This chapter discusses the gestational age at which various fetal anatomical structures can be visualized by ultrasound. Some structures are visible early in the second trimester, while others develop later. The ideal gestational age for visualization balances ease of recognition with diagnostic accuracy. Later gestational ages allow better visualization of finer anatomical details but increase the risk of detection of non-viable or lethal anomalies. Understanding what can and cannot be seen at different gestational ages is important for performing a thorough anatomic survey and differential diagnosis of fetal anomalies.

2. Ultrasound of Congenital
Fetal Anomalies

4. Ultrasound of Congenital
Fetal Anomalies
Differential Diagnosis and Prognostic Indicators
Dario Paladini MD
Head, Fetal Cardiology Unit
Department of Obstetrics and Gynecology
University Federico II of Naples
Naples
Italy
Paolo Volpe MD
Head, Fetal Medicine Unit
Department of Obstetrics and Gynecology
Hospital Di Venere
Bari
Italy

5. © 2007 Informa UK Ltd
First published in the United Kingdom in 2007 by Informa Healthcare, Telephone House, 69–77 Paul Street, London,
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6. Dedications
To my father and Carmen
To my father, Pia and my daughters, Grazia and Francesca
v

8. Contents
Preface ix
Foreword by Yves Ville xi
Acknowledgments xiii
1. Anatomic survey of the fetus and its relationship to gestational
age – what can be seen and cannot be seen 1
2. Central and peripheral nervous system anomalies 11
3. Craniofacial and neck anomalies 63
4. Cystic hygroma and non-immune hydrops fetalis 103
5. Congenital heart disease 113
6. Thoracic anomalies 183
7. Anomalies of the gastrointestinal tract and abdominal wall 207
8. Urinary tract anomalies 231
9. Skeletal dysplasias and muscular anomalies: a diagnostic algorithm 267
10. Chromosomal and non-chromosomal syndromes 301
Appendix 337
Index 353
vii

10. Preface
‘All you were craving to find in a textbook and could not’: this could represent the philosophy of this
volume. We tried to answer the questions which remained unanswered during our training in fetal med-
icine some 20 years ago. In fact, this book was conceived with the purpose to provide some help to the
operators confronted everyday with the challenging task of ultrasound diagnosis of fetal malformations.
In our early experience with fetal ultrasound, we have felt on our skin the unpleasant sensation of look-
ing at something unusual or wrong without been able to tell what it is, unable to put a name to it. The
most frequently asked questions with which the fetal medicine trainee/expert is confronted with every-
day are: ‘Is the finding real or merely an artefact’? ‘Is the diagnosis correct’? ‘Is it hereditary’? ‘Is it cor-
rectable’? ‘Which other lesions should it be differentiated from’? ‘Which are the management options
and what is the prognosis?’ However, to be able to find the description of an abnormal ultrasound find-
ing in a textbook, one generally has to search by the definite diagnosis…which has not been made yet!
This uneasy feeling was the first factor that pushed us to design this volume in its present format, i.e.
with an ample part dedicated to fetal anomalies ‘by scanning view’. We have tired to describe, for all
major ultrasound planes – organ after organ – what can be considered as a normal view and what can
not; in other words how each particular ultrasound view can differ from its normal appearance and what
are the corresponding diagnoses. From ultrasound sign to final diagnosis is the mission of this book, for
it is in this way the diagnostic process goes and not the other way round. To further ease the consulta-
tion process, we have included plenty of illustrated diagnostic flowcharts.
Another wish of our training days was to actually see the malformed babies, and not just imagine them
on the basis of the ultrasound findings. However, despite the number of textbooks published on fetal
anomalies since those days, in very few are we able to find a detailed echoanatomic correlation. Relatively
few images of specimens are given to illustrate the real aspect of major malformations altering the external
aspect of the fetus. This, we felt, was another issue we strongly wanted to deal with in detail. As a result a
whole imaging archive, covering years and years of pictures shot just after termination of pregnancy to
illustrate rare and less rare abnormalities has been included in the present volume, taking care to portray
the anomaly/abnormal feature as it appears on ultrasound.
Finally, everybody working in prenatal diagnosis knows that this represents a multidisciplinary field in
which genetics, neonatology, human dysmorphology, fetal medicine, pediatric and cardiac surgery comes
together in order to provide the unfortunate couple with a reliable estimate of the diagnosis, the cause of
the anomaly, the possible treatments if available, the chances of survival, and the recurrence risk in subse-
quent pregnancies. This is why, in the second part of each chapter, the single malformations are treated in
detail, providing the key information regarding all the above mentioned items in a structured, reader-
friendly way.
At the end, if the reader was found in this book at least some of the items he/she was craving to find in a
textbook and could not, it would mean that our training, and trainers have taught us something.
Dario Paladini
Paolo Volpe
ix

12. Foreword
FETAL IMAGING: A BRIEF HISTORY OF THE FUTURE
The first years of this century probably qualify as being mutational for fetal imaging, and this outstanding
review of the ability and performance of fetal ultrasound imaging is being timely published.
Screening and diagnosis are the two faces of fetal imaging. They differ mainly because of their indica-
tions, the level of expertise they require and, to a certain extent, the complexity of the technology support-
ing the imaging modality. These largely determine the availability of the investigation, its reproducibility
and accuracy. The number of, and gestational age at which these examinations are performed are not dri-
ven only by technical and developmental factors, but also by economic and social considerations, as well as
legal aspects surrounding termination of pregnancy. As a result, screening has moved towards earlier gesta-
tions while diagnostic accuracy is increasing at later gestations, when [TOP] is either not an options or has
stopped being relevant to the management of the pregnancy. Ultrasound screening in pregnancy can be seen
as the offer to check the largest number of pregnancies, by the largest number of operators for simple and
reproducible criteria in order to make important choices on the management of pregnancy and delivery.
Most established screening programs claim figures of around 40–70% sensitivity (for a 5% false-positive
rate) for different conditions such as congenital heart defects and Down syndrome. However divergent
their directions can be, both screening and diagnosis are demanding an ever increasing knowledge of fetal
development and mastering of the technology.
The impact of 3D ultrasound has gradually developed over and above that of a new look at already well-
documented fetal structures. Outside a small group of pioneers, promotion of 3D technology has perceived
as an expensive and obsessive campaign to demonstrate that poor 2D images obtained with an inconve-
niently large transducer could be put together into a grumpy fetal face, to be presented as a breakthrough in
fetal imaging. However, over the last 5 years this ultrasound modality has overcome these technical, as much
as cultural challenges. Image quality has gained respect from the most demanding operators and the com-
mercial often has become diverse and competitive. At the same time, 3D-champions have moved away from
pretty faces and into virtual dissection of the relevant fetal anatomy. This approach is now continuously rais-
ing the level of expertise of diagnostic ultrasound and perhaps more importantly, it is proving to be a
remarkable incentive and tool for education.
At the beginning of this century, a multiplanar approach of ultrasound was mostly considered eccentric
or unnecessary, and rarely was this concept seen as either innovative or logical. In the old days, registrars
were often described as having either surgical or obstetric skills. However, many of us have noticed that we
now also see ultrasound skills burgeoning in first year trainees and a five-year follow-up often proves as
right. It is not by chance that ultrasound has gradually moved away from being an exclusive and select
apprenticeship, to become a discipline that can be learned while providing the culture and the tools of qual-
ity assessment we have long been missing. The frontier between education and research is often subtle,
especially owing to the critical importance of subjectivity and reproducibility, two extreme and antagonis-
tic components of ultrasound examination. Education is therefore likely to remain the most significant indi-
vidual contribution each one of us can make to the improvement of perinatal care.
xi

