Voxel-based morphometric comparison of hippocampal and extrahippocampal abnormalities in patients with left and right hippocampal atrophy

We used voxel-based morphometry (VBM), an automatic whole-brain MR image analysis technique, to investigate gray matter abnormalities in patients with temporal lobe epilepsy (TLE), in whom hippocampal atrophy (HA) was demonstrated by application of the Cavalieri method of modern design stereology. VBM results (P < 0.05, corrected) indicated preferential gray matter concentration (GMC) reduction in anterior hippocampus in patients with left HA and posterior hippocampus in patients with right HA. GMC reduction was also found in right dorsal prefrontal cortex in left and right HA patients. Prefrontal atrophy may be due to epileptiform excitotoxic discharges from the reciprocally connected pathological hippocampus, and may be the underlying biological cause for executive dysfunction in patients with TLE. GMC excess in ipsilateral parahippocampal, cerebellar, and pericallosal regions was common to both left and right HA groups relative to controls, and is hypothesized to reflect diminished gray-white matter demarcation, underlying white matter atrophy, or structural displacement due to cerebrospinal fluid expansion. However, bilateral temporal lobe GMC excess was observed in left HA patients, while ipsilateral temporal lobe GMC excess was observed in right HA patients. This work demonstrates methodological consistency between automated VBM and manual stereological analysis of the hippocampus in group comparisons, indicates widespread extrahippocampal gray matter abnormalities in unilateral HA, and suggests that there may be inherent differences in the effect of TLE on temporal lobe structures depending on the side of HA.