Developmental defects of the cerebellum. A radiologic and anatomic investigation.

A classification of cerebellar malformations is proposed, based on more than fifty cases with varying degrees of abnormality, where comparative anatomic and radiologic analysis was carried out. The anatomic information was collected at surgery or autopsy and the radiologic evidence was derived from encephalography or ventriculography and vertebral angiography. The malformations were classified in four groups in order of gravity, with regard to the morphologic and etiologic features: (1) total or sub-total agenesia of the cerebellar structures (vermis and hemispheres); (2) almost complete agenesia of the vermis associated with the Dandy-Walker malformation; (3) almost complete agenesia of the vermis without the Dandy-Walker malformation; (4) partial defects of the vermis, which could be separated into four subdivisions.