13. xii FOREWORD
Screening and diagnosis address two different issues. However there is a continuum between them, so
much so that it is often difficult to draw a clear separation line. One aspect can benefit from the other when
this continuum transforms into a progressive, pragmatic and didactic approach of diagnosis. The diagnosis
path is absent from most textbooks. The essence of this book, ‘from the ultrasound sign to the diagnosis’,
clearly exposes these principles and makes it an invaluable help in the ultrasound room, as well as the being
starting material for a through investigations of any particular anomaly or risk factors. The extensive use of
illustrated flowcharts to highlight differential diagnoses, as well as identification of the abnormalities from
specific ultrasound features, will become significant assets in prenatal diagnosis.
Another strong point of this volume is the continuous effort to include 3D images for most diagnoses,
and especially those that are most likely to benefit from this development, including cranial sutures, skele-
ton, fetal brain and heart. In fact, what was long seen as alien with the most uncertain future within the 3D
family has become the most spectacular and dynamic field of research and development. The fetal heart
remains the greatest fantasy in the ‘brain’ holding the transducer. STIC and all its by-products provide the
best examples of both didactic and antiphobic tools that can help overcome the challenge fetal echocardio-
graphy remains to most sonologists and sonographers. The important distinctive feature of this book, in
comparison with other textbooks presenting 3D ultrasound images, is that these are only included if they
are an objective added value to the diagnosis or its demonstration to colleagues of other specialties
involved. 3D rendered images of craniofacial and brain anomalies, or cast-like reconstructions of cardiac
defects are shown only if they are useful and not just to demonstrate that 3D ultrasound can also make the
diagnosis: there is no reference to 3D if the diagnosis can be made confidently by 2D ultrasound.
Whether 3D will make important breakthroughs in ultrasound screening remains questionable. Fetal
heart examination is likely to represent the most sensitive indicator of the effectiveness of screening policies.
Although gestational age is a critical factor for performance, which makes different countries very unequal,
a technique that is both highly educational and accessible to telemedicine is more likely to succeed.
Finally, ultrasound-anatomical correlates presented side by side with 2D and/or 3D ultrasound images,
and relevant details of specimens from termination of pregnancy from extensively documented cases are a
great teaching tool. Rare chromosomal and non-chromosomal syndromes are also introduced and
described using the same methodology, and are more likely to make an impact on the readers than the usual
long and dry list of features usually encountered in these abnormalities.
The only book worth sitting in our ultrasound rooms has long been the Smith’s Recognizable Patterns Of
Human Malformation by Kenneth Lyons Jones for its ability to gather the critical number and description
of the most common anomalies to be identified in utero. However the ultrasound part of the mutational era
I was referring to in the introduction of this preface is best illustrated by this book that will soon become a
classic of this century.
Professor Yves Ville
Editor in Chief of Ultrasound in Obstetrics and Gynecology
Service de Gynecologie et Obstetrique
CHI Bissy
Université Paris Ouest St Bissy
France

14. Acknowledgments
We would like to thank our colleagues and friends doctors Gianluca Campobasso, Valentina De Robertis, Gabriella
Sglavo and Michele Vassallo for their valuable and fundamental help in retrieving all pictures and clinical files.
We would also like to thank our friend, geneticist, Mattia Gentile.
Finally, we would like to thank the following colleagues and units for providing us the MRI scans contained in this
book:
–Prof Marco Salvatore and Dr Mario Quarantelli
Biostructure and Bioimaging Institute
National Research Council
Naples, Italy
–Prof Maurizio Resta
Dept of Neuroradiology
SS Annuziata Hospital
Taranto, Italy
xiii

16. Chapter 1
Anatomic survey of the fetus and its
relationship to gestational age – what
can be seen and cannot be seen
In this first chapter of a book dedicated to the ultra- Table 1.1 This shows for each anatomic structure the
sound diagnosis of fetal anomalies, we have decided earliest gestational age (blue +) at which it is possible
to underscore the evolving nature of some lesions, pay- to visualize it and the ideal gestational age (black +) for
ing attention to the gestational age at which the different its visualization (the latter is identified on the basis of
abnormalities can be detected. In particular, Table 1.1 the best compromise between ease of recognition and
shows the earliest detection period, the period in which diagnostic accuracy)
the anatomic structure is confidently visualized and the
anatomic structures that can be visualized only late in 12–14 19–21 > 28
gestation (or only after birth) for developmental reasons. Anatomic structure weeks weeks weeks
Another important premise regards the gestational age Calvarium ++ +
at which the anatomic scan should be performed. It is Cerebral midline
important to understand that different health politics and and falx ++ +
sociocultural factors influence this aspect of prenatal diag- Cerebellum NP ++
nosis: available funds, health politics, legislation regarding Corpus callosum NP ++ +
termination of pregnancy (not allowed; allowed only Gyri and sulci NP NP ++
before viability; allowed also in the 3rd trimester, if severe Spine (NTD) + +
anomalies are present). According to the way in which Heart (4-chambers
these factors interact, the ultrasound screening for congen- and outflows) + +
ital anomalies is carried out routinely or only on demand Stomach + +
and in the 1st or the 2nd trimester. However, in most Abdominal wall ++ +
countries in which the national health system or insurance Kidney and bladder + +
provide economic coverage for the anomaly screening, Limbs (long bones) ++ +
this is carried out in midtrimester, usually at 18–21 weeks’ Extremities ++ +
gestation. A significant exception is Israel, where due to
various factors, the anomaly scan is often anticipated to NP, organs for which development is completed only
the end of the 1st trimester, by transvaginal ultrasound. relatively late in gestation; as a consequence their assessment
earlier in gestation may not be possible.
THE 12–14 WEEKS
EXAMINATION (TABLE 1.2)
Congenital anomalies can be divided into those clearly Fetal head. The ossification of the calvarium is evident, on
detectable at this gestational age and those which are the transthalamic view, from 12 weeks of gestation
not, with the latter group being detected only by experi- onwards. Hence, anencephaly (Figure 1.1) can be reliably
enced operators. diagnosed at this gestational age. However, care should
1

17. 2 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b a
Figure 1.1 Congenital anomalies confidently detectable at 12–14
weeks’ gestation: anencephaly, at 13 weeks. (a) Midsagittal low-
magnification view of the fetus, showing the absence of the calvar-
ium (arrows); (b) surface rendering showing the classic ‘frog’ face
aspect, due to the concurrent absence of the calvarium and the
moderate macrophthalmia, often present in anencephaly. b
be taken here, considering that the aspect of this lesion
early in gestation is different from the classic 2nd-
trimester aspect: in fact, at the end of the 1st trimester, the
cerebral hemispheres are still present, although in direct
contact with the amniotic fluid (exencephaly). By the 2nd
trimester, the cerebral parenchyma has been destructed
by repeated trauma against the uterine walls and by con-
tact with the amniotic fluid; this transforms the exen- c
cephaly into anencephaly. The only anomalies that may
sometimes give the same impression, early in gestation,
are the skeletal dysplasias characterized by severe
hypomineralization of the calvarium, such as achondro-
genesis, osteogenesis imperfecta type II or hypophos-
phatasia (see Table 9.3 in Chapter 9): in this case, the
skull may not be evident, but this is due to the lower cal-
cium content. Another important issue to be considered is
that at this gestational age, and until 18 weeks, the lower
part of the cerebellar vermis has not yet developed. As a
consequence, there is a physiologically wide communica-
tion between the fourth ventricle and the cisterna magna.
Therefore, a false diagnosis of Dandy–Walker variant can
be made if the normal times of the cerebellum develop-
ment are not taken into consideration. This diagnosis
should not be made until 18 weeks’ gestation, unless an
evident cystic posterior fossa is detected. Figure 1.2 Congenital anomalies confidently detectable at 12–14
Another malformation that may be confidently diag- weeks’ gestation. (a) Cystic hygroma, on the axial transthalamic view:
nosed in the 1st trimester is holoprosencephaly. In fact, the image demonstrates the conspicuous lymphangiectasia of the pos-
the falx is already present and evident on ultrasound at terior neck region (arrowheads). (b) Omphalocele, with the liver
12 weeks of gestation, and therefore its absence, which is (arrow) inside the sac; sagittal view. (c) Complete posterior urethral
valves. The low magnification view demonstrates the huge megacystis
one of the features typical of alobar and semilobar holo-
that fills most of the abdomen; due to the extremely severe distension,
prosencephaly, can be reliably detected (see Chapter 2).
the bladder (Bl has ruptured, producing urinary ascites (asc).
If we now consider the anomalies of the fetal neck,
then nuchal translucency, cystic hygroma and
hydrops should be taken into account. With regard
to the cystic hygroma (Figure 1.2a), it should be con- type of chromsomal aberrations (see Chapter 4).
sidered that cases detected in the 1st trimester are eti- Cystic hygroma represents a relatively simple diagno-
ologically different from those detected in the 2nd sis at 12–14 weeks’ gestation. Paradoxically, the more
trimester, in terms of incidence and prevalence and severe cases may fail to be diagnosed: in these cases,

