Stereoelectroencephalography following subdural grid placement for difficult to localize epilepsy

BACKGROUND:: Despite the use of invasive subdural recording, failure to localize or resect the epileptogenic zone (EZ) occurs. Potential causes for this include EZ originating outside of the subdural grid coverage area, involvement of eloquent cortex, or complications requiring removal of electrodes without seizure localization. No study has examined the safety and efficacy of stereoelectroencephalography (SEEG) after subdural grid placement. OBJECTIVE:: To determine the efficacy of SEEG in patients who have previously undergone subdural grid placement. METHODS:: A prospective analysis was performed on 14 patients who had subdural grid evaluation and underwent subsequent SEEG monitoring. The follow-up period after the SEEG-guided resections ranged from 11 months to 34 months with an average follow-up of 20.1 months. Magnetic resonance imaging findings, EZ localization, outcomes, type of surgery, and perioperative complications were evaluated. RESULTS:: Ten patients (71%) underwent a resection after SEEG reimplantation. Of the 4 patients (29%) not undergoing resection, 2 had seizures arising from eloquent cortex, 1 had bitemporal epilepsy, and 1 had a previous temporal lobectomy contralateral to the EZ. An estimate of the EZ was achieved in all patients based on interictal and ictal recordings. In patients undergoing resection, 60% were seizure-free at 11 months. Perioperative complications were minimal and included 1 abscess, which required burr-hole drainage and antibiotics. CONCLUSION:: SEEG is a safe and effective method after subdural grid placement is inconclusive, providing an additional opportunity for seizure freedom in this highly challenging group of patients. ABBREVIATIONS:: EZ, epileptogenic zoneFLAIR, fluid-attenuated inversion recoverySEEG, stereoelectroencephalography.