Abstracts

Rationale: Dual pathology has been defined as the coexistence of both extrahippocampal lesion and hippocampal sclerosis in a pathological state. Numerous studies have revealed that a better seizure outcome can be established by the removal of both abnormalities than lesionectomy or mesial temporal resection alone. However, it is necessary to demarcate the precise extratemporal lesion-related epileptogenic zone (ETL-EZ) for optimal seizure outcome. This study is to elucidate whether magnetoencephalography (MEG) can identify the extent of ETL-EZ for presurgical evaluation in patients with dual pathology. Methods: We retrospectively analyzed MEG data in 5 patients (A-E) who underwent resective surgery based on intracranial video-EEG (IVEEG). MEG was performed with 36-channel whole-head type system which included 204 channels of planar gradiometers. We classified distributions of an equivalent current dipole (ECD) into clusters and scatters as previously reported (Iida K et al., 2005), and compared the ECD-based distribution of epileptic areas, IVEEG results, and seizure outcome. Results: Single-cluster ECDs were located over the middle peri-sylvian (A), posterior temporal (B), and posterior temporal to inferior parietal (C) regions in 3 patients (A-C). Two independent clusters were observed in the inferior-temporal and inferior parietal to lateral occipital regions in 1 patient (D). MEG localized clusters within or extended from ETL. The remaining patient (E) had no epileptic spikes on MEG recording. All single-clusters and two independent clusters were colocalized to IVEEG- or ECoG-defined epileptic zones demarcating the ETL-EZ in 4 patients (A-D: 3 single-clusters and both of 2 clusters). All patients underwent anterior temporal lobectomy (including hippocampectomy) and lesionectomy (total: n=5; A-E; partial: n=1; A) with (n=3: BDE) or without (n=1: C) additional cortical resection of ETL-EZ on IVEEG. One patient (C) underwent additional multiple subpial transection of the ETL-EZ due to language-associated area. Four patients had excellent seizure outcome (Engel class I), and the patient with partial lesionectomy indicated more than 90 % seizure reduction (Engel class II). Conclusions: MEG can identify the extent of ETL-EZ in patients with dual pathology, as useful information for planning of IVEEG implantation.