Medicated children with OCD had smaller left and right hemisphere total surface area, reflecting a diffuse pattern of frontal surface area deficits. These findings cannot be explained by differences in illness severity, comorbidity or age at onset (Supplementary Table S35). This may indicate delayed cortical maturation, although longitudinal studies are needed to prove that. The surface area of these frontal regions matures over a more prolonged time course during adolescence (41) and may be especially prone to a maturational delay in pediatric OCD, possibly affected by medication status. Such delayed maturation may alter functional connections with other regions through decreases in growth and branching of dendritic trees and the number of synapses associated with gray matter volume (42), which may persist into adult OCD even if surface area measures normalize when transitioning into adulthood. The absence of cortical surface area abnormalities in the adult OCD patients with a childhood-onset could indicate such normalization.
