Abstracts

Rationale: The value of MEG in evaluating focal epilepsy in presurgical evaluation is multifactorial and includes guiding placement of subdural grids. We report a case of frontal lobe epilepsy where subdural grids did not clearly demonstrate ictal onset and MEG showed lateral frontal spikes. Methods: 21 year old with refractory epilepsy who had previous partial inferior frontal cortex removal underwent reoperation. Video EEG with scalp recording suggested left mesial frontal SMA epilepsy. Results: MEG suggested possible left lateral frontal focus anterior to motor strip based on spike clusters. Subdural grid placed in lateral frontoparietal area did not confirm ictal onset zone although seizures were elicited from several electrodes during cortical stimulation. Subsequent placement of additional subdural electrodes in mesial frontal areas suggested propagation to this region but again no definite ictal onset zone. Resection of areas adjacent to MEG spikes,using MRI with subdural grids corregistered to MEG, resulted in seizure relief. Conclusions: MEG may demonstrate ictal onset zone in areas not accessible to subdural grids placed on superficial layers of cortex. Lesions have been shown to obscure the ictal zone from subdural electrodes. In this non-lesional case, with conflicting scalp and VEEG information, MEG demonstrated deep neocortical seizure focus interictally which was suggested but not confirmed by subdural grids.