Abstracts

Rationale: Medial temporal lobe epilepsy (MTLE) has been traditionally associated with hippocampal and medial temporal lobe atrophy. Recent quantitative MRI studies have suggested that brain atrophy in MTLE is more pervasive than indicated by visual inspection, affecting a network of extra-hippocampal and extra-temporal limbic structures. However, it is unclear whether brain damage is a constant phenomenon across patients with MTLE, as most data on MTLE brain atrophy relates to the average volume reduction in groups of patients. This study aimed to evaluate where and how much, within the average network of brain damage, atrophy is more likely to occur in individual patients with MTLE. Methods: We studied 23 consecutive patients (mean age 38±11 years, 12 women) who were diagnosed with unilateral MTLE according to the parameters defined by the ILAE (8 right sided and 15 left sided). A gender and age matched control group was composed of 34 subjects. The study was approved by the IRB of our institution. All participants underwent high resolution MRI. Voxel based analysis of gray matter volume was performed on an isotropic T1 from all subjects. A t-test was employed to evaluate the average location and extent of brain atrophy in MTLE patients compared to controls. Gray matter images were then submitted to a voxel by voxel calculation of the fitted Receiver Operator Characteristic (ROC) curve area, plotting the sensitivity versus (1 - specificity) for a binary classifier (MTLE versus controls). An area under the curve (AUC) was calculated for each voxel and a resulting voxel based three-dimensional map of gray matter wise AUCs was obtained. Results: As a group, patients with MTLE showed a significant reduction in gray matter volume in the ipsilateral hippocampus, medial temporal lobe and limbic structures (results of t-test in upper panel on Figure 1). Compared to the group average atrophy, some areas also exhibited a significantly large AUC. In particular, the areas where the AUC was elevated were the ipsilateral hippocampus and medial temporal lobe, the ipsilateral thalamus and occipito-temporal cortex, the ipsilateral cerebellum, the cingulate, the contralateral insula, occipito-parietal and dorsolateral prefrontal cortex (lower panel on Figure 1). Conclusions: This study shows that the medial temporal lobe, occipito-temporal areas, cerebellum, cingulate, insula and thalamus are frequently atrophied in consecutive patients with MTLE. Structures such as orbito-frontal cortex, contralateral medial temporal areas and insula, putamen and caudate may be atrophied, but not as consistently (Figure 2). These findings corroborate that MTLE is associated with a typical network of brain damage.