted in correlation with other ultrasound findings.
Echo-Dense Foci and Acoustic Shadowing Echo-dense foci are defined as highly reflective areas that appear almost white on greyscale ultrasound. Such foci represent calcified structures within the tissue, but also the characteristic finding of teeth within dermoid cysts. Behind these highly reflective areas, acoustic shadowing can usually be described. However, gas-filled bowel also is highly reflective on ultrasound and misinterpretation may occur. Although the presence of echo-dense foci and acoustic shadowing within an ovarian tumour is highly indicative of cystic teratomas, these phenomena do not exclude malignancy.9
Echogenicity The echogenicity of an ovarian tumour depends on the density of a lesion. Serous fluid with water-like density is virtually anechoic. On grey-scale ultrasound this anechoic fluid appears black whereas the increased density of mucinous fluid is described as hypoechoic with a homogeneous grey appearance on ultrasound. Diluted cells within the cyst fluid also enhance density and the sonographic image of tumours containing blood or pus is therefore hypoechoic as well. Endometriomas typically are homogeneously hypoechoic tumours and the echogenicity of these cysts is often compared with a ‘ground-glass’ appearance (Fig. 18.1). Solid components within an ovarian tumour tend to be rather hyperechoic and appear inhomogeneous. The significance of the relative echogenicity of adnexal masses has been investigated and the risk of malignancy was estimated as low in anechoic lesions and vice versa in hyperechoic tumours.13 However, according to our own results, echogenicity alone does not predict malignancy.16 Differences in echogenicity may facilitate differential diagnosis, but far more important is the differentiation between fluid and solid components. The description of a complex tumour with solid elements that appear inhomogeneous and hyperechoic on grey-scale ultrasound is highly suspicious of malignancy. This is true not because of the hyperechoic areas per se but because these hyperechoic areas are solid. In contrast, differentiation of anechoic versus hypoechoic cyst fluid alone does not alter clinical decisions unless additional information is available.
Morphology Scoring Systems 316
Since the introduction of ultrasound, different scoring systems have been created in an attempt to estimate the risk of malignancy of a lesion. The first scoring
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: tubes and ovaries
Fig. 18.1 Endometrioma with ‘ground-glass’ appearance of the cyst contents.
systems included morphological features and later on additional criteria such as patient age or menopausal status were incorporated.9,18,21 All scoring systems have a number of false-positive and false-negative test results, depending on the variables included and the characteristics of the population. As the statistical probability of correctly identifying a malignant neoplasm on the basis of scoring systems increases with tumour complexity, there is a tendency to underestimate early carcinoma with few atypical morphological features. Little is known about tumour biology and the dynamics of tumour growth and this is true especially for the progression from benign to malignant disease. Therefore the incorporation of continuous variables such as wall thickness is problematic. Accurate assessment of an ovarian tumour includes morphological features and it is necessary to assign an individual therapeutic strategy. Extensive use of morphological scoring systems, however, may be associated with a reduction of the detection rate for early cancer.
Benign and Malignant Neoplasms of the Ovary Advanced ultrasound technology has clearly improved the description of ovarian lesions. However, correct interpretation of sonographic findings remains a challenge due to the histological diversity of ovarian tumours. Genuine neoplasms alone are divided into 35 subtypes according to the WHO classification.19 Description of the ultrasound characteristics of every tumour would exceed the capacity of this book. We have therefore focused our interest on the most frequent histological entities and the most pronounced sonographic features.
317
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Dysfunctional ovarian cysts Dysfunctional ovarian cysts originate from the follicle and become clinically important when they are larger than 5 cm and do not show signs of regression during an observation period of 2 months. According to our own results, 95% of these cysts disappear spontaneously. In contrast to inflammatory changes, endometriosis and malignant neoplasms, dysfunctional cysts are generally not attached to the surrounding tissue and therefore acute torsion is more likely to occur. Follicle cysts Stimulated by follicle-stimulating hormone (FSH), the Graaffian follicles develop up to a size of 20–25 mm. If they fail to ovulate, the transition to follicular cysts is fluent. Diameters of 3 cm and more are considered pathological but the maximum diameter usually does not exceed 10 cm. Luteinized follicular cysts, however, which may occur during pregnancy, could even reach a diameter of 25 cm.21 Follicular cysts are eventually found even in postmenopausal women, where they have been described up to 6 years after menopause.20 The typical sonographic finding is that of a unilocular cyst with a smooth wall, no papillary projections and echo-lucent cyst fluid. Corpus luteum cysts Histological characteristics of corpus luteum cysts and differentiation from follicular cysts are signs that ovulation has taken place. The corpus luteum cyst develops from the corpus luteum due to excessive central bleeding. The sonographic finding is that of a solitary cyst, which consists of hypoanechoic as well as hyperechoic components. The ultrasound appearance depends very much on the age of the cyst and the period of time between bleeding and first description. Haemorrhage may have a ‘web-like’ or more homogeneous hypoechoic appearance like endometriomas, and retracted blood clots adherent to the inner surface of the cyst may also be seen (Fig. 18.2). The average diameter of corpus luteum cysts is 5 cm but they may range from 2.5 to 16 cm.1 Evaluation of the flow profile of blood vessels in the cyst wall by means of colour Doppler sonography is of little help as neovascularization with low impedance to blood flow also occurs and therefore discrimination from malignant neoplasms is hardly possible on the basis of Doppler flow indices. However, differentiation of true solid tumour components from coagulated and retracted blood clots can easily be achieved by use of colour Doppler.
318
Thecalutein cysts Thecalutein cysts may develop following prolonged stimulation by luteinizing hormone or hCG. Multiple, bilateral thecalutein cysts (hyperreactio luteinalis) are found in 25% of women with gestational trophoblastic disease.11 Similar pathological findings are seen due to overstimulation by gonadotropins in patients receiving infertility treatment. Massively enlarged, multcystic ovaries can be seen on ultrasound examination. The cysts have a smooth wall and the cyst content is hypoanechoic.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: tubes and ovaries
Fig. 18.2 Haemorrhagic cyst with web-like cyst contents.
Endometriosis Endometriosis is defined by the occurrence of vital endometrial tissue outside the uterine cavity. According to the localization of the ectopic endometrium, endometriosis genitalis interna (adenomyosis uteri) can be distinguished from endometriosis genitalis externa and endometriosis extragenitalis. One of the typical locations of endometriosis genitalis externa is the ovaries.25 Endometriosis is a disease of women of reproductive age and the most typical period of first diagnosis is between 20 and 40 years of age. Transvaginal sonography shows one or more uni- or bilateral cysts of varying size (Fig. 18.3). The characteristic finding is that of homogeneous internal echoes of medium density, the so-called ‘ground-glass’ appearance. Internal septa occur in about 10–30% and the cystic wall is usually smooth.8 On macroscopic examination, the internal echoes represent brownish viscous cyst contents and the endometriosis cysts are therefore also called ‘chocolate cysts’. The patho-aetiology of these endometriomas is cyclic bleedings, which contribute to their unique macroscopic and sonographic appearance. Epithelial ovarian tumours Serous ovarian tumours Amongst the epithelial ovarian neoplasms, the serous tumours contribute the most frequent entity (Fig. 18.4). About 25% of all ovarian tumours belong to this histological group and out of these, 50–70% are benign. In up to 20% both ovaries are affected, especially in elderly patients. The sonographic findings vary from unilocular smooth-walled cysts without internal echoes to complex multilocular tumours with papillary vegetations. Even internal echoes can be found in cases of bleeding or partly mucinous cyst contents. The probability of malignancy grows with increasing cyst size and increasing complexity26,27 (Figs 18.5, 18.6).
319
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 18.3 Unilocular cyst with fluid level of hypoechoic and isoechoic cyst contents of an endometrioma.
Fig. 18.4 Serous cystadenoma.
320
Mucinous ovarian tumours Mucinous neoplasms belong to the largest ovarian tumours; diameters of 20–30 cm frequently occur. Out of the entire group of mucinous neoplasms, 10–15% are tumours of low malignant potential and 5% are ovarian carcinomas. Unlike serous ovarian tumours, mucinous lesions are frequently multilocular, and solid components can also be found (Fig. 18.7). In benign conditions the cyst walls and septa
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: tubes and ovaries
Fig. 18.5 Cystadenocarcinoma.
Fig. 18.6 Unilocular cyst with a regular wall and without internal echoes. Histology revealed a serous ovarian carcinoma stage Ia.
are thin and regular. The most characteristic finding is that of internal echoes due to the high viscosity of the mucinous cyst fluid. Compartments without internal echoes due to rather serous liquid, however, do not exclude a mucinous tumour. Fibromas and fibrothecomas Thecomas, fibromas, fibrothecomas and their malignant counterparts consist of varying proportions of stromal and thecal elements. All appear as predominantly solid tumours (Fig. 18.8). The classic sonographic finding is that of a hypoechoic
321
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 18.7 Mucinous adenocarcinoma.
Fig. 18.8 Ovarian fibroma.
322
mass with posterior acoustic shadowing. In contrast to pedunculated and broad ligament fibroids, a separate ipsilateral ovary is not seen. Colour Doppler assessment might be useful to identify the pedicle of fibroids and to describe a true solid tumour, but further differentiation is academic, as virtually all solid masses are genuine ovarian neoplasms and therefore immediate surgical excision should be considered.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Gynaecological pathology: tubes and ovaries
Germ cell tumours Germ cell tumours contribute to about 30% of all ovarian tumours in western coun tries but only to 3% of malignant neoplasms. Malignant forms appear almost exclusively in the first two decades of life, and two-thirds of malignant ovarian tumours during this period of time are germ cell tumours. Germ cell tumours are able to mimic normal embryogenesis and to develop complex and highly differentiated structures.15 Teratomas make up 95% of all germ cell tumours and out of these, the mature cystic teratomas or dermoid cysts are the clinically most relevant subgroup. Dermoid cysts are the typical tumours of women in their reproductive age and therefore it is not surprising that 10% are first described during pregnancy. The sonographic feature is that of a clearly demarcated inhomogeneous tumour. Other components without internal echoes, poor echoes and also pronounced density of internal echoes can be observed. These components typically show sharp margins, while the cystic echo-free portion is frequently crescent shaped. Occasionally teeth are described as echo-dense foci with typical acoustic shadowing. Elements such as hair and apocrine glands producing sebum contribute to a hyperechoic homo geneous ultrasound image. Although the appearance of dermoid cysts is so characteristic, almost one-quarter of these tumours are overlooked when using sonography. One explanation is that the echo patterns within the cystic teratomas are similar to those of the neighbouring bowel and only careful examination identifies the smooth-walled tumours, especially when they lack hypoechoic cystic components.
Adnexal Torsion Adnexal torsion is a rare event but may cause severe abdominal pain and an acute emergency situation with peritonitis, leucocytosis and anaemia. Acute torsion most frequently develops on the basis of pre-existing cystic ovarian enlargement or a sactosalpinx, and an increased incidence in early pregnancy has been reported.3,7 On a patho-aetiological basis the sequels of acute torsion can be explained by the imbalance of continuous arterial blood flow and diminished venous return within the adnexal mass. This causes rapid ovarian swelling due to oedema and haemorrhage. When arterial blood pressure is exceeded by the surrounding tissue, intraovarian blood flow ceases completely, resulting in acute ischaemia and necrosis. Therefore, in order to prevent the loss of the whole organ, early diagnosis and immediate surgical intervention are of crucial importance. Sonographic features are the description of a cystic adnexal mass, and eventually signs of haemorrhage or an oedema of the cyst wall can be documented. The introduction of colour Doppler has facilitated differential diagnosis. In the initial phase of acute torsion, high-resistance, low-velocity arterial flow and absent venous return have been described which are finally followed by complete absence of intraovarian blood flow.
Tubes The most important finding is that the normal fallopian tubes generally are not visible by means of transvaginal sonography unless they contrast with the surrounding tissue in some way or other.
323
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Fig. 18.9 Fallopian tube floating in peritoneal fluid.
• Visualization is achieved and the full length of the organ can sometimes be documented if the tubes are floating in abundant peritoneal fluid.
• The tube itself can be altered as a hydrosalpinx or sactosalpinx and
becomes visible due to distension with fluid (Fig. 18.9). • Finally the artificial use of echogenic contrast agents such as Echovist enables the examination of tubal patency.
Non-Infectious Diseases of the Fallopian Tubes
324
Tubal pregnancy The incidence of ectopic pregnancies has increased in the past few decades and due to improved diagnostic facilities, early detection of this potentially life-threatening disease has become more and more common. Ectopic pregnancies are mostly located within the ampullary, isthmic or interstitial part of the tube, but abdominal and ovarian pregnancies have also been described. The clinical symptoms are variable and sometimes confounding but classically, irregular vaginal bleeding, abdominal pain and a positive hCG test are found. Immediate transvaginal sonography is of crucial importance if a tubal pregnancy is suspected. Exclusion of an intrauterine pregnancy is the first diagnostic hint, but in 10–20% of patients a so-called pseudogestational sac is described. This confounding picture contributes to retained blood within the uterine cavity, but its central location in contrast to the more eccentric chorionic cavity enables differential diagnosis. The tubal pregnancy itself can be identified as an annular hyperechoic structure with a hypoechoic centre. In cases of intact ectopic pregnancy, the yolk sac and even a vital fetus might be identified. According to our own results, free fluid in the cul-de-sac can be found in three out of four tubal pregnancies. In cases of ruptured ectopics and severe haemorrhage, however, the echogenicity of the fluid is increased due to the contribution of blood.
✩✩✩✩✩✩✩✩✩✩✩ ✩ In up to two-thirds of patients with a tubal pregnancy, a corpus luteum graviditate can be identified and misinterpretation must be avoided.
Hydrosalpinx Hydrosalpinx characterized by a tube filled with serous fluid is a phenomenon rather than a disease as such, due to various reasons. The hydrosalpinx or sacto salpinx occurs following occlusion of the fimbriae with consecutive storage of the serous secretion of the tubal endothelium (Fig. 18.10). This occlusion might be due to adhesions caused by endometriosis or infections of the lower pelvis or even in the senium caused by atrophy. The sonographic appearance is that of a longish cystic tumour, sometimes shaped like a corkscrew, with a smooth wall but without internal echoes. The clinical significance depends on patient age and complaints. As long as the hydrosalpinx can be clearly separated from the ovary, follow-up is easily performed by means of sonography.
Fig. 18.10 Inclusion of the fimbriated end of a fallopian tube within fluid-filled pseudoperitoneal cysts.
Gynaecological pathology: tubes and ovaries
Fallopian tube carcinoma Primary carcinomas of the fallopian tube are a relatively rare event, comprising about 0.3% of all gynaecological cancers.28 They are almost exclusively adenocarcinomas. More frequently, the tubes are secondarily affected by neighbouring organs such as the ovaries and the endometrium. Ultrasound images may show a complex ‘sausage-like’ cystic tumour with thick walls and solid components. On colour Doppler the tumour is highly vascular and the flow profile suspicious for malignancy.
325
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Infectious Diseases of the Fallopian Tubes
326
Pelvic inflammatory disease most frequently develops due to ascending infections from the lower genital tract. However, a direct transmission from neighbouring foci such as diverticulitis or an appendiceal abscess is also possible. Acute and chronic consequences of the inflammatory process can be described. Acute salpingitis eventually presents as an ultrasound picture of a swollen tortuous tube with a distended lumen and increased blood flow in the tubal wall. Salpingitis may lead to damage of the organ structure of varying degree. Peritubal adhesions as well as obstruction of the fimbriated end and intratubal stenosis are typical complications. The obstruction of the distal parts of the fallopian tubes results in the storage of fluid in the tubal lumen and contributes to the macroscopic appearance of a hydrosalpinx. Persistent inflammatory disease in the damaged and obstructed tubes may cause a pyosalpinx. On ultrasound, internal echoes in the distended and corkscrew-shaped tube are highly indicative of the purulent exudate and thickened mucosal folds may also be identified due to chronic inflammation (Fig. 18.11). The most severe complication of a genital infection is the development of a tubo-ovarian abscess. Other adjacent organs such as the bowel or the omentum can be agglutinated to the abscess. Ultrasound findings depend on the extension of disease. In the beginning, the thick-walled dilated tube may be identified adherent to and almost embracing the ovary. Eventually fluid–debris levels can be documented in the distended tube. The structure of the ovary itself becomes more indistinct and differentiation of stroma and follicles may be impossible. Later on, ultrasound images usually show a complex mass with hypoechoic inhomogeneous components. As the neighbouring structures of fallopian tube and ovary are almost merged, they can hardly be distinguished on ultrasound.
Fig. 18.11 Fimbriated end of a pyosalpinx.
✩✩✩✩✩✩✩✩✩✩✩ ✩ Colour Doppler hardly identifies any blood vessels within the tumour, as most of the inhomogeneous areas are composed of tissue oedema, necrosis and pus.
References 1. Baltarowich OH, Kurtz AB, Pasto ME et al. The spectrum of sonographic findings in hemorrhagic ovarian cysts. Am J Roentgenol 1987;148:901–905 2. Bourne TH, Campbell S, Reynolds KM et al. Screening for early familial ovarian cancer with transvaginal ultrasonography and colour blood flow imaging. BMJ 1993;306:1025–1029 3. Demopoulos RI, Bigelow B, Vasa U. Infarcted uterine adnexa: associated pathology. NY State J Med 1978;78:2027–2029 4. Granberg S, Norstrom A, Wikland M. Tumors in the lower pelvis as imaged by vaginal sonography. Gynecol Oncol 1990;37:224–229 5. Granberg S, Wikland M, Jansson I. Macroscopic characterization of ovarian tumors and the relation to the histological diagnosis: criteria to be used for ultrasound evaluation. Gynecol Oncol 1989;35:139–144 6. Granberg S, Wikland M. Endovaginal ultrasound in the diagnosis of unilocular ovarian cysts in postmenopausal women. Ultrasound Q 1992;10:1–13 7. Isager-Sally L, Weber T. Torsion of the fallopian tube during pregnancy. Acta Obstet Gynecol Scand 1985;64:349–351 8. Kupfer MC, Schwimer SR, Lebovic J. Transvaginal sonographic appearance of endometriomata: spectrum of findings. J Ultrasound Med 1992;11:129–133 9. Lerner JP, Timor-Tritsch IE, Federman A, Abramovich G. Transvaginal ultrasonographic characterization of ovarian masses with an improved, weighted scoring system. Am J Obstet Gynecol 1994;170:81–85 10. Meire HB, Farrant P, Guha T. Distinction of benign from malignant ovarian cysts by ultrasound. Br J Obstet Gynaecol 1978;85:893–899 11. Montz FJ, Schlaerth JB, Morrow CP. The natural history of theca lutein cysts. Obstet Gynecol 1988;72:247–251 12. Morley P, Barnett E. The use of ultrasound in the diagnosis of pelvic masses. Br J Radiol 1970;43:602–616
13. Moyle JW, Rochester D, Sider L et al. Sonography of ovarian tumors: predictability of tumor type. Am J Roentgenol 1983;141:985–991 14. Van Nagell, JR van, DePriest PD et al. Early diagnosis of epithelial ovarian cancer. In: Markman M, Hoskins WJ (eds) Cancer of the ovary. Raven Press, New York, 1993: 128 15. Nogales F. Germ cell tumours of the ovary. In: Fox H (ed) Obstetrical and gynecological pathology. Churchill Livingstone, New York, 1987: 637 16. Osmers RGW, Osmers M, von Maydell B, Wagner B, Kuhn W. Preoperative evaluation of ovarian tumors in the pre-menopause by transvaginosonography. Am J Obstet Gynecol 1996;175:428–434 17. Russell P, Bannatyne P. Surgical pathology of the ovaries. Churchill Livingstone, Edinburgh, 1989 18. Sassone AM, Timor-Tritsch IE, Artner A et al. Transvaginal sonographic characterization of ovarian disease: evaluation of a new scoring system to predict ovarian malignancy. Obstet Gynecol 1991;78:70–76 19. Serov SS, Scully RE, Sobin LH. Histological classification of ovarian tumors. In: Interna tional classification of tumors, vol 9. WHO, Geneva, 1973 20. Strickler RC, Kelly RW, Askin FB. Postmenopausal ovarian follicle cyst: an unusual cause of estrogen excess. Int J Gynecol Pathol 1984;3:318–322 21. Valentin L, Sladkevicius P, Marsal K. Limited contribution of Doppler velocimetry to the differential diagnosis of extrauterine pelvic tumors. Obstet Gynecol 1994;83:425–433 22. Garner EI. Advances in the early detection of ovarian carcinoma. J Reprod Med 2005;50:447–453 23. Exacoustos C, Romanini ME, Rinaldo D et al. Preoperative sonographic features of borderline ovarian tumours. Ultrasound Obstet Gynecol 2005;25:50–59
Gynaecological pathology: tubes and ovaries
Note Further images relating to this chapter are found on the CD accompanying this book.
