Objective: Surgical intervention can be curative or palliative for drug-resistant focal epilepsy. However, if the seizure onset zone (SOZ) cannot be adequately localized via noninvasive tests, intracranial EEG (iEEG) recordings are often carried out to develop surgical plans in appropriate candidates. Stereotactic EEG (SEEG), subdural EEG (SDE), and SDE with depth electrodes (hybrid) are major tools used for investigation, but there is no class 1 or 2 evidence comparing the effectiveness of these modalities.
Methods: The authors identified an institutional cohort of patients who underwent iEEG monitoring between 2001 and 2022. Demographic data, preoperative clinical features, iEEG intervention, and follow-up data were identified. Primary study endpoints included the following: 1) likelihood of SOZ localization; 2) likelihood of surgical treatment after iEEG; 3) seizure outcomes; and 4) complications.
Results: A total of 329 patients were identified (176 in the SEEG, 60 in the SDE, and 93 in the hybrid cohort) who were followed for a median of 5.4 (IQR 6.8) years. Baseline characteristics, including demographics, mean age at epilepsy diagnosis, mean age at iEEG investigation, number of preoperative antiseizure medications, and preoperative seizure frequency, were not statistically different across the 3 cohorts. Patients in the SEEG cohort were more likely to have their SOZ localized than were the patients in the SDE group (OR 2.3) and were less likely to undergo subsequent resection (OR 0.3) or to have complications (OR 0.4), although there was no statistical difference with respect to likelihood of undergoing any subsequent neurosurgical treatment, or with respect to favorable seizure outcomes. Patients in the hybrid cohort were more likely to have SOZ localized than were patients in the SDE group (OR 3.1), but were more likely to undergo resection (OR 4.9) or any neurosurgical treatment (OR 2.5) compared to patients in the SEEG group. Patients in the hybrid cohort had better seizure outcomes compared to the SDE (OR 2.3) but not to the SEEG group.
Conclusions: Patients in the SEEG group were more likely to have their SOZ localized and patients in the SDE group were more likely to undergo resection, but they did not differ with respect to seizure outcomes.
Keywords: SEEG; epilepsy; stereotactic EEG; subdural electrodes; subdural grids; surgical outcomes.