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FIGURE 34-24. Type 1 lissencephaly (Miller-Dieker
syndrome) in 23-week fetus. Note the mild ventriculo-
megaly and lack of sulcal formation. The insula is very smooth
and shallow (arrow) and lacks the angular plateau appearance
expected at this age.
normally despite “double cortex” cerebral changes that
can be seen with MRI, but boys do poorly.
27,152,177,181
Type 2, or cobblestone lissencephaly, is associated
with malfunction of genes that also function in muscle
development (e.g., POMT1/2, FKRP, FKTN). The
conditions are grouped with congenital muscular dys-
trophy. These infants typically have additional CNS and
somatic abnormalities and lack muscle tone at birth. The
most severe phenotype, Walker-Warburg syndrome, is
also called HARD-E for hydrocephalus, agyria, retinal
dysplasia, and/or encephalocele. Less severe phenotypes
include Fukuyama syndrome and muscle-eye-brain
disease.
11,40
Ultrasound changes may be evident by 20
weeks and include VM and absent, delayed, or abnormal
sulcal development; cerebellar vermian dysplasia; eye
abnormalities; small encephalocele; and abnormal brain-
27
(Fig. 34-25). Fetal MRI and gene mutation analy-
stem
sis can help confirm the diagnosis. Postnatal outcome is
10,40,152,155,182
poor.
Chapter 34 ■ The Fetal Brain 1227
Heterotopia describes localized clusters of disorganized neurons in abnormal locations anywhere in the
brain. It is very common and has heterogeneous etiology.
Cases can be isolated or associated with many different
syndromes. Intraparenchymal nodules can be difficult
to recognize by ultrasound. Subependymal periventricular heterotopia manifests as nodular ventricular contours
181,183-185
(Fig. 34-27). Affected children may be
normal or may have variable deficits and epilepsy.
Pachygyria describes large, abnormal disordered sulci
and gyri that can accompany different syndromes.
Schizencephaly (split brain) is a rare structural malformation of the cerebrum characterized by congenital
clefts or defects that are usually symmetrical and involve
the parietal or temporal brain. The clefts are lined by
cortical gray matter, unlike porencephaly, where white
matter lines the clefts. Etiology can be destructive
(encephaloclastic) or developmental. Destructive etiologies include vascular injury, teratogen exposure (e.g.,
cocaine), infections (especially CMV), and trauma,
and appearances can be similar to porencephaly or
hydranencephaly. Developmental cases arise from disordered neuronal migration and organization and are considered to be related to polymicrogyria. The tracts may
be open (open lip), allowing CSF communication
between the ventricle and subarachnoid space, or may
be solid (closed lip, consisting of an abnormal, solid
gray matter tract between the ventricle and brain
surface).
during investigation of VM, but a case was reported at
23 weeks.
152,186-188
Most cases are found in late pregnancy
188
The diagnosis rests on detection of the
cerebral clefts or abnormal gray matter traversing from
ventricle to cortex (Fig. 34-28). Midline brain defects
may occur, including septo-optic dysplasia, dysgenesis of
the corpus callosum, and absence of the septi pellucidi.
Fetal MRI allows superior delineation of upper cortex
and gray matter.
11,152,187,188
Neurodevelopmental delay
and seizures are common. Prognosis relates to the size of
the defect. Suspected cases benefit from multidisciplinary
consultation and counseling.
187,189,190
Other Malformations
of Cortical Development
Focal Cortical Changes
Focal cortical changes typically manifest late and are
difficult to detect with ultrasound.
181
They are typically
found at MRI in fetuses referred for evaluation of other
abnormalities initially detected by ultrasound.
Polymicrogyria is characterized by numerous small,
abnormal gyri with variable distribution. It is the
most common cortical malformation in children presenting with epilepsy. Polymicrogyria may be isolated or
associated with many genetic and acquired conditions.
Presentation typically is in late pregnancy but can be
seen in the midtrimester (Fig. 34-26; see also Fig. 34-8).
Cortical malformations can accompany infections,
inborn errors of metabolism (e.g., peroxisomal disorders), mitochondrial disease, and conditions with
unknown etiology.
associated with abnormal brain development.