327
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
328
24. Togashi. Ovarian cancer: the clinical role of US, CT, and MRI. Eur Radiol 2003;13:L87–104 25. Kinkel K, Frei KA, Balleyguier C, Chapron C. Diagnosis of endometriosis with imaging: a review. Eur Radiol 2006;16: 285–298 26. Fruscella E, Testa AC, Ferrandina G et al. Ultrasound features of different histopathological subtypes of borderline
ovarian tumors.Ultrasound Obstet Gynecol 2005;26:644–650 27. Valentin L, Ameye L, Testa A et al. Ultrasound characteristics of different types of adnexal malignancies. Gynecol Oncol 2006;102(1):41–48 28. Ko ML, Jeng CJ, Chen SC et al. Sonographic appearance of fallopian tube carcinoma. J Clin Ultrasound 2005;33:372–374
19 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Doppler ultrasonography in gynaecology Bruno Cacciatore Rüdiger Osmers Juriy W Wladimiroff
Abstract Two-dimensional colour-coded Doppler, two-dimensional power Doppler and three-dimensional power Doppler techniques are used for determining the location, nature and quantity of vascularization in adnexal masses. Malignancy is associated with reduced arterial downstream impedance in the presence of neo-angiogenesis. Doppler techniques have been used for identifying pelvic inflammatory disease, cystic endometriosis and adnexal torsion. Variable reports have appeared on Doppler utero-ovarian blood flow as a predictor of pregnancy in assisted reproduction.
Keywords Adnexal tumour, colour-coded Doppler, in vitro fertilization, pelvic inflammatory disease, resistance index, three-dimensional power Doppler, two-dimensional power Doppler.
Introduction There are different transvaginal techniques for examining vascularity in the female genital tract. They include colour-coded Doppler, two-dimensional (2D) and three-dimensional (3D) power Doppler ultrasonography.
Adnexal Masses Most Doppler studies are focused on preoperative differentiation between benign and malignant tumours. Normal cell growth depends on adequate blood supply. Tumour growth is characterized by neo-angiogenesis. The vascular architecture is altered. Malignant tumours appear to produce substances that promote the
329
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ formation of new blood vessels, making their growth, invasion and spread possible. These newly formed vessels often lack a complete muscular layer. Vascular tone and flow impedance are therefore lower than in benign masses. Furthermore, these vessels generate arteriovenous anastomoses that may cause major pressure gradients and high-velocity flow patterns. These altered flow patterns can be visualized by means of colour-coded Doppler ultrasonography. High diastolic flow velocities have been established in malignant lesions. Different indices such as the resistance index (RI) and pulsatility index (PI) have been introduced to establish downstream impedance in tumour vessels. Assessment of the vascularity of a tumour starts off with the exact location and distribution of vessels in relation to the tumour, followed by Doppler ultrasonography. Colour-coded Doppler allows qualification of resistance to flow as well as location and intensity of vascularization of adnexal masses. With respect to the RI, a lowest value of ≤0.45–0.50 has been suggested as a sign of potential malignancy.1 Others found the time-averaged maximum velocity to be a useful parameter.2 Colour-coded Doppler ultrasonography has been reported as a means of increasing the diagnostic accuracy of adnexal malignancies.3,4 It is difficult, however, to differentiate between primary ovarian carcinoma and metastatic tumours to the ovary.5 When encountering adnexal masses in premenopausal women, there appears to be no significant difference in sensitivity and specificity of colour-coded Doppler ultrasonography between the follicular and luteal phase of the menstrual cycle.6 Sonographic analysis of adnexal masses including power Doppler ultrasonography appears to improve preoperative diagnosis of malignancy.7 Quantitative assessment includes calculation of the tumour vascularity index which is determined by quantification of the number of pixels in a defined region of interest according to the formula: number of coloured pixels/total number of pixels minus the number of pixels in the fluid or avascular areas.8 In the case of power Doppler ultrasonography, the pulse repetition frequency (PRF) should be set at about 500 Hz and the gain kept high, i.e. just below the level at which background noise appears. The colour box (region of interest) must be kept small to avoid artificial echoes and to preserve a high frame rate. Diagnostic accuracy for ovarian malignancy is not essentially different between colour-coded Doppler and power Doppler ultrasonography.9 Contradictory reports have appeared on the use of 3D power Doppler imaging; some do not consider this technique to be superior to 2D power Doppler ultrasonography.10 Others suggest that this modality may further improve early detection of ovarian carcinoma.11 Some reports have appeared on the possible use of 3D power Doppler ultrasonography in the investigation of intratumoral vascularization and volume of cervical cancer.12
Other Pelvic Pathology
330
Both colour-coded and 2D power Doppler ultrasonography have been reported to improve the diagnosis of pelvic inflammatory disease.13 The former technique also appears to assist in the diagnosis of cystic endometriosis14 and adnexal torsion.15
✩✩✩✩✩✩✩✩✩✩✩ ✩
In Vitro Fertilization
References 1. Alcazar JL, Lopez-Garcia G. Transvaginal color Doppler assessment of venous flow in adnexal masses. Ultrasound Obstet Gynecol 2001;17:434–438 2. Valentin L. Comparison of Lerner score, Doppler ultrasound examination, and their combination for discrimination between benign and malignant adnexal masses. Ultrasound Obstet Gynecol 2000;15: 143–147 3. Guerriero S, Alcazar JL, Coccia ME et al. Complex pelvic mass as a target of evaluation of vessel distribution by color Doppler sonography for the diagnosis of adnexal malignancies: results of a multicenter European study. J Ultrasound Med 2002;21:1105–1111 4. Guerriero S, Ajossa S, Garau N, Piras B, Paoletti AM, Melis GB. Ultrasonography and color Doppler-based triage for adnexal masses to provide the most appropriate surgical approach. Am J Obstet Gynecol 2005;192:401–406 5. Alcazar JL, Galan MJ, Ceamanos C, Garcia-Manero M. Transvaginal gray scale and color Doppler sonography in primary ovarian cancer and metastatic tumors to the ovary. J Ultrasound Med 2003;22:243–247 6. Leeners B, Funk A, Rath W. Effect of menstrual cycle on Doppler measurements of adnexa tumors. Zentralbl Gynakol 2000;122:203–206 7. Marret H, Ecochard R, Giraudeau B, Golfier F, Raudrant D, Lansac J. Color Doppler energy prediction of malignancy in adnexal masses
using logistic regression models. Ultrasound Obstet Gynecol 2003;22:218–219 8. Marret H, Sauget S, Giraudeau B, Body G, Tranquart F. Power Doppler vascularity index for predicting malignancy of adnexal masses. Ultrasound Obstet Gynecol 2005;25:508–513 9. Taylor A, Jurkovic D, Bourne TH, Natucci M, Collins WP, Campbell S. Comparison of transvaginal color Doppler imaging and color Doppler energy for assessment of intraovarian blood flow. Obstet Gynecol 1998;91:561–567 10. Alcazar JL, Castillo G. Comparison of 2-dimensional and 3-dimensional powerDoppler imaging in complex adnexal masses for the prediction of ovarian cancer. Am J Obstet Gynecol 2005;192:807–812 11. Kupesic S, Plavsic BM. Early ovarian cancer: 3-D power Doppler. Abdom Imaging 2006;31(5):613–619 12. Hsu KF, Su JM, Huang SC et al. Threedimensional power Doppler imaging of early-stage cervical cancer. Ultrasound Obstet Gynecol 2004;24:664–671 13. Molander P, Sjoberg J, Paavonen J, Cacciatore B. Transvaginal power Doppler findings in laparoscopically proven acute pelvic inflammatory disease. Ultrasound Obstet Gynecol 2001;17:233–238 14. Pascual MA, Tresserra F, Lopez-Marin L, Ubeda A, Grases PJ, Dexeus S. Role of color Doppler ultrasonography in the diagnosis of endometriotic cyst. J Ultrasound Med 2000;19:695–699
Doppler ultrasonography in gynaecology
The role of Doppler ultrasonography has also been studied in women undergoing assisted reproduction. Using colour-coded Doppler ultrasonography, different utero-ovarian blood flow changes during the peri-implantation period have been established in conception and non-conception cycles. Doppler assessment of uterine arterial resistance may help to determine the time interval within the menstrual cycle that provides the most optimal endometrial receptivity for embryo implantation.16 In another study uterine and ovarian vascular impedance values as expressed by a PI in the uterine artery of >3.26 and in perifollicular vessels of >1.08 were indicative of reduced pregnancy chances.17 Combined colourcoded and 3D power Doppler ultrasonography suggested that follicles containing oocytes capable of producing a pregnancy have a well-defined and more uniform perifollicular vascular network.18 At variance with these data are two other studies in which endometrial and subendometrial blood flow measured by 3D power Doppler ultrasound were not good predictors of pregnancy.19,20
331
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
332
15. Pena JE, Ufberg D, Cooney N, Denis AL. Usefulness of Doppler sonography in the diagnosis of ovarian torsion. Fertil Steril 2000;73:1047–1050 16. Chien LW, Lee WS, Au HK, Tzeng CR. Assessment of changes in uteroovarian arterial impedance during the peri-implantation period by Doppler sonography in women undergoing assisted reproduction. Ultrasound Obstet Gynecol 2004;23:496–500 17. Ozturk O, Bhattacharya S, Saridogan E, Jauniaux E, Templeton A. Role of uteroovarian vascular impedance: predictor of ongoing pregnancy in an IVF-embryo transfer programme. Reprod Biomed Online 2004;9:299–305 18. Vlaisavljevic V, Reljic M, Gavric Lovrec V, Zazula D, Sergent N. Measurement of
perifollicular blood flow of the dominant preovulatory follicle using threedimensional power Doppler. Ultrasound Obstet Gynecol 2003;22:520–526 19. Järvelä IY, Sladkevicius P, Kelly S, Ojha K, Campbell S, Nargund G. Evaluation of endometrial receptivity during in-vitro fertilization using three-dimensional power Doppler ultrasound. Ultrasound Obstet Gynecol 2005;26:765–769 20. Ng EH, Chan CC, Tang OS, Yeung WS, Ho PC. The role of endometrial and subendometrial blood flows measured by three-dimensional power Doppler ultrasound in the prediction of pregnancy during IVF treatment. Hum Reprod 2006;21:164–170
20 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Medico-legal implications of ultrasound imaging in obstetrics and gynaecology Hylton B Meire
ABSTRACT Medical litigation is increasing in frequency throughout the western world and in a minority of cases, especially in obstetric care, may be settled for huge sums of money. This chapter outlines the type of cases which may give rise to medical litigation and emphasizes the need to practise a form of defensive medicine. However, this should lead to improved standards of patient care, reduce the risk of threatened litigation and enable a swift and robust defence to be mounted when litigation is threatened.
Keywords Claim, claimant, defence, defendant, documentation, expert witness, litigation, normal practice, protocol.
Introduction There has been a rapid and continuing increase in the frequency with which medical personnel are being sued by their patients in recent years. This is fuelled by increasing media attention and publicity, improved patient education and a consequent increase in patients' expectations. Regrettably there is now an assumption that if all has not gone well with a pregnancy or a gynaecological procedure, this is necessarily somebody's fault and they should be made to pay for their presumed mistake. There can be little doubt that the upward trend in medical litigation is at least in part fuelled by the legal profession, who, with very few exceptions, are usually the only real winners in the majority of cases.
333
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
334
The objectives of this chapter are to highlight the sort of cases which most commonly give rise to legal claims and also to make some suggestions which may reduce the risk of litigation and improve the ability to successfully defend a claim if and when one is received. The reader should be reassured by the fact that, in my experience over the last 20 years, only one in 20 claims actually proceeds as far as trial in court. The large majority are dropped as being unsubstantiated, a smaller proportion are settled out of court and only if doubt remains does the case come to trial.
The Legal Process The initial step of the legal process occurs when the potential claimant seeks advice from a lawyer and asks the question ‘Have I got grounds for a claim?’. Although it is common for this step to be taken soon after the clinical event has occurred, it is by no means unusual for claims to be raised several years after the event. The English legal system is now attempting to limit the delay to no more than 3 years after the relevant clinical event. Regrettably the majority of lawyers working in a provincial general practice environment will not have sufficient knowledge or experience to make a judgement as to whether or not a potential claim is valid. It is therefore almost invariable for the initial lawyer to seek an opinion from a more senior professional colleague with a specialty interest in medical claims. Thus, it must be remembered that the claimant may rapidly accrue significant legal expenses. If senior legal opinion suggests that there are possible grounds for a claim it is then usual for the legal team to request the services of one or more medical experts who will assess the case and offer a professional opinion on their interpretation of liability. If their advice is that there are grounds for a valid claim, the claim will then be forwarded to the defendant, the individual or team who are claimed to be responsible for the adverse clinical event. The defendant may be a single individual, a clinical team or possibly an entire management board. The defendant will then appoint legal representatives who will seek additional expert advice and the merits of the claim will be judged by comparison between the reports from the claimant's and defendant's experts. In the UK the legal system has recently been amended to require the two teams of experts to join together in a secret meeting at which the merits or otherwise of the claim will be discussed. If all the experts are agreed then the case will either be settled or dropped according to their recommendations. Only if the experts cannot agree will the legal teams consider taking the case to trial. Not surprisingly, the processes outlined above are lengthy and seldom run according to the initial planned timetable. It is by no means unusual for the entire process to take many years, usually between two and 10. Clearly, the total cost of the professional legal fees for this process can be enormous, irrespective of the ultimate outcome. It is perhaps regrettable that most claimants are unaware of the cost and time scale involved in making a claim and the majority of claimants regret having initiated the procedure because they find the years of anxiety and uncertainty are seldom compensated by the ultimate settlement, if any.
✩✩✩✩✩✩✩✩✩✩✩ ✩
The Trial Process
• a contemporaneous protocol from the institution concerned for the type of scan undertaken in the case in question • a request form indicating the type of scan and reason for the scan • recorded images of the investigation • a formal report indicating what structures were seen and what conclusions were drawn from the images.
If any or all of this information is unavailable then clearly the experts and the judge will be greatly impeded in their attempts to achieve an accurate judgement.
Reducing the Risk of Litigation
Medico-legal implications of ultrasound imaging in obstetrics and gynaecology
Unless a medical professional is being accused of a criminal event, all medicolegal cases in the UK are tried in a civil court of law. In a civil court the claimant's case will be presented by the claimant, other witnesses of fact, the medical expert witnesses and the legal team. The defendant's case will be presented by the defendant, possibly additional witnesses of fact, the defendant's experts and legal team. The case is heard by a judge who has to determine whether, ‘on the balance of probability’, the claimant has a valid case. Needless to say, the judge will usually have little if any knowledge of medicine or ultrasound and thus he or she is highly reliant upon the opinion of the expert witnesses. In addition, the majority of cases are judged on the basis of what was or was not ‘normal practice’ at the time of the relevant clinical incident and whether ‘a responsible body of medical personnel’ would have acted in the same way as those whose expertise is being called into question. Legal decisions are also influenced by preceding cases – ‘precedent’ or ‘case law’. The expert witnesses will themselves require the maximum possible amount of firm evidence on which to base their opinions and their role will be greatly facilitated if the claimant or defendant can produce the following items:
It is unfortunate that one inevitable consequence of the current increase in litigation against the medical profession is that doctors now have to practise ‘defensive medicine’. However, in ultrasound imaging, this is more likely to lead to improved clinical practice than is perhaps the case in other specialties such as surgery. There are a number of simple guidelines which may assist in preventing the types of event which may lead to litigation. These are all common sense and some are listed below. Never undertake a type of scan with which you are not entirely familiar (unless in a learning environment) This advice is particularly relevant to independent practitioners working on their own and trying to establish or expand their clinical practice. If doctors undertake a procedure for which they have not received the appropriate special training, avoidable failures are almost inevitable and successful defence impossible.
335
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ Record sample images (and be able to retrieve them) In the narrative above the value of good-quality recorded images and their value in rapidly refuting a potential claim is emphasized. Always act professionally and responsibly Perhaps one of the most common inadvertent faults which gives rise to litigation stems from inadequate time being allocated for the scan. It is better to postpone a scan and rebook the patient than to cut corners if time is short. For example, if the bladder is not adequately filled one should wait for it to fill, do a transvaginal scan or rebook the patient for an alternative time or date. It is also important to ensure that the medical professional who will receive the report and may have to act on its findings is fully aware of the training and expertise of the ultrasound operator. It is therefore advisable to compile a formal report for every examination and to ensure that one's name, speciality and grade are indicated at some point on this report. Be aware of the common traps (and avoid them!) There are many well-known pitfalls including difficulties in imaging pelvic structures when the uterus is retroverted, correctly differentiating between a pelvic cyst and a normal bladder and failing to correctly identify a pseudogestation sac. An adequately trained operator should be aware of all the common traps and must be vigilant to avoid them. If the scan is suboptimal, say so and explain why It is, in fact, unusual for a scan to be entirely satisfactory. There are many factors which may compromise the adequacy of a scan including patient size, fetal position, inadequate equipment and inappropriate request. There is no shame in confessing to failure to achieve an entirely adequate scan and if the requesting medical professional is informed that the scan was in some way suboptimal, he or she will be better able to place the findings in clinical context and determine whether or not a repeat examination is advisable.
336
Ensure the equipment is appropriate This assumes that the operator has at least some influence over the adequacy of the equipment. It is therefore important to ensure that the equipment is maintained and calibrated on a regular basis and that any equipment which is significantly below the current ‘state of the art’ should be replaced as soon as possible. For those who are obliged to use inadequate equipment and have no opportunity to ensure its prompt replacement, it is advisable to write a polite letter to your manager explaining the situation and emphasizing the potential financial consequences of litigation in the event that inadequate equipment were found to be responsible for a failed diagnosis. Make sure you keep a copy of the letter!
