Abstracts

Rationale: Intracranial electroencephalography (iEEG) provides high spatiotemporal resolution and therefore invaluable information when the results of non-invasive studies are inconclusive. The chronic monitoring presents unique challenges associated with a need for coverage of unique anatomical structures over the convex hemispheres with a limited number of electrodes of variable types and configurations. We have been increasingly utilizing a combination of surface and depth electrodes with a larger number of electrode contacts for optimum electrode coverage. The goal of this study was to assess the outcomes and morbidity of epilepsy surgery involving iEEG and compare the effectiveness of surface versus depth electrodes in detection of seizure foci and delineation of resection areas. Methods: A retrospective analysis of medical records of patients undergoing iEEG monitoring at University of Iowa Hospitals and Clinics during 2013-2015 was performed. The basic demographic information, results of presurgical non-invasive studies, electrode coverage, iEEG monitoring results, extent of surgical resections, perioperative complications, and surgical outcomes were reviewed. Results: Forty-three patients underwent iEEG monitoring during January 2013 and December 2015. Appropriate localization of seizure foci followed by resection/disconnection occurred in 35 patients (81%). Twenty-nine patients (83%) of the 35 patients who underwent resection/disconnection achieved Engel class I outcome. Among these 35 cases, seizure foci were detected and resection areas delineated predominantly by surface electrodes in 14 cases (40%), depth electrodes in 4 cases (11%), and both surface and depth electrodes in 17 patients (49%). Complications included one intraparenchymal hemorrhage, one subdural hemorrhage, and one infection, all requiring electrode removal. Conclusions: Intracranial EEG can be performed with a low level of morbidity and provides invaluable information to guide seizure focus resection and obtain favorable outcomes. In some cases, the information collected with surface electrodes may be critical in localization of seizure foci and not obtainable with depth electrodes, and vice versa. Appropriate combinations of surface and depth electrodes tailored to individual cases provide optimum electrode coverage to maximize the utility of the intracranial electrode monitoring and guide epilepsy surgery. Funding: None