Abstracts

Rationale: To determine whether intraoperative electrocorticography (ECoG) can aid in tailoring the extent of resection in temporal lobe epilepsy (TLE) and predict outcome. We investigated an association between intraoperative ECoG findings and seizure outcome in a series of TLE patients. Methods: Consecutive patients who underwent temporal lobe surgery between 1993 and 2009 were included. Patient demographics including date of surgery, seizure localization, duration of epilepsy, and results of pre-operative surgery evaluation including ECoG data were analyzed. Surgical outcome, pathology, and Engel criteria were obtained. For patients who underwent a second operation for epilepsy (N=2), ECoG data from the first operation was used. Recorded spikes were classified based on frequency of occurrence as occasional, frequent, very frequent and ictal patterns. Results: One-hundred-and-seven temporal lobe resections were performed on 99 unique patients. Of these, 56 patients (57%) underwent intraoperative ECoG recordings at the time of surgery, immediately prior to and after resection, without any other prolonged intracranial recordings. Temporal lobectomy was performed in 42 of those patients, 14 underwent lesionectomy. Thirty-five patients were male (62%). The mean age at surgery was 40 years (yrs) (range= 23-82 yrs), and the average duration of epilepsy was 24 yrs (range =2-51 yrs). Thirty-four (61%) of the surgeries involved the left temporal lobe. The average follow-up period was 5 yrs (range: 6 months-17 years). Neuropathology revealed mesial temporal sclerosis in 32% (18 patients), mild gliosis (21), neoplasia (11), heterotopia (2), vascular malformation (1), and normal appearing tissue (3). ECoG was performed with intraoperative subdural electrodes using an 8-contact strip in 77% of cases, the remaining involved various configurations of grids and strips. Pre-resection recording from 1 or 2 locations was accomplished in 64% of cases, while recording from >2 locations occurred in 36%. Epileptic discharges were detected in 89% of pre-resection recordings, with 62% occurring in the inferomedial temporal lobe. Spike frequency was categorized as occasional (58%), frequent (38%), or very frequent (2%). Ictal patterns were also identified (2%). After the initial resection, spikes were still identified in 54% of cases (n=30). Of those, 63% (n=19) went on to have further resection. On follow up after an average of 5 yrs, Engel class I was achieved in 23 out of the 26 patients who were spike-negative after their initial resection (88%), and in 19 patients out of the 30 patients (63%) who continued to have spikes after the initial resection (p < 0.05). Conclusions: Intraoperative ECoG in TLE surgery predicts outcome. Lack of intraoperative ECoG spikes after temporal lobe resection lead to improved outcome. While ECoG is not routinely performed in temporal lobe surgeries for epilepsy, our data suggests that ECoG may help predict outcome, with the absence of post-resection spikes linked to Engel I scores. Prospective studies to validate this observation are needed.