✩✩✩✩✩✩✩✩✩✩✩ ✩
Defending a Claim
Recording Images It is by no means invariable practice to record images of all ultrasound examinations. Some institutions record none whatsoever whilst others only record images to show their measurements or document any suspect abnormalities. However, in view of the current and increasing level of litigation, it is advised that sample images should be recorded from every ultrasound examination and should be stored in some retrievable form. Whilst this inevitably leads to additional cost, this may be a small price to pay for successfully refuting a potential claim for damages. If images are recorded it is vital that they contain the correct demographic data, including both the patient's name and the date on which the scan was performed.
Medico-legal implications of ultrasound imaging in obstetrics and gynaecology
One of the first tasks for the defendant and expert witness is to establish whether the normal practice of the institution concerned was followed and how this normal practice compared with that of other similar institutions at the time in question. Both the medical and legal profession accept that different standards would be applied to an independent practitioner using ultrasound as part of general obstetric care compared with a district hospital practitioner or a university or research centre. It is therefore essential for each practitioner or institution to establish a series of written and dated protocols or guidelines for the execution of each type of scanning procedure. These should be reviewed and updated periodically and the review date included as a footnote on the protocol. Clearly, it is also important for each practitioner to be aware of the content of the protocols and to follow them. The value of a protocol can be illustrated by considering the expectations for the diagnosis of cardiac malformations. The majority of independent practitioners would be expected to undertake a simple four-chamber view of the fetal heart while a district hospital would be expected to undertake a more careful study of the position of the heart. A university institution would be expected to do all the above and study the connections and great vessels arising from the heart. As training and expertise progress, the more complicated and sophisticated scans are being progressively included in the district hospital and independent practitioner's protocols. It is thus important for the expert witness to be aware of the level of assimilation of the more complex scans outside specialist institutions and to compare his or her knowledge of these with the contemporaneous protocol for the institution in question when litigation arises.
Documentation Many obstetric scans are undertaken as a routine procedure and may therefore not be formally requested by a medical practitioner. This may lead to uncertainties as to exactly what kind of scan has been undertaken, particularly in an environment where early pregnancy scans are performed for either dating the
337
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ pregnancy or checking for anomalies. It is therefore wise to ensure that some form of routine documentation is generated for every examination indicating which specific type of scan is being undertaken. One must ensure that there are protocols in existence for each type of scan. In addition to indicating the type of scan, the request form should carry a brief relevant medical history of the patient. For example, past obstetric history, drug history and family history may be relevant, including the existence of concomitant medical disease such as diabetes or epilepsy. If, for example, the requesting clinician fails to note on the request form that the patient is a diabetic and the ultrasound scan overlooks a minor degree of sacral regression, it would be to the ultrasonologist's advantage to be able to show that he or she was not aware that the patient was diabetic. It is also important to generate a formal report for every scan. This may be computer-generated or a standard pro-forma. The advantage of the pro-forma is that it helps to emphasize the type of scan that was undertaken and the range of structures which were inspected. If, for example, a newborn baby is found to have an abnormal hand and inspection of the hands is not included in either the protocol or pro-forma report, the failure to detect the abnormality can be defended. However, if the report merely says ‘limbs normal’, this lack of specificity will lead to uncertainty and difficulty in maintaining a viable defence.
Conclusion The recurrent and increasing rate of medical litigation should encourage all of us to take greater care in both the conduct and documentation of our scans. These actions will be beneficial to both us and our patients. We must be aware that patients' expectations are continuing to rise and that distressed parents may wish to try to make someone pay, even if no individual is specifically at fault. Regrettably many patients are badly advised to pursue cases with little hope of success and in the process, generate unnecessary distress and anxiety in both themselves and their medical attendants. Threatened action does not mean that the practitioner is at fault and experience shows that the majority of cases never come to court. Careful, sensible and professional conduct, together with good documentation, will almost always enable you to successfully defend any threatened litigation.
338
21 ✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Ethics and patient information Frank A Chervenak Laurence B McCullough
ABSTRACT In this chapter we develop a framework for the ethical dimensions of obstetric and gynaecological ultrasound and communicating with patients, including counselling about decision making concerning information obtained from ultrasound examinations. We begin by defining ethics, and two fundamental principles of medical ethics – beneficence and respect for autonomy. We then show how these two principles should interact in clinical judgement and communicating with patients about obstetric and gynaecological ultrasound. In particular, we explain the role of the principles of beneficence and respect for autonomy in understanding the concept of the fetus as a patient and the clinical implications of this concept for counselling pregnant women. We then consider clinical topics in the ethics of obstetric and gynaecological ultrasound. Throughout this chapter we emphasize a preventive ethics approach that appreciates the potential for ethical conflict and adopts ethically justified strategies to prevent those conflicts from occurring. Preventive ethics creates an approach to communicating with patients that builds and sustains a strong physician–patient relationship.
Keywords Beneficence, competence, confidentiality, ethics, fetal patient, respect for autonomy, routine ultrasound.
Introduction The field of ultrasound in obstetrics and gynaecology tends to focus on its tech nological aspects. We will argue, in contrast, that ethics is an essential dimension of obstetric and gynaecological ultrasound and forms the basis of communication of information to patients. To this end, we first define medical ethics and two of its basic principles: beneficence and respect for autonomy. On the basis of these
339
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ principles, we then identify two concepts of the fetus as a patient and explore their implications for the previable and viable fetus. With this background, we address the clinical topics of competence and referral, ultrasound screening, dis closure of results and confidentiality of findings. This chapter takes a preventive ethics approach to these topics. The usual approach to medical ethics is to wait for ethical conflicts to occur and then respond to them. We believe that this approach takes an often unacceptable bio psychosocial toll on patients and their families, as well as on physicians and others on the healthcare team. To avoid this outcome, preventive ethics aims to establish policies and practices that anticipate and seek to prevent ethical conflicts.17, 44
Ethics, Medical Ethics and Ethical Principles Ethics should not be confused with morality, because ethics is the disciplined study of morality, our actual beliefs about good and bad behaviour and character. Ethics is based on the academic disciplines of the humanities, especially philoso phy. Medical ethics should be understood as the disciplined study of morality in medicine with its main focus on the obligations of physicians to their patients. Ethics should not be confused with the many sources of morality in pluralistic societies.29 In various national settings these include, but are not limited to, law, the political heritage and aspirations of people, the world's religions, ethnic and cultural traditions, families, the traditions and practices of medicine (including medical education and training) and personal experience. These sources of moral ity are often important reference points for medical ethics. For example, debates about abortion in the United States frequently make reference to the law, espe cially Supreme Court decisions over the past 30 years. The traditions and practices of medicine, including education and training, provide an important source of morality for physicians, because they are based on the obligation to protect and promote the interests of the patient.4,44 This obli gation informs physicians about what morality in medicine ought to be in very general, abstract terms. Providing a more concrete, clinically applicable account of that obligation is the central task of medical ethics. To make concrete the general ethical obligation to protect and promote the interests of patients, medical ethics focuses on the question of ‘How ought the physician to conduct himself or herself with patients?’. Among the relevant tools of ethics for answering this question are ethical principles, because they help phy sicians to interpret and implement their general moral obligation to protect and promote the interests of the patient, which has been the traditional moral foun dation of the physician–patient relationship in world cultures.4,44
The Principle of Beneficence
340
The oldest principle in medical ethics is beneficence, which obliges one to act in a way that is reliably expected to produce a greater balance of goods over harms in the lives of others.4,5,44 Using this principle in clinical practice depends on reliable
✩✩✩✩✩✩✩✩✩✩✩ ✩
Ethics and patient information
accounts of both the goods and harms relevant to the care of the patient and of how these goods and harms should be reasonably balanced against each other when not all of them can be achieved in a particular clinical situation. In medicine, the prin ciple of beneficence obliges the physician to act in a way that is reliably expected to produce the greater balance of clinical goods over harms for the patient. Beneficence-based clinical judgement has an ancient pedigree. For example, one of its earliest expressions in western thought occurs in the Hippocratic Oath and accompanying texts.5,44 Beneficence-based clinical judgement makes an impor tant claim: to interpret reliably the interests of the patient from medicine's per spective.44 This perspective should be based on the best available evidence, which includes (in descending order of reliability) accumulated scientific research, clini cal experience and reasoned responses to uncertainty. This perspective is thus not the function of an individual clinical perspective of a particular physician and therefore should not be based merely on clinical impression or intuition of an individual physician. The clinical goods that physicians are competent to seek for patients are the prevention and management of disease, injury, handicap, unnec essary pain and suffering and the prevention of premature or unnecessary death.44 Pain and suffering become unnecessary when they do not result in a greater bal ance of the other goods of medical care. We note an inherent risk of paternalism in beneficence-based clinical judge ment. That is, if it is, mistakenly, considered to be the sole source of moral respon sibility and therefore moral authority in medical care, beneficence-based clinical judgement invites the unwary physician to conclude that beneficence-based judgements can be imposed on the patient in violation of her autonomy.4,5,44 Paternalism is a dehumanizing response to the patient and therefore should be avoided in the practice of obstetric and gynaecological ultrasound. The preventive ethics response to this inherent paternalism is for the physician to engage in communication with the patient in a way guided by the principle of benef icence. That is, physicians explain the diagnostic, therapeutic and prognostic reason ing that leads to their clinical judgement about what is in the interest of the patient, so that the woman can assess that judgement for herself. This general rule can be put into clinical practice in the following way. The physician should disclose and explain to the patient the major factors of this reasoning process, including matters of uncer tainty. (Note that this does not require that the patient be provided with a complete medical education.) This is especially relevant when diagnosis of a fetal anomaly or gynaecological condition involves uncertainty, e.g. regarding prognosis. The phy sician should then explain how and why other clinicians might reasonably differ from this clinical judgement, especially in matters of clinical controversy. The physi cian should then present a well-reasoned response to this critique. The outcome of this communication process is that beneficence-based clinical judgement takes on a rigor that it sometimes lacks and the process of its formulation includes explaining it to the patient. Beneficence-based clinical judgement, when well formed, will fre quently result in the identification of a continuum of clinical strategies that protect and promote the patient's interests. Awareness of this feature of beneficence-based clinical judgement provides an important preventive ethics antidote to paternalism
341
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ by increasing the likelihood that one or more of these alternatives will be accept able to the patient. This process of explaining beneficence-based clinical judgement enhances the patient's ability to understand and deal effectively with the technical aspects of medical care, an essential consideration in obstetric and gynaecological ultrasound, given its increasing diagnostic and technological sophistication.
The Principle of Respect for Autonomy In addition to the principle of beneficence, there has been increasing emphasis in the literature of ethics in medicine on the principle of respect for autonomy.5,29 In general, this principle obligates one always to acknowledge and carry out the value-based preferences of others, irrespective of what one might think the con sequences for them of doing so might be. The female or pregnant patient increasingly brings to her medical care her own perspective on what is in her interest. The principle of respect for autonomy takes this fact as the basis of autonomy-based clinical judgement. In American medical ethics, autonomy-based clinical judgement finds its roots in the medical practice of the 19th century51 and in the law of malpractice, dating from the second decade of our century, and then in ethics, dating from three decades ago.5,31 Because each patient's perspective on her interests depends on her values and beliefs, it is impos sible to specify the goods and harms of autonomy-based clinical judgement in advance. Indeed, it would be inappropriate to do so, because the definition of her goods and harms and their balancing are the prerogative of the pregnant patient. Autonomy-based clinical judgement is intentionally antipaternalistic in nature. To understand the moral demands of this principle in clinical practice, we need a clinically applicable concept of autonomy. To this end, we identify three sequential autonomy-related behaviours on the part of the female or pregnant patient in the decision-making process:
• paying attention to, absorbing and retaining information about her
condition and, for the pregnant woman, the condition of her fetus and alternative diagnostic and therapeutic responses to it • understanding that information; that is, evaluating and rank-ordering those responses • expressing a value-based preference for a particular response. The physician has a role to play in each of these. They are, respectively:
• to recognize the capacity of each female and pregnant patient to deal
342
with medical information (and not to underestimate that capacity), provide information, i.e. disclose and explain all alternatives supported in beneficence-based clinical judgement, and recognize the validity of the values and beliefs of the patient • not to interfere with but, instead, to assist the female or pregnant patient in her evaluation and ranking of diagnostic and therapeutic alternative responses to her condition should she wish such assistance • to elicit and implement the patient's value-based preference.44
✩✩✩✩✩✩✩✩✩✩✩ ✩
Beneficence-based and autonomy-based clinical judgements in obstetric and gynaecological ultrasound are usually in harmony. Synergy between beneficence and respect for autonomy occurs when the physician's management plan is car ried out in conjunction with the patient's informed consent.31 Beneficence-based and autonomy-based clinical judgements can sometimes come into conflict. In situations of conflict or potential conflict, the physician should not view either beneficence or respect for autonomy to be automatically overriding of the other principle. Instead, both principles should be understood as theoretically equally weighted, with their differences negotiated in clinical judge ment and practice. The competing demands of both principles must be balanced and negotiated to determine which management strategies protect and promote both the female or pregnant woman's and the fetal patient's interests. In the tech nical language of ethics, we are treating these principles as prima facie or poten tially limited in nature.4,5,44 The process of negotiating conflict between the two principles is a function of several factors involved in clinical judgement: subject matter; probability of net medical benefit; availability of reasonable alternatives; and the ability of the patient to participate in the informed consent process. When the subject matter is primarily technical in nature, such as the selection of method and technique of ultrasound examination, clinical judgement is justifi ably beneficence based. This is because technical matters largely concern the cal culation of medical goods and harms for patients with a particular diagnosis and treatment plan. Such decisions are justifiably within the physician's purview. The individual values and beliefs of a particular patient cannot readily be taken into account in this process. This is usually a straightforward matter in gynaecological ultrasound. The eth ics of obstetric ultrasound are more complicated because sometimes there is a second patient. A fundamental consideration in the ethics of obstetric ultrasound is the concept of the fetus as a patient.
Ethics and patient information
The Interaction of Beneficence and Respect for Autonomy in Clinical Judgement and Practice
The ETHICAL Concept of the Fetus as a Patient The concept of the fetus as a patient is essential to obstetric clinical judgement and practice generally, as well as to obstetric ultrasound. Developments in fetal diagnosis and management strategies to optimize fetal outcome1,2,37,39 have become widely accepted,33,41,42,45,46,52,55,59 encouraging the development of this concept. This concept has considerable clinical significance because, when the fetus is a patient, directive counselling, i.e. recommending a form of management, for fetal benefit is appropriate and when the fetus is not a patient, non-directive counselling, i.e. offer ing but not recommending a form of management, is appropriate. These apparently straightforward roles for directive and non-directive counselling are often difficult to apply in actual perinatal practice because of uncertainty about when the fetus is a patient. One approach to resolving this uncertainty would be to argue that the
343
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
344
fetus is or is not a patient in virtue of personhood3,29,2,34,56–58 or some other form of independent moral status.27,28,30,54 We now show that this approach fails to resolve the uncertainty and we therefore defend an alternative approach that does resolve the uncertainty.44 One approach for establishing whether or not the fetus is a patient involves attempts to show whether or not the fetus has independent moral status, lead ing to the first sense of the concept of the fetus as a patient. Independent moral status for the fetus means that one or more traits that the fetus possesses in and of itself, and therefore independently of the pregnant woman or any other factor, generate and therefore ground ethical obligations to the fetus on the part of the pregnant woman and her physician. A striking variety of characteristics has been proposed for this role, e.g. moment of conception, implantation, central nervous system development, quickening and the moment of birth.38,40,49 Given the variability of proposed characteristics, there is, understandably, considerable variation among ethical arguments about when the fetus acquires independent moral status. Some argue that the fetus has independent moral status from the moment of conception or implantation.6,7,50 Others believe that independent moral status is acquired in degrees, thus result ing in ‘graded’ moral status.27,30,57 Still others hold, if only by implication, that the fetus never has independent moral status as long as it is in utero.28 Despite an ever-expanding theological and philosophical literature on this sub ject, there has been no closure on a single authoritative account of the indepen dent moral status of the fetus.9,53 Given the absence of a single method that would be authoritative for all the markedly diverse theological and philosophical schools of thought involved in this endless debate, it should be apparent that closure is impossible. For closure ever to be possible, debates about such a final author ity within and between theological and philosophical traditions would have to be resolved in a way satisfactory to all, an inconceivable intellectual and cultural event in both national and global contexts. We therefore propose to abandon these futile attempts to understand the fetus as a patient in terms of independent moral status of the fetus. We turn, instead, to an alternative approach that makes it possible to identify ethically distinct senses of the fetus as a patient and their clinical implications for directive and non-directive counselling.44 In its first sense, the independent moral status of the fetus, the fetus as a patient has no stable or clinically applicable meaning. We therefore consider a second sense of the con cept of the fetus as a patient. Our analysis of this second sense begins with the recognition that being a patient does not require that one possesses independent moral status.54 Rather, being a patient means that one can benefit from the applications of the clinical skills of the physician. Put more precisely, a human being without independent moral status is properly regarded as a patient when two conditions are met: that a human being (a) is presented to the physician and (b) there exist clinical interventions that are reliably expected to be efficacious, in that they are reliably expected to result in a greater balance of goods over harms for the human being in question.44 We call this the dependent moral status of the fetus.
✩✩✩✩✩✩✩✩✩✩✩ ✩
The viable fetal patient One such link is viability. Viability is not, however, just an intrinsic property of the fetus because viability must be understood in terms of both biological and technological factors.35,43,53 Both factors are required for a viable fetus to be able to exist ex utero and thus achieve independent moral status. These two factors do not exist as a function of the autonomy of the pregnant woman. When a fetus is viable, i.e. when it is of sufficient maturity that it can survive into the neonatal period and achieve independent moral status given the availability of the requi site technological support, and when it is presented to the physician, the fetus is a patient. Viability exists as a function of biomedical and technological capacities, which are different in different parts of the world. As a consequence there is, at the pres ent time, no worldwide, uniform gestational age to define viability. In the United States, we believe, viability presently occurs at approximately 24 weeks of gesta tional age.21,36,61 When the fetus is a patient, directive counselling for fetal benefit is ethically justified. It is very important to appreciate in obstetric clinical judgement and practice that the strength of directive counselling for fetal benefit varies accord ing to the presence and severity of fetal anomalies. As a rule, the more severe the fetal anomaly, the less directive counselling should be for fetal benefit.15,18,44 In particular, when there is ‘(1) a very high probability of a correct diagnosis and (2) either (a) a very high probability of death as an outcome of the anomaly diagnosed or (b) a very high probability of severe irreversible deficit of cogni tive developmental capacity as a result of the anomaly diagnosed’,22 counselling should be non-directive in recommending between aggressive and non-aggressive management.20,25 By contrast, when lethal anomalies can be diagnosed with cer tainty there are no beneficence-based obligations to provide aggressive manage ment.8,14,23 Such fetuses are not patients; they are appropriately regarded as dying fetuses and the counselling should be non-directive in recommending between non-aggressive management and termination of pregnancy, but directive in rec ommending against aggressive management, for the sake of maternal benefit.15 Any directive counselling for fetal benefit must occur in the context of balanc ing beneficence-based obligations to the fetal patient against beneficence-based and autonomy-based obligations to the pregnant woman.23, 44 Any such balancing must recognize that a pregnant woman is obligated only to take reasonable risks
Ethics and patient information
We have argued elsewhere that beneficence-based obligations to the fetus exist when the fetus is reliably expected later to achieve independent moral sta tus (sometime during the second year postpartum).44 That is, the fetus is a patient when the fetus is presented for medical interventions, whether diagnostic or ther apeutic, that reasonably can be expected to result in a greater balance of goods over harms for the child or person the fetus can later become during early childhood. The ethical significance of the concept of the fetus as a patient, therefore, depends on links that can be established between the fetus and its being reliably expected to later achieve independent moral status.
