Unusual MRI findings in rhombencephalosynapsis.

Rhombencephalosynapsis is mainly characterized by fusion of the cerebellar hemispheres and vermian agenesis. We report severe cerebellar hypoplasia, pachygyria of the cerebrum, an isolated (trapped) fourth ventricle, and facial hemangioma in association with this condition. Our findings suggested that the frequency of rhombencephalosynapsis appears to be higher than previously thought (approximately 0.13%), and it should not be misinterpreted as Chiari II malformation.