Brain circuitries of obsessive compulsive disorder: a systematic review and meta-analysis of diffusion tensor imaging studies.

The potential role of white matter (WM) abnormalities in the pathophysiology of obsessive compulsive disorder (OCD) is substantially unexplored. Apart from alterations in the WM tracts within cortico-striato-thalamo-cortical circuitry, recent theorizations predict the existence of more widespread WM abnormalities. In this paper we systematically reviewed the current diffusion tensor imaging literature in OCD and purposely evaluated the prevalence and functional significance of specific WM tissue changes in the disorder. The relationship between clinical variables (medication status, symptom severity) and WM microstructural changes was also assessed. The reviewed studies are consistent with the existence of microstructural alterations in the fronto-basal pathways targeting the orbitofrontal cortex and the anterior cingulate cortex. Moreover, altered anatomical connectivity between lateral frontal and parietal regions and microstructural abnormalities in intra-hemispheric bundles linking distinctive areas of the prefrontal cortex to posterior parietal and occipital association cortices, are consistently reported. Finally, microstructural abnormalities in the corpus callosum, characterized by decreased connectivity in the rostrum and hyperconnectivity in the genu, are substantiated by a large body of evidence.