18. ANATOMIC SURVEY OF THE FETUS AND ITS RELATIONSHIP TO GESTATIONAL AGE 3
the outer cutaneous contour may be in close contact 30% of the cases with a cardiac defect. Among abdom-
with the uterine wall, due to the oligohydramnios and inal and wall malformations, both omphalocele (Figure
the large retronuchal swelling, and therefore the hypoe- 1.2b) and gastroschisis can be recognized early in ges-
choic hygroma may escape diagnosis if its thin septa tation, because of the favorable fetal lie: in fact, at
are not recognized (see Figure 4.2a). Finally, it should 12–14 weeks’ gestation, the limbs are more frequently
be underlined that the hygroma, especially if non-sep- abducted, giving a good view of the abdominal wall.
tated, may be transient and regress almost completely However, care should be taken in diagnosing an
by the 2nd trimester, sometimes evolving into a nuchal omphalocele at 12 weeks’ gestation, since the physio-
edema. In these cases, the feto/neonatal outcome may logic herniation of the bowel in the cord regresses only
also be good, but a significant percentage of cases are at the end of the 11th week. Therefore, if an omphalo-
associated with Noonan syndrome or Noonan-like cele containing only bowel loops is suspected at that
phenotype.1 As far as nuchal translucency (NT) is con- gestational age, it is safer to wait 1 or 2 weeks in order
cerned, illustration of this important marker of chro- to get a confirmation of the diagnosis.
mosomal anomalies is beyond the scope of this book. An anomaly that is extremely difficult to recognize
We think it useful only to underline here that measure- early in gestation is bilateral renal agenesis. This diffi-
ment of NT is not an integral part of the 12–14 weeks culty arises because the kidneys can be visualized, but
scan. Screening of chromosomal anomalies by NT mea- not always as confidently as they should. In addition,
surement with or without biochemistry should be the important sign that always leads to this diagnosis in
requested by the parent or proposed by the examiner the 2nd trimester, namely severe oligohydramnios,
prior to the ultrasound examination. Should such develops only after 16 weeks’ gestation, because until
screening be required, it must be performed according that time the amniotic fluid is produced uniquely by
to the protocol set up by the Fetal Medicine ultrafiltration and the contribution of the fetal urine to
Foundation.2 This screening procedure includes not its maintainance is marginal.
only relatively simple sonographic measurements but On the contrary, a megacystis from complete urethral
also pre- and post-test counseling sessions. valves or urethral atresia (Figure 1.2c) is strikingly
evident at 12 weeks, regardless of the rather normal
Trunk and abdomen. Most thoracic (pulmonary) amount of amniotic fluid, due to the severe enlargement
anomalies appear only in the 2nd or even the 3rd (some of the bladder in the fetal abdomen: often, the whole
cases of congenital diaphragmatic hernia) trimester. abdomen of the fetus is occupied by the megacystis. For
Only a moderate to severe hydrothorax can be detected further details, see the description of this anomaly in
at 12–14 weeks’ gestation. With regard to congenital Chapter 8.
heart disease, only very experienced operators are able
to detect cardiac lesions at this gestational age, by Osteomuscular system. At 12 weeks’ gestation, all long
transvaginal or transabdominal ultrasound. However, bones are visible on ultrasound. Therefore, the lethal
it should be recalled here that an enlarged NT with a skeletal dysplasias, characterized by severe micromelia
normal karyotype represents an indication for early (see Figure 9.8 in Chapter 9) and often hypomineraliza-
fetal echocardiography, since it is associated in up to tion, are generally recognizable.
THE MIDTRIMESTER ANOMALY SCAN (TABLE 1.2)
As already mentioned, in most countries, the survey fetal viability. Usually, the examination protocol
of the fetal anatomy needed to perform a screening includes:
of congenital anomalies is carried out in the 2nd
trimester, usually between the 18th and 21st weeks • a biometric assessment usually consisting of biparietal
of gestation. In this regard, the ideal time for the diameter, head circumference, abdominal circumfer-
sonographic assessment of fetal anatomy should be ence, and femur length
at 24–26 weeks’ gestation, to give an optimal bal- • anatomic assessment that, depending on different
ance between the amount of amniotic fluid and the national guidelines, consists of visualization of all or
volume and developmental stage of the fetal organs. part of the following structures:
In most cases where the timing of the anomaly – head: skull, cerebral hemispheres, falx, cerebellum
scan is shifted, this is due to the fact that in those and cisterna magna, lateral ventricles, orbits, lips,
countries where there is a legal time limit for termi- and facial profile
nation of pregnancy, this is usually set at 22–24 – thorax: 4-chamber view (with or without outflows)
weeks’ gestation, which represent the limit of and the lungs

19. 4 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
Table 1.2 Average gestational age at diagnosis for Acoustic window impairment. The diagnostic accuracy
most common anomalies of midtrimester screening for the detection of congenital
anomalies will be illustrated below. Here, we wish to
< 18 18–21 > 28 underline how important it is, for medicolegal reasons,
Congenital anomaly weeks weeks weeks to describe in the report and to express in the pre- and
Anencephaly +++ −(+) − post-test counseling the existence of any factor that may
Hydrocephaly + ++ +++ reduce the diagnostic accuracy of the ultrasound exami-
Microcephaly NP + +++ nation. These include maternal and fetal limitations.
Holoprosencephaly ++ +++ −
Agenesis of the Maternal causes of impaired acoustic window. The most
corpus callosum NP + +++ important factor that may greatly reduce the diagnostic
Dandy-Walker potential of a transabdominal ultrasound examination is
complex NP +++ + the presence of maternal obesity, which, unfortunately, is
Spina bifida + +++ + becoming a real problem due to the increased prevalence
Congenital heart of this condition in the populations of the developed coun-
disease ++ +++ ++ tries. The impairment of the acoustic window exhibits a
Diaphragmatic positive linear correlation with the thickness of the
hernia + ++ ++ abdominal subcutaneous adipose tissue.3 It is common
CAML and experience, however, that in some cases resolution and
sequestration NP +++ + penetration are also significantly reduced in the absence of
Esophageal atresia NP ++ ++ evident maternal overweight, probably due to individual
Duodenal atresia NP ++ +++ differences in subcutaneous adipose tissue water and fat
Ileo-jejunal atresia NP + +++ content. Another factor that may limit the diagnostic
Omphalocele +++ +++ + accuracy of the midtrimester scan is an increased tone or
Gastroschisis +++ +++ + contracture of the abdominal musculature, usually due to
Bilateral renal maternal anxiety. The presence of striae rubrae from dys-
agenesis NP +++ − metabolic conditions or of large abdominal scars or burns
ARPKD + ++ + can also have a significant impact on the quality of the
Multycystic kidney + +++ + ultrasound examination. Finally, the most frustrating con-
Posterior urethral dition to be confronted with in the course of an ultra-
valves +++ + − sound examination is, in our experience, a previous
Limb reduction abdominoplasty. In this case, several concurrent factors
defects +++ +++ − contribute to the limitation of diagnostic accuracy: the
NIHF ++ +++ − extensive cleavage of the whole abdominal subcutaneous
Tumors (all sites) NP + +++ tissue from the underlying muscular fascia associated with
a long cutaneous surgical wound scar, residual abdominal
ARPKD, autosomal recessive polycystic kidney disease; fat, and a dramatic increase in abdominal firmness repre-
CAML, cystic adenomatoid malformation of the lung; NIHF, sent a frustrating although not insurmountable problem.
non-immune hydrops fetalis; NP, assessment not possible.
Fetal causes of impaired acoustic window. The most
– abdomen: stomach, liver, bowel, kidneys and common cause of (fortunately transient) impairment of
bladder, and abdominal wall the acoustic window is represented by an unfavorable
– limbs: presence of the four limbs and of the extremities fetal lie: an anterior spine, especially if associated with a
– spine transverse lie, makes assessment of the heart and the cran-
• evaluation of the fetal adnexa, placenta and amniotic iofacial area often impossible. However, in these cases, it
fluid is often sufficient to rescan the woman after 20–60
minutes to let the fetus change its position and remove the
Pretest information. Prior to the scan, the woman cause of the acoustic window impairment. Fetal crowding
should be informed about the potential diagnostic is also a potential cause of acoustic window impairment,
accuracy of the examination, of its screening nature, with the degree of impairment increasing with the number
and of the technical and practical limitations of the of fetuses. Another factor that can significantly limit the
ultrasound examination. In addition, it is useful to diagnostic accuracy of the midtrimester scan is an abnor-
inform the couple that the scan will not have a prede- mal amount of amniotic fluid. In particular, severe oligo-
fined duration, but that this depends on several factors, hydramnios, from premature rupture of membranes
including acoustic window limitations (e.g. maternal or renal anomalies, and severe polyhydramnios, from
obesity) and fetal lie. fetal anomalies, twin-to-twin-transfusion syndrome, or

