Macrocephaly occurs in 20% of individuals with autism on average and is usually due to megalencephaly—abnormal enlargement of the brain during childhood. The enlargement is rarely present at birth; it develops during early childhood when head growth accelerates during the first 18 months of life. Mean total brain, lobar, white matter, and gray matter volumes, including volume of the cortex, are significantly increased by 2 to 3 years of age in children with autism when compared with typically developing and also nonautistic developmentally delayed individuals.
Key Point: Head enlargement, if any, usually develops after infancy.
Increased Neuron Number and Head Size in Autism
Janet E. Lainhart, MD; Nicholas Lange, ScD. Journal of the American Medical Association (JAMA) November 9, 2011, Vol 306, No. 18, pp 1951-2048.
(http://jama.ama-assn.org/content/306/18/2031.extract?ct)
Excerpt:
Macrocephaly occurs in 20% of individuals with autism on average and is usually due to megalencephaly—abnormal enlargement of the brain during childhood. The enlargement is rarely present at birth; it develops during early childhood when head growth accelerates during the first 18 months of life. Mean total brain, lobar, white matter, and gray matter volumes, including volume of the cortex, are significantly increased by 2 to 3 years of age in children with autism when compared with typically developing and also nonautistic developmentally delayed individuals.