Abstracts

Rationale: Epilepsy surgery is offered in select cases of refractory focal epilepsy. Non-invasive investigations including scalp video EEG monitoring (sVEM), MRI, PET, SPECT and MEG help delineate epileptogenic zone. However, complex cases especially MRI-negative may require invasive video EEG monitoring (iVEM).iVEM can be achieved using subdural grids or strips, epidural electrodes or SEEG. SEEG has become popular due to more spatial resolution, lower morbidity, better tolerance and is superior in sampling deeply located areas. Very few studies have looked into the indications, surgical and non-surgical outcomes of SEEG. Methods: Seventy-two admissions for SEEG were made from 2014 to 2018 at Calgary Epilepsy Program. They included 69 patients (38 males, 31 females) with 3 patients undergoing SEEG twice. Mean age was 34.98± 12.52 (18-70) years. Mean duration of epilepsy was 18.63± 13.16(1-52) years. 37 (51.3%) had lesional MRI.  The frequency of disabling seizures was daily in 12 (17%), weekly in 36 (50%), biweekly in 15 (21%), monthly in 6 (8%) and bimonthly in 3 (4%). Five (7%) had previous iVEM and 11 (15%) had history of previous epilepsy surgery. Results: Reasons for SEEG were obscure/diffuse/non-localising ictal onset (55), ictal-interictal discordance (15), discordant semiology (12) and proximity to eloquent cortex (24). Among lesional cases, sVEM-lesional MRI discordance was cited in 23 and dual or multiple pathology in 10. 23 out of 68 (34%) had discordant nuclear imaging and 13 out of 68(19%) had discordant neuropsychology.  Thirty (42%) had unilateral implantation and 17 (24%) had additional electrodes implanted during course of SEEG. The average number of electrodes and contacts per implantation were 11.22± 3.55 (4-22) and 84.33± 26.79 (32-154) respectively. The average number of seizures recorded and the average duration of monitoring were 49.22± 188.36 (1-1583) and 14.61± 8.37(5-47) days respectively. Seven patients (10%) had complications including intracerebral hematoma (4), broken electrode (4), extradural hematoma (1), subarachnoid hemorrhage (1).Forty-eight (67%) were offered resective surgery after SEEG, of which 40 underwent surgery. Eighteen (45%) had at least one year follow up with average 23.88±12.63 (12-45) months of which 11 (61%) had Engel class I outcome. Follow up of 25 patients who continued on medical management were available of which 6 (24%) became seizure free, 12 had reduction in seizure frequency, 4 remained stable and 3 had increase in seizure frequency at last follow up. Conclusions: SEEG monitoring is an important relatively safe tool for presurgical evaluation with good surgical and non-surgical outcomes. Whether seizure freedom following non-surgical management is related to SEEG or natural course needs to be determined. Funding: No funding