Abstracts

Rationale: Only about 40% of nonlesional epilepsy patients achieve seizure-free status after surgery. Moreover, few electrophysiological studies have included magnetoencephography (MEG) when assessing the diagnostic value of presurgical modalities in a nonlesional epilepsy population. Here, we compare four electrophysiological modalities, SPECT, PET, video-EEG (VEEG), and MEG, with intracranial EEG (iEEG) to determine the value of individual modalities to surgical decisions in adult nonlesional neocortical epilepsy patients. Methods: We retrospectively analyzed 23 adult patients (30.7±9.0 years; 10 females) with no abnormal MRI findings who had undergone surgical resection for intractable epilepsy between 2005 and 2011 at Seoul National University Hospital, Korea. The mean postoperative follow-up period was 2.9 years (SD = 1.3 years). Localization of individual presurgical tests was determined for hemispheric and lobar locations based on visual analysis. For MEG, the interictal spike was visually inspected and localized using the single equivalent current dipole (ECD) method. Each localization result was compared with the ictal onset zone (IOZ) defined by using iEEG and concordance rates for each modality were calculated. Thereby, we elucidated the value of preoperative MEG ECDs in predicting surgical outcome. Results: Postoperative seizure outcome was Engel class I in 5 (22%) patients, class II in 3 (13%), class III in 10 (43%), and class IV in 5 (22%) patients. The highest to the lowest hemispheric concordance rates, compared to the iEEG IOZ, were MEG (83%) > ictal VEEG (78%) > PET (70%) > ictal SPECT (57%). The highest to lowest lobar concordance rates, compared to the iEEG IOZ, were ictal VEEG = MEG (65%) > PET (57%) > ictal SPECT (52%). MEG had the highest concordance rate with IOZ at both hemispheric and lobar levels. Statistical analysis showed MEG to have a significantly higher hemispheric concordance with the IOZ than that of ictal SPECT (p < 0.05). We further analyzed the effects of MEG ECD clustered-area resection on surgical outcome. Patients who had resection of MEG ECDs showed a better surgical outcome than those without such resection (p < 0.05). Conclusions: Our results show that MEG-based localization had the highest concordance with the iEEG-defined IOZ. Furthermore, MEG ECD resection has prognostic significance in predicting surgical outcome.