gms | German Medical Science

Objective: For patients with pharmacoresistant focal epilepsy resective surgery is a safe and effective therapeutic option. Extra-temporal location and non-lesional epilepsy are known to be negative prognostic factors for seizure outcome because the epileptogenic zone (EZ) is difficult to identify. The success of resective epilepsy surgery relies on the accurate localization of the EZ, which might be improved using stereotactically implanted depth electrodes. This retrospective study analyses risk profile and patient outcome for both lesional and non-lesional epilepsy using individually adjusted invasive video-EEG-monitoring with stereotactically implanted depth electrodes and navigated resection.

Methods: After review of patients with pharmacoresistant focal epilepsy in our multidisciplinary epilepsy board, an individually adjusted implantation plan for stereoelectroencephalography (SEEG) electrodes was created. The EZ was determined by invasive video-EEG-monitoring, mapped to the electrode positions in the post-implantation CT and integrated into the pre-resection MRI. Resection volumes were analysed by iPlan Cranial 3.0 (BrainLAB, Germany). Patients were considered "seizure-free" with Engel class IA-C at last follow-up. Characteristics of the lesional and non-lesional group were analysed by chi-square/ Fisher’s exact test for categorical variables and a Student’s t-test / Mann-Whitney U test for continuous variables.

Results: Among 914 patients with medically refractory epilepsy presented at the epilepsy department, 70 patients with focal epilepsy were included for invasive SEEG monitoring and microsurgical resection (median age: 35.2 years). Structural MRI at 1.5 and 3T showed a lesion in 41 patients (58.6%), but were considered non-lesional in 29 patients (41.4%). Median follow-up time was 31.5 months. Transient and permanent overall morbidity rate was 4.3% and 1.4%. 58 of 70 (82.9%) patients had excellent seizure outcome (Engel class IA-C); 50 patients (71.4%) were Engel class IA. The outcome did not differ between the lesional (78.6%) vs. non-lesional (86.0%), temporal (80%) vs. extratemporal (84%) group nor hemispheric location (right: 82% vs. left: 85%).

Conclusion: This study suggests that seizure outcome even in non-lesional epilepsy is equally good to lesional epilepsy, as the EZ can be precisely defined by using individualized stereotactically implanted depth electrodes followed by subsequent MRI-navigated tailored focus resection.