20. ANATOMIC SURVEY OF THE FETUS AND ITS RELATIONSHIP TO GESTATIONAL AGE 5
idiopathic, can be responsible for an impairment of the a
acoustic window for different reasons: in oligohydram-
nios, the natural contrast agent represented by the amni-
otic fluid is absent and, in addition, the limbs are often
adducted, and these two factors usually limit the assess-
ment of the fetal limbs and heart. With severe polyhy-
dramnios, the increased fetal movements and the
significant increase in the distance between the transducer
and the fetal body are the two main limitations.
b c
The abdominal acoustic windows. It is useful to know
that the normal anatomy of the human abdominal wall
provides a few preferential ‘channels’ to exploit in the
case of an impaired acoustic window. These preferential
points of access are characterized by a reduced amount
of subcutaneous adipose tissue with a consequently
reduced transducer–fetus median distance. Two of these
anatomic regions are the periumbilical area, where
there is virtually no adipose tissue and which may be
d e
exploited if no air is left between the transducer and the
actual maternal umbilicus, and the lateral regions of the
abdomen (i.e. iliac fossae), where the mean thickness of
the abdominal adipose tissue is less than in the hypogas-
tric area (between the symphysis and the umbilical
area). To take advantage of this type of approach, the
patient may be asked to roll onto one side (which one
depends on the position of the fetus) in order to better
expose the lateral abdominal area to the operator.
Often, using this type of approach, the increased muscu- Figure 1.3 Evolving (late-onset) malformations: a few examples of
lar resistance offered by some patients (see above) also evolving lesions are shown. (a) Microcephaly: compare the reduced
head area (<3 standard deviations) with the normal abdominal area.
tends to be reduced. A third preferential point of access
(b) Aortic coarctation: the axial 3-vessel and trachea view shows the
is the suprapubic area/fold. In general, at 20–22 weeks
severely hypoplastic aortic arch (tubular hypoplasia). (c) Left-sided
with the fetus in the vertex position, the fetal head may congenital diaphragmatic hernia: the presence in the thorax of the
be approached through the suprapubic area, while the stomach is evident. (d) Jejunal atresia: extremely severe dilatation of
craniofacial anatomy may be assessed through the peri- jejunal loops. (e) Aneurysm of the vein of Galen: on the transventric-
umbilical area. A useful hint may be to use the maternal ular view, the huge midline vascular lake, consistent with the diagno-
bladder as a wedge: a full bladder will push the uterus sis of aneurysm of the vein of Galen, is highlighted on power
(and the fetus) upwards, towards the umbilical area; on Doppler.
the contrary, an empty bladder may allow the fetal head
to descend into the pelvis, where it can be explored in gestation (late onset), because it is due to an arrest in
through the suprapubic window. the development/growth of a given anatomic structure
(microcephaly or semilunar valve stenosis); or (ii) that it
The 3rd-trimester examination. This ultrasound scan is already present at midtrimester but has the potential
usually aims at the recognition of growth restriction. A to progress toward more severe stages in the 3rd
second endpoint is the detection of late-onset congenital trimester (diaphragmatic hernia, semilunar valve
anomalies. stenoses, or upper renal obstructive lesions). As a result,
the midtrimester anomaly can be unremarkable in all
Evolving and late-onset malformations (Figure 1.3 and conditions covered by the former definition. A partial
Table 1.3). The term ‘evolving’ may indicate two condi- list of the most common evolving lesions is given in
tions: (i) that a malformation may potentially arise late Table 1.3.
3D ULTRASOUND
Three-dimensional (3D) ultrasound has become an inte- of fetal anomalies. It represents for the new century
gral part of the ultrasound assessment of a large number what Doppler velocimetry represented for the 1980s

21. 6 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
Table 1.3 The most common (but not all) late-onset ultrasound, from the volume acquisition procedure to
(> 24 weeks’ gestation) malformations offline navigation and reconstruction. Of all the cur-
rently available techniques and imaging modes, we will
In a significant Also only illustrate only those petinent to the diagnosis of fetal mal-
Congenital number of after formations. In addition, it should be pointed out that the
anomaly Always cases birth names and the techniques used by the various producers
Hydrocephalus + of 3D ultrasound systems differ. Since all 3D ultrasound
Microcephaly + + images in this book have been obtained with General
Agenesis of the Electric–Kretz equipment, the terms and the procedures
corpus callosum + described here relate to the equipment and technologies
Semilunar valve developed by this manufacturer.
stenosis + +
Volume acquisition procedure. The volume acquisition
Aortic coarctation + +
procedure is based on the particular technology of volu-
Cardiomyopathy + +
metric transducers. The acquisition of the volume is based
Premature closure
on the movement of the array housed inside the trans-
of DA +
ducer: when the procedure is activated, this array per-
Patent DA +
forms a slow, single sweep, automatically recording one
Diaphragmatic
single 3D dataset. This volume consists of a high number
hernia + +
of 2D frames (or slices). Once the volume has been
Esophageal atresia + +
acquired, it can be processed directly on the ultrasound
Duodenal atresia + +
system or, more comfortably, offline, on a PC, with the
Ileojejunal atresia +
help of dedicated software.
Meconium ileus + +
ARPKD +
Quality of the volume. The quality of the acquired
ADPKD + +
volume depends first of all on all the usual limitations
Vesico-ureteral
due to the physics of ultrasound (maternal obesity,
reflux + +
fetal lie, etc.), which obviously apply to 3D ultrasound
Achondroplasia +
too. In addition, the quality of the volume is condi-
Arthrogryposis
tioned by the presence/absence of fetal movements dur-
(FADS) +
ing the acquistion time: the more movements that
Vein of Galen
occur, the less adequate is the acquired volume.
aneurysm +
Another important factor affecting the quality of the
Tumors (all sites) +
volume is involuntary movement of the hand holding
ADPKD, autosomal dominant polycystic kidney disease; the transducer during the acquisition. However, an
ARPKD, autosomal recessive polycystic kidney disease; DA, easy and fast way to assess the quality of an acquired
ductus arteriosus. volume consists in assessing how many abnormal
‘waves’ are present on the b window (the upper-right
end-side one) on the multiplanar screen (Figure 1.4).
Multiplanar imaging. This image modality represents the
and 1990s – an enormous contribution to the field of key approach to the study of fetal anatomy in normal
fetal medicine. Unfortunately, the clinical use of 3D and abnormal conditions. In the three windows, the
ultrasound has been in part obstructed by its use (mis- three orthogonal planes are displayed (Figure 1.5): using
use?) to display portraits of the fetal face. The heavy the cursors, it is possible to navigate the volume, repro-
marketing campaign launched some years ago by all ducing all possible views on the three planes; in addition,
producers of 3D ultrasound equipment has led to a to better assess the relationships between different
misunderstanding in the population that since 3 is anatomic structures, it is possible to move the dedicated
‘better’ than 2, then 3D ultrasound should see more and caliper on one plane and evaluate the corresponding
better than 2D ultrasound. While this may be partly true changes on the other two planes.
in those cases in which a fetal malformation has been
detected, and only for some organ systems, as explained Surface mode. From the acquired dataset, it is possible
in the various chapters, the use of 3D ultrasound in the to retrieve all the information needed to reconstruct the
screening setting so far has not been validated at all. In surface appearance of a given structure (surface mode).
this section, we will illustrate briefly the approach to 3D The combination of various filters and thresholds allows

