Abstracts

Rationale: Intracranial recording for seizure localization is invaluable in certain selected surgical patients. Comprehensive preoperative noninvasive data collection is used to generate a hypothesis about the best approach to place intracranial electrodes with the aim to further narrow and identify the epileptic focus. Despite best efforts preoperative evaluation often fails to localize or even lateralize the epileptic focus or generates contradictory results. Among such patients if a single epileptic focus is still suspected many Epilepsy Centers perform bilateral survey intracranial recording. Details about the value of such approach are limited. Methods: Retrospective review of patients with bilateral intracranial survey studies in our Epilepsy Center with at least one year follow-up. Data collected and analyzed included demographic, clinical, preoperative evaluation, methods and results of intracranial survey recording, any interventions performed based on the results of intracranial survey and long term seizure prognosis. Patients with suspected mesial temporal lobe epilepsy with intracranial recording done to lateralize seizure focus or rule out bitemporal lobe epilepsy were excluded. Results: 15 patients were identified (8 females). At time of survey recording patients age ranged between 2- 53 (mean 22.4 years). Average time from diagnosis of epilepsy was 8.8 years. 9/15 had bitemporal and bifrontal sampling most commonly with bilateral anterior, inferior and posterior frontal and anterior, posterior and subtemporal coverage with or without bilateral hippocampal depths. 4/15 had bilateral posterior coverage with parietal-occipital and temporal-parietal-occipital coverage. 2/15 had bilateral frontal-temporal-parietal-occipital electrode placement. Interhemispheric coverage was done in 6/15 patients. Based on the results of intracranial survey 3/15 had temporal lobe resection. All 3 were seizure free or substantially better (modified Engel classes I and II). Three patients had no further surgeries 2 due to failure of survey study to further define seizure focus and one due to multifocality. 9/15 underwent further intracranial studies mostly with unilateral subdural grid placement of those 6/9 eventually had surgical resection of seizure focus, 2 with parietal lobe resection, 1 orbitofrontal , 2 lateral frontal and 1 frontal-parietal ( 2 classes I- II and 4 classes III-IV) . Overall analysis shows that in our patients with intracranial survey study helpful information in further surgical planning or surgical eligibility was obtained in 86 % of the cases. Among patients who eventually had surgical resection 55 % were seizure free or substantially better. Conclusions: Bilateral survey intracranial studies should be considered for further surgical planning in a subset of epilepsy surgery candidates. Considering the type of patients selected for intracranial survey study the procedure does not appear to imply worse long term surgical prognosis.