Abstracts

Rationale: Recording of electrical activity directly on the brain cortical surface using electrocorticography (ECoG) is routinely performed to aid in defining resection margins during tailored temporal lobe resections for epilepsy. However, ECoG post-resection recording is controversial as to whether the presence of confirmed epileptic spikes indicates an active seizure focus thus prompting the surgeon to perform further resection. This is commonly known as “chasing” the spikes among the epilepsy surgical community. While a number of studies have investigated post-resection spikes and outcome, few studies have been conducted since the year 2000 when newer digital ECoG recordings gained more widespread use. Furthermore, few studies have examined the long term (≥ 2 yrs.) predictive value of post-resection ECoG spikes on outcome. The goal of this study is to assess whether post-resection ECoG epileptic spikes will predict long term outcome after temporal lobectomy. Methods: Medical records of 50 patients who underwent neurosurgery for medically refractory seizures at the Via Christi Comprehensive Epilepsy Center were reviewed. Data was obtained for the following: 1. Pre-operative electroencephalogram (EEG) or video-EEG, 2. PRE-resection ECoG, 3. POST-resection ECoG, 4. Pathology of mesial temporal sclerosis or gliosis, and 5. Post-operative outcome based upon the Engel classification system (“good outcome”: grade I, “poor outcome”: grade II, III, or IV). Patients were excluded if they were less than 18 years of age, had prior brain surgery, extra-temporal lobe epilepsy, extra-temporal interictal spikes, lesional or neoplastic pathological findings, or post-operative follow-up less than 2 years. Patients were then analyzed in two groups based upon the presence or absence of post-resection ECoG spikes. Results: Of the initial 50 patients, 20 qualified for further analysis. Of those 20 patients, 15 had post-resection ECoG spikes. In the group with post-resection spikes, 14 (93.3%) had good long term post-operative outcomes and 1 (6.7%) had a poor long term post-operative outcome (mean follow-up: 40.6 mo., median follow-up: 34 mo.). Of the five patients in the group without post-resection spikes, 2 (40%) had good long term post-operative outcomes while 3 (60%) had poor long term post-operative outcomes (mean follow-up: 50.2 mo., median follow-up: 58 mo.). Conclusions: Our pilot study suggests that the presence of post-resection spikes on ECoG for MTS temporal lobe epilepsy does not necessarily predict poor long term outcome and that further justification and studies need to be provided if “chasing” of spikes is to be pursued.