An MRI study of autism: the cerebellum revisited.

We addressed the controversies surrounding the size of the neocerebellar vermis in autism and examined cerebellar size in light of recent reports of enlarged brain size in this disorder. In this study we use detailed MRI (1.5 mm) to examine the area of cerebellar lobules I through V and VI and VII and the volume of the total cerebellum in 35 autistic subjects and 36 controls. No abnormalities in the size of cerebellar lobules VI and VII in autistic individuals were detected, but the volume of the total cerebellum was significantly increased. We conclude that selective neocerebellar size abnormalities are not present in autistic individuals. Enlarged total cerebellar volume detected in this study is consistent with previous reports of regional brain enlargement in autism and also consistent with theories hypothesizing that the primary defect in autism is the result of abnormal development of a distributed neural network involving a number of regions of the brain.