345
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
346
of medical interventions that are reliably expected to benefit the viable fetus or child later. On this account, no pregnant woman is obligated to her fetal patient and to accept the risks to herself of experimental fetal intervention. The unique feature of obstetric ethics is that whether, in a particular case, the viable fetus ought to be regarded as presented to the physician is, in part, a function of the pregnant woman's autonomy. Any strategy for directive counselling for fetal benefit that takes account of obligations to the pregnant woman must be open to the possibility of conflict between the physician's recommendation and a pregnant woman's autonomous decision to the contrary. Such conflict should be managed preventively through informed consent as an ongoing dialogue throughout the pregnancy, augmented as necessary by negotiation and respectful persuasion.17,44 The previable fetal patient The only possible link between the previable fetus and the child it can become is the pregnant woman's autonomy. This is because technological factors can not result in the previable fetus becoming a child. This is simply what previable means. The link, therefore, between a fetus and the child it can become, when the fetus is previable, can be established only by the pregnant woman's deci sion to confer the status of being a patient on her previable fetus. The previable fetus, therefore, has no claim to the status of being a patient independently of the pregnant woman's autonomy. The pregnant woman is free to withhold, confer or, having once conferred, withdraw the status of being a patient on or from her previable fetus according to her own values and beliefs. The previable fetus is pre sented to the physician solely as a function of the pregnant woman's autonomy. Counselling the pregnant woman regarding the management of fetal anomalies when the fetus is previable should be strictly non-directive in terms of continu ing the pregnancy or having an abortion (assuming that this is a legally available option), if she refuses to confer the status of being a patient on her fetus. If she does confer such status in a settled way, at that point beneficence-based obliga tions to her fetus come into existence and directive counselling for fetal benefit becomes appropriate for these previable fetuses. Just as for viable fetuses, such counselling must take account of the presence and severity of fetal anomalies, extreme prematurity and obligations owed to the pregnant woman. For pregnancies in which the woman is uncertain about whether to confer such status, we propose that the fetus be provisionally regarded as a patient.44 This justifies directive counselling in favour of fetal therapy, when indicated. In particular, non-directive counselling is appropriate in cases of what we term near-viable fetuses,44 i.e. those which are 22–23 weeks gestational age for which there are anecdotal reports of survival.21,44 In our view, aggressive obstetric and neonatal management should be regarded as clinical investigation, i.e. a form of medical experimentation, not standard of care.21 There is no ethical obligation on the part of a pregnant woman to confer the status of being a patient on a nearviable fetus, because the efficacy of aggressive obstetric and neonatal manage ment has yet to be proven.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Clinical Topics
The ethical obligation to provide competent obstetric ultrasound examinations derives from both beneficence and respect for autonomy. Either principle alone, and certainly both in combination, requires physicians to provide patients with accurate and reliable clinical information. To meet this ethical obligation, the cli nician must address the following ethical considerations. First, ensuring an appro priate level of competence imposes a rigorous standard of training and continuing education. Two problems result when physicians do not maintain this baseline level of competence in the techniques and interpretation of ultrasound imaging. First, they may cause unnecessary harm to the woman or fetal patient, e.g. from mistaken diagnosis of fetal anomalies, thus violating beneficence-based obliga tions. Second, incomplete or inaccurate reporting of results by the physician to the pregnant woman undermines the informed consent process regarding the management of pregnancy. This constitutes an unacceptable ethical violation of autonomy-based obligations of the physician to the pregnant woman. Because physicians may rely on them, the general competence of obstetric sonographers is essential to avoiding these ethically unacceptable consequences for the exercise of the pregnant woman's autonomy. Second, these obligations have important implications for physicians who employ a sonographer. Such physicians are ethically obligated to adequately super vise the sonographer's clinical work. To do this properly, the physician should know more than the sonographer, especially about the application of sonographic findings to the diagnosis of anomalies. This more advanced fund of clinical and scientific knowledge is essential for the physician to fulfill his or her additional ethical obligation to regularly review the sonographer's work. In addition, physi cians should provide the opportunity for continuing education of obstetric sonog raphers. This is an especially important consideration for achieving strandards of quality, e.g. in nuchal translucency measurement in the first trimester.47 In medical care, patients properly rely for their protection on the personal and professional integrity of their clinicians. A crucial aspect of that integrity is will ingness on the part of physicians to refer to specialists when the limits of their own knowledge are being approached. Like other virtues, such as self-sacrifice and compassion, integrity directs physicians to focus primarily on the patient's interests, as a way to blunt mere self-interest.44
Ethics and patient information
Competence and Referral in Ultrasound Examination
Routine Ultrasound Screening And Risk Assessment of Pregnant Women The clinical ethical issues here focus on the physician's responsibilities under informed consent, an autonomy-based concern. This process includes disclosure of and discussion about what obstetric ultrasound examinations can and cannot detect, the level of sophistication of the ultrasound techniques employed, and the incomplete and sometimes uncertain interpretation of ultrasound images.
347
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ In the face of medical uncertainty about the clinical goods and harms of routine ultrasound, it is obligatory to inform pregnant patients about that uncertainty and to give them the opportunity to make their own choices about how that uncertainty should be managed. We have argued that prenatal informed consent for sonogram (PICS) should be an indication for the routine use of obstetric ultrasound.26,44 The timing of routine ultrasound should be governed, as a rule, by the ethical principle of respect for autonomy, because the information obtained is relevant to the woman's decision about whether she will seek an abortion (assuming that is legally available to her). In pregnancies that will be taken to term, routine ultra sound during the second trimester can enhance a pregnant woman's autonomy. If anomalies are detected and she does not choose abortion, she may begin to prepare herself for the decisions that she will confront later about the management of those anomalies in the intrapartum and postpartum periods. Providing this infor mation early in pregnancy permits a pregnant woman ample time to deal with its psychological and other sequelae before she must confront such decisions. Respect for autonomy has important implications for first-trimester ultra sound screening for trisomy 21. First-trimester screening provides sophisticated information about risk to pregnant women that they can incorporate into their subsequent decisions about invasive testing.48 Many women prefer not to have an invasive test when provided with risk estimates based on first-trimester screening, which is reassuring.11,62 Many women may find it important to have a diagnosis of an abnormal fetus early, in order to make an earlier decision about whether to continue or terminate their pregnancies.12,13 Both of these aspects of first-trimester screening are important enhancements of the autonomy of pregnant women. To prevent information overload from presenting too many choices unnecessarily, all pregnant women in the first trimester should be offered risk assessment and invasive diagnosis. Physicians should be guided by the autonomous decisions of pregnant women in response to this offer.24
Disclosure of Results of Ultrasound Examinations
348
Significant clinical ethical issues arise about the disclosure of results of ultrasound examinations. The first clinical ethical topic here concerns the phenomenon of apparent bonding of pregnant women to their fetuses as a result of the woman seeing the ultrasound images.10 Such bonding can sometimes benefit pregnancies that will be taken to term but can also at other times complicate decisions to terminate a pregnancy. We recommend that these matters, like abnormal findings, should be discussed with the pregnant woman. A second topic is a matter of ongoing debate: the disclosure of the fetus's gender.44,60 We propose that respect for maternal autonomy dictates responding frankly to requests from the pregnant woman for information about the fetus's gender. The woman should be made aware of the uncertainties of ultrasound gen der identification, as part of the disclosure process. The sonographer can use his or her own experience to help the pregnant woman understand those uncertainties. A third clinical topic may, at first, seem a non-issue, i.e. videotaping or the Polaroid photography of ‘baby pictures’. There is nothing intrinsically wrong with
✩✩✩✩✩✩✩✩✩✩✩ ✩
Confidentiality of Findings Confidentiality concerns the obligation of physicians to protect clinical informa tion about patients from unauthorized access.44 The obligation of confidentiality derives from the principles of beneficence (patients will be more forthcoming) and respect for autonomy (the patient's privacy rights are protected). Others, including the pregnant woman's spouse, sex partner and family, should be under stood as third parties to the patient relationship, in respect to information about the results of obstetric or gynaecological ultrasound. Diagnostic information about a woman's condition or pregnancy is confidential. It can therefore be jus tifiably disclosed to third parties only with the pregnant woman's explicit permission. This is because a potentially acceptable condition for releasing confidential information, avoiding grave harm to others, does not apply in this context.5,44 To avoid awkward situations, physicians should establish policies and procedures that reflect this analysis of the ethics of confidentiality.19
Ethics and patient information
the practice if it is a side product of a legitimate ultrasound examination. In fact, it may help the bonding of the prospective parents to the fetal patient. However, when videotaping or Polaroid photography are performed to generate revenues, this practice trivializes the ultrasound examination and may result in harm because problems that could be diagnosed could be missed.16
Conclusion Ethics complements the scientific and technological aspects of obstetric and gynaecological ultrasound. In this chapter we have provided an ethical framework for clinical judgement and practice in communicating information about obstetric and gynaecological ultrasound and subsequent decision making. Implementing this framework on a daily basis is essential to creating and sustaining the physician– patient relationship in this important subspecialty of obstetrics and gynaecology. This framework emphasizes preventive ethics to clinical topics in obstetric and gynaecological ultrasound, i.e. an appreciation that the potential for ethical conflict is built into clinical practice and the use of effective communication and informed consent to prevent such conflict from occurring. References 1. American College of Obstetricians and Gynecologists. Committee on Ethics. Patient choice: maternal–fetal conflict. American College of Obstetricians and Gynecologists, Washington, DC, 1987 2. American College of Obstetricians and Gynecologists. Technical bulletin. Ethical decision-making in obstetrics and gynecology. American College of Obstetricians and Gynecologists, Washington, DC,1989
3. Anderson G, Strong C. The premature breech: cesarean section or trial of labor? J Med Ethics 1988;14:18–24 4. Beauchamp TL, McCullough LB. Medical ethics: the moral responsibilities of physicians. Prentice-Hall, Englewood Cliffs, 1984 5. Beauchamp TL, Childress JF. Principles of biomedical ethics, 4th edn. Oxford University Press, New York, 1994
349
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
350
6. Bopp J (ed). Restoring the right to life: the human life amendment. Brigham Young University, Provo, 1984 7. Bopp J (ed). Human life and health care ethics. University Publications of America, Frederick, 1985 8. Brett A, McCullough LB. When patients request specific interventions: refining the limits of the physician's obligations. N Engl J Med 1986;315:1347–1351 9. Callahan S, Callahan D (eds). Abortion: understanding differences. Plenum Press, New York, 1984 10. Campbell S, Reading AE, Cox DN et al. Ultrasound scanning in pregnancy: the short-term psychological effects of early real time scans. J Psychosom Obstet Gynecol 1986;1:57–161 11. Chasen ST, McCullough LB, Chervenak FA. Is nuchal translucency screening associated with different rates of invasive testing in an older obstetric population? Am J Obstet Gynecol 2004;190(3):769–774 12. Chasen ST, Skupski DW, McCullough LB, Chervenak FA. First-trimester nuchal translucency screening: reply. J Ultrasound Med 2002;21:483–487 13. Chasen ST, Skupski DW, McCullough LB, Chervenak FA. Prenatal informed consent for sonogram: the time for first-trimester translucency has come. J Ultrsound Med 2001;20:1147–1152 14. Chervenak FA, Farley MA, Walters L et al. When is termination of pregnancy during the third trimester morally justifiable? N Engl J Med 1984;310:501–504 15. Chervenak FA, McCullough LB. An ethically justified, clinically comprehensive management strategy for third-trimester pregnancies complicated by fetal anomalies. Obstet Gynecol 1990;75:311–316 16. Chervenak FA, McCullough LB. An ethical critique of boutique fetal imaging: the case for the medicalization of fetal imaging. Am J Obstet Gynecol 2006;192(1):31–33 17. Chervenak FA, McCullough LB. Clinical guides to preventing ethical conflicts between pregnant women and their physicians. Am J Obstet Gynecol 1990;162:303–307 18. Chervenak FA, McCullough LB. Does obstetric ethics have any role in the obstetrician's response to the abortion controversy? Am J Obstet Gynecol 1990;163:1425–1429
19. Chervenak FA, McCullough L. Ethics in obstetric ultrasound. J Ultrasound Med 1989;8:493–497 20. Chervenak FA, McCullough LB, Campbell S. Is third trimester abortion justified? Br J Obstet Gynaecol, 1995;102:434–435 21. Chervenak FA, McCullough LB, Levene MI. An ethically justified, clinically comprehensive approach to peri-viability: gynaecological, obstetric, perinatal, and neonatal dimensions. J Obstet Gynaecol 2007;27:3–7 22. Chervenak FA, McCullough LB. Nonaggressive obstetric management: an option for some fetal anomalies during the third trimester. JAMA 1989;261:3439–3500 23. Chervenak FA, McCullough LB. Perinatal ethics: a practical method of analysis of obligations to mother and fetus. Obstet Gynecol 1985;66:442–446 24. Chervenak FA, McCullough LB, Sharma G, Davis J, Gross S. Enhancing patient autonomy with risk assessment and invasive diagnosis: an ethical solution to a clinical challenge. Am J Obstet Gynecol 2008; 199:19.e1–4 25. Chervenak FA, McCullough LB, Campbell S. Third trimester abortion: is compassion enough? Br J Obstet Gynaecol 1999;106:293–296 26. Chervenak FA, McCullough LB, Chervenak JL. Prenatal informed consent for sonogram (PICS): an indication for obstetrical ultrasound. Am J Obstet Gynecol 1989;161(4):857–860 27. Dunstan GR. The moral status of the human embryo. A tradition recalled. J Med Ethics 1984;10:38–44 28. Elias S, Annas GJ. Reproductive genetics and the law. Year Book Medical Publishers, Chicago, 1987 29. Engelhardt Jr HT. The foundations of bioethics, 2nd edn. Oxford University Press, New York, 1996 30. Evans MI, Fletcher JC, Zador IE et al. Selective first-trimester termination in octuplet and quadruplet pregnancies: clinical and ethical issues. Obstet Gynecol 1988;71:289–296 31. Faden RR, Beauchamp TL. A history and theory of informed consent. Oxford University Press, New York, 1986 32. Fleming L. The moral status of the fetus: a reappraisal. Bioethics 1987;1:15–34 33. Fletcher JC. The fetus as patient; ethical issues. JAMA 1981;246:772–773
✩✩✩✩✩✩✩✩✩✩✩ ✩ 49. Noonan JT (ed). The morality of abortion. Harvard University Press, Cambridge, MA, 1970 50. Noonan JT. A private choice. Abortion in America in the seventies. The Free Press, New York, 1979 5 1. Powderly KE. Patient consent and negotiation in the Brooklyn gynecological practice of Alexander J.C. Skene: 1863–1900. J Med Philos 2000;25:12–27 52. Pritchard JA, MacDonald PC, Gant NF. Williams' obstetrics, 17th edn. AppletonCentury-Crofts, Norwalk, CT, 1985: xi 53. Roe v. Wade, 410 US 113 (1973) 54. Ruddick W, Wilcox W. Operating on the fetus. Hastings Cent Report 1982;12:10–14 55. Shinn RL. The fetus as patient: a philosophical and ethical perspective. In: Milunsky A, Annas GJ (eds) Genetics and the law III. Plenum Press, New York, 1985: 317–324 56. Strong C. Ethical conflicts between mother and fetus in obstetrics. Clin Perinatol 1987;14:313–328 57. Strong C. Ethics in reproductive medicine: a new framework. Yale University Press, New Haven, CT, 1997 58. Strong C, Anderson G. The moral status of the near-term fetus. J Med Ethics 1989;15:25–27 59. Walters L. Ethical issues in intrauterine diagnosis and therapy. Fetal Ther 1986;1: 32–37 60. Warren MA. Gendercide. The implications of sex selection. Rowman and Littlefield, Totowa, NJ, 1985 61. Whyte HE, Fitzhardinge PM, Shennan AT et al. External immaturity: outline of 568 pregnancies of 23–26 weeks' gestation. Obstet Gynecol 1993;82:1–7 62. Zoppi MA, Ibba RM, Putzolu M, Floris M, Monni G. Nuchal translucency and the acceptance of invasive prenatal chrom osomal diagnosis in women aged 35 and older. Obstet Gynecol 2001;97:916–920
Ethics and patient information
34. Ford NM. When did i begin? Conception of the human individual in history, philosophy and science. Cambridge University Press, Cambridge, 1988 35. Fost N, Chudwin D, Wikker D. The limited moral significance of fetal viability. Hastings Cent Rep 1980;10;10–13 36. Hack M, Fanaroff AA. Outcomes of extremely-low-birth-weight infants between 1982 and 1988. N Engl J Med 1989;321:1642–1647 37. Harrison MR, Golbus MS, Filly RA. The unborn patient. Grune and Stratton, New York, 1984 38. Hellegers AE. Fetal development. Theol Stud 1970;31:3–9 39. Liley AW. The foetus as a personality. Aust NZ J Psychiatry 1972;6:99–105 40. Macklin R. Abortion: contemporary ethical and legal aspects. In: Reich WT (ed) Encyclopedia of bioethics, 2nd edn. Macmillan, New York, 1995: 6–16 41. Mahoney MJ. Fetal–maternal relationship. In: Reich WT (ed) Encyclopedia of Bioethics. Macmillan, New York, 1978: 485–489 42. Mahoney MJ. The fetus as patient. West J Med 1989;150:517–540 43. Mahowald M. Beyond abortion: refusal of cesarean section. Bioethics 1989;3:106–121 44. McCullough LB, Chervenak FA. Ethics in obstetrics and gynecology. Oxford University Press, New York, 1994 45. Murray TH. Moral obligations to the notyet born: the fetus as patient. Clin Perinatol 1987;14:313–328 46. Newton ER. The fetus as patient. Med Clin North Am 1989;73:517–540 47. Nicolaides KH. Nuchal translucency and other first-trimester sonographic markers of chromosomal anomalies. Am J Obstet Gynecol 2004;191:45–67 48. Nicolaides KH, Chervenak FA, McCullough LB. Evidence-based obstetric ethics and informed decision-making by pregnant women about invasive diagnosis after firsttrimester assessment of risk for trisomy 21. Am J Obstet Gynecol 2005;193(2):322–326
351
✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Test yourself – questions and answers
Chapter 2 Biological Effects and Safety Aspects 1. Which mode of operation can give the highest output intensity? a. B-mode b. Doppler imaging c. Spectral Doppler d. M-mode 2. Which of the following fetal tissues is likely to heat most during an ultrasound examination? a. skull bone b. brain c. eye d. myocardium 3. Which of the following safety indices is most appropriate for second- and third-trimester scanning? a. TIS b. MI c. TIC d. TIB 4. A diagnostic exposure that produces a maximum in situ temperature rise of no more than a. 1.5°C b. 2.5 °C c. 3.5°C above normal physiological levels (37°C) may be used without reservation on thermal grounds. 353
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
354
5. Which of the following statements are correct? Prenatal ultrasound exposure has been clearly shown to induce: a. childhood malignancies b. hearing impairment c. reduced birthweight d. dyslexia Select one choice from the following: a. only a, b and c b. only a and c c. only b, c and d d. none of them
Chapter 3 Scanning Techniques in Obstetrics and Gynaecology 1. Transrectal scan can provide important information if transvaginal scanning is not feasible or contraindicated in the following cases except: a. obesity b. ruptured membranes c. virginal patients d. senile atrophic vagina e. vaginal malformations 2. Which statements about orientation are true? a. If the uterus is retroverted the bladder and the uterine fundus are on opposite sides of the screen. b. If the uterus is anteverted the uterine fundus and the bladder are on opposite sides of the screen. c. On a transverse section the right and left sides of the gynaecological patient are matching those on an MRI picture. d. On a transverse section the right and the left sides of the gynaecological patient are the exact reverse of those on a CT picture. e. b and c are true. f. a and c are true. 3. The basic fetal ultrasound exam contains all features below except: a. document fetal number, presentation b. placental location and amniotic fluid volume c. survey of fetal anatomy including the brain d. evaluation of the adnexa of the patient e. documentation of fetal heartbeats 4. Which of the statements below is not correct regarding the endometrium? a. Endometrial thickness varies with the day in the menstrual cycle. b. Endometrial measurements should be done preferably on the transverse section of the uterus.
