Voxel-based morphometry of the thalamus in patients with refractory medial temporal lobe epilepsy

Previous research has suggested that patients with refractory medial temporal lobe epilepsy (MTLE) show gray matter atrophy both within the temporal lobes as well as in the thalamus. However, these studies have not distinguished between different nuclei within the thalamus. We examined whether thalamic atrophy correlates with the nuclei's connections to other regions in the limbic system. T1-weighted MRI scans were obtained from 49 neurologically healthy control subjects and 43 patients diagnosed with chronic refractory MTLE that was unilateral in origin (as measured by ictal EEG and hippocampal atrophy observed on MRI). Measurements of gray matter concentration (GMC) were made using automated segmentation algorithms. GMC was analyzed both voxel-by-voxel (preserving spatial precision) as well as using predefined regions of interest. Voxel-based morphometry revealed intense GMC reduction in the anterior portion relative to posterior thalami. Furthermore, thalamic atrophy was greater ipsilateral to the MTLE origin than on the contralateral side. Here we demonstrate that the thalamic atrophy is most intense in the thalamic nuclei that have strong connections with the limbic hippocampus. This finding suggests that thalamic atrophy reflects this region's anatomical and functional association with the limbic system rather than a general vulnerability to damage.