Posterior fossa magnetic resonance imaging in autism

Objective: To determine whether the sizes and volumes of the posterior foss a structures are abnormal in non-mentally retarded autistic adolescents and adults. Method: Volume measurements of the cerebellum, vermis, and brainst em were obtained from coronal magnetic resonance imaging scans in 16 autist ic subjects and 19 group-matched healthy controls. For the purpose of compa rison with previous studies, area measurements of the midbrain, pens, medul la, total cerebellar vermis, and its three subregions were also obtained fr om a larger sample of 22 autistic males (mean age: 22.4 years; range: 12.2- 51.8 years) and 22 individually matched controls (mean age 22.4 years; rang e: 12.9-52.2 years). Results: The total volume of the cerebellum and the ce rebellar hemispheres were significantly larger in the autistic subjects wit h and without correcting for total brain volume. Volumes of the vermis and the brainstem and all area measurements did not differ significantly betwee n groups. Conclusions: There is an increase in the volume of the cerebellum in people with autism consistent with the increase in regional and total b rain size reported in this developmental disorder. This finding is also con cordant with evidence of cerebellar abnormalities from neuropathological an d neuropsychological studies that point to the role of this structure, as p art of a complex neural system, in the pathophysiology of autism.