21,152
Many metabolic conditions are
191-193
All
these are rarely encountered prenatally. The most
common is Zellweger (cerebrohepatorenal) syndrome,
which is lethal and has multiple abnormalities, including
neuronal impairment, hepatic disorders, cystic renal
malformations, and chondrodysplasia punctata. It may
manifest in the first trimester as nuchal thickening
194
and
in the second trimester as VM, cortical renal cysts,
and hepatomegaly. Third-trimester changes include
1228 PART IV ■ Obstetric Sonography
A B
CC
C
E
D
FIGURE 34-25. Type 2 lissencephaly (cobble-
stone cortex, Walker-Warburg phenotype) at
21 weeks. A, Coronal view shows the large, smooth ven-
tricles and the very small brainstem (arrow). B, Defect in
vermis (arrow). C, Midsagittal view shows the “Z” kink in
the brainstem (arrow), which represents failure of brainstem
to straighten and lose the early embryologic flexures, normally occurring after 12 to 13 weeks. Also, the cerebellar
vermis is very small (arrowhead). The third ventricle is malformed. The corpus callosum (cc) is malformed and extremely
elevated. There is a minute occipital encephalocele (open
arrowhead). This fetus also had eye abnormalities. D, In a
different fetus at 36 weeks, transvaginal scan shows smooth
cortex, abnormal for this gestational age. E, Coronal
T2-weighted MR image shows the smooth cortex and abnormal bands of high signal intensity in the parenchyma. Note
the prominent extra-axial CSF spaces.
A B
Chapter 34 ■ The Fetal Brain 1229
C D
FIGURE 34-26. Polymicrogyria. A, Irregular appearance to the cortex and cortical calcification (arrow) on coronal transvaginal
sonogram at 25 weeks. B and C, Coronal and axial T2-weighted MR images show sawtooth appearance to the cortex at 25 weeks. Note
how the calcifications were better visualized on the sonogram than on MRI. D, Polymicrogyria at 30 weeks’ gestational age. Note prominent extra-axial CSF.
abnormal gyration, periventricular leukodystrophy, and
subependymal pseudocysts.
confirmed by DNA and biochemical testing of fetal cells
obtained by chorionic villus sampling (CVS).
195
The diagnosis can be
194
Tuberous sclerosis (TSC) is a multisystem, hamartomatous condition with abnormal proliferation of anomalous cerebral cell types. There is notable involvement of
the brain, skin, heart, and kidneys. It is autosomal dominant, and two genes have been discovered to date, TSC1
and TSC2. However, about 70% of cases represent a new
(de novo) mutation. Epilepsy and neurologic impairment
are common. Morbidity and mortality predominantly
relate to CNS and renal disease. The diagnosis is made
clinically based on a list of findings, including tubers,
subependymal nodules, giant cell astrocytomas, cardiac
rhabdomyomas, and renal angiomyolipomas.
196
Prenatal diagnosis generally is made in late pregnancy
after discovery of echogenic cardiac rhabdomyomas
and demonstration of subependymal nodule or cortical
tubers on neurosonography or MRI (Fig. 34-29). In
1230 PART IV ■ Obstetric Sonography
A B
FIGURE 34-27. Periventricular nodular heterotopia and agenesis of the corpus callosum ACC). A, In fetus
with ACC at 31 weeks, note the very nodular lining of the ventricle wall (arrow). This represents accumulations of neurons that have
failed to migrate to the cortex. Note the separation of the hemispheres and abnormal alignment of interhemispheric sulci (arrowheads).
B, Transverse T2-weighted MR image in a different fetus at 35 weeks shows ACC and nodular heterotopias (arrows).
A B
FIGURE 34-28. Open-lip schizencephaly. A, There are large gaps in the parietal regions with no brain tissue at the periphery
(arrowhead). There is partial sparing of the frontal and occipital regions. B, Coronal T2-weighted MR image in a different fetus with
absent septal leaflets (absent septum pellucidum) shows region of schizencephaly (arrow).
at-risk fetuses, MRI has shown lesions as early as 21
197
weeks.
