CROSS-SECTIONAL AREA OF THE POSTERIOR HIPPOCAMPUS IN AUTISTIC PATIENTS WITH CEREBELLAR AND CORPUS-CALLOSUM ABNORMALITIES

Using MRI methods previously shown to optimize visualization of cytoar chitectonic details in the body of the hippocampal formation caudal to the pes hippocampi, we imaged and quantified the hippocampus proper i ncluding the subiculum and the dentate gyrus in 33 autistic patients b etween the ages of 6 and 42 years and in 23 age-matched normal healthy volunteers. Measures of these structures in autistic patients and nor mal healthy volunteers differed nonsignificantly, by less than 1.4%, r egardless of whether or not the autistic patients were retarded or had a history of seizure episodes. By contrast, measures of vermian lobul es VT and VII and the posterior portion of the corpus callosum in thes e same autistic and normal volunteers differed significantly, by more than 9.9%. The lack of a significant difference in the cross-sectional size of the posterior hippocampal formation between autistic and norm al 6- to 42-year-olds is discrepant with predictions based on some, bu t not all, autopsy studies. This suggests that there is a need for add itional quantitative autopsy study of the hippocampal formation and qu antitative MRI study of rostral hippocampal regions that we did not ex plore in the present report. Also, quantitative autopsy and MRI studie s have yet to examine hippocampal development in autistic patients you nger than 6 years of age; whether early stages of growth are normal or not is unknown.