Abstracts

Rationale: Patients with medically-refractory partial-onset seizures frequently have poorly localized ictal patterns on extracranial EEG and require evaluation using bilateral subdural strip electrodes. Many patients who receive implanted electrodes, however, have multifocal epilepsy or have seizures recorded in nonresectable areas and are unable to have focal resective surgery. We examined a series of 43 patients who had bilateral subdural electrodes implanted to determine factors associated with successful and unsuccessful surgical treatment using this recording technique.Methods: Methods: We identified 43 patients with bilateral subdural electrodes implanted greater than one year prior to the study. Four patients had insufficient follow-up to determine outcome. We determined clinical histories (seizure onset, seizure etiology, seizure frequency), imaging results, scalp video EEG findings and compared these results with results of subdural electrode recording and patients’ seizure outcomes.Results: Results: A total of 17 of 39 patients had none or rare seizures on follow-up. Of these patients, 11 had focal resection surgery (9 temporal, 1 frontal, 1 occipital lobe). Twenty two of the 39 patients either did not receive resections (16 patients) or did not benefit from resections (6 patients). Interestingly, 6 patients who declined surgery entered remissions without receiving epilepsy surgery. Factors associated with successful localization using bilateral subdural strips and resective surgery were: structural abnormalities on MRI and having symptomatic epilepsy (MTS, tumor, trauma, infection). The majority of patients benefiting from surgery had single ictal foci identified on subdural recordings, however, some had bifocal onsets and unilateral foci on subsequent recordings using subdural grid electrodes. Patients tolerated strip placement and subsequent surgery well—one patient had a transient language/motor deficit.Conclusions: Conclusion: The overall “yield” for patients with poorly localized seizures on scalp VEEG studied with bilateral subdural strip recordings was not high (28% successful surgery), though, morbidity was low. The majority of patients with successful surgery outcomes had poorly localized ictal onsets on scalp recordings, but had structural abnormalities on MRI or known seizure etiologies.