OBJECTIVE: To determine whether increased brain volume in autism, suggested in previous studies, is the result of general or regional brain size differences and to study the effect of gender on brain size and pattern of enlargement. METHOD: Total brain volume and cerebral cortical lobe volumes were examined in 35 autistic and 36 comparison subjects using magnetic resonance imaging and an automated method of brain volume measurement. RESULTS: After controlling for height and nonverbal IQ, the authors detected a significant diagnosis x gender effect (F = 7.4; p = .009) for total brain volume. A repeated-measures analysis of variance indicated that the pattern of enlargement (brain region x diagnosis) in autistic subjects differed from that in controls (F = 4.88; p = .0004). Subsequent sex-specific analysis revealed significantly increased total brain volume in autistic males but not females. Analysis of lobe sizes showed significant enlargement in autistic subjects in temporal, parietal, and occipital, but not frontal lobes. CONCLUSIONS: These results suggest that brain size is increased in autism and that differences are not generalized but appear to be the result of a pattern of enlargement with increases in the size of specific cortical lobes.
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