Voxel-based morphometry reveals gray matter network atrophy in refractory medial temporal lobe epilepsy

Background: Conventional volumetric studies have shown that brain structures functionally and anatomically related to the hippocampus are smaller in patients with drug-refractory medial temporal lobe epilepsy (MTLE). Objectives: To determine the extent of gray matter atrophy in the brains of patients with MTLE and to examine the pattern of atrophy; Design: We performed a voxel-based morphometric study of 43 consecutive patients with unilateral drug-refractory MTLE (21 patients with right-sided MTLE and 22 patients with left-sided MTLE) whose magnetic resonance images showed signs of unilateral hippocampal atrophy. The data from the patients with MTLE were compared with the data from 49 healthy control subjects to identify differences between groups in gray matter concentration (GMC). Setting: Academic hospital's epilepsy clinic. Results: We observed that patients with left- and right-sided MTLE exhibited GMC reduction in the hippocampus ipsilateral to the seizure origin. In addition, we found GMC reduction in the ipsilateral parahippocampal and isocortical temporal regions. Patients with MTLE also showed GMC reduction in subcortical nuclei such as the thalamus and caudate, in the cerebellum, in the midbrain, and in parieto-occipital regions. Conclusions: Patients with MTLE exhibit a reduction in GMC in regions outside the temporal lobe, specifically in areas that are connected to the hippocampus and parahippocampal region, suggesting an anatomical route for atrophy.