In at-risk families, if the abnormal gene is
known, diagnosis is possible using CVS or amniocentesis. Diagnosis in other suspected cases may be aided by
looking for subtle manifestations of TSC in the parents.
neural commissures connecting the cerebral hemispheres.
The corpus callosum starts to develop at about 12 weeks
from the lamina terminalis near the anterior end of the
third ventricle, as a bundle of fibers connecting the left
to the right hemisphere, and becomes detectable by
about 15 weeks and complete by 20 weeks. It develops
Agenesis/Dysgenesis of
Corpus Callosum
These disorders describe abnormalities of the development of the corpus callosum, which is the largest of the
in an anteroposterior manner, beginning anteriorly with
the rostrum and then forming the genu, body, and
finally the splenium posteriorly.
14,23,111,198
The normal
corpus callosum measures 17 mm at 18 weeks and grows
to 44 mm by term. There is no gender difference in
A B
Chapter 34 ■ The Fetal Brain 1231
C D
FIGURE 34-29. Tuberous sclerosis at 30 weeks on MRI. A, Typical hamartoma, or giant-cell tumor, is visible at the
foramen of Monro indenting the anterior frontal horn of the lateral ventricle (arrow). Both ventricles are dilated. B, Rhabdomyomas
involving the heart are visible as echogenic cardiac masses in the left and right ventricles (arrows). C and D, Subependymal hamartomas
in a different fetus with cardiac rhabdomyomas. Sagittal views demonstrate low-signal-intensity lesions projecting into the body and
temporal horn of the lateral ventricles. These subependymal tubers were not identified sonographically. (C and D from Levine D. MR
imaging of fetal brain and spine. In Magnetic resonance imaging of the brain and spine. Philadelphia, Lippincott 2008.)
length, but the corpus callosum is thicker in girls.
Corpus callosum development is associated with the
development of the leaflets of the cavum septi pellucidi
23
(CSP).
When the septal leaflets are present, at least the
anterior portion of the corpus callosum has formed.
Agenesis of the corpus callosum (ACC) may be
complete or partial, developmental or acquired.
The prevalence of ACC in neonates is about 3:1000
to 7:1000, but is higher in developmentally disabled
199-201
111,198
individuals. It may be an isolated abnormality with
very little functional disturbance, but most cases have
additional problems. Additional CNS abnormalities
occur in up to 80%, especially Dandy-Walker malformation, inferior vermian hypoplasia, and abnormal neuronal migration. Somatic and metabolic abnormalities
are seen in up to 60%, including face, congenital
heart disease, and skeletal and genitourinary abnormalities. The high incidence of associated malformations
1232 PART IV ■ Obstetric Sonography
suggests that ACC is part of a widespread developmental
disturbance.
111,198,202
Developmental disturbances after the corpus callosum
has started to form usually interrupt the formation of the
more posterior parts of the corpus callosum, but insults
after callosal development is complete can cause secondary atrophy of previously developed central portions.
Because callosal development is not complete until 20
weeks, early diagnosis of ACC may be difficult.
The key to early diagnosis is the cavum septi pellucidi
(CSP), which is generally seen by 17 weeks.
111,198,203
2
If the
cavum of the septum pellucidum is absent or has an
abnormal shape, ACC and other malformations should
be suspected. In the second trimester, however, ACC can
easily be missed.
29,204
Ultrasonic appearances are subtle
on axial scans (Fig. 34-30; see also Fig. 34-27; Videos
34-7 and 34-8).
Once the diagnosis is suspected, coronal and parasagittal views and 3-D ultrasound help to confirm the diagnosis. On coronal views the third ventricle is elevated;
the medial walls of the anterior horns are indented from
their medial aspect by the bundles of Probst (buildup of
fibers that failed to cross midline; Viking horn configuration). As a result, on the coronal view the anterior horns
configuration changes from V to U (Viking horn appearance), and an interhemispheric cyst may be present. On
parasagittal views the corpus callosum is absent, and in
the third trimester the sulci on the interhemispheric
brain surface show a “sunburst’’ orientation radiating
from the thalamus.