✩✩✩✩✩✩✩✩✩✩✩ ✩
Chapter 4 Investigation of Early Pregnancy
Test yourself – questions and answers
c. If fluid is in the cavity the anterior and posterior stripes should be measured separately and then added up for a single number representing the total thickness. d. In postmenstrual patients an echo less than 5 mm thick is usually consistent with lack of significant tissue on sampling. e. Saline infusion sonohysterography is the best tool to demonstrate endocavitary findings. 5. A full urinary bladder is useful for the following except: a. chorionic villus sampling b. localizing the placenta and measuring its distance from the internal os c. in every gynaecological patient using transvaginal scanning d. evaluating placenta accreta close to the bladder wall
(Note: more than one answer can be correct) 1. The following statements about multiple pregnancies are correct except one. a. The chorionicity of the multiple pregnancy is established before 5 LMP-based weeks. b. The identification of the amnionicity is made earlier than the chorionicity. c. In dichorionic pregnancies, the dividing wall consists of four layers. d. In the early second trimester, the lambda sign allows differentiation between mono- and dichorionicity. 2. One of the following sonographic findings is suggestive for early pregnancy failure. a. The crown–rump length (CRL) is twice the expected length. b. The diameter of the yolk sac is less than 6 mm. c. The heart rate of the embryo is less than 70 beats per minute (bpm). d. The diameter of the amniotic cavity is larger than the diameter of the yolk sac. 3. Two of the following ultrasound findings are possible signs for an ectopic pregnancy (positive pregnancy test). a. haemoperitoneum without an intrauterine gestational sac b. cyst in the ovary and an intrauterine trophoblast ring c. fluid in the uterine cavity and an extraovarian solid mass d. two yolk sacs in the gestational cavity without embryonic echo 4. Three of the following first-trimester findings are suspicious for a chromosomal disorder. a. The placenta is large and contains cysts; the embryo is alive. b. The fetus at 12 weeks seems to have an oedema; there is a nuchal translucency of >3 mm. 355
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
356
c. The embryo has a CRL of 25 mm; the heart rate is as high as 185 bpm. d. The embryo has a CRL of 10 mm; the yolk sac diameter is 7 mm. 5. One of the following findings is probably consistent with a normal early pregnancy. a. CRL 4 mm, diameter of yolk sac 5 mm, diameter of amniotic cavity 7 mm, heart rate 110 bpm b. CRL 23 mm, diameter of yolk sac 5 mm, diameter of amniotic cavity 24 mm, heart rate 170 bpm c. CRL 29 mm, diameter of yolk sac 5 mm, diameter of amniotic cavity 34 mm, heart rate 150 bpm d. CRL 2 mm, diameter of yolk sac 3 mm, diameter of amniotic cavity 4 mm, heart rate 90 bpm e. CRL 13 mm, diameter of yolk sac 9 mm, diameter of amniotic cavity 12 mm, heart rate 130 bpm
Chapter 5 Normal Fetal Anatomy at 18–22 Weeks 1. Basic guidelines by the American Institute of Ultrasound in Medicine include views of: a. the great vessels of the heart b. hands and feet c. anterior abdominal wall d. face e. all of the above 2. A sequential segmental approach to the heart would include specifice views of all of the following except: a. view of the upper abdomen to show normal solitus b. left and right ventricular outflow views c. four-chamber view d. ductus venosus e. pulmonary artery and ductal arch 3. Markedly echogenic bowel has been associated with what types of outcome? a. normal b. aneuploidy c. fetal infection d. fetal demise e. all of the above 4. All of the following is true about the fetal anatomic survey except: a. it is usually performed during the second trimester b. it is the ideal time for nuchal translucency evaluation c. it requires a systematic approach d. it gives the opportunity to provide important information about the fetus
✩✩✩✩✩✩✩✩✩✩✩ ✩
Chapter 6 Amniotic Fluid and Placental Localization Test yourself – questions and answers
1. The water content of amniotic fluid is: a. 50–60% b. 70–80% c. 98–99% 2. The normal amniotic fluid index ranges between: a. 5 and 25 cm b. 10 and 30 cm c. 20 and 40 cm 3. There is a high association with pulmonary hypoplasia when severe oligohydramnios develops: a. before 20–25 weeks of gestation b. at 30–35 weeks of gestation c. at 35–40 weeks of gestation 4. The association between chronic polyhydramnios and fetal anomalies is approximately: a. 1 in 25 b. 1 in 15 c. 1 in 5
Chapter 7 Assessment of the Placenta and Umbilical Cord 1. All the following statements concerning placenta accreta are correct except one. a. This anomaly is characterized by myometrial invasion by placental villous tissue. b. It occurs when the decidua basalis is partially or completely absent. c. It is more common in primigravidae than multigravidae. d. Placentas accreta have an overall maternal and fetal mortality of around 10%. e. Caesarean hysterectomy is often needed. 2. The only statement about chorioangioma that is correct is: a. Chorioangiomas are malignant tumours characterized by a proliferation of villous capillaries and trophoblastic tissue. b. Chorioangiomas are often diagnosed during the first trimester of pregnancy. c. Most chorioangiomas are large, single, round, encapsulated, near the cord insertion. d. All chorioangiomas can be complicated by fetal hydrops, due to the chronic shunting, and by polyhydramnios. e. The fetal risk depends more on the proportion of angiomatous versus myxoid tissue inside the tumour than on its exact size. 3. The only ultrasound feature mentioned below that is specific to a triploid partial mole is: a. fetal bilateral cerebral ventriculomegaly b. severe fetal growth restriction
357
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ c. vaginal bleeding d. fetal symmetrical growth restriction and placental Swiss cheese appearance e. bilateral ovarian theca-lutein cyst 4. The correct terminology for a placental lesion resulting from bleeding due to rupture of fetal vessels branching from the cord is: a. subchorionic cyst b. membranous cyst c. thrombotic cyst d. subchorionic haemorrhage e. subamniotic haematoma 5. All the following statements concerning the single umbilical artery syndrome are correct except one. a. The absence of one umbilical artery is associated with a high incidence of trisomy 21. b. The single umbilical artery cord is one of the most common anatomical defects in the human fetus. c. Single umbilical artery is often found in association with major fetal abnormalities. d. The single umbilical artery is found almost invariably in cases of the acardia malformation and sirenomelia or caudal regression syndrome. e. When isolated, the single umbilical artery is associated with a 15–20% incidence of poor fetal growth.
Chapter 8 Examining the Cervix by Transvaginal Ultrasound
358
1. The risk of spontaneous early preterm delivery increases with decreasing cervical length. At a cervical length of 25 mm, the risk is approximately: a. 25% b. 15% c. 10% d. 1% 2. Cervical funnelling is: a. the early onset of labour b. protrusion of membranes into the endocervical canal c. shortening of the cervix 3. A short cervical length is synonymous with cervical incompetence: a. correct b. incorrect 4. Ultrasound measurement of cervical length allows differentiation between true and false labour: a. correct b. incorrect
✩✩✩✩✩✩✩✩✩✩✩ ✩
Chapter 9 Fetal Biometry, Estimation of Gestational Age, Assessment of Fetal Growth 1. What is the aim of CRL measurement? a. to determine fetal weight b. to determine true gestational age c. both d. other aims 2. The accuracy of pregnancy dating: a. increases with gestational age b. decreases with gestational age c. is independent from gestational age 3. The measurement of biparietal diameter: a. is used for dating pregnancy in the second trimester b. is very accurate for dating pregnancy in the third trimester c. is taken at the same level as the measurement of the cerebellar diameter 4. The abdominal circumference: a. is used for fetal dating in the third trimester b. is used for the evaluation of fetal growth disturbances in the second trimester c. is the main factor in fetal weight determination in most of the mathematical equations 5. For a confident diagnosis of IUGR: a. the calculated fetal length should be below normal values b. the calculated fetal weight should be below normal values c. both AC and fetal weight estimation, made at least 2–3 weeks apart, should be below normal values
Test yourself – questions and answers
5. True cervical incompetence is responsible for which percentage of preterm labour: a. 40% b. 30% c. <10%
Chapter 10 Prenatal Diagnosis of Fetal AnomalIES 1. What is the estimated frequency of congenital anomalies detected by a clinical examination performed within the first week of life? a. 1% b. 2% c. 6% d. 10% e. 15%
359
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩ 2. What is the proportion of congenital anomalies that are probably identified by a well-performed ultrasound sonogram at midgestation in a patient who does not have specific risk factors? a. 1% b. 10% c. 50% d. 90% e. virtually all 3. What is the normal measurement of the posterior horn or atria of lateral ventricles in the midtrimester fetus? a. <1 mm b. <5 mm c. <10 mm d. <15 mm e. < 20 mm 4. Which of the following views of the fetal heart should always be obtained at midgestation even in a pregnancy without specific risk factors? a. five-chamber view b. four-chamber view c. transverse view of great vessels d. view of the aortic arch e. view of the pulmonary artery 5. Which of the following strategies of trisomy 21 screening has the greatest accuracy? a. anatomic scan and soft markers evaluation around midgestation b. nuchal transluciency measurement at 11–14 weeks c. nuchal translucency measurement plus biochemistry at 11–14 weeks d. biochemistry around 16 weeks e. biochemistry around 16 weeks and ultrasound at midgestation
Chapter 11 Evaluation of Fetal AND Uteroplacental Blood Flow
360
1. For the assessment of true flow velocities, the angle of insonation should be close to: a. 90° b. 60° c. 25° d. 0° 2. The gestational age-related decrease in impedance to flow in the uterine arteries during normal pregnancy is determined by: a. increasing vessel compliance b. slowing of fetal heart rate c. trophoblast invasion of the spiral arteries
✩✩✩✩✩✩✩✩✩✩✩ ✩
Test yourself – questions and answers
3. Uterine artery screening studies are best performed at: a. 10–14 weeks b. 15–18 weeks c. 20–24 weeks d. 25–30 weeks 4. A moderate reduction in umbilical artery end-diastolic blood flow velocity requires: a. additional Doppler information from systemic vessels (fetal middle cerebral artery and ductus venosus) b. hospital admission and close fetal heart rate monitoring c. emergency caesarean section 5. Increased end-diastolic flow velocity in the fetal middle cerebral artery indicates: a. fetal infection b. imminent delivery c. fetal growth restriction/fetal hypoxaemia d. fetal anaemia e. c+d 6. Abnormal flow velocities in the fetal ductus venosus associated with fetal growth restriction/fetal hypoxaemia are characterized by: a. a reduction in the systolic flow component b. a reduction in the early diastolic flow component c. an increase in the late diastolic flow component d. a reduction in the late diastolic flow component
Chapter 12 Invasive Procedures in Obstetrics 1. Chorion villus sampling is preferably performed: a. before 10 weeks b. at 11–14 weeks c. at 15–20 weeks 2. Amniocentesis is performed using a: a. 14 gauge needle b. 16 gauge needle c. 20 gauge needle d. 24 gauge needle 3. Main diagnostic indications for amniocentesis are: a. fetal karyotyping b. vaginal bleeding c. oligohydramnios 4. When blood sampling the umbilical vein, the needle should puncture the vessel at an angle of: a. 5–10° b. 20–30° c. 50–60° d. 80–90°
361
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Chapter 13 Multiple Pregnancies
362
1. Early assessment of chorionicity and amnionicity in multiple pregnancies is of particular importance since: a. fetal surveillance should be undertaken in appropiate intervals regardless of zygocity b. in monochorionic twins the rates of mortality and morbidity are markedly higher and clinical counselling, management and surveillance differ according to chorionicity and amnionicity c. one-third of monozygotic twins are dichorionic and diamniotic if splitting occurs after day 4 postconception d. risk of twin–twin transfusion syndrome in dichorionic twins can be assessed early 2. Sonographic features of monochorionic twinning are: a. presence of the lambda sign, easily identifiable intertwin membrane and different gender b. absent lambda sign, very thin or absent intertwin membrane, same gender c. present lambda sign, lack of intertwin membrane, unique yolk sac d. absent lambda sign, discordant gender, unique yolk sac 3. When assessing the risk for chromosomal abnormalities in multiple pregnancies: a. in dizygotic twins the risk that at least one fetus is affected is obtained by doubling the age-related risk; in monozygotic twins it is equal to the risk of a singleton pregnancy, both fetuses being affected if the karyotype is abnormal b. an increased NT can indicate the early onset of a twin–twin transfusion syndrome in dichorionic twins, and therefore falsely increase the risk c. squaring the singleton risk for chromosomal abnormalities in monozygotic twins derives the risk that both fetuses are affected d. regardless of chorionicity, the risk calculation based on NT measurement and maternal age can be transferred from singleton to twin pregnancies 4. Regarding placental vascular anastomoses in monochorionic twinning, it is FALSE to say that: a. due to their existence, death of one fetus may affect the co-twin due to an acute hypotensive and anaemic episode leading to death or neurological damage b. they are the underlying cause of the twin–twin transfusion syndrome, where a net imbalance in intertwin blood flow may ensue as early as the 17th week and in a rapid fashion for 1 or 2 weeks c. anastomoses are always present in dichorionic placentae and a continuous blood exchange between both fetuses takes place d. in early pregnancy the presence of one arterio-arterial and one venovenous anastomosis between both cord insertions may result in the reversed perfusion of one of the fetuses, with its consequent transformation into an acardiac twin
✩✩✩✩✩✩✩✩✩✩✩ ✩
Chapter 14 Three-Dimensional and Four-Dimensional Ultrasound Application in Prenatal Diagnosis 1. The advantage of 3D ultrasound is that it can: a. demonstrate the face of the baby b. provide a reliable diagnosis of the fetal gender c. be combined with colour Doppler d. be used to acquire a volume data set with different ways of image display 2. A volume data set: a. can be acquired with manual moving of the transducer over the region of interest b. can be acquired with 3D, 4D or with spatial or temporal image correlation (STIC) c. is a result of an offline analysis of cine loops acquired separately d. can only be acquired with the newest matrix transducers 3. Tomography imaging can be performed: a. on every 3D volume b. only when a volume data set was acquired with colour Doppler c. only when a manual acquisition was achieved by a parallel shift of the transducer d. only with a volume data set acquired from a transvaginal transducer 4. The fetal skeleton is best demonstrated with: a. minimum mode b. maximum mode c. STIC d. inversion mode 5. STIC is the technique of choice for: a. the fetal brain b. early pregnancy (nuchal translucency, nasal bone) c. the fetal heart d. analysing fetal breathing movements
Test yourself – questions and answers
5. Regarding monoamniotic twins, the following is FALSE: a. the finding of close proximity and synchronous movements of the fetuses, without separation during a period of observation time, is sonographically typical for them b. cord entanglement has been responsible for the demise of one or both fetuses in the majority of cases c. absence of intertwin membrane, single yolk sac, placental cord insertions close to each other and unusual fetal proximity to each other are their sonographic criteria d. monoamniotic twins occur in 5% of monochorionic twins, representing 1% of all twins and showing a significantly increased risk for structural anomalies and poor perinatal outcome
363
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Chapter 15 Fetal Movement Patterns and Behavioural States 1. In cases of fetal brain anomalies, changes in fetal movements are usually: a. qualitative in nature b. quantitative 2. Shaking of the maternal abdomen during quiet sleep (i.e. during a flat FHR pattern): a. results in a change from quiet sleep to REM sleep b. has no effect on fetal behaviour 3. Fetal micturition usually occurs: a. during quiet sleep b. at the transition from quiet sleep to REM sleep c. during REM sleep 4. Which association is the strongest? a. Absence of fetal breathing movements is strongly associated with imminent preterm delivery. b. Presence of fetal breathing movements is strongly related to imminent preterm delivery. c. Absence of fetal breathing movements indicates that imminent preterm delivery is unlikely. d. Presence of fetal breathing movements indicates that imminent preterm delivery is unlikely. 5. Betametasone administration to the mother results in a temporary: a. reduction of fetal breathing movements b. reduction of fetal body movements c. reduction of fetal heart rate variation d. all three answers are correct
Chapter 16 Normal Gynaecological Anatomy (Uterus, Tubes, Ovaries)
364
1. Endometrial thickness should be measured: a. from a transverse view of the uterus where the endometrium appears to be at its thickest b. from a transverse view of the uterus where the endometrium appears to be at its thinnest c. from a sagittal section through the uterus where it appears to be at its thickest d. from a sagittal section through the uterus where the endometrium appears to be at its thinnest e. any of the above 2. The gold standard for assessing tubal patency is: a. laparoscopy with dye b. hysterosalpingography
✩✩✩✩✩✩✩✩✩✩✩ ✩
Test yourself – questions and answers
c. hystero-contrast salpingosonography d. all of the above e. there is no gold standard 3. In the late proliferative phase of the menstrual cycle the endometrium has the following appearance at ultrasound examiantion. a. ‘triple layer’, thick b. hyperechogenic, thick c. hyperechogenic with echo enhancement d. pencil-line e. none of the above 4. In the luteal phase of the menstrual cycle: a. blood flow velocities in the uterine arteries are lower and pulsatility index values are higher than in the follicular phase b. blood flow velocities in the uterine arteries are lower and pulsatility index values are lower than in the follicular phase c. blood flow velocities in the uterine arteries are higher and pulsatility index values are higher than in the follicular phase d. blood flow velocities in the uterine arteries are higher and pulsatility index values are lower than in the follicular phase e. none of the above is true 5. At ultrasound examination the corpus luteum is: a. an anechoic cystic structure b. an echogenic cystic structure with smooth walls c. an echogenic cystic structure with crenellated walls d. a cystic structure whose content has the same ultrasound morphology as clotted blood e. any of the above
Chapter 17 Gynaecological Pathology: The Uterus 1. The ultrasound appearance of uterine fibroids most commonly is: a. echo-dense b. anechoic 2. In premenopausal women, endometrial polyps are best visualized by ultrasound: a. in the follicular phase of the menstrual cycle b. at the beginning of the luteal phase of the menstrual cycle c. just before the onset of the menstrual period 3. In the peri- and postmenopause, the following endometrial thickness is highly unlikely to harbour significant pathology and chance of malignancy: a. 8 mm or less b. 6 mm or less c. 4 mm or less
365
Ultrasound in obstetrics and gynaecology
✩ ✩✩✩✩✩✩✩✩✩✩✩
Chapter 18 Gynaecological Pathology: Tubes and Ovaries (Note: more than one answer can be correct) 1. Which of the following sonographic signs serve as the most important feature(s) to estimate the risk of ovarian malignancy? a. tumour size b. tumour structure (complexity) c. a+b d. cyst wall thickness e. a+d f. echo-dense foci 2. Endometriosis is sonographically characterized by: a. complete lack of internal echoes b. irregular echoes with solid components c. homogeneous internal echoes of medium density 3. Pyosalpinx is sonographically characterized by: a. a normal image b. a swollen tortuous tube without any internal echoes c. a swollen tortuous tube with internal echoes.
