Rhombencephalosynapsis

Rhombencephalosynapsis is a rare congenital abnormality characterised by dorsal fusion of the cerebellar hemispheres, agenesis or hypogenesis of the vermis, fusion of dentate nuclei and superior cerebellar peduncles (Toelle et al., 2002). In this sense, it may be viewed as a condition with failure to form the midline structures of the cerebellum, akin to holoprosencephaly, which affects primarily the cerebral cortex. There are often associated cerebral cortical malformations, such as corpus callosum hypoplasia or cortical dysplasia (Mendonca et al., 2004), but major features of holoprosencephaly are not typically associated. Clinical findings range from mild truncal ataxia and normal cognitive abilities to severe cerebral palsy and mental retardation. This broad spectrum may be a result of the frequent association with hydrocephalus.