Mesial temporal lobe epilepsy with hippocampal sclerosis: comparative clinical and arterial spin labeling findings according to neocortical MRI changes.

Purpose: High-field strength MRI reveals that Mesial Temporal Sclerosis (MTS) can be divided into two entities-(1) MTLE-HS (Mesial Temporal lobe epilepsy with hippocampal involvement), (2) MTLE-HS[N] (Mesial temporal lobe epilepsy with hippocampal sclerosis, and neocortical changes). The purpose of the study was to identify clinical, electrophysiological, histopathological, post-operative outcome differences between these entities and evaluate the role of Arterial spin labeling (ASL) in this regard.

Methods: Prospective observational study in MTS-patients undergoing epilepsy protocol-MRI (including 3D-ASL with pseudo-continuous tagging), followed by anterior-temporal lobectomy + amygdalohippocampectomy (ATL + AH). Based on T2WI/3D-FLAIR MRI findings, patients were classified into MTLE-HS and MTLE-HS[N]. The ASL, clinical, VEEG, histopathological characteristics, postoperative outcomes were compared.

Results: The MTLE-HS[N] and MTLE-HS groups had 63 and 37 patients respectively. MTLE-HS[N] group showed earlier age of epilepsy onset (7.82 ± 6.19y vs. 11.12 ± 8.1y, P-value = 0.04) and higher incidence of neocortical epileptogenesis (66.67% vs. 13.51%, P-value < 0.001). Histopathology revealed diffuse temporal neocortical astrogliosis in all patients, myelin loss in some patients from both groups and neocortical dysplasia in 6 patients with no significant differences in individual histopathological characteristics or postoperative outcomes. Within the MTLE-HS[N] group, more patients with neocortical epileptogenesis had ASL abnormality (P < 0.05). Qualitative ASL abnormality was also seen in most (83.33%) patients with neocortical dysplasia.

Conclusion: Although MTLE-HS and MTLE-HS[N] show differences in certain clinical, electrophysiological features, the postoperative outcomes were not different. MRI cannot predict the histopathological substrate responsible for temporal neocortical changes. ASL may be useful in predicting neocortical epileptogenesis. It could also help to postulate the presence of dysplasia, although this needs further evaluation for confirmation.