PRENATAL DIAGNOSIS OF CONGENITAL ANOMALIES Roberto Romero, M.D. Associate Professor of Obstetrics and Gynecology Director of Perinatal Research Yale University School of Medicine New Haven, Connecticut Gianluigi Pilu, M.D. Attending Physician Section of Prenatal Pathophysiology Second Department of Obstetrics and Gynecology University of Bologna School of Medicine Bologna, Italy Philippe Jeanty, M.D. Assistant Professor Department of Radiology Vanderbilt University Nashville, Tennessee Alessandro Ghidini, M.D. Research Fellow Department of Obstetrics and Gynecology Yale University School of Medicine New Haven, Connecticut John C. Hobbins, M.D. Professor of Obstetrics and Gynecology and Diagnostic Imaging Yale University School of Medicine Director of Obstetrics Yale-New Haven Hospital New Haven, Connecticut APPLETON & LANGE Norwalk, Connecticut/San Mateo, Califomia ©1987-2002 Romero-Pilu-Jeanty-Ghidini-Hobbins 0-8385-7921-3 Notice: Our knowledge in clinical sciences is constantly changing. As new information becomes available, changes in treatment and in the use of drugs become necessary. The author(s) and the publisher of this volume have taken care to make certain that the doses of drugs and schedules of treatment are correct and compatible with the standards generally accepted at the time of publication. The reader is advised to consult carefully the instruction and information material included in the package insert of each drug or therapeutic agent before administration. This advice is especially important when using new or infrequently used drugs. Copyright © 1988 by Appleton & Lange A Publishing Division of Prentice Hall All rights reserved. This book, or any parts thereof, may not be used or reproduced in any manner without written permission. For information, address Appleton & Lange, 25 Van Zant Street, East Norwalk, Connecticut 06855. 88 89 90 91 92 / 10 9 8 7 6 5 4 3 2 1 Prentice-Hall of Australia, Pty. Ltd., Sydney Prentice-Hall Canada, Inc. Prentice-Hall Hispanoamericana, S.A., Mexico Prentice-Hall of India Private Limited, New Delhi Prentice-Hall International (UK) Limited, London Prentice-Hall of Japan, Inc., Tokyo Prentice-Hall of Southeast Asia (Pte.) Ltd., Singapore Whitehall Books Ltd., Wellington, New Zealand Editora Prentice-Hall do Brasil Ltda., Rio de Janeiro Library of Congress Cataloging-in-Publication Data Prenatal diagnosis of congenital anomalies. Includes index. 1. Prenatal diagnosis. 2. Fetus---Abnormalities --- Diagnosis. I. Romero, Roberto. [DNLM: 1. Abnormalities ---diagnosis. 2. Fetal Diseases--diagnosis. 3. Prenatal Diagnosis---methods. QS 675 P926] RG628.P74 1987 618.2'2 87-14557 ISBN 0-8385-7921-3 Production Editor: Donald L. Delauter Design: M. Chandler Martylewski PRINTED IN THE UNITED STATES OF AMERICA ©1987-2002 Romero-Pilu-Jeanty-Ghidini-Hobbins The Central Nervous System Normal Sonographic Anatomy of the Porencephaly/ 50 Fetal Central Nervous System/ 1 Hydranencephaly/ 52 HYDROCEPHALUS/ 21 Microcephaly/ 54 Aqueductal Stenosis/ 24 Holoprosencephaly/ 59 Communicating Hydrocephalus/ 27 Inienecphaly/ 65 Dandy-Walker Malformation/ 30 Agenesis of the Corpus Callosum/ 67 Choroid Plexus Papilloma/ 34 Lissencephaly/ 70 NEURAL TUBE DEFECTS/ 36 Intracranial Arachnoid Cysts/ 71 Spina Bifida/ 36 Intracranial Tumors/ 73 Anencephaly/ 43 Acrania/ 75 Cephalocele/ 46 Choroid Plexus Cyst/ 76 Aneurysm of the Vein of Galen/ 77 Normal Sonographic Anatomy of the Fetal Central Nervous System INTRACRANIAL ANATOMY tional ages is critical for the recognition of congenital anomalies. The objective of the sonographic examination of the fetal central nervous system (CNS) is to reconstruct with a Axial Planes two-dimensional tool a complex three-dimensional Axial planes are obtained by scanning the head of the structure.In this effort, the larger the number of scanning fetus at an angle of about 20 degrees to the canthomeatal planes obtained, the more accurate the representation will line.9 Four different levels are commonly used (Fig. 1-2), appear.The three planes traditionally used for such an The first scanning plane passes through the bodies of the evaluation are the axial, sagittal, and coronal (Fig. 1-1). lateral ventricles. In Figure 1-3A, the different The sonographer should be aware that important appearances of this view throughout gestation can be developmental changes occur in the fetal brain well after seen. At 16 weeks, the lateral ventricles occupy most of the end of embryogenesis and up to the third trimester. the relative hemispheres and are partially filled with the The lateral ventricles and subarachnoid cisterns decrease echogenic choroid plexuses. At midgestation, the size of steadily in size throughout gestation, resulting not only in the lateral ventricles has considerable diminished, but in a geometric modification of the cerebral structures but many cases it is still possible to observe the two walls also in important changes in the sonographic appearance that line the ventricular cavity on both sides. During the of the fetal brain. During the early second trimester, the