Chapter 19 Doppler Ultrasonography in Gynaecology 1. Which cut-off level has been suggested for the resistance index (RI) in tumour vessels as a sign of potential malignancy? a. 0.9–1.0 b. 0.8–0.9 c. 0.6–0.7 d. 0.45–0.5 2. 3D power Doppler imaging has replaced 2D Doppler imaging in detecting potential ovarian malignancy. a. correct b. incorrect
Chapter 20 Medico-Legal Implications of Ultrasound Imaging in Obstetrics and Gynaecology (Note: more than one answer can be correct) 1. Defending a claim is facilitated if: a. no images were recorded b. a contemporaneous written protocol is available c. the scan was performed in a research institution d. several years elapsed before the claim is initiated 366
✩✩✩✩✩✩✩✩✩✩✩ ✩
Test yourself – questions and answers
2. Most patients initiating a claim: a. win a substantial financial settlement b. do not go to court c. regret initiating the claim d. do not need an expert witness 3. Phocomelia can be excluded: a. by a competent 20-week anomaly scan b. only after 30 weeks of pregnancy c. if both hands and feet are confidently seen d. none of the above 4. Ultrasound should always achieve a correct preoperative diagnosis of: a. uterine fibroid (myoma) b. benign ovarian cyst c. dysgerminoma d. none of the above 5. The recent increase in medical litigation is attributable to: a. a decline in the quality of medical practice b. increasing patient expectations c. changes in the law d. poor advice from lawyers
Chapter 21 Ethics and Patient Information 1. Informed consent is most closely related to which ethical principle? a. beneficence b. non-maleficence c. justice d. respect for autonomy e. confidentiality 2. The ethical principle of beneficence is most closely associated with: a. primum non nocere b. greater balance of goods over harms for the patient c. justice d. non-maleficence e. confidentiality 3. For which of the following anomalies diagnosed at 20 weeks should the sonologist give directive counselling for abortion? a. anencephaly b. hydrocephalus c. Down syndrome d. all of the above e. none of the above
367
✩ ✩✩✩✩✩✩✩✩✩✩✩
Ultrasound in obstetrics and gynaecology
Answers Chapter 2: 1 c; 2 a; 3 d; 4 a; 5 d. Chapter 3: 1 a; 2 g; 3 c; 4 b; 5 c. Chapter 4: 1 b; 2 c; 3 a, c; 4 a, b, d; 5 b. Chapter 5: 1 c; 2 d; 3 e; 4 b. Chapter 6: 1 c; 2 a; 3 a; 4 c. Chapter 7: 1 c; 2 e; 3 d; 4 e; 5 a Chapter 8: 1 d; 2 b; 3 b; 4 a; 5 c. Chapter 9: 1 b; 2 b; 3 a; 4 c; 5 c. Chapter 10: 1 b; 2 c; 3 c; 4 b; 5 c. Chapter 11: 1 d; 2 c; 3 c; 4 a; 5 e; 6 d. Chapter 12: 1 b; 2 c; 3 a; 4 d. Chapter 13: 1 b; 2 b; 3 a; 4 c; 5 a. Chapter 14: 1 a+d; 2 b; 3 a; 4 b; 5 c. Chapter 15: 1 a; 2 b; 3 b; 4 d; 5 d. Chapter 16: 1 c; 2 e; 3 a; 4 d; 5 e. Chapter 17: 1 a; 2 a; 3 c.
368
✩✩✩✩✩✩✩✩✩✩✩ ✩ Chapter 18: 1 c; 2 c; 3 c
Chapter 20: 1 b; 2 b, c; 3 d; 4 d; 5 b. Chapter 21: 1 d; 2 b; 3 e.
Test yourself – questions and answers
Chapter 19: 1 d; 2 b.
369
✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩✩ ✩
Index
Note: Page numbers in italics refer to figures and page numbers in bold refer to tables.
A
abdomen cysts, 190 (see also specific anatomical region) gestational age estimation/prediction, 147, 147–8 normal fetal anatomy at 18–22 weeks, 81, 95–7, 95–7 abdominal circumference (AC), embryo/fetus first trimester, 64–5, 65 gestational age estimation/prediction, 147, 147–8 macrosomia, 154 second trimester, 95, 95, 96 abdominal wall anterior, normal fetal anatomy at 18–22 weeks, 97–8 fetal anomalies, 185–90 abortion spontaneous, 69 threatened, 69 see also miscarriage abscesses adnexal, 50 tubo-ovarian, 326 absent end-diastolic flow (AEDF), umbilical artery, 215–17, 216 achondrogenesis, 195 achondroplasia, 195 acidaemia, fetal, 220 acoustic absorption coefficient of tissue, 24 acoustic energy, 22 acoustic output, 22–3, 23 acoustic power, 22 acoustic streaming, 21, 27 adenoma, fetal hepatic, 197 adenomatous hyperplasia, 49 adenomyosis, 47, 307, 307–8 adnexal masses, 49–50 differential diagnosis, 314 Doppler studies, 329–30
echogenicity, 316 malignant, 314 see also ovarian cysts; ovarian tumours adnexal torsion, 53, 323 adrenal glands, normal fetal anatomy at 18–22 weeks, 101 ADR linear scanner, 7, 10 alcohol, effect on fetal movements, 281 alloimmune thrombocytopenia, fetal, 238 American Fertility Society classification of congenital uterine anomalies, 300, 302 amniocentesis (AC), 229, 234–5 approach, 234–5 early, 234 multiple pregnancies, 235, 252 safety, 235 timing, 234 amnion, 110 amnionicity determination, 68, 69, 250, 250–1 amniotic cavity diameter, 57, 67, 67, 68, 70 amniotic fluid, 109–14 fetal urinary production, 110 flow across the chorionic plate, 110 lung fluid, 110 physiology, 110 volume, 111–13 abnormal, 112–13 assessment methods, 111, 112 normal, 112 quantitation of, 45 amniotic fluid depth (AFI), 45 amniotic fluid index technique, 111, 112 A-mode, 6, 8, 23 amputation, congenital, 196 anaemia, fetal blood transfusion, 238 middle cerebral artery Doppler, 217, 218–19, 220
371
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩ anencephaly, 161–2 diagnosis, 161–2 effect on fetal movements, 278–9 incidence, 161 prognosis, 162 aneuploidy, 233–4 angiomyxoma, umbilical cord, 130, 130 anhydramnios, 112, 190 anophthalmia, 168–9 anorectal atresia, 188 anterior abdominal wall, normal fetal anatomy at 18–22 weeks, 97–8 antiarrhythmic drugs, fetal cardiac dysrhythmias, 181 anti-La antibodies, 181 anti-Ro antibodies, 181 aorta, 93, 93, 94 aortic arch, 94, 94 coarctation, 173–4 interruption, 173–4 tubular hypoplasia, 173–4 aortic stenosis, 173 appropriate for gestational age (AGA), 152 arcuate uterus, 300, 301, 302 Arnold–Chiari malformation, 84 artery-to-artery anastomosis, 224 artifacts, 17–19 attenuation shadows, 17–18 edge shadows, 17, 18 enhancement, 18, 18 reverberation, 19, 19 ascites, hydrops fetalis, 199 asepsis, invasive obstetric procedures, 232 Asherman syndrome, 49 asphyxiating thoracic dysplasia, 196 asplenia, 95, 171–2 atria, normal fetal anatomy at 18–22 weeks, 90 atrial fibrillation, 181 atrial flutter, 180–1 atrial septum defects, 170–1 normal fetal anatomy at 18–22 weeks, 90 atrioventricular block, 181–2 atrioventricular malformations, ductus venosus blood flow, 222 atrioventricular septal defect, 169, 170–1 atrioventricular valve ductus venosus blood flow, 223 normal fetal anatomy at 18–22 weeks, 90 regurgitation, 221 attenuation shadows, 17–18 audible sound, 2 autonomy, 342, 343, 348, 349 autosomal dominant cystic kidneys, 192 autosomal mutations, 159 autosomal recessive cystic kidneys, 191–2 axial plane, 14, 15 axial resolution, 14–15, 15 azimuth plane, 16
B 372
banana sign, 161, 162 beam see ultrasound beam Beckwith–Wiedemann syndrome, 185
Beemer–Langer syndrome, 196 behavioural states, fetal, 276–8, 277 beneficence, 340–2, 343, 349 b-human chorionic gonadotropin (b-hCG), hydatidiform mole, 72 betametasone, effect on fetal movements, 281 b2-microglobulin, obstructive uropathies, 239 b-mimetics, atrioventricular block, 182 bicornuate uterus, 300, 302 bilateral uterine artery notch, 212 bimanual pelvic examination prior to scanning, 36–7 binocular diameter (BOD), 86, 149 biological effects and safety aspects of ultrasound, 21–31 acoustic output of diagnostic ultrasound scanners, 22–3, 23 evidence from epidemiology, 27–8 management of safety, 28–9 manufacturers’ obligations, 29 non-thermal mechanisms and their safety implications, 26–7 safety practice, 29–31 tissue warming by diagnostic ultrasound, 23–6, 25 user’s responsibility, 28–9 biophysical profile testing, 44–5 biparietal diameter (BPD) first trimester, 63, 65 gestational age estimation, 144, 146–7 macrosomia, 154 second trimester, 80 birthweight and ultrasound, 27 bladder empty or full when scanning, 34, 34–5 exstrophy, 186–7 mass, 51 normal fetal anatomy at 18–22 weeks, 99, 101 polyps, 52 scanning routine, 51–2, 52 shunting, 241 stones, 52 bleeding irregular uterine, 49 vaginal see vaginal bleeding blood flow fetal and uroplacental, 209–24, 277 normal fetal anatomy at 18–22 weeks, 91, 92 blood perfusion rate of tissue, 24 blood transfusion, fetal, 199, 237–8 complications, 238 indications, 238 technique, 237–8 volumes, 238 B-mode, 7, 9 spatial-peak temporal-average intensity, 23, 23 uterine abnormalities, 300 uterine fibroids, 305 body movements, fetal, 274–5, 275 body stalk anomaly, 186 bones heating of, 24, 25 normal fetal anatomy at 18–22 weeks, 102–4, 102–5
✩✩✩✩✩✩✩✩✩✩✩ ✩
C
caffeine, effect on fetal movements, 281 calculi, bladder, 52 calvarium, normal fetal anatomy at 18–22 weeks, 80–5, 81 transcerebellar view, 83, 84–5 transthalamic view, 80–2, 82 transventricular view, 82–4, 83 cardiac anomalies, fetal, 169, 169–82, 170 see also specific anomaly cardiac apex, 89 cardiac dysrhythmias, 180–2 cardiac failure, 178 cardiomegaly, 221 cardiosplenic syndrome, 171–2 cardiovascular system, 3D/4D imaging, 268 cavum septum pellucidum (CSP), 80–1, 82 cavum vergae, 80–1 central nervous system, fetal anomalies, 160–6 see also specific anomaly cephalic index (CI), 147 cerclage, cervical, 137, 137–9 cerebellum agenesis, 84 hemispheres, embryo/fetus, 61, 83, 83, 84 normal fetal anatomy at 18–22 weeks, 84 cerebral anomalies, fetal, 160–6 see also specific anomaly cerebral lesions, destructive, 165–6 cerebral ventricles, 60, 61, 83, 84 cerebroplacental ratio (CPR), 218 cervical pregnancy, 46, 73 cervical teratoma, fetal, 197 cervix fibroids, 45–6 funnelling, 134–5, 135 incompetence, 137, 137–9 length and cervical incompetence, 137 and preterm delivery, 134, 135–6, 136 measurement technique, 136, 136 normal ultrasound morphology, 286, 286 scanning orientation, 41, 41 scanning routine, 45–6 transvaginal ultrasound examination, 46, 133–9
cervical incompetence treatment, 137, 137–9 clinical judgement of preterm labour, 136–7 follow-up, 138–9 measurement technique, 136, 136 preterm birth prediction, 134–6 prophylactic cerclage, 138–9 childhood malignancies and ultrasound, 27 choledocal cysts, 190 chondroectodermal dysplasia, 196 chorioangiomas, 121, 124, 124–5 choriocarcinoma, 72–3 chorion frondosum, 114, 114, 115 chorionic cavity see gestational sac chorionicity determination, 68, 69, 249, 250, 250–1 chorion laeve, 114, 115 chorion villus sampling (CVS), 229, 232–4 approach, 233, 233 multiple pregnancies, 233–4, 251–2 safety, 234 timing, 232 choroid plexus cyst, 84, 166, 204 choroid plexuses, 60, 61, 82–3 chromosomal anomalies, fetal, 159, 199–204, 200–1 effect on fetal movements, 278–282 individual risk assessment using midtrimester ultrasound, 201–4 maternal age risk, 202–3, 203 maternal autonomy, 348 in oesophageal atresia, 187 in omphalocele, 185 ultrasound findings with chromosomal aberrations, 199–201 circle of Willis, 217 circummarginate placentation, 122 circumvallate placentation, 122–3 cisterna magna (CM), 83, 84–5 absent, 161, 162 large, 161 mega, 164 normal, 161 clavicles gestational age estimation/prediction, 149 normal fetal anatomy at 18–22 weeks, 104–5 cleft lip/palate, 85–6, 166–8, 167 cloacal exstrophy, 186–7 coarctation of the aortic arch, 173–4 coefficients of correlation, 143 colour Doppler, 52–3 adnexal masses, 330 aortic stenosis, 173 atrioventricular septal defects, 171 in gynaecology, 329 in vitro fertilization, 331 spatial-peak temporal-average intensity, 23, 23 tetralogy of Fallot, 178 uterine artery, 212 ventricular septum, 91, 91 competence, 347 complete atrioventricular block, 181–2 complete transposition, 176–7 confidentiality, 349
Index
bowel echogenic, 189 hyperechogenic, 204 normal fetal anatomy at 18–22 weeks, 97 perforation, 189 brain cavities, embryo/fetus, 60 lesions, effect on fetal movements, 278 normal fetal anatomy at 18–22 weeks, 80–5, 81 transcerebellar view, 83, 84–5 transthalamic view, 80–2, 82 transventricular view, 82–4, 83 brain-sparing effect, 216, 218 Braxton Hicks contractions differentiating from the placenta, 117 fetal behavioural states, 277 breathing movements, fetal, 273, 276
373
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩
374
congenital amputation, 196 congenital anomalies fetal, 157–60 causative factors, 158–9 classification, 158 effect on fetal movements, 278–9 incidence, 158 morbidity, 159–60 mortality, 159 prevalence, 158 uterine, 299–303, 301, 302, 302 see also specific anomaly conjoined twins, 68, 247, 256 conotruncal malformations, 176–9 presentation, 176 prevalence, 176 prognosis, 176 contractions Braxton Hicks see Braxton Hicks contractions uterine see uterine contractions cord see umbilical cord cordocentesis see fetal blood sampling (FBS) corpus callosum, 81–2, 82 agenesis of, 160, 164 corpus luteum, 53, 288, 289, 291, 291–2 cysts, 318, 319 corrected transposition, 176–7 corticosteroids, effect on fetal movements, 281 cotyledons, placental anatomy, 115 counselling, genetic, 230 coupling gel, 38–9 cranial vault absence see anencephaly craniofacial anomalies, fetal, 166–9 see also specific anomaly cross-sectional studies, fetal biometry, 142 crown–rump length (CRL) comparing with amniotic cavity, 70 first trimester, 57, 58–61, 59–63, 63 gestational age estimation/prediction, 146 multiple pregnancies, 248 crux of the heart, 90 curvilinear regression analysis, 143 cystadenocarcinoma, 321 cystic adenomatoid malformation of the lungs, 182 cystic dysplasia of the kidneys, 191 cystic fibrosis, 189 cystic lungs, 182–3 cysts abdominal, 190 choledocal, 190 choroid plexus, 84, 166, 204 corpus luteum, 318, 319 dermoid, 323 follicle, 318 hepatic, 190 inclusion, 289, 290 kidneys, 191–2 mesenteric, 190 omental, 190 ovarian see ovarian cysts placental, 118 theca-lutein, 125, 318 vestigial, 130
D
Dandy–Walker complex, 161, 164–5 Dandy–Walker malformation, 84, 85, 164, 165 Dandy–Walker variant, 164 dating see gestational age estimation/prediction decidua basalis, 114, 114 decidua capsularis, 114, 114 decidua parietalis, 114 dermoid cysts, 323 destructive cerebral lesions, 165–6 diabetes, maternal, effect on fetal movements, 280 diamniotic (DA) twins, 68, 248 diaphragmatic hernia, 183–4 dichorionic (DC) twins, 68, 248 dominant autosomal mutations, 159 Donald, Ian, 3 Doppler effect, 2 Doppler indices, 210–12, 211 see also specific index Doppler ultrasound colour see colour Doppler ductus venosus, 219–23 Ebstein’s anomaly, 179 endometrium, 310 fetal and uroplacental blood flow, 209–24 fetal growth restriction outcomes, 222 in gynaecology, 329–31 indications in pregnancy, 210 middle cerebral artery, 217–19, 219, 220 normal uterine and ovarian vascularization, 291, 291–2 pulsed see pulsed Doppler spectral, 23, 23 truncus arteriosus, 179 in twin pregnancies, 223–4 umbilical artery, 214–17, 216 umbilical vein, 223 uterine artery, 209–10, 212–14, 213, 214 uterine sarcoma, 306 in vitro fertilization, 331 double bubble sign, 96, 188 double-outlet right ventricle (DORV), 177 drugs, effect on fetal movements, 281–2 ductus venosus, 219–23, 221, 222 duodenum atresia, 187–8 normal fetal anatomy at 18–22 weeks, 96 dwarfism, short-limbed, 154 dynamic focusing, 14
E
ears, normal fetal anatomy at 18–22 weeks, 86–7 Ebstein’s anomaly, 179–80, 221 echocardiography Ebstein’s anomaly, 179 fetal cardiac assessment, 169 tetralogy of Fallot, 178 truncus arteriosus, 179 echogenic bowel, 189 echogenic foci, heart, 180, 204 echogenic intracardiac focus/chorda tendinae, 91
✩✩✩✩✩✩✩✩✩✩✩ ✩
F
face, normal fetal anatomy at 18–22 weeks, 81, 85–7, 85–7 facial clefts, 85–6, 166–8, 167
fallopian tubes, 292, 292, 293 carcinoma, 325 ectopic pregnancy, 324–5 hydrosalpinx, 325, 325 infectious diseases, 326–7 non-infectious diseases, 324–5 visualization, 323–4, 324 febrile patients, obstetric scanning on, 31 feet gestational age estimation/prediction, 150 normal fetal anatomy at 18–22 weeks, 103, 104 femur gestational age estimation/prediction, 148, 148 normal fetal anatomy at 18–22 weeks, 102, 102, 103 short, 204 fertile women, normal ultrasound morphology ovaries, 288, 289 uterus, 286–8 fetal akinesia deformation sequence (FADS), 196, 279 fetal anomalies, 157–206 abdominal wall, 185–90 cardiac, 169–82 central nervous system, 160–6 chromosomal defects see chromosomal anomalies, fetal congenital, 157–60 craniofacial, 166–9 effect on fetal movements, 278–9 gastrointestinal tract, 185–90 hydrops fetalis, 198–9 maternal autonomy, 348 multiple pregnancies, 253 renal, 190–4 selective fetocide for, 244 skeletal, 194–7 thoracic, 182–4 tumours, 197–8 ultrasound accuracy in detecting, 204–6, 205 urinary tract, 190–4 see also specific anomaly fetal biometry, 141–54 aims of, 141 anomalies and syndromes, 154 biometric parameters, 146–50 abdominal size, 147, 147–8 crown–rump length, 146 data report, 150 gestational sac, 146 head measures, 146–7 limbs, 148, 148–9 other measurements and dating, 149, 149–50 biometric ratios, 151 coefficients of correlation, 143 confidence limits, 144 curvilinear regression analysis, 143 dating see gestational age 3D/4D imaging, 268–9 displaying data and curve fitting, 142–3 fetal growth evaluation see fetal growth evaluation
