Abstracts

Rationale: Prior research demonstrated the utility of electrocorticography (ECoG) over the intraventricular surface of the hippocampus in determining the extent of hippocampal resection in patients with temporal lobe epilepsy (TLE) (McKhann et al., J Neurosurg. 2000; 93: 44-52). However, patients undergoing reoperation were not included in the analysis, and no data was presented concerning spike frequency or occurrence of electrographic seizures. We report 4 patients with TLE in whom intraventricular hippocampal ECoG was performed, capturing ictal discharges in 2 patients. Methods: Four patients with TLE (3 right temporal, 1 left temporal) were retrospectively reviewed. Two had undergone previous resection of the right anterior temporal lobes without seizure freedom. All surgeries but one (the initial resection in one patient with right TLE, 12 years earlier) were performed by the same neurosurgeon. All ECoG studies were read by board-eligible or board-certified electroencephalographers. ECoG was performed over the intraventricular surface of the hippocampal remnant (if reoperation) or the hippocampus after initial anterolateral temporal lobe resection (if initial operation). Results: ECoG performed for 5-10 min over the intraventricular surface of the hippocampus revealed seizures (4 in one patient, and 2 in the second) in both previously resected patients. In one of these patients, previous subdural electrode recording had shown recurrent but much less frequent electrographic seizures involving parahippocampal contacts. Interictal spikes, approximately 15-20 per min, were seen in the patient with left temporal lobe epilepsy after temporal tip resection, but no discharges were noted in the patient who underwent initial right anterior temporal lobectomy. Interestingly, most spikes detected in the 2 of 3 patients with discharges were positive, as previously reported. The third patient had focal negative discharges. Results were used to tailor the hippocampal resection. After final resection, ECoG showed no electrographic seizures and no or infrequent (<5 per min) interictal spikes. All 4 patients have remained seizure free with follow-up between 2 and 6 months. Conclusions: Our series suggests benefit of recording ECoG over the intraventricular surface of the hippocampus in patients with TLE undergoing resection, as previously shown, and also raises the possibility that, especially in repeat resections, ictal data may be obtained that is not identifiable from neocortical recording. Further research in a larger cohort of patients with TLE undergoing surgical resection or re-resection and a longer follow-up period are needed to confirm these hypotheses.