Intraoperative Electrocorticography in Temporal Lobe Epilepsy Surgery K. Medani1 , E. Bubrick2, T. Loddenkemper2,3, J. Madsen1,4 and B. Dworetzky2 1 Department of Neurosurgery, Brigham and Women’s Hospital/ Harvard Medical School, 75 Francis Street, Boston, MA  02115 2 Department of Neurology, Brigham and Women’s Hospital/ Harvard Medical School, 75 Francis Street, Boston, MA  02115 3 Department of Neurology, Children Hospital Boston/ Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115 4 Department of Neurosurgery, Children Hospital Boston/ Harvard Medical School, 300 Longwood Avenue, Boston, MA 02115 RATIONALE RESULTS CONCLUSIONS One-hundred-and-seven temporal lobectomies were performed on 99 patients. Of these, 56 patients (57%) underwent intraoperative ECoG recordings immediately prior to and following resection. Temporal lobectomy was performed in 42 of those patients, while 14 underwent lesionectomy. Thirty-five patients were male (62%). The mean age at surgery was 40 years 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 (32%), gliosis (38%), neoplasia (20%), heterotopia (3%), vascular malformation (2%), and no abnormalities (5%). ECoG was performed with intraoperative subdural electrodes using an 8-contact strip in 77% of cases. Various other grids and strips were used for the other 23%. Pre-resection recording from 1 or 2 locations was accomplished in 64% of cases, while recording from more than 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 present in 54% of cases (n=30). Of those, 63% (n=19) went on to have further resection. At follow-up, 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).   There is much debate in the literature on the usefulness of electrocorticography for tailoring resection of the temporal lobe in cases of refractory epilepsy. We investigated an association between intraoperative electrocorticography (ECoG) findings and seizure outcome in a series of patients who underwent temporal lobectomy. Lack of intraoperative ECoG spikes after temporal lobe resection is associated with better outcome. While ECoG is not routinely performed in temporal lobe surgeries for epilepsy, our data suggest that the absence of post-resection ECOG spikes predicts Engel I outcome. Prospective studies to validate this observation are needed. METHODS References 1- The Treatment of Epilepsy: Principles and Practice, 2nd ed. Elaine Wyllie, M.D. Baltimore, William & Wilkins, © 1996. 2-Surgical outcomes in lesional and non-lesional epilepsy: a systematic review and meta-analysis. Tellez-Zeneteno JF, Hernandez Ronquillo L, Moien-Afshari F, Wiebe S. Epilepsy Res. 2010 May; 89(2-3):310-8. Epub 2010 Mar 15.    3- Andre Palmini (2006). "The concept of the epileptogenic zone: a modern look at Penfield and Jasper’s views on the role of interictal spikes'". Epileptic Disorders 8(Suppl 2): S10–15.  Our institutional review board approved this study. Consecutive patients who underwent temporal lobe surgery between 1993 and 2009 were included. Age, gender, date of surgery, seizure localization, duration of epilepsy, and results of pre-operative surgery evaluation including ECoG data were collected. Neuropathology, and surgical outcome (Engel criteria) were obtained by chart review. ECoG spikes were classified by location (inferomesial, lateral, anterior, or superior), and by frequency (occasional, frequent, very frequent, or ictal). Statistical analysis was performed using Chi-Square test. A significance level of p <0.05 was considered significant. Statistical analysis was performed using SPSS for Windows 17.0 (SPSS Inc., Chicago, IL). Acknowledgment Great thanks are attributed to the Department of General surgery at Wayne State University/ Detroit Medical Center for supporting this poster presentation.