Abstracts

Rationale: The purpose of this study was to evaluate: 1-If bilateral implants localize seizure onset in patients with poor lateralization on phase I evaluation. 2- How often therapeutic and palliative surgery is performed after bilateral implants? 3- Surgical outcomes based upon Engel classification. Methods: IRB approved retrospective chart review was conducted on the UTHSCSA Epilepsy registry from 2008-2016. Cases were identified based on recommendation from epilepsy surgical case conference for bilateral implantation. Pre-surgical data were evaluated for lateralizing features on scalp VEEG or MRI, for those who underwent surgery, outcomes were measured by Engel classification. Results: Bilateral implants were placed on 15 patients who had poorly lateralized seizure onset after phase I evaluation. Invasive bilateral implants were able to lateralize seizures on 10 patients (66%). Implants failed to provide more information on 5 patients (34%). Seven cases (46%) underwent surgical resection (6) or transection (1) after implant. Three patients had bilateral or multiregional seizure onset and were determined poor candidates for resective surgery. Surgery led to Engel class I outcome in 4 of 7 patients ?" 2 with mesial temporal sclerosis and 2 with non-lesional MRI. All 4 patients underwent anteromedial temporal lobectomy. The remaining 3 surgical patients had modest to no improvement after surgery. Patient 1 had normal MRI with seizure onset in right medial frontal region and supplemental motor area. The patient underwent right medial frontal and inferior parietal resection along with multiple subpial transections in primary motor area with Engel class III outcome. Patient 2 MRI showed right hemispheric parieto-occipital cortical dysplasia. Invasive monitoring showed multiregional seizure onset. Anterior two-thirds corpus callosotomy was performed with Engel class IV outcome. Patient 3 had a small right anterior hippocampus with increased FLAIR signal. Invasive monitoring showed clinical seizures arising from left fronto-parietal lobes and electrographic seizures arising from the right anterior temporal lobe. Pallative right anterior temporal lobectomy was performed with Class IV outcome. Conclusions: In medically refractory focal epilepsy, epilepsy surgery remains the most effective treatment option and has the greatest possibility of rendering the patient seizure free. Intracranial EEG helps define the borders of the epileptogenic area for resection when the seizure onset zone is not well defined on phase I monitoring. In our patients with poor lateralization on phase I monitoring, bilateral invasive monitoring was beneficial in 33% of patients with Engel class I outcome in 4 and Engel class III in 1 patient. These results suggest that bilateral invasive monitoring may offer substantial benefits to a subset of patient with poor lateralization of seizure onset on initial evaluation. Further research is necessary to better characterize the patients most likely to benefit from bilateral implantation. Funding: none