BACKGROUND: Many neuroimaging studies exploring the volumes of brain structures in obsessive-compulsive disorder (OCD) have been published in the past 2 decades. In this study, we attempted to provide a complete overview of structural alterations in OCD by meta-analyzing magnetic resonance imaging (MRI) data. METHODS: We conducted a systematic search of MRI studies that reported volumetric measurements in both OCD patients and healthy subjects. Data were entered into the meta-analysis through calculation of the standardized mean differences (SMDs) between the volumes of cerebral regions in OCD patients and the corresponding volumes in control subjects. We then performed a meta-regression to explore the influence of clinical covariates on effect sizes. RESULTS: Although no volumetric differences were found for the whole brain, intracranial region, gray matter, or prefrontal cortex, OCD patients did show a reduced volume of the left anterior cingulate cortex (ACC) and the left and right orbitofrontal cortex (OFC). No significant volumetric differences within the basal ganglia were observed, although the left and right thalamic volumes were significantly increased in OCD patients. The severity of obsessive or compulsive symptoms correlated significantly with the effect sizes for the left and right thalamus. CONCLUSIONS: Our findings indicate volumetric differences between OCD patients and control subjects in the cortical and thalamic regions, suggesting that structural alteration of the thalamocortical pathways may contribute to the functional disruptions of frontosubcortical circuits observed in OCD.
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