22. ANATOMIC SURVEY OF THE FETUS AND ITS RELATIONSHIP TO GESTATIONAL AGE 7
a b
c
Figure 1.4 Overall quality of the volume. It is possible to assess
the overall quality of the acquired volume by looking at the b win-
dow (top right). The number of the vertical artefacts (arrows) cor-
responds to the number of gross fetal movements. In this case,
from the regular rhythm of the artefacts it can be deduced that the
STIC volume was acquired during a period of fetal breathing.
a b Figure 1.6 Three-dimensional ultrasound – surface mode. Using
the surface mode, and adjusting threshold and filters, it is possible to
display the surface of the fetal face. This example is the same as in
Figure 1.5, a 32-week-old fetus of Afro-American origin: note the
typical ethnic features.
c
Figure 1.5 Three-dimensional ultrasound – multiplanar imaging.
Once the 3D volume is opened, the three orthogonal planes are
shown. By moving the small caliper (yellow in a, red in b, blue in
c), it is possible to assess in detail the anatomic structure of inter-
est. This example illustrates the multiplanar rendering of a normal
fetal face at 32 weeks of gestation. Figure 1.7 Three-dimensional ultrasound – maximum mode.
This image modality allows one to ‘see through’ the soft tissues,
displaying the fetal bones. This example shows the upper spine
one to obtain the desired mixture of contrast, light, and with the occipital bone (Occ) and the scapulae (S) on the left and
transparency (Figure 1.6). the lower spine with the iliac wings (Sa) on the right.
Maximum mode. If the degree of transparency is coronal to the one the operator is insonating in 2D. In
increased, and the maximum-mode option is activated, gynecologic ultrasound it is able to provide impressive
the soft tissues become transparent and the fetal skeleton images of the normal and abnormal uterine cavity. In
is displayed (Figure 1.7). obstetrics, its use is of crucial importance for the assess-
ment of cranial sutures (Chapter 3), thoraco-abdominal
Volume Contrast Imaging C (coronal). This applica- topographic anatomy (Figure 6.10), and of limb
tion allows quick display on screen of the plane abnormalities (Figure 1.8).

23. 8 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b a
Figure 1.8 Volume contrast imaging C (Coronal). (a) Occipital
cephalocele at 19 weeks gestation. The VCI-C shows the parieto-
occipital sutures and the small cephalocele (arrows). (Occ, occipital
bone; Pa, parietal bones) (b) normal hand bones and soft tissues at
24 weeks of gestation. b
Inversion mode. This is one of the latest developments.
It can be used to assess sonolucent structures (vessels,
cavities, etc.). In fact, its algorithm inverts the color code
assigned to black and white pixels (voxels in 3D). The
final output is a cast-like image of the studied structure;
originally developed for the heart, it can also be applied
to cystic structures (Figure 1.9).
Tomographic ultrasound imaging (TUI). This image
modality is a new way of displaying diagnostic infor-
mation contained in a static or dynamic 3D dataset. In
particular, it allows 2D slices to be displayed from any Figure 1.9 Three-dimensional ultrasound – inversion mode. This
given volume, on any of the three orthogonal planes image modality allows one to create cast-like reconstructions of
similar to CT or MR scans (Figure 1.10). This display hollow anatomic structures. (a) Lateral cerebral ventricles in early-
mode can be advantageously used to demonstrate onset severe hydrocephalus. Note the oval ‘defect’ represented by
the choroid plexus. (b) Four-chamber view of a normal heart. The
brain or cardiac fetal anomalies and to evaluate ovar-
arrows indicate the leaflets and the chordae tendinae of the atrio-
ian tumors or endometrial cavity abnormalities in
ventricular valves.
gynaecologic ultrasound.
High definition flow. The algorithm of this particular
power Doppler application has been designed to pene- blood flow using the same gray-scale schemes. This leads
trate very small vessels with extremely reduced dimen- to a higher frame rate and better spatial resolution in
sions and low blood velocities. It is of great advantage comparison with power and color Doppler. In addition,
not only to assess the cerebral blood supply in normal it shows good depiction of small vessels and, due to its
and abnormal condition, but to display virtually all non-Doppler derived origin, it is not angle dependent
parenchymal circulation (Figure 1.11.) (Figures 5.23, 5.56c and 5.57).
B-flow. B-flow imaging is a new technique which Other image modalities. Many possible combinations
employs digitally encoded sonographic technology to of rendering modes are available. The Cardio-STIC
provide direct visualization of blood flows in gray scale. technique developed for the study of the fetal heart is
It displays simultaneously both tissue morphology and described in Chapter 5.
OUTLINE OF THIS BOOK
The rationale behind this book is the concept that, in anomaly is an abnormal view – that is, the ‘non-normal
everyday practice, what raises the suspicion of a fetal appearance’ of a conventional scanning view. This is

24. ANATOMIC SURVEY OF THE FETUS AND ITS RELATIONSHIP TO GESTATIONAL AGE 9
Figure 1.10 Tomographic ultrasound imaging (TUI). Carcinoma of the right choroid plexus at 35 weeks gestation. The image shows the
large malignant tumor (T) infiltrating the brain posteriorly (arrowheads) with secondary hydrocephalus (lv, lateral ventricles; arrow, 4th ven-
tricle). The multislice, tomographic imaging allows assessment on the single panel of images the extension of the tumor and its relationship
with the surrounding anatomic structures.
a b
Figure 1.11 High definition flow (HD flow). The HD flow is able to show very small vessels with low velocity. (a) Pulmonary arterial and
venous blood flow at 28 weeks gestation (Ao, descending aorta arrows; pulmonary veins). (b) Transvaginal transfontanellar view of cere-
bral blood vessels at 24 weeks gestation. (BA, basilar artery; PCA, pericallosal artery; SS, sagittal sinus)
why, in each chapter, the first part does not consist of are illustrated. In several cases, the first part of the
the classic nosologic approach, but rather of a section chapter is further enriched with diagnostic flowcharts
dedicated to the various ultrasound views necessary to that may help in the differential diagnosis by sign. For
assess each organ. Then, the abnormal aspect of each example, these flowcharts illustrate all anomalies to
view is illustrated, and the anomalies possibly respon- be ruled out in the case of non-visualization of the
sible for the abnormal aspect of the ultrasound view fetal stomach (Figure 7.7) or bladder (Figure 8.8), or,

25. 10 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
in the case of micromelia, which additional signs chromosomal anomalies, Risk of non-chromosomal
should be sought to make a differential diagnosis syndromes, Obstetric management, Postnatal therapy,
among all skeletal dysplasias possibly associated with and Prognosis, survival, and quality of life. Of particu-
micromelia (Figure 9.8). The philosophy behind this lar interest, under the Ultrasound diagnosis heading,
approach – from sign to diagnosis – is mantained in important subheadings give the differential diagnosis
all chapters. with anomalies featuring similar ultrasound signs and
The second part of each chapter is dedicated to the the ultrasound prognostic indicators.
illustration of the various abnormalities. Again, to In conclusion, we did not intend to write an extensive
maintain the practical approach, for each anomaly a textbook on fetal anomalies – there are already excellent
summarizing box is given at the beginning, and the ones available – instead, our idea was to produce a ver-
various headings then include; Definition, Etiology satile text that might be consulted in everyday practice
and pathogenesis, Ultrasound diagnosis, Risk of and that might help in difficult situations.
REFERENCES
1. Nisbet DL, Grifin DR, Chitty LS. Prenatal features of Noonan 3. De Vore GA, Medearis AL, Bear MB, et al. Fetal echocardio-
syndrome. Prenat Diagn 1999; 19: 642–7. graphy: factors that influence imaging of the fetal heart during
2. Snijders RJM, Noble P, Sebire N, Nicolaides KH. UK multicentre the second trimester of pregnancy. J Ultrasound Med 1993; 12:
project on assessment of risk of trisomy 21 by maternal age and 659–63.
fetal nuchal-translucency thickness at 10–14 weeks of gestation.
Lancet 1998; 352: 343–6.