Index
ectopic heartbeats, 180 ectopic pregnancy cervical, 46, 73 early pregnancy failure, 73–4, 74 identification, 73 prevalence, 73 scanning with full bladder, 35 tubal, 324–5 edge shadows, 17, 18 elevation plane, 14, 15 Ellis–Va Creveld syndrome, 196 embryo early anomalies, 74–5 head width, 57, 60 measurements, 63–6, 63–7 placental localization, 114, 114–15 sensitivity to thermal effects, 25 sonoanatomic development, 58–61, 59–62 see also fetus embryo-fetoscopy, 242 embryonic pole, 58 encephalocele, 161 diagnosis, 162 incidence, 161 prognosis, 162–3 endometrioma, 316, 317 endometriosis, 319, 320 endometrium hyperplasia, 309–10 malignancy, 49, 309–10, 310 measuring the thickness of, 47, 47–8 menstrual cycle changes, 286–7, 287 ovulation, 48 polyps, 49, 308–9, 309, 310, 310 scanning routine, 47–9 thickness measurement, 286, 309 enhancement, 18, 18 epignathus, 197 epithelial ovarian tumours, 319–21 equipment, 37–9 see also specific item ethics, 339–49 autonomy, 342, 343 beneficence, 340–2, 343 competence, 347 confidentiality, 349 disclosure of results, 348–9 fetus as a patient, 343–6 referral, 347 routine screening of pregnant women, 347–8 euryopia, 168 examination table, 36, 37 exomphalos, 185 extraembryonic structures, 67, 67–8 extremities gestational age estimation/prediction, 148, 148–9 normal fetal anatomy at 18–22 weeks, 81, 102–4, 102–5 eye movements, fetal, 272, 276, 277
375
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩
376
fetal biometry—(Continued) fetal weight estimation, 150–1 F test, 143 linear regression analysis, 143 longitudinal and cross-sectional studies, 142 multiple pregnancies, 252 other parameters, 151 patient selection and study design, 142 prediction of date and size, 143–4 principles of, 141–4 reference values, 142 sample size, 142 fetal blood sampling (FBS), 229, 235–7 complications, 237 technique, 236, 236–7 fetal growth evaluation, 151–4 definition, 151–2 fetal growth restriction see fetal growth restriction (FGR) macrosomia see macrosomia screening and diagnostic strategies, 153 unsolved problems, 152 fetal growth restriction (FGR), 152, 153 ductus venosus flow, 220–2 fetal movements in, 279, 279–80 middle cerebral artery Doppler, 217, 218 multiple pregnancies, 247, 252 outcome parameters according to Doppler assessment, 222 prediction in twin pregnancies, 224 single umbilical artery (SUA) syndrome, 129 third trimester, 217, 218 umbilical artery Doppler, 215, 216 umbilical vein Doppler, 223 uterine artery flow, 212, 214 fetal heart rate (FHR), 57 abnormalities, middle cerebral artery velocity, 218 behavioural states, 276, 277 first trimester, 57, 59, 59, 61, 65–6, 66, 71 second trimester to term, 89 fetal hydrops see hydrops fetalis fetal movements, 271–82 abnormal conditions affecting, 278, 278–82 altered brain or muscular development, 278–9 drugs, medication, stress and fetal stimulation, 281–2 intrauterine growth retardation, 279, 279–80 maternal diabetes, 280 preterm contractions and/or rupture of membranes, 280, 280 behavioural states, 276–8, 277 body movements in normal pregnancy, 274–5, 275 breathing in normal pregnancy, 273, 276 emergence of patterns, 272–4, 273, 274 methodology, 272 fetal shunts, 238–42 complications, 241 delivery and shunt removal, 241 indications, 239 instrumentation, 240, 240
outcome, 242 techniques, 239–41 fetocide, selective for fetal abnormality, 244 fetoscopy, diagnostic and operative, 242 fetus acidaemia, 220 age see gestational age estimation/prediction anaemia see anaemia, fetal anatomical survey see second trimester, normal fetal anatomy behavioural states, 276–8, 277 blood flow evaluation, 209–24 blood transfusion see blood transfusion, fetal brain, scanning orientation, 41, 42 breathing movements, 44 dating see gestational age estimation/ prediction early anomalies, 74–5 ethics, 343–6 exam, 43–4, 115–16 see also (obstetric scanning) gender disclosure, 348 growth evaluation see fetal growth evaluation growth restriction see fetal growth restriction (FGR) head width, 57, 60 karyotyping, 201–2, 229–30 see also amniocentesis (AC); chorion villus sampling (CVS) lung fluid, 110 measurements, 63–6, 63–7 micturition, 277 moral status, 344–5 movements, 44 multiple pregnancies monitoring, 252 normal anatomy at 18–22 weeks see second trimester, normal fetal anatomy as a patient, 343–6 previability, 346 scanning see obstetric scanning sensitivity to thermal effects, 25 sonoanatomic development, 58–61, 59–62 stimulation, effect on fetal movements, 281–2 tissue warming, 24, 25 tone, 44 tumours, 197–8 urinary production, 110 viability, 345–6 weight estimation, 150–1 fever, obstetric scanning on patients with, 31 fibroblast growth factor receptor type 3 (FGFR3) gene, 195 fibroid polyps, 305, 308 fibroids cervical, 45–6 uterine see uterine fibroids fibromas, ovarian, 321–2, 322 fibrothecomas, ovarian, 321–2 fibula gestational age estimation/prediction, 148 normal fetal anatomy at 18–22 weeks, 103–4 first trimester, 57–77 bleeding, 69 description of the sonoanatomic development, 58–62, 59–62
✩✩✩✩✩✩✩✩✩✩✩ ✩
G
gallbladder, normal fetal anatomy at 18–22 weeks, 96, 97 gas body activation, 26 gas body effects of diagnostic ultrasound, 26 gas bubble contrast agents, 26 gastrointestinal tract anomalies, fetal, 185–90 gastroschisis, 185–6 genetic counselling, 230 genitalia, normal fetal anatomy at 18–22 weeks, 81, 101, 102 germ cell ovarian tumours, 323 gestational age estimation/prediction, 143–4, 144–6 accuracy, 145–6 biometric parameters, 146–50 conceptual age, 145 errors of measurements, 145
menstrual age, 145 multiple pregnancies, 248 gestational sac definition, 122 detection, 122 early pregnancy evaluation, 63, 67, 67, 69, 70 gestational age estimation/prediction, 146 gestational trophoblastic disease (GTD), 71–3, 124, 125, 125–6 see also choriocarcinoma; hydatidiform mole; placental tumours; gestational trophoblastic gloves, 38 Goldenhar syndrome, 168 Graafian follicles see follicles Grannum placental classification, 119 gut herniation, embryo/fetus, 60, 61, 62, 66 gynaecological anatomy, 285–96 gynaecological pathology ovaries, 313–23 tubes, 323–7 uterus, 299–310 see also specific pathology gynaecological scanning orientation, 39 routine, 45–9, 46–8 see also specific anatomical area
Index
diagnostic ultrasound during, 29–30 evaluation of early pregnancy failure, 69–75 early anomalies, 74–5 early pregnancy loss, 69–71, 71, 71–3, 72 ectopic pregnancy, 73–4, 74 extraembryonic structures, 67, 67–8 fetal movements, 273–4, 274 measurement of the embryo/early fetus, 63–6, 63–7 multiple pregnancy, 68, 69 placental location, 116 scanning routine, 43–4 standardisation of transvaginal and transabdominal imaging in gynaecology, 75–7, 76 ultrasound, multiple pregnancies, 248–52, 249, 250 umbilical vein Doppler imaging, 223 uterine artery Doppler, 214 flow velocities, 52 focal trophoblastic hyperplasia, 126 focusing, beam, 12–14, 13 follicles, 288, 289, 291–2 cysts, 318 follicle-stimulating hormone (FSH), 318 Fontan procedure, 173 forebrain cleavage see holoprosencephaly four-dimensional (4D) ultrasound, 259–69 glass body mode rendering, 268, 269 inversion mode rendering, 267, 267–8 maximum mode rendering, 265, 266 minimum mode rendering, 266, 267 real-time, 260 single plane of choice, multiplanar orthogonal planes or multiple tomographic parallel slices, 261–4, 262–4 spatial and temporal image correlation, 260–1 surface mode rendering, 264–5, 265 volume acquisition, 260–1 volume calculation, 268–9 volume data display, 261–9 free pelvic fluid, 51 frequency levels, 2, 4, 5 frontal bone scalloping, 162 F test, 143 funipuncture see fetal blood sampling (FBS)
H
habituation, 281–2 haemangioma fetal hepatic, 197 placental, 124, 124–5 umbilical cord, 130 haematoma intrauterine, 70, 71, 121 placental, 127, 128 umbilical cord, 130–1 haematometra, 49 hamartoma, fetal mesenchymal, 197 renal, 198 handedness and ultrasound, 27 hands, normal fetal anatomy at 18–22 weeks, 103, 104 head circumference (HC), embryo/fetus, 64, 80, 147 head width, embryo/fetus, 57, 60, 63, 64, 64, 65, 146–7 heart defects, 169, 169–82, 170 (see also specific defect) echogenic foci, 180, 204 normal fetal anatomy at 18–22 weeks, 81, 88–94, 90–4 univentricular, 172–3 ventricles, normal fetal anatomy at 18–22 weeks, 90, 92 see also entries beginning cardiac heart rate, fetal see fetal heart rate (FHR) hepatoblastoma, fetal, 197 hernia, diaphragmatic, 183–4 heterotaxy, 95, 171–2 hiccups, fetal, 273–4 history taking, 38
377
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩ holoprosencephaly, 160, 163–4 alobar, 163 lobar, 163–4 semilobar, 164 human chorionic gonadotropin (hCG), 318 beta, 72 ectopic pregnancy, 73 maternal serum, 125–6 humerus gestational age estimation/prediction, 148 normal fetal anatomy at 18–22 weeks, 102, 102 hydatidiform mole, 71–3, 72, 121 complete, 71, 72, 72, 125–6 invasive, 71, 72 partial, 71, 72, 125, 126 hydranencephaly, 165–6 hydrocephalus, 82 hydrometra, 49 hydronephrosis, 192–3, 204 hydrops fetalis, 198–9 and chorioangiomas, 124 ductus venosus blood flow, 222 pleural effusions, 183 hydrosalpinx, 325, 325 hydrosonography see saline infusion sonography hydroureteronephrosis, 193 hyperechogenic bowel, 204 hyperechogenic lungs, 182–3 hyperreactio luteinalis, 125, 318 hypertelorism, 168 hypoplastic left heart syndrome, 174–5 hypotelorism, 168 hystero-contrast salpingosonography (HyCoSy), 285, 293–6, 295 procedure, 293–5 prophylactic antibiotics, 295 timing of examination, 293 uterus abnormalities, 300 hysteroscopy, uterine fibroids, 305
I
378
iliac bone, gestational age estimation/prediction, 150 imaging in medicine, 75–7, 76 inclusion cysts, 289, 290 infantile polycystic kidneys, 191–2 infarcts, placental, 121, 126–7 inferior vena cava, 92–3 infertility intramural uterine fibroids, 306 submucosal uterine fibroids, 306 informed consent, 347–8 infrasound, 2 instrumentation see physics and instrumentation; specific instrument intensity, sound waves, 4 interocular diameter (IOD), 86 interruption of the aortic arch, 173–4 interstitial pregnancy, 73 interventricular septum, 90 intestinal obstruction, 188–9 intracranial tumours, fetal, 197 intrauterine fetal blood transfusion see blood transfusion, fetal
intrauterine growth retardation (IUGR) see fetal growth restriction (FGR) intrauterine haematoma, 70, 71, 121 invasive procedures in obstetrics, 229–44 asepsis, 232 counselling, 230 multiple pregnancies, 251–2 procedures, 232–44 training, 230–2, 231 see also specific procedure in vitro fertilization, 331 irregular uterine bleeding, 49 isomerism, 171–2
J
Jeune syndrome, 196
K
karyotyping, fetal, 201–2, 229–30 see also amniocentesis (AC); chorion villus sampling (CVS); fetal blood sampling (FBS) kidneys cystic, 191–2 fetal anomalies, 190, 190–2 normal fetal anatomy at 18–22 weeks, 98–9, 99, 100 see also entries beginning renal
L
labia, normal fetal anatomy at 18–22 weeks, 101, 102 lambda sign, 68, 250, 250 large bowel, normal fetal anatomy at 18–22 weeks, 97 large for gestational age (LGA), 152 last menstrual period (LMP), gestational age estimation/prediction, 145 lateral plane, 14, 15 lateral resolution, 16 latex allergy, 38 left isomerism, 171–2 legal claims see medico-legal implications of ultrasound leiomyomata see uterine fibroids lemon sign, 162 limb deficiency, 196 limbs see extremities linear regression analysis, 143 litigation see medico-legal implications of ultrasound liver cysts, 190 normal fetal anatomy at 18–22 weeks, 96, 97, 97 tumours, fetal, 197 loculated pelvic fluid, 51 longitudinal sound waves, 3–4 longitudinal studies, fetal biometry, 142 lung fluid, fetal, 110 lungs cystic, 182–3 hyperechogenic, 182–3 normal fetal anatomy at 18–22 weeks, 81, 94–5 luteinizing hormone (LH), 318
✩✩✩✩✩✩✩✩✩✩✩ ✩
M
after fetal shunts, 241 early anomalies, 74–5 early pregnancy loss, 69–71, 71, 71–3, 72 ectopic pregnancy, 73–4, 74 evaluation of early, 69–75 multiple pregnancies, 253 rates, 57 risk, 230, 230 uterine anomalies, 300–1 mitral valve, normal fetal anatomy at 18–22 weeks, 90 M-mode, 9, 11 ectopic heartbeats, 180 fetal heart beat, 66, 66 spatial-peak temporal-average intensity, 23 moles, 71–3 monoamniotic (MA) twins, 68, 247, 250, 256 monochorionic (MC) twins, 68, 248 diagnosis, 250 fetal monitoring, 252 twin–twin transfusion syndrome (TTTS), 253 morality, 340 Morrison pouch, fluid in, 51 mucinous ovarian tumours, 320–1, 322 multicystic kidneys, 191 multiplanar mode, 3D/4D imaging, 261–4, 262 multiple pregnancy, 247–56 amniocentesis in, 235 chorion villus sampling in, 233–4 determination of chorionicity and amnionicity, 68, 69 diamniotic (DA) twins, 68, 248 dichorionic (DC) twins, 68, 248 Doppler ultrasound, 223–4 first-trimester ultrasound, 248–52 chorionicity and amnionicity, 249, 250, 250–1 invasive diagnostic procedures, 251–2 nuchal translucency, 251 number of fetuses, 248–9, 249 pregnancy dating, 248 growth discrepancy and fetal monitoring, 252 higher order multiple pregnancies, 256 malformations and fetal demise, 253 monoamniotic (MA) twins, 68, 247, 250, 256 monochorionic (MC) twins see monochorionic (MC) twins mortality and morbidity, 247–8 reduction, 243–4 selective fetocide for fetal abnormality, 244 twin reversed arterial perfusion, 224, 248, 255, 255 twin–twin transfusion syndrome see twin–twin transfusion syndrome (TTTS) myelomeningocele, 162, 162 myoma, submucosal, 49 myometrium calcified blood vessels, 289, 289 normal ultrasound morphology, 286 scanning routine, 46, 46–7
Index
macrosomia, 153–4 definition, 152 risk factors, 153 Majewski syndrome, 196 malignant tumours adnexal, 314 childhood, 27 endometrial, 309–10 ovarian, 53, 313–15 maternal age, chromosomal defects risk, 202, 203 maternal diabetes, effect on fetal movements, 280 maternal emotions effect on fetal movements, 281 and fetal behavioural states, 277 maternal serum human chorionic gonadotropin (MShCG), 125–6 mean abdominal diameter (MAD), 65, 65 mechanical index (MI), 22, 29 meconium ileus, 188, 189 meconium peritonitis, 189 median cleft syndrome, 168 medical litigation see medico-legal implications of ultrasound medication, effect on fetal movements, 281–2 medico-legal implications of ultrasound, 333–8 defending a claim, 337 documentation, 337–8 legal process, 334 recording images, 337 reducing the risk of litigation, 335–6 trial process, 335 mega cisterna magna, 164 megacystis, 193, 194, 239 megacystis-microcolon-intestinal hypoperistalsis syndrome (MMIHS), 193 megapascals (MPa), 22 meningocele, 162 menopausal transition, uterus and ovaries in, 290–1 menstrual cycle endometrial polyps during, 308 ovarian changes during, 288, 289 uterine and ovarian vascularization, 291 uterus during, 286–7, 287 mesencephalon, 60 mesenchymal tumours, placental, 124, 124–5 mesenteric cysts, 190 mesoblastic nephroma, 198 microcephaly, 154, 165 microphthalmia, 168–9 micturition, fetal, 277 middle abdominal diameter (MAD), 147–8 middle cerebral artery, 217 middle cerebral artery Doppler, 217–19, 219, 220, 222 fetal anaemia, 217, 218–19 fetal growth restriction, 217, 218 twin pregnancies, 224 miscarriage, 69–75 after amniocentesis, 235 after chorion villus sampling, 234 after fetal blood sampling, 237
N
Nabothian (inclusion) cysts, 45 nasal bone absent or hypoplastic, 203 ossification, 75
379
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩ Naumoff syndrome, 196 neck cervical teratomas, 197 normal fetal anatomy at 18–22 weeks, 81, 85–7, 85–7 nephroblastoma, fetal, 198 neural tube defects, 161–3 fetal karyotyping, 202 see also specific defect neuroblastoma, fetal, 198 Noonan syndrome, 173 Norwood repair, 175 nuchal cord complications, 131 nuchal fold, 87, 203 nuchal oedema, 203 nuchal translucency (NT), 74, 87, 233–4, 251
O
380
obstetrics, invasive procedures in see invasive procedures in obstetrics; specific procedure obstetric scanning biophysical profile, 44–5 orientation, 39 routine, 43–5 occipitofrontal diameter (OFD), 64, 147 see also head width, embryo/fetus ocular defects, 168–9 OEIS complex, 186–7 oesophageal atresia, 187 oligohydramnios, 109, 112–13 intrauterine growth retardation, 153 renal agenesis, 190 omental cysts, 190 omphalocele, 185 orbital diameter (OD), 86, 86 orbits defects, 168–9 normal fetal anatomy at 18–22 weeks, 86, 86 organ-oriented scanning, 41, 42 orientation, 39–42, 40–3 ossification embryo/fetus, 61, 66–7 nasal bone, 75 osteogenesis imperfecta, 195 outer orbital diameter (OOD), 86 ovarian cysts complex, 315 cyst wall and septal wall thickness, 315–16 dermoid, 323 dysfunctional, 318 echo-dense foci and acoustic shadowing, 316 endometrioma, 316, 317 fetal, 190 general considerations, 313–15 postmenopausal women, 289, 290 simple, 315 size, 315 structure, 315 ovarian follicles see follicles ovarian tumours, 313–17, 317–23 benign and malignant cysts, 313–15 cyst wall and septal wall thickness, 315–16 echo-dense foci and acoustic shadowing, 316 echogenicity, 316