111,198
Before about 24 weeks, the
metopic suture of the frontal bone and anterior fontanelle offer a clear window for visualizing the corpus
callosum. Multiplanar 3-D ultrasound scanning is
helpful to obtain midsagittal views, but attention should
be paid to identifying the actual corpus callosum, not
only the pericallosal sulcus.
205,206
If the head is deep
in the pelvis, transvaginal scans can provide especially
clear views. Color flow Doppler scans can be used to
demonstrate an abnormal course of the cingulate and
ULTRASOUND FINDINGS OF ABSENCE
OF CORPUS CALLOSUM
Mild ventriculomegaly (VM) with very thin anterior
horns and pointing (teardrop shape =
colpocephaly).
Ventricles are parallel.
Too many lines between hemispheres on axial
views (3 lines = falx + medial surface of each
hemisphere).
Cavum septi pellucidi is absent.
Too many sulci perpendicular to the
interhemispheric fissure (hairy midline).
Third-trimester midsagittal view shows radial
orientation of sulci from the thalamus (sunburst
appearance).
pericallosal arteries. Normally these vessels follow the
contour of the calloso-marginal sulcus, but with ACC
they assume a more radial course. Occasionally, fetuses
with callosal abnormalities develop interhemispheric
cysts or a midline lipoma. MRI is helpful to confirm the
diagnosis and search for additional, subtle abnormalities,
such as migrational disorders.
111,183,198,204
Pitfalls in sonographic interpretation include mistaking the high position of the third ventricle, other fluid
spaces, and the fornices for the cavum of the septum
pellucidum. If the axial head views do not show the
normal appearance of the septal leaflets, additional views
can be obtained to evaluate the corpus callosum.
the corpus callosum is hypoechoic, but the surrounding
pericallosal sulcus is echogenic. On 3-D reconstructions,
some authors have incorrectly labeled the echogenic pericallosal sulcus as the corpus callosum. Lipomas associated with callosal dysgenesis are echogenic and can
parallel the superior margin of the corpus callosum. Care
must be taken to correctly identify structures on 3-D
reconstructions.
184,205
Investigation of suspected cases includes detailed ultrasound, karyotype (chromosomal abnormalities occur in
about 10%), microarray, screen for TORCH infections,
and MRI. Prognosis relates to the associated anomalies.
The prognosis for isolated ACC can be good, but up to
15% to 36% will develop problems that may not become
apparent until later in life. If other anomalies are detected,
outcome is poor.
183,198,202,208,209
Absence of Septi Pellucidi and
Septo-Optic Dysplasia
Septal agenesis is rare and occurs in about 2 to 3 per
100,000 pregnancies. It may be isolated but more often
is seen in association with other developmental abnormalities, such as septo-optic dysplasia, ACC, holoprosencephaly, and malformations of cortical development.
Septo-optic dysplasia (SOD; De Morisier syndrome)
is heterogeneous in etiology and appearance. It manifests
as variable degrees of hypoplasia of the optic nerves,
absence of septi pellucidi, pituitary hypoplasia, and
endocrine defects. The prognosis is variable and includes
disturbed vision and hypothalamic-pituitary insufficiency, including growth deficit and diabetes insipi-
111,210
dus.
At ultrasound, there is absence of the septi
pellucidi. On coronal views the frontal horns are squared
with inferior pointing. Differentiation from mild degrees
of holoprosencephaly can be difficult. In holoprosencephaly the fornices are more likely to be fused. Multiplanar 3-D and MRI are helpful.