26. Chapter 2
Central and peripheral nervous
system anomalies
NORMAL ANATOMY OF THE BRAIN: ULTRASOUND APPROACH,
SCANNING PLANES AND DIAGNOSTIC POTENTIAL
Timing of examination. Ultrasound screening for fetal Brain anomalies by scanning view. The axial scans used
brain malformations is performed at 19–22 weeks’ gesta- in the midtrimester screening of brain malformations are
tion. For the assessment of the fetal brain, the 2nd trimester as follows.
anomaly screening scan includes the following axial planes:
transthalamic, transventricular, and transcerebellar.1–3 Axial transventricular view and related malformations.
This has become the standard approach. However, major This is the most cephalad axial scan plane of the fetal
developmental events occur in the second half of the gesta- head. It allows visualization of the sonolucent lateral ven-
tional period, including neuronal proliferation, migration tricles with the echoic choroid plexuses, filling the ventric-
and organization; and the same is true for acquired lesions, ular bodies and atria (Figure 2.1a) and of the Cavum Septi
such as hemorrhage and tumors, which usually occur late Pellucidi (CSP). To exclude the presence of ventricu-
in gestation. Therefore, although it is possible to detect most lomegaly, the width of the atria is measured at the level of
fetal brain anomalies in the 2nd trimester, migration, prolif- the glomus of the choroid plexus. The measurement is
eration and organization4,5 disorders as well as acquired made perpendicular to the ventricular axis by positioning
lesions can become apparent only in the 3rd trimester. the calipers on the inner sides of the echogenic ventricular
walls (inner to inner borders) and should be less than
Ultrasound approach and scanning planes. The screening 10 mm. The site for the measurement, at the level of the
examination for anomalies of the central nervous system glomus, is chosen because, regardless of the etiology,
(CNS) is performed by abdominal ultrasound, mainly dilatation of the lateral ventricle generally involves the
using transverse scanning planes that are easily obtained. caudal portion (atrium and posterior horn) first.2 The
Coronal and sagittal views are more difficult to obtain, and 10 mm cutoff applies throughout gestation; any measure-
often require a transvaginal scan, but they may become ment of 10 mm or more indicates the presence of ventricu-
necessary in a targeted examination (fetal neurosonogram) lomegaly (Figures 2.1b and 2.2). As mentioned above, the
in patients with an increased risk of CNS anomalies.6,7 body of the choroid plexus typically occupies most of the
Transvaginal ultrasound with high-frequency transducers ventricle; a separation of the choroid plexus from the
has been used in the 1st trimester of pregnancy to study the medial ventricular wall by 3 mm or greater may represent
development of the fetal brain, monitoring its typically fast another sign indicating the presence of ventriculomegaly
morphologic changes, and to detect the presence of some (Figure 2.1b); in a few cases, this sign has also been associ-
early-detectable brain malformations (anencephaly, alobar ated with an abnormal outcome, even in the presence of
holoprosencephaly, etc.). Later in gestation, when the fetus normal atrial size. Morphologic evaluation of the cerebral
is in the vertex position, the vaginal approach can be ventricles allows the operator to detect midline defects
extremely helpful in the evaluation of complex malforma- such as holoprosencephaly (single or partially separated
tions and of normal and abnormal midline structures. In ventricles: Figure 2.1c) and to suspect agenesis of the cor-
fact, due to the proximity between the transducer and the pus callosum (colpocephaly: Figure 2.1d). Alobar holo-
fetal head and to the consequent use of higher-frequency prosencephaly is in fact characterized by a single common
transducers in comparison with transabdominal scanning, ventricle, whereas in semilobar holoprosencephaly the
the fetal brain can be better evaluated, and coronal and ventricles are separated only posteriorly, where a rudi-
sagittal views are much more easily obtained, in a similar mentary horn is present. The rarer lobar variant is charac-
fashion as neonatal transfontanellar ultrasound.6 terized by completely separated lateral ventricles except in
11

27. 12 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b
c d
Figure 2.1 Transventricular scans of the fetal brain showing (a) the distal lateral ventricle and the echogenic choroid plexus within it;
the arrows indicate the glomus of the choroid plexus. (b) Mild dilatation of the distal lateral ventricle with separation of the choroid plexus
from the medial wall of the ventricle; (c) a single ventricular cavity (arrow); (d) a mild dilatation of the posterior part of the lateral ventricle
(colpocephaly) (arrows) while the anterior part is normal (arrowhead).
the foremost portion, where there is fusion of the anterior septo-optic dysplasia are also associated with absence of
horns. In corpus callosum agenesis, colpocephaly may be the CSP. In addition, some neuronal proliferation and
present; in addition, there is an increased distance between migration disorders can be detected on the transthalamic
the ‘parallel’ bodies of the lateral ventricle, and the third view. These include microcephaly, which is characterized
ventricle is enlarged and upwardly displaced in 50–60% of by a marked reduction of the fetal head circumference,
cases. Some destructive brain lesions are detected on this and hemimegalencephaly, in which the two cerebral
axial scan, too: hydranencephaly, which is characterized hemispheres are of different size, although a certain
by a large endocranial cyst, and porencephaly, which is degree of asymmetry can also be present in some intracra-
characterized by a parenchymal cyst that commonly com- nial neoplasms (Figure 2.3b). In the same plane, some
municates with the ventricular system. Anomalies associ- skull deformities, due to craniosynostoses or to
ated with absence of the CSP are reported below. other anomalies of the CNS, can also be recognized
(Figure 2.4).
Axial transthalamic view and related malformations. The
axial transthalamic view is the classic plane in which the Axial transcerebellar view and related malformations.
biparietal diameter (BPD) and the fetal head circumfer- This view is used to assess the posterior cranial fossa
ence (HC) are measured. On this view, the CSP, the thal- and the related structures, namely the cerebellum, the
ami and the symmetry of the cerebral hemispheres can be cisterna magna and the fourth ventricle (Figure 2.5a).
assessed (Figure 2.3a). Hence, the various midline malfor- The nomograms for the transverse cerebellar diameter
mations associated with absence of the CSP can be are given in the Appendix. As for the cisterna magna, the
detected on this view (and on the transventricular view). distance between the posterior margin of the cerebellar
These include holoprosencephaly and complete agenesis vermis and the internal occipital bone surface should be
of the corpus callosum, both featuring absence of the CSP measured. The normal range is 3–10 mm. It should also
and abnormal lateral ventricles. Severe hydrocephaly and be taken into consideration that the cerebellar vermis has

28. CENTRAL AND PERIPHERAL NERVOUS SYSTEM ANOMALIES 13
Normal
Biventricular
hydrocephalus
Triventricular
hydrocephalus
Intraventricular
hemorrhage
Agenesis of corpus
callosum
Aneurysm of vein of
Galen
Figure 2.2 Ventricular anomalies evident
on axial transventricular scans.
a b
Figure 2.3 Transthalamic scans of the fetal
brain showing (a) the thalami (large
arrows), the cavum of the septum pellu-
cidum (small arrow), and the symmetry of
the hemispheres; (b) the asymmetry of the
hemispheres due to an intracranial hypere-
choic tumor.
not completed its macroscopic development in the early cerebellar vermis closure, which is normal in the early
second trimester; as a result, a premature scan can mis- second trimester, can be misinterpreted as a vermian
lead the operator and cause misinterpretation of a normal defect.8–9 Therefore, the screening examination for the
pattern: an ample fourth ventricle and the still incomplete detection of posterior fossa abnormalities should not be

