The relative contributions of brain, cerebrospinal fluid-filled structures and non-neural tissue volumes to occipital-frontal head circumference in subjects with autism.

An increased prevalence of macrocephaly defined by occipital-frontal circumference (OFC) is a consistent finding in autism. Several possible mechanisms have been proposed, the most compelling being early brain overgrowth. However, the proportion of non-neural tissues (NNT) that contribute to OFC has not been reported. Using quantitative magnetic resonance imaging (MRI) methods we analyzed the relationships between OFC and total brain (TBV), ventricular, surface cerebrospinal fluid (CSF)/meningeal, and NNT volumes in subjects with autism. Sixty male subjects (34 autistic; 26 controls) seven years of age and older were used in this study. Compared to other measures, NNT volume was most significantly related to OFC (r values > 0.8, p 0.06). In contrast, the OFC-TBV relationship was less robust in those with autism (r=0.25, p