Authors :
Presenting Author: Zoe Lusk, BS – Stanford University
Abby Kwon, HS – Stanford University; Josef Parvizi, MD, PhD – Professor of Neurology, Neurology and Neurological Sciences, Stanford University
Rationale:
For patients with refractory epilepsy to proceed with surgical interventions to decrease their seizures, they must first undergo phase II monitoring with intracranial electrodes. With the recent technological advances in epilepsy, we wanted to examine how the practice of phase II monitoring had changed in the last fifteen years.Methods:
We evaluated patients with refractory epilepsy from 2008-2022 undergoing phase II intracranial EEG monitoring as part of their pre-surgical planning. Our cohort included 170 patients. The course of their phase II evaluation was examined along with the surgical interventions for these patients.Results:
The median age of patients undergoing phase II evaluation was 34 years. In total, 182 phase II evaluations were included, with 35.2% subdural electrodes, 57.7% depth electrodes, and 7.1% with a mixture of both. From 2008-2014 ,the majority of the patients were subdural cases (61.3% SD, 29.3% D), however, starting in 2015 the predominant method for intracranial motoring shifted to depth cases (16.8% SD, 77.6% D). Seizure onset zones were identified in 78.8% of phase II operations (61.3% Temporal, 14.0 % Frontal, 7.3% Parietal, 3.3% Occipital, 4% Insular, and 10% multiple regions). Of the patients where the seizure onset zone was unclear, twelve patients (7%) returned to the hospital for a second phase II evaluation. Of the 182 phase II cases, we collected electrode localization information for 121 cases. Overall, depth cases allowed for additional coverage in the insular and subcortical regions, however, 26.3% of depth electrodes compared to 1.9% of subdural electrodes were in either white matter, out of the brain, or in a lesion area of the brain. In total, 1200 depth electrode shafts and 467 grids or strips were implanted for a total of 21,372 contacts. Out of 170 patients, 148 patients (87.1%) were subsequently treated with epilepsy surgery. Of these patients, 54.7% underwent resection (41.9% lobectomy, 12.8% LITT), 39.2% experienced neurostimulation (35.1% RNS, 4.1% DBS), and 3.4% underwent a combination of these treatments. There was a definite shift in the form of treatment offered with the approval of RNS in 2014. From 2008-2015, most patients underwent resection (72.4% resective surgery, 18.4% RNS). Starting in 2016, RNS surpassed resective surgery (of those undergoing treatment 2016-2022: 52.0% RNS, 35.6% resective surgery).
Conclusions:
Our observations show a definitive transformation in the modes of monitoring and choices of surgical treatment during the last fifteen years, clearly depicting a shift from subdural electrode placement to depth electrode placement, and from VNS and resection to new technologies of neuromodulation such as RNS and DBS.Funding: No funding sources.