Abstracts

Rationale: The utility of post resection electro-corticographic (ECoG) recordings following epilepsy surgery, in predicting outcome or guiding additional resection is unclear. We perform post-resection ECoG in patients undergoing resective surgery for epilepsy, though this is not generally used to modify the surgical plan. Thus we make predictive assessments of the inherent value of post-resection ECoG in seizure outcome. Additionally, given the relatively large numbers, we are able to control for relevant confounders such as location of the epilepsy, presence of an obvious lesion and duration of the epilepsy. Methods: From a prospectively compiled database of 195 patients undergoing epilepsy surgery by a single surgeon at the University of Texas Comprehensive Epilepsy Program, we compiled a list of all adult patients (Age>18) who had undergone post-resection ECoG following respective surgery and had follow-up data for a minimum of six months post-operatively. Demographic data, clinical details such as duration of epilepsy, age at onset, the type of resection (neocortical vs. limbic), lobe of resection, etiology of epilepsy (from histo-pathology, imaging and clinical presentation) and outcome (Engel and ILAE scores) were compiled and updated based on most recent follow-up. An ordered logistic regression analysis was used to predict seizure outcome as measured by the ILAE scale was performed (Stata). Independent variables in the model were post resection ECoG (0=no findings, 1=subtle or rare discharges 2=significant discharges), age of onset of epilepsy, duration of epilepsy, resection type (1=mesial temporal, 2=temporal neocortical and 3=extra-temporal) and pathology type (1=cavernoma/tumor, 2=mesial temporal sclerosis (MTS) / focal cortical dysplasia (FCD), 3=gliosis / heterotopic neurons/encephalomalacia). Results: Seventy five patients were included in the analysis (mean age 35 yrs, 56 % female). The mean duration of years living with epilepsy prior to surgery was 17.9 years. There were 52 (69.3%) mesial temporal lobe surgeries, 7 (9.3%) temporal neocortical only and 16 (21.3%) extratemporal neocortical cases. Pathology identified 15 cases of cavernoma/tumor (group 1), 40 cases of mesial temporal sclerosis/ focal cortical dysplasia (group two) and 20 cases of other non-specific pathologies such as gliosis, encephalomalacia (group three). A logistic regression model incorporating these variables revealed that more nonspecific pathologies categorized in group 3 (gliosis and heterotopias and encephalomalacias) > MTS/FCD > defined lesions categorized in group 1 (such as tumor/cavernoma) predicted a higher i.e. worse ILAE outcome score (OR 1.65 (1.29; 5.46). Also, the presence of post resection spikes significant > rare >none predicts higher ILAE outcome score (OR=1.91 (1.08; 3.38). Conclusions: The underlying pathology and the presence of post resection spike discharges alone, not the location of surgery predict worse outcomes after epilepsy surgery. This study clearly demonstrates the significant impact of no epileptiform discharges on seizure free outcome.