Magnetic resonance imaging (MRI) has found evidence of brain enlargement in a relatively large sample of children with autism, compared with children who do not have the disorder, according to a study in the December issue of Archives of General Psychiatry.

Autism is a complex neurodevelopmental disorder defined by social deficits, abnormalities in communication, and stereotyped, repetitive behaviors. While the neuroanatomical basis of this condition is not yet known, numerous lines of evidence suggest that abnormalities in brain volume may be characteristic of autism, according to background information in the article.

Heather Cody Hazlett, Ph.D., of the University of North Carolina, Chapel Hill, and colleagues examined brain volume and head circumference (HC) in children with and without autism.

They analyzed data from an ongoing MRI study on 51 children with autism - aged 18 to 35 months - and a comparison group made up of 25 children without autism (14 with typical development, and 11 with developmental delay without evidence of a pervasive developmental disorder). Retrospective longitudinal HC measurements were also gathered from medical records on a larger sample of 113 children with autism and 189 control children, from birth to age three years.

“Significant enlargement was detected in cerebral cortical volumes but not cerebellar volumes in individuals with autism,” the authors report. “Enlargement was present in both white and gray matter, and it was generalized throughout the cerebral cortex.”

The cerebral cortex of the brain is responsible for the processes of thought, perception, and memory, among other functions. The cerebellum is a structure that controls complex motor functions. Gray matter (GM) represents information processing centers in the brain, while white matter (WM) represents connections between those processing centers.

“[In children with autism] head circumference appears normal at birth, with a significantly increased rate of HC growth appearing to begin around 12 months of age,” the authors write.

“The findings from this study confirm the presence of generalized cerebral cortical GM and WM brain volume enlargement at age two in individuals with autism,” they conclude. “Given the strong relationship between HC and brain volume, the onset of this enlargement appears likely to be during the postnatal [after birth] period and may begin as late as the latter part of the first year of life.”

http://archpsyc.ama-assn.org/