Abstracts

Rationale: Good surgical outcome of epilepsy can be achieved when there are concordant neurophysiological and structural studies. Non-lesional neocortical epilepsy is associated with a poor surgical outcome.Historically, invasive EEG has been the most utilized procedure to further evaluate for potential surgery. Recently, MEG/MSI has become a valuable tool in identifying the epileptogenic zone, primarily by localizing interictal epileptiform discharges. Eleven non-lesional neocortical pediatric epilepsy patients with MSI as part of the pre-surgical evaluation for epilepsy surgery from Minnesota Epilepsy Group were reviewed.Methods: Six female and 5 male (ave 11.7 yrs ) with medically refractory neocortical epilepsy were included in the study. All the patients underwent standard clinical evaluation including continuous scalp EEG recording, MRI with epilepsy protocol and MSI. MEG was recorded with a 148-MEG channel whole-head system housed in a magnetically shielded room, scalp EEG was recorded simultaneously. Interictal epileptiform activity was modeled as single equivalent current dipole. Results: With the guidance of MSI, MRIs of the 11 patients were re-evaluated . Three patients were identified with extra subtle findings, such as, blurred gray white matter, thickening of cortex, or mild white matter changes and/or focal atrophic change. Eight patients underwent invasive subdural electrode implantation, 5 of these patients had resective surgery. Among the 5 patients with resective surgery, four patients have been seizure free with medication (5 months to 7 yrs, median 44.5 months follow-up), the other patient has had an 80 percent reduction in seizures (29 months follow-up). The resected region correlated completely with MSI clusters of interictal spikes in 4 patients, there was a partial overlap in one patient. The pathological findings indicate 3 patients with focal cortical dysplasia, 2 with mild to moderate astrogliosis. In the 3 patients who underwent subdural electrode implantation without further resection, ictal ECoG defined the epileptogenic zone, which overlapped with MSI localization of the interictal epileptiform activity. Unfortunately there was overlap with the eloquent cortices, and resective surgery was not performed. This overlap was seen by MSI and confirmed with subdural electrode mapping. Two of the 3 remaining patients are scheduled for surgery. One patient had diffuse bilateral MSI abnormalities and was not considered a good surgical candidate.Conclusions: With our limited data, we conclude that MSI should be considered as a standard test in non-lesional neocortical epilepsy for presurgical evaluation. Guided by MSI epileptogenic localization re-evaluation of structural imaging may re-categorize the non-lesional to lesional , Secondly, MSI, a non-invasive procedure, may improve invasive electrode placement or in some cases guide the surgery directly. Lastly, invasive evaluation might be avoided after MSI indicated a patient may be a non-surgical candidate based on the epileptogenic zone overlapping with eloquent cortex. We thank Ms Lisa Buck for her technical support.