What is the role of MRI in the workup of autism spectrum disorder (ASD)?

Updated: Sep 30, 2019
  • Author: James Robert Brasic, MD, MPH; Chief Editor: Caroly Pataki, MD  more...
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Magnetic resonance imaging (MRI) studies in patients with autism yield inconsistent results. However, typical findings include enlargement of the total brain, the total brain tissue, and the lateral and fourth ventricles, along with reductions in the size of the midbrain, the medulla oblongata, the cerebellar hemispheres, and vermal lobules VI and VII. [131, 132] Although vermal hypoplasia is found in some individuals with autism, vermal hyperplasia is identified in others. [133]

The volume of the gray matter is bilaterally decreased in the amygdala, the precuneus, and the hippocampus of people with autism spectrum disorder. Adolescents with autism spectrum disorder have shown greater decreases in the volume of the gray matter of the right precuneus than have adults. The volume of the gray matter in the middle-inferior frontal gyrus has been found to be slightly increased in people with autism spectrum disorder. [134]

Imaging studies in patients with autistic disorder who exhibit head banging may show enlargement of the diploic space in the parietal and occipital bones, with loss of gray matter adjacent to the bony changes. These findings resemble those of posttraumatic encephalopathy in athletes in contact sports (eg, football, hockey) and professional boxers (dementia pugilistica).

In one study, MRI performed during the presentation of a bedtime story during natural sleep in children aged 12-48 months provided evidence of atypical hemispheric lateralization for language in toddlers who develop autism. [135] Study subjects who developed autism failed to exhibit the left hemispheric response to spoken language that is typical of normally developing toddlers and instead demonstrated abnormal right temporal cortical responses.

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