A Two-Year Longitudinal Pilot MRI Study of the Brainstem in Autism

Background: Research has demonstrated the potential role of the brainstem in the pathobiology of autism.  Previous studies have suggested reductions in brainstem volume and the existence of a relationship between this structure and sensory abnormalities.  However, very little is known regarding the developmental aspects of the brainstem across childhood and adolescence.

Objectives: The goal of this pilot study was to examine brainstem development via MRI volumetry using a longitudinal research design.

Methods: Subjects included 22 boys with autism and 22 gender- and aged-matched controls (age range = 7-17 years), all without intellectual disability.  Structural MRI scans were obtained twice for each participant, once at baseline and again at two-year follow-up.  Brainstem volumetric measurements were performed using the BRAINS2 software package.

Results: There were no significant differences in age and total brain volume between the two groups, but full-scale IQ was higher in controls.  Autism and control groups showed different patterns of growth in brainstem volume.  While whole brainstem volume remained relatively stable in controls over the two-year period, the autism group showed increases with age achieving normalization by age 15 years.  This normalization of whole brainstem volume was primarily driven by increases in gray matter volume.  These changes were similar across the left and right brainstem regions.

Conclusions: Findings from this study are suggestive of developmental brainstem abnormalities in autism primarily involving gray matter structures.  These results are consistent with autism being a neurodevelopmental disorder with alterations in brain-growth trajectories.  More longitudinal MRI studies are needed integrating longitudinal cognitive/behavioral data to elucidate the clinical significance of these atypical growth patterns.