Intracranial Calcifications
Fetal intracranial calcifications are rare. They usually
occur late in gestation (see Figs. 34-22, B; 34-26, A; and
34-31, A), are often associated with fetal infections, and
207
Also,
111
A B
Chapter 34 ■ The Fetal Brain 1233
C
E
FIGURE 34-30. Agenesis of corpus callosum (ACC). A, Ventricular view at 21 menstrual weeks shows characteristic borderline
dilation of occipital ventricle (arrow) and pointed, slightly spread anterior horns. This “teardrop” ventricle configuration is called colpo-
cephaly. The midline fluid space (arrowhead) is the elevated dilated third ventricle, which should not be mistaken for the cavum septi
pellucidi, which should be more rectangular and is absent in fetuses with ACC. B, Coronal view through the anterior ventricles (arrows)
shows that the frontal horns have a
separated from the falx (arrow), and the septal leaflets are absent. C, Axial ventricular view at 33 weeks demonstrates ventriculomegaly
and too many sulci perpendicular to the interhemispheric fissure (arrows), the axial correlate of the “sunburst’’ sign. D, Transverse
T2-weighted MR image at 29 weeks shows colpocephaly with teardrop-shaped ventricles and parallel orientation of the frontal horns. E,
Coronal MR image in a different fetus at 30 weeks shows the vertical orientation of the frontal horns and lack of crossing fibers of the
corpus callosum. F, Sagittal view from fetus at 31 weeks with partial ACC shows the sunburst pattern posteriorly, where interhemispheric
sulci extend farther inferiorly than normal due to lack of corpus callosum.
U or “Viking horn” configuration instead of the normal V orientation. The hemispheres are excessively
D
F
1234 PART IV ■ Obstetric Sonography
suggest a poor prognosis. Anatomically, calcifications
occur in areas of cell necrosis and may line ventricles or
occur in the parenchyma. Associated severe CNS changes
are common, including microcephaly, VM, intracranial
hemorrhage, and porencephalic cysts. Differential diagnosis includes intrauterine infections (especially CMV
and toxoplasmosis), teratoma, tuberous sclerosis, SturgeWeber syndrome, and venous sinus thrombosis.
211,212
Branching linear densities are described in the thalami
and basal ganglia. These represent mineralization of the
thalamostriate vessels (Fig. 34-31). Some believe these
relate to calcification, whereas others suggest mineral
deposits such as iron.
213
These mineralized densities may
be seen in normal fetuses but also occur in association
with many conditions, including infection (CMV,
rubella, syphilis), aneuploidy (especially trisomy 13),
alcohol, asphyxia, twin-twin transfusion, dysmorphism,
and congenital disorders.
211,213-215
Infections
A variety of organisms can cross the placenta and infect
the fetus causing encephalitis, variably followed by
microcephaly, VM, calcifications, and malformations of
cortical development. The TORCH group is seen most
often, but other organisms include varicella, congenital
lymphocytic choriomeningitis, parvovirus B19,
echo-
virus, and parasites. About 5% of VM has been attrib-
uted to infections. CMV is the most common infection,
followed by toxoplasmosis (Toxoplasma gondii is a pro-
tozoan parasite acquired through contact with uncooked
meat and animals, particularly cats and cat litter) and
herpes simplex.
more to the age when infection first occurred and affected
brain development than to the specific organism.
63, 216
The severity of injury often relates
63
Cytomegalovirus, the most common infection,
affects about 0.2% to 2.0% of live births. CMV is typically acquired through contact with people, especially
children, because CMV is prevalent in the population.
After maternal infection, transmission to the fetus ranges
from 25% to 70%. Even supposedly immune mothers
may still infect their fetus. Fetal infection varies from
mild to severe. About 60% of infected fetuses are symptomatic to varying degree. Of these, 20% die. Among
survivors, 90% develop neurologic sequelae of possibly
late onset.
217
Early-onset infections before 20 weeks can result in
malformations of cortical development, striking periventricular echoes and cysts, calcifications, schizencephaly,
thalamostriate vessel echogenicity, and abnormalities
of the corpus callosum and cerebellum (Fig. 34-32).
Infections acquired in later pregnancy generally have
normal cortical appearances but may also develop periventricular and parenchymal echogenicity, as well as
IUGR, hydrops, hepatosplenomegaly, and large or
small placenta.
The general consensus is that ultrasound plays a
limited role in the prenatal diagnosis of CMV because
it is only about 20% sensitive. However, positive ultrasound findings predict infection in about 80%, and
major findings such as microcephaly, cortical malformations, and parenchymal lesions strongly predict a
poor prognosis.
