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On sagittal images the cerebellar primary fissure is indistinct. The 4th ventricle is small and diamond shaped. Coronal images show an absence of a vermis with continuous cerebellar white matter tracts and cortex across the midline consistent with rhomboencephalosynapsis.
There is also posterior corpus callosum dysgenesis. Hydrocephalus is seen secondary to aqueductal stenosis with ventriculoperitoneal shunt tip seen in lateral ventricle.
The findings, in this case, are consistent with rhombencephalosynapsis which is thought to be caused by a failure of vermian differentiation which is required in order to form separate cerebellar hemispheres or by vermian agenesis which allows cerebellar hemispheres to become apposed and then fuse in the midline.
Rhombencephalosynapsis is sometimes associated with midline supratentorial abnormalities as seen in this case where posterior corpus callosal dysgenesis is observed.
Case courtesy of Dr Guillermo Bolivar
- Ishak GE, Dempsey JC, Shaw DW, Tully H, Adam MP, Sanchez-Lara PA, Glass I, Rue TC, Millen KJ, Dobyns WB, Doherty D. Rhombencephalosynapsis: a hindbrain malformation associated with incomplete separation of midbrain and forebrain, hydrocephalus and a broad spectrum of severity. (2012) Brain : a journal of neurology. 135 (Pt 5): 1370-86. doi:10.1093/brain/aws065 - Pubmed
- Anne G. Osborn, Karen L. Salzman, Miral D. Jhaveri, A. James Barkovich. Diagnostic Imaging: Brain. (2015) ISBN: 9780323377546