The stereotactic approach for mapping epileptic networks: a prospective study of 200 patients

Abstract

Object Stereoelectroencephalography (SEEG) is a methodology that permits accurate 3D in vivo electroclinical recordings of epileptiform activity. Among other general indications for invasive intracranial electroencephalography (EEG) monitoring, its advantages include access to deep cortical structures, its ability to localize the epileptogenic zone when subdural grids have failed to do so, and its utility in the context of possible multifocal seizure onsets with the need for bihemispheric explorations. In this context, the authors present a brief historical overview of the technique and report on their experience with 2 SEEG techniques (conventional Leksell frame-based stereotaxy and frameless stereotaxy under robotic guidance) for the purpose of invasively monitoring difficult-to-localize refractory focal epilepsy. Methods Over a period of 4 years, the authors prospectively identified 200 patients with refractory epilepsy who collectively underwent 2663 tailored SEEG electrode implantations for invasive intracranial EEG monitoring and extraoperative mapping. The first 122 patients underwent conventional Leksell frame-based SEEG electrode placement; the remaining 78 patients underwent frameless stereotaxy under robotic guidance, following acquisition of a stereotactic ROSA robotic device at the authors' institution. Electrodes were placed according to a preimplantation hypothesis of the presumed epileptogenic zone, based on a standardized preoperative workup including video-EEG monitoring, MRI, PET, ictal SPECT, and neuropsychological assessment. Demographic features, seizure semiology, number and location of implanted SEEG electrodes, and location of the epileptogenic zone were recorded and analyzed for all patients. For patients undergoing subsequent craniotomy for resection, the type of resection and procedure-related complications were prospectively recorded. These results were analyzed and correlated with pathological diagnosis and postoperative seizure outcomes. Results The epileptogenic zone was confirmed by SEEG in 154 patients (77%), of which 134 (87%) underwent subsequent craniotomy for epileptogenic zone resection. Within this cohort, 90 patients had a minimum follow-up of at least 12 months; therein, 61 patients (67.8%) remained seizure free, with an average follow-up period of 2.4 years. The most common pathological diagnosis was focal cortical dysplasia Type I (55 patients, 61.1%). Per electrode, the surgical complications included wound infection (0.08%), hemorrhagic complications (0.08%), and a transient neurological deficit (0.04%) in a total of 5 patients (2.5%). One patient (0.5%) ultimately died due to intracerebral hematoma directly ensuing from SEEG electrode placement. Conclusions Based on these results, SEEG methodology is safe, reliable, and effective. It is associated with minimal morbidity and mortality, and serves as a practical, minimally invasive approach to extraoperative localization of the epileptogenic zone in patients with refractory epilepsy.

Emerging surgical therapies in the treatment of pediatric epilepsy

“…• After subdural grid failure permanent morbidity after evaluation with surface electrodes (3-6%) compared with the use of SEEG electrodes (0-3%) because of the need for craniotomy and invasive grid placement in both adult and pediatric patients (34)(35)(36)(37)42); however, comparisons of surface electrodes and SEEG as well as complication rates have been limited because of differing study indications, methodology, and techniques. Larger studies of SEEG monitoring in pediatric patients have reported that efficacy of seizure foci identification and safety are similar to those reported in studies of adults (22,41,43,44).…”

A new tool for touch-free patient registration for robot-assisted intracranial surgery: application accuracy from a phantom study and a retrospective surgical series

“…1,11,12,15,25 Patient registration can be performed in frame-based or frameless conditions. Since the fall of 2008, we have used a robotic assistant in frame-based conditions for implanting all SEEG electrodes at Niguarda Hospital.…”

Effect of invasive EEG monitoring on cognitive outcome after left temporal lobe epilepsy surgery

“…However, invasive EEG monitoring is sometimes needed in patients with poorly localized, multifocal, or discordant scalp EEG ictal patterns to map seizure onset or in those whose epileptogenic zone is in close proximity to functional cortex to minimize functional deficits following resection. [3][4][5][6][7][8] These EEG techniques invade the brain parenchyma along the trajectories of multiple depth electrodes (stereotactic EEG [SEEG]) and/or cover the cortex with a "foreign body" (subdural grids) and often extend beyond the eventual resection area. Furthermore, greater histopathologic changes are evident in the resected tissue of patients who have undergone invasive EEG monitoring as compared to those who undergo surgical resection without prior monitoring.…”