Volumetric analysis of hippocampal sub-regions in late onset depression: a 3 tesla magnetic resonance imaging study.

BACKGROUND While many studies have reported reduced volume of hippocampus in late onset depression (LOD), the status of hippocampus sub-regions (anterior/posterior) is yet to be explored. Evaluating hippocampal sub-regions might facilitate better elucidation of the neurobiological basis of LOD. METHODS Twenty five elderly subjects with LOD (mean age=65.28yr, SD=5.73, 15 females) and 20 healthy controls (mean age=65.35yr, SD=5.67, 7 females) were examined using 3-tesla magnetic resonance imaging (MRI). They were also evaluated with Montgomery Asberg Depression Rating Scale (MADRS) and Hindi Mental State Examination (HMSE). We examined the difference in volume of Hippocampal sub-regions between the LOD group and control group controlling for the age, sex and intracranial volume. RESULTS Left posterior hippocampus volume was significantly smaller in LOD group than the control group (1.01±0.19ml vs 1.16±0.25ml, F=7.50, p=0.009). There was a similar trend for the right posterior hippocampus (1.08±0.19ml vs 1.18±0.27ml, F=3.18, p=0.082). Depression severity (mean MADRS score=20.64±8.99) had a significant negative correlation with volumes of right posterior hippocampus (r=-0.37, p=0.012) and left posterior hippocampus (r=-0.46, p=0.001) in the LOD group. CONCLUSIONS Specific reduction of posterior hippocampus volume and its relationship with depression severity indicates sub region specific hippocampal volumetric abnormalities in LOD. Future studies need to evaluate sub region specific hippocampal volume in LOD longitudinally for better understanding of the pathogenesis of LOD in view of the functional differences between anterior and posterior hippocampus.