Abstracts

RATIONALE: Our aim was to clarify the utilities and the limitations of recent whole head magnetoencephalography (MEG) for presurgical seizure localization in neocortical epilepsy.
METHODS: Twenty epileptic foci in 19 patients with intractable neocortical epilepsy were preoperatively examined using whole head MEG (Neuromag204) system. Data were analyzed using the equivalent current dipole (ECD) method. ECDs were superimposed onto individual sectional and three-dimensional MR images. Seizure localization on MEG was determined by the cluster of interictal spike sources (over 10 ECDs) or ictal onset sources, and compared with electrocorticography (ECoG) using chronically implanted electrodes in 18 foci and intraoperative ECoG in 2. We evaluated #1) reliability of interictal and ictal MEG, and #2) localization accuracy in the cerebral lateral, medial, and basal surfaces.
RESULTS: In this consecutive series, MEG determined 18 (90%) of 20 foci from ictal and interictal data. Sixteen (80%) were perfectly concordant with the epileptogenic zone determined by ECoG.
#1) MEG obtained 18 interictal spike zones. Those were strictly concordant with the interictal spike zone on ECoG in 17 (94%), and concordant with epileptogenic zone in 15 (83%). Ictal MEG data were obtained in 5 and identified 4 foci (80%) except 1 lateral frontal focus manifesting sudden clinical onset with large movement.
#2) Of 14 lateral, 3 medial, and 3 basal foci, MEG accurately or nearly identified 14 (100%), 1 (33%), and 3 foci (100%), respectively. Two (66%) in the medial surface were failed.
CONCLUSIONS: Recent whole head MEG is the sensitive examination as the presurgical seizure localization method in neocortical epilepsy. However, there are some limitations in appropriately interpreting interictal or ictal data of some patients, and in localizing the deeply underlying spike sources such in the cerebral medial surface.