The Cerebellum in Chiari Type II Malformation

Abstract

Chiari type II malformation (CII) is a congenital deformity of the brainstem and cerebellum. In CII, the size of the posterior fossa is small and its contents are crowded. The cerebellar weight, volume, and cell content are reduced in CII. However, this reduction is not uniform and appears to involve the cerebellar hemispheres more than the vermis. The anatomical location of the vermis allows it to expand upwards, downwards, and along the ventral-dorsal axis when it is compressed in CII. This expansion seems to leave its ocular motor functions intact unlike the cerebellar hemispheres, which have no room for expansion and therefore undergo atrophy with consequent impairment of their functions.