Diagnostic ultrasound ( PDFDrive )

1534 PART V Pediatric Sonography
A
B
FIG. 45.27 Mega–Cisterna Magna. (A) and (B) Axial and sagittal sonograms show an enlarged cisterna magna (CM) with no connection to
the fourth ventricle and no ventriculomegaly.
Alobar Middle interhemispheric Semilobar Lobar
Normal brain
FIG. 45.28 Holoprosencephaly Classiication. Holoprosencephaly classiication. Normal versus four types—alobar (most severe), middle
interhemispheric, semilobar, and lobar.
addition to occurrence with holoprosencephaly, callosal agenesis,
and Chiari II malformations, other associations suggest that
septo-optic dysplasia may occur from destructive processes that
cause schizencephaly and chronic severe hydrocephalus. 31
Intermediate in severity between alobar and lobar is semilobar
holoprosencephaly, with fusion of the cortex and ventricle
anteriorly but variable separation posteriorly; facial anomalies
are mild or absent. Anomalies of the face and calvaria accompany
and help predict the severity of the brain malformation, because
the face develops at the same time as the brain during diverticulation.
Cases of holoprosencephaly are usually suspected as a result
of the accompanying facial anomalies, with more severe facial
anomalies predicting more severe intracranial anomalies. Holoprosencephaly
is most frequently seen in trisomy 13 and 18
syndromes and can also be caused by teratogens, the most
common mechanism in infants of diabetic mothers. 31,60-62
Alobar Holoprosencephaly
Alobar holoprosencephaly is the most severe form of this disorder.
Infants with this defect usually die within the irst months of
life or are stillborn. Facial features may include cebocephaly
(hypotelorism and malformed nose; Fig. 45.30D), cyclopia, and
Alobar Holoprosencephaly:
Sonographic Findings
Single midline crescent-shaped ventricle
Thin layer of cerebral cortex
No falx
No interhemispheric issure
No corpus callosum
Fused thalami and basal ganglia
Fused echogenic choroid plexus
Absent third ventricle
Large dorsal cyst
ethmocephaly (cyclopia or hypotelorism with a midline proboscis
above the eyes). he brain surrounds a single midline horseshoeor
crescent-shaped ventricle with a surrounding thin, primitive
cerebral cortex 59 (Fig. 45.30). he hemispheres are fused as a
pancakelike mass of tissue in the most anterior portion of the
calvaria. Only in holoprosencephaly will the splenium of the
corpus callosum be the only segment present. 31 he thalami are
fused, and there is no falx, corpus callosum, or interhemispheric