Diffusion tensor tractography of the corpus callosum in major depressive disorder: a case-control study

Major Depressive Disorder (MDD) is a common and disabling psychiatric disorder that has been associated with alterations in white-matter microstructure, including abnormalities of the corpus callosum. This study aimed to compare the brain tracts of the corpus callosum using diffusion tensor tractography in MDD patients and healthy individuals. This case-control study included 30 patients with MDD referred to the 5 Azar Hospital Psychiatric Center in Gorgan, Golestan, Iran, and 30 healthy controls with normal MRI findings and no history of psychiatric medication use. Fractional anisotropy (FA) and mean diffusivity (MD) were assessed for the whole corpus callosum and its five anatomical subregions: the rostrum, genu, body, isthmus, and splenium. Group differences in corpus callosum diffusion measures were assessed using analysis of covariance (ANCOVA), with diagnostic group and sex entered as fixed factors and age and education included as covariates. After adjustment for age, sex, and education, whole corpus callosum fractional anisotropy (FA) was significantly lower in the MDD group than in controls (F(1, 55) = 13.15, p < 0.001, η² = 0.178). Regional analyses showed lower FA in the rostrum, genu, body, isthmus, and splenium, and these effects remained significant after false discovery rate correction. In contrast, no significant group differences were observed for whole or regional mean diffusivity MD (all p > 0.05). These findings support altered interhemispheric white matter integrity in MDD and suggest that FA may be more sensitive than mean diffusivity for detecting group-related microstructural differences in this sample.