212,218,219
Investigation of fetuses with
suggestive cerebral findings includes maternal history,
TORCH screen, and amniocentesis (for CMV and parvovirus B19), although these tests are not completely
accurate.
218,220
Treatment depends on the etiology of
the infection. For example, with toxoplasmosis, successful antimicrobial treatment postnatally can decrease
the size of the calcifications and improve neurologic
221
status.
FIGURE 34-31. Echogenic mineralized thalamostri-
ate vessels (arrow). These form an echogenic arborizing
(branching) pattern in the thalamus and may be seen in normal
fetuses but can be associated with many fetal conditions.
Vascular Malformations
A variety of vascular abnormalities involve the fetal
brain. The most common is aneurysm of vein of Galen,
which describes dilation of the vein in association with
a spectrum of arteriovenous malformations, some of
which may be pial.
216,222,223
Typically, prenatal ultrasound shows an elongated anechoic structure behind the
thalamus in the expected region of the vein of Galen,
with flow on color Doppler (Fig. 34-33). Findings of
high-output cardiac failure may include prominent neck
veins, edema, and hydrops.
216,223,224
The dilated vein may be the vein of Galen but often
is a persistent dilated prosencephalic vein of Markowski
or falcine sinus, the course of which is not into the
straight sinus but rather cephalad in the falx to the
Chapter 34 ■ The Fetal Brain 1235
LIV
S
A B
FIGURE 34-32. Fetal cytomegalovirus (CMV) infection at 28 weeks. A, CMV infection shows enlarged ventricles with
thick, calcified walls (straight arrows). There is also calcification in the brainstem (curved arrow). B, Hepatosplenomegaly compressing the
fetal stomach helps confirm fetal infection; LIV, liver; S, spleen.
CC
CC
cb
A B
FIGURE 34-33. Vein of Galen aneurysm. A, Midsagittal view shows a hypoechoic “cyst” (arrow) behind the brainstem and
under the splenium of the corpus callosum (cc); cb, cerebellum. At first glance it could be mistaken to be a cavum veli interpositi. B, Color
Doppler examination shows the extensive vascularity due to the arteriovenous malformation associated with this dilated vein.
225
superior sagittal sinus.
The differential diagnosis
includes cystic lesions such as arachnoid cyst, cavum veli
interpositi, hematoma, and pineal tumor. Doppler
examination establishes the diagnosis.
216,224
Arteriovenous malformations frequently result in
cardiac overload and heart failure in utero and post-
216
natally.
Of prenatally diagnosed cases, 50% die prenatally or in early childhood, generally from progressive
heart failure. Variable neurodevelopmental sequelae were
found in 10%, and about 25% had normal development. Prognosis of prenatally detected cases is poor if
additional findings are present, including hydrops and
cerebral changes such as VM, edema, and porenceph-
223
aly.
Postnatal treatment includes hemodynamic stabi-
lization and angiographic embolization as needed.
216,224
Thrombosis of Dural Sinuses
Thrombosis in dural sinuses can be idiopathic (40%),
but cases can be seen with hypercoagulable states such
as trauma, infection, polycythemia, and deficiency of
physiologic anticoagulants (e.g., antithrombin protein
C, protein S, factor V Leiden). Ultrasound typically
reveals an echogenic mass (the thrombus) surrounded by
a hypoechogenic area in the region of the venous sinuses,
generally near the torcula and associated with absence of
1236 PART IV ■ Obstetric Sonography
sd
FIGURE 34-34. Sagittal sinus thrombosis. There is an
echogenic mass (arrow) in a fluidlike space in the midline anteriorly. This represents thrombus in a dilated sagittal sinus. There is
also a subdural collection (sd). (Courtesy Dr. Katherine Fong, Mt.
Sinai Hospital, Toronto).
flow (Fig. 34-34). The more proximal sinuses may be
dilated and the brain compressed. Many dural thromboses are initially misdiagnosed as tumors or subdural
bleeds. Most cases are found in the second and third
trimesters and can be confirmed with MRI. The prognosis is variable and may be favorable if no other abnormalities are found and the brain appears normal.
