Habenula volume increases with disease severity in unmedicated major depressive disorder as revealed by 7T MRI.

The habenula is a paired epithalamic structure involved in the pathogenesis of major depressive disorder (MDD). Evidence comes from its impact on the regulation of serotonergic and dopaminergic neurons, the role in emotional processing and studies on animal models of depression. The present study investigated habenula volumes in 20 unmedicated and 20 medicated MDD patients and 20 healthy controls for the first time by applying a triplanar segmentation algorithm on 7 Tesla magnetic resonance (MR) whole-brain T1 maps. The hypothesis of a right-side decrease of habenula volumes in the MDD patients was tested, and the relationship between volumetric abnormalities and disease severity was exploratively investigated. Absolute and relative total and hemispheric habenula volumes did not differ significantly between the three groups. In the patients with short duration of disease for which medication effects could be ruled out, significant correlations were found between bilateral habenula volumes and HAMD-17- and BDI-II-related severities. In the medicated patients, this positive relationship disappeared. Our findings suggest an involvement of habenula pathology in the beginning of MDD, while general effects independent of severity or stage of disease did not occur. Our findings warrant future combined tractographic and functional investigation using ultra-high-resolution in vivo MR imaging.