Diagnostic ultrasound ( PDFDrive )

CHAPTER 34 The Fetal Brain 1177
C
C
12 mm
A
B
C
FIG. 34.11 Ventriculomegaly. (A) Mild ventriculomegaly
of 12 mm. Note placement of calipers (+) in the
CSF (black luid) touching the inner surface of the ventricle
wall. There is prominent space (>3 mm) between the choroid
and ventricle wall. The cavum septi pellucidi has been
compressed but is still visible (arrow). (B) Marked ventriculomegaly
at 27 weeks shows the convex margin of the
ventricle. The choroids (C) are drooping (toward the dependent
ventricle), and the cavum septi pellucidi has fenestrated,
allowing free communication between the ventricles.
(C) Aqueduct stenosis with massive ventriculomegaly
at 35 weeks. The septal lealets have fenestrated
(open arrow), allowing the upper choroid (arrowhead) to fall
across the midline. The cerebral cortex is greatly thinned
but present (small arrows), allowing differentiation from
hydranencephaly.
predicted by ventricular size, cortical thinning, and appearance. 66
A single institution study of 29,000 pregnancies found VM in
0.38% of fetuses (1 in 265). Of these, 57% were not isolated and
had other abnormalities. In the 43% with IVM, VM was mild
in 40% (10-15 mm) and marked in 60% (>15 mm). Abnormal
neurodevelopmental outcome was poorest with nonisolated (91%)
and marked IVM cases (68%) but was seen in only 19% of mild
VM cases. 77
he approximate frequencies of cerebral abnormalities
seen with VM are aqueduct stenosis, 30% to 40%; Chiari II
malformation with spina biida, 25% to 30%; Dandy-Walker
complex, 7% to 10%; and less common conditions including
agenesis of the corpus callosum. In general, associated CNS
and somatic malformations are common. Chromosomal and
genetic abnormalities are more common with nonisolated
(25%-36%) than isolated (3%-6%) VM and include the trisomies
and X-linked hydrocephalus in males and numerous other
conditions. 67,71,78,79
Pathogenesis of Ventriculomegaly
CSF is secreted by the choroid plexus of the lateral, third, and
fourth ventricles, as well as by the cerebral capillaries. 80 CSF
lows from the lateral ventricles with assistance of ciliary activity
of ependymal cells through the foramina of Monro, third ventricle,
aqueduct of Sylvius, and fourth ventricle and out the foramina
of Magendie and Luschka into the subarachnoid space of the
posterior fossa, from where it courses over the surface of the
brain to be absorbed by the pacchionian or arachnoid granulations
and lymphatics. 66,81
Ventricular enlargement generally occurs in one of four
scenarios. First and most commonly, there is obstruction of CSF
low in the brain, usually at the aqueduct (intraventricular