Abstracts

Rationale: Subdural Electrodes (SDE) have been the mainstay of the process for the evaluation of patients with non-lesional or ill-defined focal epilepsy in North America. The advent of stereo-electroencephalography (SEEG) in North America over the past decade has transformed the way in which many centers perform intracranial evaluations to localize regions for resection/ablation/neuromodulation. Both techniques have relative advantages, but in a majority of patients, either one could be applied. The relative efficacy, morbidity and costs of these two approaches therefore need to be compared. Methods: All 261 intracranial procedures performed by a single neurosurgeon, over an interval of 12 years, were compiled from a prospectively compiled surgical database. Demographics, epilepsy characteristics, duration of monitoring, procedural morbidity and eventual outcomes were all ascertained. Χ2 tests were performed to evaluate distinctions between the two groups. Results: Both SEEG (n=125) and SDE (n=136) groups were identical in age (SEEG = 30.0 ± 12.2 years; SDE = 30.6 ± 13.9 years), gender (SEEG = 47.2% male; SDE = 42.6% male) and duration of epilepsy (SEEG = 16.3 ± 11.9 years vs SDE = 17.3 ± 12.2 years). The duration of intracranial monitoring was comparable (SEEG = 7.6 ± 3.7 days vs SDE = 8.1 ± 2.7 days). A greater proportion of SDE patients underwent resective surgery (91.2%), compared to SEEG patients (77.6%, p = 0.0024) who underwent resective/ablative surgery. None of the SDE patients and 5.6 % of SEEG patients underwent placement of the RNS device. 8.8% of SDE patients and 8.8% of SEEG patients were not thought to be candidates for further cranial intervention. The seizure outcomes (Engel I or II) in this group, at 6 months post-resection, trended to favor SEEG (77.8%) relative to SDE (65.5%, p = 0.07).Similar numbers of SDE (6) and SEEG (7) patients underwent placement of additional electrodes after the initial implant, during the same hospital stay, to further delineate the seizure onset site. There were 6 symptomatic hemorrhagic sequelae and two infections in the SDE cohort vs no complications in the SEEG cohort (p = 0.006). Only one patient from the SDE cohort experienced long term neurological sequelae related to the intracranial evaluation. Direct costs for these two types of phase 2 procedures are being compiled. Conclusions: SEEG and SDE lead to nearly identical seizure free outcomes at 6 months post-resection as there is no significant difference between the seizure free outcomes for these cohorts (p > 0.05). Longer term outcomes are being assessed using a Cox proportional hazards model. The procedural morbidity for these two approaches is significantly different: 5.9% (SDE) and 0% (SEEG), (p < 0.05), which should factor into decision making when patients with pharmaco-resistant epilepsy are being considered for an intracranial evaluation. Funding: N/A