By Peggy Peck, Managing Editor, MedPage Today
Reviewed by Robert Jasmer, MD; Assistant Professor of Medicine, University of California, San Francisco
December 09, 2005
CHAPEL HILL, N.C., Dec. 9 - MRI scans indicate that the brains of children with autism are larger than those of healthy children, suggesting an unusual pattern of brain growth that may have its onset in shortly before a child's first birthday.
The increased brain volume was detected in the cerebral cortical volumes but not in cerebral volumes, according to Heather Cody Hazlett, Ph.D., of the University of North Carolina here.
The brains of children with autism are about 5% larger than brains of non-autistic children, and the enlargement is due mainly to larger grey matter and white matter volumes in the cerebral cortex, Dr. Hazlett and colleagues reported in the December issue of Archives of General Psychiatry.
Magnetic resonance imaging studies were conducted in 51 children with autism and 25 controls. The control group included developmentally delayed children as well as typically developing children. All children were evaluated between ages 18 and 35 months.
The researchers also retrospectively assessed head circumference data from birth to age three years in 113 children with autism and 189 controls. In the autistic children, "head circumference appears normal at birth, with a significantly increased rate of head circumference growth [P=.001] appearing to begin around 12 months of age," they wrote.
While this study confirmed earlier reports of "generalized cerebral cortical [grey matter] and [white matter] brain volume enlargement at age two in individuals with autism," the authors said the findings are limited by the small control arm. They cited difficulty in ascertaining and scanning large numbers of children without autism at age two.
Also because typically developing children are also very active children who were scanned without sedation, it was difficult to obtain high quality scans.
Nonetheless, the researchers pointed out that "the data we present on the possible timing of brain enlargement in autism also raise the possibility that the onset of autistic symptoms may be associated with postnatal changes in brain volume, and there may exist a presymptomatic period in autism in which intervention may have more potent effects."