29. 14 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
1: due to hydrocephaly/tumors
2:
Anomalies of the skull due to fronto-parietal synostosis
3: due to coronal suture synostosis,
(Transthalamic view)
in Apert syndrome
Normal
Macrocrania1
Microcephaly
Scaphocephaly2
Acro(turri)cephaly3
Hypomineralization
Figure 2.4 Anomalies evident on
the axial transthalamic scan.
performed before 19–21 weeks’ gestation. On the axial cerebellar vermis, cystic dilatation of the fourth ventricle,
transcerebellar plane, the cisterna magna, the cerebellum, and an abnormally wide posterior fossa. In the case of an
and the fourth ventricle are displayed, and it is therefore arachnoid cyst, the cerebellar vermis is present, but is usu-
possible on this view to demonstrate the anomalies of ally compressed and displaced, as are the cerebellar hemi-
these structures, such as abnormal width of the posterior spheres. The study of the vermis should be performed
cranial fossa (Chiari II malformation, Dandy–Walker with particular attention being paid to its inferior portion:
continuum) and/or the presence of a ‘cyst’ in the if the cerebellum is insonated with an excessive downward
posterior fossa, (Dandy–Walker continuum, arachnoid angle, the plane will cut through the fourth ventricle
cyst) (Figures 2.5b and 2.6). In the classic Dandy–Walker rather than the vermis itself, erroneously suggesting an
malformation, there is complete or partial agenesis of the enlarged cisterna magna or even partial agenesis of the

30. CENTRAL AND PERIPHERAL NERVOUS SYSTEM ANOMALIES 15
a b
Figure 2.5 (a) Axial transcerebellar scan
of the fetal head showing the cerebellar
hemispheres, the vermis (arrow), and the
cisterna magna (CM). (b) In this image, the
cerebellum is V-shaped because of a large
defect in the inferior vermis connecting the
cystic fourth ventricle to the area of the cis-
terna magna (arrow).
a
Normal
Dandy–Walker
malformation
Dandy–Walker
variant
Megacisterna magna
Spina bifida
(Arnold–Chiari II)
Incorrect alignment
(angled too much toward
the fourth ventricle)
Figure 2.6 Anomalies evident on the axial
transcerebellar scan.

31. 16 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b
Figure 2.7 (a) This transcerebellar
scan is too oblique downward. A
direct connection (the arrow indicates
Correct the vallecula) seems to appear between
the cisterna magna and fourth ventri-
cle, producing a false-positive image of
Incorrect partial absence of cerebellar vermis.
(b) Schematic diagram showing correct
and incorrect axial views through the
posterior fossa.
a b c
P
S
Figure 2.8 Midsagittal view of the fetal head showing (a) the corpus callosum (CC), the third ventricle (3v), the cerebellar vermis (V), and
the cisterna magna (arrows); (b) the fastigium, the primary fissure of the cerebellum (arrow), the brainstem (BS), the tentorium (T), and the
corpus callosum (arrows). (c) The Primary fissure (PF), always visible at 21 weeks’ gestational, delineates the posterior part from the anterior
part of the vermis. The posterior vermis shows characteristic fissures (SF: secondary fissure) and its volume is greater than the volume of the
anterior vermis. The fastigium (F)and primary fissure represents two main anatomical landmarks of the vermis (BS: brain stem)
cerebellar vermis. (Figure 2.7). A likely explanation of midline intracranial structures such as the corpus callosum
this artefact may be the following: the fluid-filled vallec- and the cerebellar vermis (Figure 2.8). Several authors have
ula cerebelli tends to expand slightly in the anterior advocated the use of this scanning plane in the evaluation
aspect and has a very thin membranous roof that is of fetal brain anatomy.6,7,9,10 Unfortunately, scanning in this
impossible to visualize with the resolution currently avail- plane is particularly difficult with two-dimensional ultra-
able with ultrasound equipment. The juxtaposition of the sound. Several approaches have been described, but they all
vallecula with the adjacent cerebellar hemispheres creates require considerable manual skills, time, and, frequently, a
the false impression of a continuum between the cis- transvaginal examination. Three-dimensional ultrasonog-
terna magna and the fourth ventricle, mimicking a raphy is now widely available, and one of its advantages is
Dandy–Walker variant9. In doubtful cases, and in those the possibility to obtain a volume and ‘slice’ it along differ-
in which a posterior fossa cyst is detected, a midsagittal ent directions from those used to acquire it. With this tech-
view will resolve the issue (see below) (Figure 2.8). The nique, obtaining midsagittal and other informative sagittal
most important structure that needs to be carefully eval- and coronal views has become much easier. Once the vol-
uated is the cerebellar vermis and its anatomy, since this ume has been acquired, multiplanar imaging allows navi-
is involved in a significant number of posterior fossa gation at will within the volume, enabling reconstruction
anomalies. Unfortunately, it is difficult to make a correct of virtually all scanning planes (Figure 2.9a). It should be
evaluation of vermian integrity when a cyst is present, noted that the structures displayed best will be those per-
particularly if its mass effect is significant. pendicular to the insonating beam when the volume is
acquired. Finally, a new image modality allowing 2D slices
Three-dimensional ultrasound navigation of the fetal to be displayed from any given volume similar to CT or
brain. Axial views are extremely useful in the context of MRI scans is represented by tomographic ultrasound
screening, but have significant diagnostic limitations. imaging (TUI) (Figure 2.9b).
While examining the fetal brain, one of the most important
views is probably the midsagittal section of the fetal head: Midsagittal view of the fetal head and related malfor-
this view provides unique information on important mations. The midsagittal view allows visualization of

32. CENTRAL AND PERIPHERAL NERVOUS SYSTEM ANOMALIES 17
a
b
Figure 2.9 (a) Multiplanar
analysis of an ultrasound vol-
ume of the fetal brain
obtained from the sagittal
plane (a); the two orthogonal
planes, coronal and axial are
simultaneously displayed.
From this position it is pos-
sible to navigate into the vol-
ume to demonstrate the
different anatomical details.
(b) Tomographic ultrasound
imaging (TUI) of the fetal
brain; the TUI panel allows
demonstration of the exten-
sion of a cerebral tumor.
the corpus callosum with the cavum septi pellucidi, morphology is essential when assessing for vermian
the third ventricle, the brain stem, the cerebellar ver- anomalies. At 21–22 weeks the primary fissure is usu-
mis, the fourth ventricle and the cisterna magna ally present. The primary fissure delineates the ante-
(Figure 2.8a,b). It therefore allows detection and rior from posterior lobes of the vermis; the volume of
characterization of agenesis of the corpus callosum, the posterior lobe is greater than the volume of the
and vermian abnormalities. Knowledge of vermian anterior lobe (Fig. 2.8b,c).

33. 18 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b
Figure 2.10 (a) Midcoronal
view of the fetal head. The
frontal horns (FH), genu and
cavum septi pellucidi (arrow),
are shown. (b) Posterior coro-
nal view of the fetal brain
showing the occipital horns
(OH) and the cerebellum
(arrow).
Right and left parasagittal views. Proximal parasagittal pellucidi (Figure 2.10a), the thalami, the caudate nuclei, the
views allow study of the lateral ventricles with the choroid lateral ventricular bodies, and the atria with the choroid
plexuses. Outermost parasagittal views allow visualization plexuses. Posterior coronal views allow visualization of the
of the insula and the parietal and temporal operculum. occipital horns, and the posterior fossa (cerebellar hemi-
spheres, cisterna magna, and tentorium) (Figure 2.10b).
Coronal views. The midcoronal views allow visualization Anterior coronal views show the anterior horns of the lat-
of the anterior horns, the corpus callosum, the cavum septi eral ventricles and the interhemispheric fissure.
CHARACTERIZATION OF MAJOR ANOMALIES
CEREBRAL VENTRICULOMEGALY
Incidence. High: 0.3–1.5 per 1000 births; probably higher in utero.
Ultrasound diagnosis. Axial transventricular view. Uni- or biventricular dilatation ≥ 10 mm. It can be isolated or
associated with other congenital (DWM, corpus callosum agenesis) or acquired (hemorrhage, infections) CNS
anomalies.
Risk of chromosomal anomalies. Moderate to high: 1.5–12% for isolated ventriculomegaly; 9–36% if
ventriculomegaly is associated with other malformations; almost absent if ventriculomegaly is associated with
acquired lesions.
Risk of non-chromosomal syndromes. High.
Outcome. Variable, and depending on the etiology and associated lesions; poor if associated with syndromes or
other CNS anomalies.
Definition. Ventriculomegaly may be the consequence of the diagnosis of hydrocephalus in the postnatal period
a variety of conditions that can result in a dilatation cannot be completely extended to the fetus. Indeed,
of the cerebral ventricular system. The incidence of con- in utero, hydrocephalus may be present even with a
genital enlargement of the cerebral ventricles ranges normal head circumference, and the underlying cause of
between 0.3 and 1.5 per 1000 live births in different series.9 an altered flow of the cerebrospinal fluid (CSF) cannot be
However, this may be an underestimate, as most available identified in all cases. However, fetal progressive, severe
surveys are based upon clinical data, and enlarged ventri- ventricular enlargement can be presumed to be indicative
cles are presumably asymptomatic at birth in many cases. of hydrocephalus. The mean ventricular size measure-
ment is not reliable as a means of distinguishing between
Etiology and pathogenesis. Ventriculomegaly may be sec- the different causes of ventriculomegaly. However, even
ondary to brain destruction (congenital infection or if there is no statistically significant difference, the mean
a vascular mechanism), malformations, hydrocephalus, value is lower for fetuses with underlying genetic causes
or a combination of two processes (i.e. hydrocephalus (excluding cerebral malformations) than for those in
and malformation). It may also be related to a brain which hydrocephalus is due to destructive causes; indeed,
neoplasm or to a genetic abnormality not associated with a discrete number of fetuses with borderline ventricu-
a brain malformation. The well-known classic criteria for lomegaly have a chromosomal anomaly.

