Midsagittal structural differences and sexual dimorphism of the corpus callosum in obsessive-compulsive disorder

Neurobiological abnormalities in various brain regions, including the orbitofrontal cortex, basal ganglia, and thalamus, have been found in patients with obsessive-compulsive disorder (OCD), and impairment in white matter connectivity in these regions has recently been suggested. To investigate structural connectivity in OCD, we used the midsagittal area and thickness to assess the morphology of the corpus callosum (CC), the largest connecting fiber tract in the human brain. Midsagittal magnetic resonance images of the CC were acquired from 69 adult patients with OCD and 69 matched normal controls. We calculated and compared the total area and the areas of five subregions of the CC as well as the distances between 200 equidistant points on the top and bottom of lines on the surface of the CC in the two groups. The absolute total area of the CC was significantly larger in OCD patients than in controls when brain size, age, gender, and IQ were controlled. Significant enlargements in CC1, CC2, and CC5 were seen in OCD patients before correction for multiple comparisons. The thickness of the caudal part of the splenium was greater in OCD patients than in controls. The analysis according to gender showed that only male OCD patients differed from male controls with respect to the area of the CC. These findings reflect structural abnormalities in the CC, and especially in the splenium, in adult patients with OCD. Abnormal interhemispheric connectivity, including the parietotemporal and occipital areas, may affect the pathophysiology of OCD. Sexual dimorphism in the CC of OCD patients should be considered.