Diagnostic ultrasound ( PDFDrive )

1208 PART IV Obstetric and Fetal Sonography
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FIG. 34.36 Hydranencephaly. (A) Transverse thalamic view at 38 weeks shows asymmetrical cerebral destruction with preserved interhemispheric
issure. (B) Hydranencephaly at 17 weeks shows cranium illed with luid. At irst, the appearance suggests alobar holoprosencephaly, but the
presence of the falx (arrow) and lack of thalamic fusion as indicated by the large third ventricle help conirm hydranencephaly.
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. Commonly there is partial
sparing in the distribution of the anterior and posterior cerebral
arteries, including portions of the frontal, temporal, and occipital
lobes. he basal ganglia and thalami are hypoplastic, but the
brainstem and cerebellum are intact. Cases are sporadic, with
an incidence of about 1 per 5000 pregnancies. Many consider
hydranencephaly to be the most severe form of porencephaly
following occlusion of the internal carotid artery or middle
cerebral artery. It may be associated with infections, toxins,
hypoxic conditions, and trauma and may occur as a complication
of twin-twin transfusion syndrome.
On ultrasound, the cerebral cortex is absent and the cerebrum
is replaced initially by mildly echogenic luid that becomes clear
over time (Fig. 34.36). he 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. Findings start with cerebral echogenicity, thought to result
from ischemia or hemorrhage, followed by characteristic luid
replacement of the cerebrum. he diferential diagnosis includes
other conditions causing large, luid-illed cranial spaces, such
as severe hydrocephalus, alobar holoprosencephaly, bilateral
subdural collections, schizencephaly, and atelencephaly. With
hydrocephalus, there is generally uniform VM and a peripheral
thin cerebral mantle, and color Doppler ultrasound shows low
in the middle cerebral arteries. In holoprosencephaly there is
thalamic fusion and absence of the falx. Subdural collections
compress the brain into the midline. Large schizencephalic clets
can appear similar to hydranencephaly, but in schizencephaly
the lips of the clets are lined by gray matter, which may be
identiiable on MRI.
Most afected fetuses die in utero. At birth, diagnosis can be
readily made clinically by cerebral transillumination. Most die
in the irst year, but survival in a vegetative state to 32 years has
been described. 96,249,250
TUMORS
Prenatal intracranial solid tumors are rare, occurring in about
1.4 to 3.6 per 100,000 pregnancies, and account for about 10%
of all perinatal tumors. About 45% are teratomas, followed by
neuroepithelial tumors (astrocytomas, medulloblastoma,
choroid plexus papilloma, gliomas) (43%), craniopharyngioma
(7%), mesenchymal tumors (meningioma, sarcoma) (5%), and
hemangioblastoma (0.4%). Most are sporadic. A few are associated
with familial syndromes that have genetic abnormalities,
such as neuroibromatosis, tuberous sclerosis, von Hippel–
Lindau, and Li-Fraumeni syndrome. Fetal brain tumors tend
to be supratentorial in location, unlike tumors in older children,
which are more likely to involve posterior fossa structures. 251-253
he prenatal sonographic inding is an enlarged head containing
a complex intracranial mass, occasionally with calciications,
macrocephaly, and HC (Fig. 34.37). he tumors grow quickly
and can erode into the orbit, oral cavity, or neck. Associated