third trimester, only the lateral wall can be visualized. fluid-filled lateral ventricles are large. This causes The distance between the midline echo and the lateral enhancement of sound transmission, and the distal wall of the ventricle is now approximately one third of cerebral cortex appears more echoic than later in the hemispheric width. This value will remain constant gestation. Familiarity with the normal ultrasound throughout life (Fig. 1-3B). appearance of the fetal brain in different scanning planes The axial view has been used to derive nomograms for and at different gesta- the normal size of the ventricles The ©1987-2002 Romero-Pilu-Jeanty-Ghidini-Hobbins 2 THE CENTRAL NERVOUS SYSTEM or 19th week, the temporal lobe is convex and the lobe of the insula is apposed to the calvarium. In the following weeks, the insula deepens medially while the adjacent frontal and temporal lobes (so-called opercula) move progressively closer to each other, forming the sylvian fissure. The beginning of sylvian fissure demarcation is already visible at 22 weeks of gestation, However, it is not until 32 to 34 weeks of gestation that the opercularization is complete3 (Fig. 1-7). The third axial section corresponds to the biparietal diameter level (Fig. 1-8A,B). In this scanning plane, the thalami appear as two triangular echo-free areas. Between the thalami, the slitlike third ventricle can be seen. It is sometimes possible to visualize a cross-section of the aqueductus of Sylvius posterior to the third ventricle. On both sides of the thalami, the hippocampal gyrus appears as a circular space delineated medially by the ambient cistern and laterally by the atrium of the lateral ventricle. Anterior to the Figure 1-1. Schematic representation of the scanning planes used thalami, it is possible to visualize the frontal horns of the for the study of fetal cerebral anatomy: (1) axial, (2) sagittal, and lateral ventricles. During the (3) coronal. ratio between the distance from the midline echo to the lateral ventricular wall (lateral ventricular width, LVW)and the hemispheric width (HW) measured from the midline echo to the inner echo of the calvarium is illustrated in Figure 1-4. Tables 1-1 and 1-2 are the corresponding nomograms. It should be stressed that after the 20th week of gestation, the choroid plexus is considerably reduced in size. It is no longer observes in the previously described axial plane and can only be imaged in a lower section (Fig. 1-5A,B). Because the lateral ventricles diverge inferiorly and posteriorly, the measurement of the LVW:HW ratio at this level would result in a falsely elevated value. Therefore, this measurement should not be taken in a section that displays the choroid plexus later than 20 weeks of gestation. Furthermore, in normal fetuses, it is usually possible with current high-resolution ultrasound equipment to visualize both the lateral and medial walls of the lateral ventricle. This observation is important because it has been suggested that simultaneous demonstration of both ventricular walls in the third trimester is an early sign of hydrocephaly.4 The sonographer should be aware that such findings may be entirely normal in this scanning plane. The second scanning plane passes through the frontal Figure 1-2. Schematic representation of the axial examination of the horns, atria, and occipital horns of the lateral ventricles fetal head. In the four scanning planes (from rostral to caudal), the (Fig. 1-6). At 18 weeks, the atria are round and are following structures can be recognized: bodies of the lateral ventricles (B), frontal horns (FH), atria (At), and occipital horns (OH) of the entirely filled with the echogenic choroid plexus. Later in lateral ventricles, thalami (T), sylvian and vein of Galen cisterns (sc, gestation, the atria decrease in size and assume a convex vgc), third ventricle (3v), ambient cistern (ac), hippocampal gyrus shape due to the development of the calcar avis. The (HG), cerebral peduncles (P), chiasmatic cistern (cc), and cerebellum occipital horns appear as a fluid-filled posterior (C). LV, lateral ventricles; 4v, fourth ventricle. prolongation of the atria. In this scanning plane, it is possible to appreciate the progressive opercularization of the insula. Until the 18th ©1987-2002 Romero-Pilu-Jeanty-Ghidini-Hobbins NORMAL SONOGRAPHIC ANATOMY OF THE FETAL CENTRAL NERVOUS SYSTEM 3 Figure 1-3. A. Axial scans at the level of the bodies (B) of the lateral ventricles at 16, 23, and 30 weeks. Note the prominent choroid plexus (CP) in the 16-week fetus and the progressive shrinking of the ventricular cavity. The arrowheads indicate the medial and lateral walls of the ventricle. Figure 1-3. B. Anatomic specimen from an adult brain correspond- ing to the axial section shown in Figure 1-3A. Note the similarity in ventricular versus hemispheric size with the ultrasound image of the 30-week fetus. (Reproduced with permission from Matsui, Irano : An Atlas of the Human Brain for Computed Tomography. Tokyo, Igaku Shoin, 1978.) Figure 1-4. A. Measurement of the LVW:HW ratio.