Abstracts

Identifying the ictal focus in patients with frontal lobe epilepsy is inherently difficult because EEG patterns are often poorly localizing or non-localizing. Deciding where to place subdural grids for further localization of the non-lesional, frontal, ictal focus can also be difficult due to the large cortical surface area of the frontal lobe and the size of the craniotomy required for thorough frontal lobe coverage. MEG may however provide valuable assistance in determining whether a refractory epilepsy patient is truly a candidate for resective surgery and guide efficient subdural electrode grid/strip placement to seek the final localization in preparation for resection. It may also be helpful in: large lesional cases where a total lesion resection is not feasible, question of frontal vs. temporal focality, question of multi-focality, the setting of normal MRI findings, and when the MRI and EEG findings are discordant., A retrospective chart study was done of ten patients with presumed frontal lobe foci who were evaluated for epilepsy surgery. All ten patients were studied with MRI, MEG, routine and/or video-EEG and some had subdural strip/grid video-EEG monitoring as well. The cases were all discussed in a multi-disciplinary surgery conference prior to the final treatment plan being implemented., Three of 10 had frontal, epileptiform EEG findings on routine EEG, 4 of 10 had non-lateralizing and non-localizing ictal video-EEG and 1 had no EEG changes during a clinical seizure event. Only 4 had an abnormal MRI; 1 with a diffuse dysplasia, 1 with abnormal temporal lobe signal, and 2 with areas of encephalomalacia from prior cerebral hemorrhages. The MEG was beneficial in 9 cases in determining surgical candidacy. In 1 case the MEG showed no abnormality and a repeat study is planned. 3 cases were multifocal and had VNS implanted. 2 of the 3 multifocal cases showed multifocality on the MEG and was consistent with clinical semiology inspite of the fact that video-EEG only showed a single focus. 2 of 10 patients are seizure free and a third patient has had a significant reduction in seizure frequency and severity (focal motor only now). The 2 seizure free patients both had normal MRI scans. In 2 cases, surgery is still pending, however EEG, MRI and MEG are fully concordant in one, and EEG and MEG are concordant in the second with a normal MRI so a positive surgical outcome is hoped for. One patient who underwent resection has had no change in seizure frequency. Interestingly, the MEG suggested a focus different from the focus identified by grid mapping and thus it would suggest the possibility that MEG provided the more accurate information., This data suggests that MEG is a helpful tool in the assessment of complex, frontal lobe surgical evaluations.,