A two-year longitudinal pilot MRI study of the brainstem in autism.

•Autism and control groups showed different patterns of brainstem growth.•Whole brainstem volume remained stable in controls over the two-year period.•Whole brainstem volume increased in the autism group over the two-year period.•Normalization of brainstem volume was primarily driven by increases in gray matter.•Autism is a neurodevelopmental disorder with alterations in brain-growth trajectories.