216,226
Hemorrhagic Lesions
Intracranial hemorrhage describes bleeding in and
around the brain. The incidence is about 1 in 10,000
live births.
227
The most common sites are similar to those
seen in premature neonates. In a series of 109 cranial
bleeds, 89 were intracerebral (79 intraventricular, 10
infratentorial), and 20 were subdural.
228
As in neonates,
cerebral bleeds are graded from 1 to 4 and may be followed by chemical ventriculitis (thick echogenic ventricular lining), hydrocephalus, porencephalic cysts,
white matter injury, and periventricular leukomalacia.
About half are idiopathic. Predisposing factors include
hypoxia, fetal coagulation disorders (including alloim-
mune thrombocytopenia and maternal anticoagulation), death of a monochromic co-twin, seizures, viral
or bacterial infection, febrile disease, drugs (cocaine),
maternal-fetal hemorrhage, and trauma.
216,227-230
At ultrasound, the bleed appears as an echogenic collection in the ventricles and surrounding brain (Fig.
34-35). This hemorrhage later organizes and condenses
into clots and may be associated with VM and echogenic
thickening of ventricular walls (chemical ventriculitis).
The findings may resolve or progress to hydrocephalus,
porencephaly, cerebral clefts, and cortical malformations. Those with ischemia may also develop cystic
leukomalacia. Subdural hemorrhages appear as an echogenic collection underlying the skull and compressing
the adjacent brain.
227,228
The prognosis varies greatly and depends largely on
fetal age, extent of injury, and underlying factors. About
50% die in utero or shortly after birth, and about half
the survivors have deficits. As expected, some with mild
changes may resolve completely, and more severe (grade
3-4) changes and cerebral changes predict a poor outcome.
Ultrasound can accurately diagnose bleeds, but MRI
can more accurately define the extent of the lesion and
may demonstrate additional ischemic changes in white
227,228
matter.
trauma and drug history, as well as maternal screen for
antiplatelet antibodies and thrombophilia.
Investigation of suspected cases includes
227,228
Hydranencephaly
Hydranencephaly is a rare disorder in which almost all
the cerebral hemispheres in the approximate distribution
of the supraclinoid middle cerebral artery are absent and
replaced by CSF and debris covered by a thin, membranous sac. There is partial sparing in the distribution of
the anterior and posterior cerebral arteries, including
portions of the frontal, temporal, and occipital lobes. The
basal ganglia and thalami are hypoplastic, but the brainstem and cerebellum are intact. Cases are sporadic, with
an incidence of about 1 in 5000 pregnancies. Many
consider hydranencephaly as the most severe form of
porencephaly following occlusion of the internal carotid
artery or middle cerebral artery. The exact predisposing
cause is unknown but may be associated with infections,
toxins, hypoxic conditions, and trauma and may be a
complication of twin-twin transfusion syndrome.
231-233
At ultrasound, the cerebrum is replaced by mildly
echogenic fluid, and the parietal cerebral cortex is absent.
Partial sparing is evident in the frontal and occipital
lobes (Fig. 34-36). The falx is present but may be hypoplastic. Posterior fossa structures appear normal. Most
cases are found in late pregnancy, but cases have been
described as early as 11 weeks.
234
Findings start with
cerebral echogenicity, thought to result form ischemia or
hemorrhage, followed by characteristic fluid replacement
of the cerebrum.
235
The differential diagnosis includes
other conditions causing large, fluid-filled cranial spaces,
such as severe hydrocephalus, alobar holoprosencephaly,
bilateral subdural collections, and schizencephaly. With
hydrocephalus, there is generally uniform ventricular
enlargement and a peripheral thin cerebral mantle, and
color Doppler ultrasound may show flow in the middle
cerebral arteries. In holoprosencephaly there is thalamic
fusion and absence of the falx. Subdural collections
compress the brain into the midline.
232,233
Large schizen-
cephalic clefts can appear similar to hydranencephaly,
but in schizencephaly the lips of the clefts are lined by
gray matter, which may be identifiable on MRI.
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