Abstracts

Rationale: Epilepsy centers around the world are increasingly using intracranial electrodes (iEEG) for further localization of epileptogenic zones and/or functional mapping of eloquent cortices. The threshold for offering iEEG video monitoring varies between epilepsy centers. This step in pre-surgical investigation is designed with the goal of balancing the risks associated with an invasive procedure and resources, while assessing whether there is a potentially curative resective surgical option for the patient. Examining patients with focal epilepsy who undergo iEEG recording, but do not undergo subsequent resective surgery may be helpful in evaluating the use of this invasive but potentially powerful diagnostic method. Methods: We selected the last 60 patients who underwent iEEG monitoring as part of their pre-surgical evaluation from our patient database. The implantation procedures were performed by multiple neurosurgeons in the same center. This study was approved by our institutional review board (IRB). We reviewed the treatment and clinical course of the patients who did not undergo resection despite undergoing invasive monitoring. The reason for not proceeding to resection after electrode extraction and plan of treatment after monitoring was collected. Results: Of 60 patients reviewed, 50 patients underwent either temporal lobectomy (10 left and 17 right) or iEEG-guided cortical resection of epileptogenic focus (23 patients). Ten patients (16.6%) did not proceed to resection. The reasons that no resection was preformed included: bilateral/multifocal seizure foci (5 patients), involvement of eloquent cortex (2 patients), concern for profound cognitive deficit following a temporal lobectomy (2 patients), and failure to identify a distinct focus (1). The average length of iEEG monitoring was 8.6 days (range 3-14 days). Subdural grids were used for six patients, stereotactic EEG for four, and one patient was monitored using both simultaneously. One patient underwent a resective surgery two years later, one underwent multiple subpial transections and subsequent VNS implantation; five other patients were implanted with a vagus nerve stimulator. The rest of the patients were managed only with further AED adjustment trials. One patient is being evaluated for responsive neurostimulation. Conclusions: The proportion of patients who are implanted with intracranial electrodes but who do not get resective surgery in our center is 16.6%, comparable to reports from other centers. Multifocality and risk of permanent unacceptable deficit from surgery are the most common reasons for not proceeding to resective surgery. These patients often continue to have poor seizure control despite further adjustment or addition of AEDs or VNS implantation. As iEEG monitoring at epilepsy centers involves increasingly more complex epilepsy cases, studying the clinical course and outcomes of patients who undergo iEEG recording without then proceeding to resective surgery provides insight into the limitations of this technique and guide the selection of appropriate candidates. Funding: None.