Agenesis of the vermis cerebelli and malformations of the posterior fossa in childhood and adolescence.

Three cases of cerebellar vermis agenesis are reported and the relevant literature (19 other cases) is reviewed. Other posterior fossa malformations, such as a mega-cisterna magna, arachnoid cyst and Dandy-Walker syndrome, are discussed both from the pathological and clinical view point. We put forward a hypothesis that agenesis of the cerebellar vermis and Dandy-Walker syndrome could be regarded as two different stages of the same malformation.