34. CENTRAL AND PERIPHERAL NERVOUS SYSTEM ANOMALIES 19
a b c
Figure 2.11 (a) Chiari II malformation: dilatation of the lateral cerebral ventricles, small posterior fossa (arrows) and obliteration of the cis-
terna magna (arrows). (b) Dandy–Walker malformation with ventriculomegaly, cystic dilatation of the fourth ventricle (arrow), and enlarged
posterior fossa. (c) Axial scan showing the teardrop configuration of the lateral ventricle due to mild enlargement of its posterior part
(colpocephaly).
The presence of uni- or bilateral ventriculomegaly Ventriculomegaly associated with CNS malformations.
seems to be of some discriminatory value. Ventricu- As stated above, ventriculomegaly is associated
lomegaly tends to be unilateral in cases of destruction with typical malformation patterns of the CNS. In the
and bilateral in cases of malformation, and this differ- Chiari II malformation (Figure 2.11a), ventriculomegaly
ence is statistically significant.11 In apparently isolated is associated with a small posterior fossa, a small dysmor-
ventriculomegaly, we must distinguish between border- phic cerebellum, an effaced cisterna magna, and a spinal
line and moderate to severe ventriculomegaly. The term defect with myelomeningocele; for a conclusive diagnosis,
borderline ventriculomegaly is commonly used to indi- the latter defect must be detected. The association of ven-
cate cases characterized by an atrial width of triculomegaly with the presence of a dilatation of the
10–15 mm. Some authors have reported a different rate fourth ventricle and complete or partial agenesis of the
of abnormal neurologic outcome in fetuses with atria cerebellar vermis are the typical sonographic signs of the
> 12 mm compared with those with atria measuring Dandy–Walker continuum (Figure 2.11b). The ‘teardrop’
10–12 mm (a mild form of borderline ventricu- appearance of the lateral ventricles (colpocephaly)
lomegaly). In fact, an isolated borderline ventricu- (Figure 2.11c) with ‘parallel bodies’ which are shifted lat-
lomegaly of 10–12 mm might be considered as a erally, and upward displacement of the third ventricle
variant of the norm.12 The higher incidence of this suggest agenesis of the corpus callosum, the presence of
anomaly in male fetuses is related to the fact that their which must be confirmed on coronal and sagittal views.
mean atrial size is slightly greater than that of females.
Borderline ventriculomegaly may resolve even before Ventriculomegaly associated with cerebral destruction.
birth, and has no consequence in a vast majority of Ventriculomegaly associated with destructive lesions can
cases. However, it has been suggested that in a distinct be unilateral or bilateral. The most common causes are
minority of cases, this finding can be the earliest mani- hypoxia, infection, or vascular lesions. When ventricu-
festation of brain lesion from heterogeneous causes, lomegaly is associated with hyperechogenic foci located in
including primary cerebral maldevelopment (i.e. the brain and periventricular cysts, a fetal infection should
lissencephaly). Severe ventriculomegaly is usually be suspected. If multiple nodular subependymal calcifi-
referred to as hydrocephalus and is defined on the basis cations, which sometimes group together to form peri-
of an atrial width of more than 20 mm. When the atrial ventricular hyperechogenic bands (Figure 2.12a), are
width is between 15 and 20 mm the ventriculomegaly is present, cytomegalovirus (CMV) infection should be sus-
defined moderate. Aqueductal stenosis, regardless of its pected. In addition, free-floating particles, consisting of
cause, is responsible for the progression of ventricular exudate and shedded ependymal cells, may be detected
dilatation. Although it is generally a multifactorial dis- within the cerebral ventricles (Figure 2.12b), which
ease, there can be an X-linked transmission character- are often dilated, as this particulate matter frequently
ized by mental retardation, spastic paraplegia, and obstructs ventricular foramina, leading to secondary
adducted thumbs. Aqueductal stenosis can also be obstructive hydrocephalus. In such cases, a differential
acquired, following intrauterine infection or intraven- diagnosis with intraventricular hemorrhage should be
tricular hemorrhage. made: maternal serology for CMV and other infectious
agents and the findings at earlier ultrasound examinations
Ultrasound diagnosis. We report the most common often resolve the differential diagnostic issue. In the case
sonographic patterns of ventriculomegaly. of hypoxia-induced hemorrhage, ventricular dilatation

35. 20 ULTRASOUND OF CONGENITAL FETAL ANOMALIES
a b
Figure 2.12 (a) Cytomegalovirus
infection: a periventricular hypere-
chogenic band (arrow). (b) Axial scan
of the fetal brain, showing hyperechoic
clots within the frontal horn of the
proximal lateral ventricle (arrow) and
in the third ventricle (arrow).
a b
Figure 2.13 (a) Axial scan of the
c d lateral ventricles showing mild ventricu-
lomegaly: the arrow indicates the atrium
of the distal lateral ventricle. (b) Severe
ventriculomegaly: overall enlargement
of both lateral ventricles with dangling
choroid plexus (arrow). (c) Severe tetra-
ventricular hydrocephaly (LV, lateral
ventricle; 3°, third ventricle; 4°, fourth
ventricle). (d) Triventricular hydro-
cephalus: coronal scan of the fetal brain
showing dilatation of the third ventri-
cle and lateral ventricles with a typical
‘Mickey Mouse’ configuration.
occurs in severe forms only, and is generally associated neurologic outcome is significantly less frequent in the for-
with intraventricular fibrin strands and/or blood clots mer group. Isolated borderline ventriculomegaly may also
(grade 3). If this is the case, then a hyperechoic hemor- be unilateral. It should be noted that ventricular asymme-
rhagic lesion (grade 4) is often found in the parenchyma; try, defined as a difference in atrial size greater than 2 mm,
this will successively become hypoechoic, due to the without dilatation may be observed in normal fetuses.
liquification of the blood clot, and eventually disappears,
leaving a poroencephalic cyst filled with CSF and in Severe ventriculomegaly. This is usually referred to
communication with the ventricular system. as hydrocephalus, and is defined by an atrial width
of more than 20 mm (Figure 2.13b,c). In the fetus,
Isolated ventriculomegaly. The diagnosis of isolated ventriculomegaly is more frequently the result of a
ventriculomegaly is made when no other associated non-communicating hydrocephalus (where the obstruc-
sonographically detectable anomaly of the CNS can tion is located inside the ventricular system, as in aqueduc-
be found. An atrial width of 10–15 mm is defined as tal stenosis), whereas a communicating hydrocephalus
borderline ventriculomegaly (Figure 2.13a). As mentioned (where the obstruction is located outside the ventricular
above, some authors distinguish a mild form of borderline system) is significantly less frequent (Table 2.1).
ventriculomegaly, with atria of 10–12 mm, from borderline The reverse is the case in postnatal life. The typical sono-
ventriculomegaly, with atria of 13–15 mm. An abnormal graphic pattern of aqueductal stenosis is triventricular