Alobar holoprosencephaly with rhombencephalosynapsis and atretic parietal cephalocele
Presentation
Macrocephaly with delayed motor development and palpable midline parietal soft tissue mass. The CT (not available) revealed a large dorsal cyst with no midline structures. A double VP shunt was inserted and an MRI was requested for evaluation.
Patient Data
The MRI sequences demonstrate:
small posterior fossa with a small abnormal-shaped 4th ventricle, absent cerebellar vermis, fusion of the cerebellar hemispheres with transversely oriented inferior cerebellar folia in keeping with rhombencephalosynapsis
dorsal cyst of holoprosencephaly of CSF signal on all sequences with absent 3rd and lateral ventricles
residual cortical tissue fused across the midline anteriorly
absent midline structures (septum pellucidum, corpus callosum, posterior aspect of the interhemispheric fissure/falx cerebri and olfactory tract)
fused thalami
hypotelorism
atretic parietal cephalocele through a bony defect in the parietal bone
Case Discussion
MRI features most consistent with alobar holoprosencephaly with associated rhombencephalosynapsis, hypotelorism and atretic parietal cephalocele.
Alobar holoprosencephaly is the most severe of the classical three subtypes, with both semi-lobar and lobar holoprosencephaly having less severe clinical manifestations. It may be associated with other congenital brain malformations.
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