epithelial, 319–21 fibromas, 321–2, 322 fibrothecomas, 321–2 germ cell, 323 malignant, 53, 314 morphology scoring systems, 316–17 mucinous, 320–1, 322 screening, 53, 314 serous, 319, 320, 321 teratomas, 323 tumour size, 315 tumour structure, 315 see also ovarian cysts; specific tumour ovarian volume, 286 ovaries anatomy, 49–50 dominant, 288, 291 mass, 50 normal ultrasound morphology in menopausal transition, 290–1 postmenopausal women, 288–9, 290 women of fertile age, 288, 289 vascularization as assessed by Doppler ultrasonography, 291, 291–2 ovulation endometrium during, 48 gestational age estimation/prediction, 145
P
paternalism, 341 patient information, 35–6, 339–49 peak systolic velocities (PSV), middle cerebral artery, 217, 218–19, 219 peak velocity index for veins (PVIV), 211, 212, 220 pedicle sign, 308–9, 309 pelvic fluid, 51, 51 pelvic inflammatory disease, 326, 326, 330 pelvic scanning, orientation, 39, 40 penis, normal fetal anatomy at 18–22 weeks, 101, 102 pentalogy of Cantrell, 185 peritoneal fluid, scanning routine, 51, 51 peritonitis, meconium, 189 persistent common atrioventricular canal, 171 physics and instrumentation, 1–19, 14–16 artifacts, 17–19, 18–19 history of ultrasound, 2–3 measurement, 16 resolution, 14–16, 15 sound, 2 sound waves and propagation, 3–9, 4, 6–9, 11 time gain compensation, 16–17, 17 transducers, 9–11, 10, 11 ultrasound beam, 11–14, 12–13 piezoelectric material, 5–6 placenta assessment, 121–7 congenital abnormalities, 122–6 cysts, 118 development evaluation, 115 functional anatomy, 115 grading, 119 haematoma, 127, 128
✩✩✩✩✩✩✩✩✩✩✩ ✩ effect on fetal movements, 280, 280 intrauterine haematoma, 121 oligohydramnios, 113 prenatal informed consent for sonogram (PICS), 348 preterm birth (PTB) categories, 133–4 causes of, 134 morbidity and mortality, 133 preterm contractions, effect on fetal movements, 280, 280 preterm delivery (PTD), 133–4 after fetal shunts, 241 prediction by transvaginal ultrasound of the cervix, 134–6, 135 preterm labour (PTL) definition, 133 judgement using transvaginal ultrasound of the cervix, 136–7 preterm prelabour rupture of membranes (PPROM), 133, 137 primum atrial septal defect, 170, 171 probes, cleaning, 38 pseudocysts, 130 pseudogestational sac, 324 pulmonary artery, 93, 93, 94 pulmonary atresia, 175, 177–8, 178 pulmonary hypoplasia, 183, 184 pulmonary stenosis, 175, 177, 178 pulmonary valve, absent, 178 pulsatility index for veins (PIV), 211, 212, 220 pulsatility index (PI), 52, 211, 211, 330 pulsed Doppler ectopic heartbeats, 180 tetralogy of Fallot, 178 uterine artery, 212 pyelectasia, 192 pyeloureteral junction obstruction, 239 pyometra, 49 pyosalpinx, 326, 326
Index
infarcts, 121, 126–7 localization, 109, 114–19, 122 embryology, 114, 114–15 indications, 115–18, 116–18 placental morphology, 118–19, 119 major structural abnormalities, 122–7 morphology, 118–19 secondary abnormalities, 126–7 thrombosis, 121, 126–7 tumours see placental tumours various locations of, 116–17, 116–18 vascular abnormalities, 121, 126–7 placenta accreta, 121, 123 placenta extrachorialis, 122–3 placental abruption, uterine artery flow, 212 placental lakes, 118, 119 placental tumours, 124–6 gestational trophoblastic, 125–6 mesenchymal, 124, 124–5 placenta percreta, 123 placenta praevia, 118 placenta velamentosa, 128 pleural effusions, 183 polydactyly, 196 polyhydramnios, 113 chorioangiomas, 124 diaphragmatic hernia, 184 epignathus, 197 fetal akinesia deformation sequence, 196 intestinal obstruction, 188–9 oesophageal atresia, 187 pleural effusions, 183 sacrococcygeal teratoma, 198 polyploidy, maternal age risk, 202 polyps bladder, 52 endometrial, 49, 308–9, 309, 310, 310 fibroid, 305, 308 polysplenia, 95, 171–2 porencephaly, 165, 166 posterior urethral valves, 193 postmenopausal women normal ultrasound morphology ovaries, 288–9, 290 uterus, 288–9, 290 ovarian cysts, 289, 290 pouch of Douglas, 285, 292, 292 pre-eclampsia prediction in twin pregnancies, 224 uterine artery flow, 212, 214 pregnancy cervical see cervical pregnancy Doppler ultrasound indications, 210 ectopic see ectopic pregnancy first trimester see first trimester interstitial see interstitial pregnancy loss see miscarriage; specific reason/issue multiple see multiple pregnancy reduction in multifetal pregnancies, 243–4 routine screening in, 347–8 second trimester see second trimester third trimester see third trimester premature rupture of the membranes (PROM), 134
Q
quartz crystal, 5–6, 10
R
radar, 3 radiation pressure, 21, 27 radius gestational age estimation/prediction, 148–9 normal fetal anatomy at 18–22 weeks, 105 recessive autosomal mutations, 159 recording images, 38 referral, 347 renal agenesis, 190, 190–1 bilateral, 191 unilateral, 191 renal arteries, 100 renal medullae, normal fetal anatomy at 18–22 weeks, 100 renal pelvis, normal fetal anatomy at 18–22 weeks, 101 resistance index (RI), 52, 211, 211 adnexal masses, 330 uterine sarcoma, 306
381
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩ resolution, 14–16, 15 respiratory tree obstruction, 182 retained products of conception, 49 reverberation, 19, 19 reversed end–diastolic flow (REDF), umbilical artery, 215–17, 216 right isomerism, 171–2 risks see biological effects and safety aspects
S
382
sacrococcygeal teratoma, 198 sacrum, gestational age estimation/prediction, 150 safety aspects see biological effects and safety aspects Saldino–Noonan syndrome, 196 saline infusion sonography, 285, 293, 294 endometrial hyperplasia and malignancy, 309–10 endometrial polyps, 308 uterine fibroids, 305–6 salpingitis acute, 50, 326 chronic, 50 sarcoma, uterine, 306–7 scanning techniques, 33–54 bimanual pelvic examination, 36–7 colour Doppler studies see colour Doppler empty or full bladder, 34, 34–5 equipment, 37–9 examination table, 36, 37 general aspects, 34 orientation, 39–42, 40–3 patient information, 35–6 scanning routine, 42–52 adnexal masses, 49–50 gynaecological scanning, 45–9, 46–8 obstetric scanning, 43–5 peritoneal fluid, 51, 51 urinary bladder, 51–2, 52 screening for ovarian masses, 53 transperineal and transrectal, 53–4 ultrasound-guided puncture procedures, 54 scapula gestational age estimation/prediction, 150 normal fetal anatomy at 18–22 weeks, 104 scattergrams, 143 schizencephaly, 165, 166 screening fetal growth evaluation, 153 ovarian masses, 53, 314 routine, in pregnancy, 347–8 scrotum, normal fetal anatomy at 18–22 weeks, 101, 102 S/D (systolic/diastolic) ratio, 211, 211 second trimester diagnostic ultrasound during, 30 normal fetal anatomy, 79–105, 81 abdomen, 81, 95–7, 95–7 anterior abdominal wall, 97–8, 98–9 brain/calvarium, 80–5, 81, 82–3 face and neck, 81, 85–7, 85–7 genitalia, 81, 101, 102 heart, 88–94, 90–4
lungs and thorax, 81, 94–5 scan guidelines, 80 skeleton and extremities, 81, 102–4, 102–5 spine, 81, 87–8, 88, 89 urinary tract, 81, 98–101, 99–100 placental location, 116–17, 116–17 risk assessment of chromosomal aberrations, 201–4 uterine artery Doppler, 214, 214 seizures, fetal, 278 septum secundum, 170 serial ultrasonography, leiomyomata, 46–7 serous ovarian tumours, 319, 320, 321 sex chromosome abnormalities, 199, 200, 202 short limb polydactyly syndromes, 196 shunts see fetal shunts single umbilical artery (SUA) syndrome, 128–9, 129 situs inversus, 95 skeletal dysplasia, 194–6, 202 skeleton fetal anomalies, 194–6 normal fetal anatomy at 18–22 weeks, 81, 102–4, 102–5 sleep, fetal, 281 sliding organs sign, 45 small bowel normal fetal anatomy at 18–22 weeks, 97 obstruction, 188 small for gestational age (SGA) definition, 152 multiple pregnancies, 252 umbilical artery Doppler, 215 snow-storm appearance, 72, 72, 125 soft markers, chromosomal defects, 202, 203, 205–6 sonar, 3 sonohysterography, uterine changes in patients taking tamoxifen, 48 sonoporation, 26 sound, 2 sound waves, 3–9, 4 propagation, 3–9 pulse, 6, 7 wavelength, 5, 5 spatial and temporal image correlation (STIC), 260–1, 266 spatial-peak temporal-average intensity, 22, 23 spectral Doppler, spatial-peak temporal-average intensity, 23, 23 spina bifida, 161, 161 closed, 162 diagnosis, 162, 162 incidence, 161 prognosis, 163 spine, embryo/fetus first trimester, 60, 61 second trimester, 81, 87–8, 88, 89 spleen, normal fetal anatomy at 18–22 weeks, 97 spontaneous abortion, 69 startle movements, fetal, 273–4 stenopia, 168 steroids, atrioventricular block, 182 stomach, embryo/fetus first trimester, 60 second trimester, 95–6
✩✩✩✩✩✩✩✩✩✩✩ ✩
T
tachyarrhythmias, 180–1, 222 tamoxifen, uterine changes, 48 Taussig–Bing anomaly, 177 techniques see scanning techniques; specific techniques teratology, thermal, 25 teratomas cervical, fetal, 197 fetal, 197 intracranial, fetal, 197 ovarian, 323 sacrococcygeal, fetal, 198 umbilical cord, 130 tetralogy of Fallot, 177–8 thalami, normal fetal anatomy at 18–22 weeks, 82 thanatophoric dysplasia, 194–5 theca-lutein cysts, 125, 318 thecomas, ovarian, 321–2 thermal index (TI), 22, 28–9 bone at depth (TIB), 28–9 bone at the surface (TIC), 28–9 soft tissue (TIS), 28–9 thermal teratology, 25 third trimester diagnostic ultrasound during, 30 fetal growth restriction, 217, 218 thoracoamniotic shunts, 183 thorax fetal anomalies, 182–4 (see also specific anomaly) normal fetal anatomy at 18–22 weeks, 81, 94–5 threatened abortion, 69 three-dimensional (3D) ultrasound, 259–69 endometrium, 48, 48 glass body mode rendering, 268, 269 in gynaecology, 329 inversion mode rendering, 267, 267–8 maximum mode rendering, 265, 266 minimum mode rendering, 266, 267 orientation, 41–2, 43 real-time, 260 single plane of choice, multiplanar orthogonal planes or multiple tomographic parallel slices, 261–4, 262–4 spatial and temporal image correlation, 260–1 static, 260 surface mode rendering, 264–5, 265 uterine abnormalities, 300, 301, 310 uterine fibroids, 306 uterus, 48, 48 volume acquisition, 260–1
volume calculation, 268–9 volume data display, 261–9 thrombosis placenta, 121, 126–7 umbilical cord, 130–1 tibia gestational age estimation/prediction, 148 normal fetal anatomy at 18–22 weeks, 103–4 time gain compensation (TGC), 16–17, 17 tissue warming, 23–6, 25 tomographic ultrasound imaging (TUI), 261, 263–4 tracheal obstruction, 184 tracheo-oesophageal fistula, 187 training, invasive obstetric procedures, 230–2, 231 transabdominal puncture procedures, 54 transabdominal sonography (TAS) full or empty bladder, 34, 34–5 gynaecological examination, 285 orientation, 39 patient information, 35 standardization of imaging in gynaecology, 75–7, 76 transducers, 9–11, 11 fetal movement observation, 272 self-heating, 24 translabial scanning, 53–4 transperineal scanning, 53–4 transposition of the great arteries, 176 transrectal scanning, 36, 53–4 transvaginal puncture procedures, 54 transvaginal sonography (TVS) adenomyosis, 308 bimanual pelvic examination preceding, 36–7 cervix examination see cervix, transvaginal ultrasound examination contraindications, 36 endometriosis, 319 full or empty bladder, 34–5 gynaecological examination, 285 indications, 314 orientation, 39, 40, 41 ovarian cancer, 53 patient information, 35 standardization of imaging in gynaecology, 75–7, 76 uterine abnormalities, 310 transversal waves, 3 transverse cerebellar diameter (TCD), 149, 149 tricuspid valve atresia, 172 dysplasia, 179–80 normal fetal anatomy at 18–22 weeks, 90 regurgitation, 216 triploidy, 199, 200, 200–1 trisomy 13, 199, 200, 200–1 fetal karyotyping, 202 maternal age risk, 202, 203 single umbilical artery (SUA) syndrome, 129 trisomy 18, 199, 200–1 fetal karyotyping, 202 maternal age risk, 202, 203 single umbilical artery (SUA) syndrome, 129 soft markers, 204
Index
stones, bladder, 52 stress, effect on fetal movements, 281–2 stuck twin phenomenon, 253, 254 subseptate uterus, 300, 302, 302 sucking movements, fetal, 273 superior vena cava, 92–3, 93 supraventricular tachycardia, 180, 181 swallowing movements, fetal, 273 Swiss cheese appearance, 125 systolic/diastolic ratio, 211, 211
383
Index
✩ ✩✩✩✩✩✩✩✩✩✩✩ trisomy 21, 199, 200–1 echogenic foci, 180 maternal age risk, 202, 203 nasal bone ossification, 75 nuchal fold, 87 soft markers, 203–4 trophoblast, placental development, 114 trophoblastic disease, gestational, 71–3, 124, 125, 125–6 see also choriocarcinoma; hydatidiform mole; placental tumours, gestational trophoblastic truncus arteriosus, 178–9 truncus arteriosus communis, 170 tubal pregnancy, 324–5 tubes see fallopian tubes tubo-ovarian abscess, 326 tubular hypoplasia of the aortic arch, 173–4 tumours fallopian tube, 325 fetal, 197–8 ovarian see ovarian tumours placental see placental tumours umbilical cord, 129–30, 130 Turner syndrome, 173, 199, 200, 200–1, 202 twin reversed arterial perfusion (TRAP) sequence, 224, 248, 255, 255 twins diamniotic (DA) twins, 68, 248 dichorionic (DC) twins, 68, 248 Doppler imaging in, 223–4 monoamniotic (MA) twins, 68, 247, 250, 256 monochorionic (MC) twins see monochorionic (MC) twins see also multiple pregnancy twin–twin transfusion syndrome (TTTS), 248, 253–5, 254 causes, 253 diagnosis, 253 Doppler imaging, 223–4 embryo-fetoscopy complications, 242 nuchal translucency, 251 therapy, 254–5
U
384
ulna gestational age estimation/prediction, 148–9 normal fetal anatomy at 18–22 weeks, 105 ultrasound beam, 11–14 focusing, 12–14, 13 near field and far field, 11–12, 12 tissue warming, 24 ultrasound-guided fetal blood sampling see fetal blood sampling (FBS) ultrasound-guided puncture procedures, 54 umbilical arteries, 98 Doppler, 214–17, 216, 222, 224 single umbilical artery (SUA) syndrome, 121, 128–9, 129 umbilical cord abnormal position, 131 congenital abnormalities, 128–30 haematoma, 130–1 looping, 131
major structural abnormalities, 127–31 secondary abnormalities, 130–1 thrombosis, 130–1 tumours, 129–30, 130 vascular abnormalities, 130–1 umbilical cord insertion abnormal, 121, 128 fetal blood sampling, 236, 236–7 site, 97–8, 98 umbilical vein, 96–7, 97, 223 univentricular heart, 172–3 ureteropelvic junction obstruction, 192 ureters, fetal enlarged, 193 patency, 52, 52 urethra, 51 urethral obstruction, 193–4, 239 urethral valves, posterior, 193 urethrovesical junction, 52 urinary production, fetal, 110 urinary tract 3D/4D imaging, 267, 268 fetal anomalies, 101, 192–4 fetal enlargement, 192–4 normal fetal anatomy at 18–22 weeks, 81, 98–101, 99–100 uterine artery Doppler, 209–10, 212–14, 213, 214 uterine contractions fetal behavioural states, 277 preterm, effect on fetal movements, 280, 280 uterine fibroids, 46, 46–7, 303, 303–6, 305 classification, 305 clinical presentation, 303 degeneration, 304 diagnosis, 304 intramural, 303, 304, 306 location, 304 pedunculated, 304 submucosal, 46, 46, 304–5, 305, 306 subserous, 304 ultrasound appearance, 303, 303–4 uteroplacental blood flow evaluation, 209–24 uterus anomalies, 49 arcuate, 300, 301, 302 bicornuate, 300, 302 congenital anomalies, 299–303, 301, 302, 302 diameter measurement, 285 length measurement, 286 menstrual cycle changes, 286–7, 287 normal ultrasound morphology in menopausal transition, 290–1 postmenopausal women, 288–9, 290 women of fertile age, 286–8 sarcoma, 306–7 scanning routine, 45 size in nulliparous women, 287 subseptate, 300, 302, 302 three-dimensional (3D) ultrasound, 48, 48 vascularization as assessed by Doppler ultrasonography, 291, 291–2 width measurement, 285–6 see also endometrium; myometrium
✩✩✩✩✩✩✩✩✩✩✩ ✩
V
vesicoureteric reflux, 192 vestigial cysts, 130 VOCAL software, 269
W
wavelength, 5, 5 Wilms tumour, fetal, 198
Index
vaginal bleeding first trimester, 69 partial hydatidiform mole, 126 vascular anastomosis, 224 twin reversed arterial perfusion (TRAP) sequence, 255 twin–twin transfusion syndrome, 253 vascular chorioangiomas, 121, 124, 124–5 VATER association, 187 ventricles, embryo/fetus cerebral, 60, 61, 83, 84 heart, 90, 92 ventricular septal defect, 170, 170–1 ventricular septum, normal fetal anatomy at 18–22 weeks, 90–1, 91, 94 ventricular tachycardias, 181 ventriculomegaly, 160, 163
X
X-linked disorder, 159
Y
yolk sac alteration, 61 appearance, 58, 59 diameter, 57, 67, 67, 68 early pregnancy evaluation, 70
385
