Background: Increasing evidence indicates that brain growth in children with autism may be accelerated early in life and then slow, resulting in more significantly enlarged brain volumes in younger children(Courchesne, Neuron 2007). One previous report in older children has found increased cortical thickness (Hardan, AJP, 2006), however cortical thickness has not been characterized in younger children with autism.

Objectives: Assess cortical thickness and brain volumes in a cohort of young children with autism. 

Methods: 20 subjects meeting strict criteria for Autistic Disorder (18 males, age 4.5(sd1.2));  31 healthy controls matched on age and sex. Diagnoses were established by trained raters using the ADOS and ADIR.  Autistic subjects were sedated during MRI procedure; controls were not sedated.  All subjects were scanned using the same 1.5T scanner and protocol (Giedd, Cerebral Cortex 1996).  Volumes for total brain volume and white and gray matter lobar regions and cortical thickness at 40,973 vertices were obtained using fully automated methods developed by the Montreal Neurological Institute (MNI) (Zijdenbos, IEEE TMI, 2002; Lerch, Neuroimage, 2005).  2-tailed t-tests were used to compare brain volumes; effects of diagnosis on cortical thickness at each vertex were determined using linear regression followed by adjustment for multiple comparison using FDR.

Results: Total gray matter was significantly larger in subjects with autism (780.78cc ± 78.0 vs 732.5cc ± 74.5, p < .031); gray matter was larger in frontal, temporal, and parietal but not occipital lobes; total brain volume and white matter were not different.  The cortex was significantly thicker in individuals with autism across broad regions with most pronounced effects in frontal and temporal regions. 

Conclusions:Increased cortical thickness contributes to larger gray matter volumes in young children with autism.  Future directions include comparison of brain structures in regressive and nonregressive autism subtypes.