Abstracts

Rationale: In patients with refractory epilepsy, noninvasive pre-surgical evaluation including video-electroencephalogram (vEEG) monitoring, magnetic resonance imaging (MRI) of the brain is warranted in order to determine the ictal onset zone (seizure focus). Pre-surgical invasive procedures such as intracranial implantation of subdural electrodes (SDE) are needed when the ictal-onset zone cannot be determined based on non-invasive methods. However, it is unclear if this invasice procedure add any value to the surgical outcome. In this study, we aimed to evaluate the surgical outcome of epilepsy surgery for patients who underwent pre-surgical invasive EEG monitoring using SDE.Methods: This is a retrospective study of patients who had a resective surgery after intracranial SDE-EEG monitoring at king Faisal specialist hospital & research center (KFSH&RC) in Jeddah between January 2007 and April 2014. The age, gender, duration of epilepsy, MRI of the brain and pathology results, as well as electrophysiological and surgical outcome data were retrieved using medical charts with minimum of 12 months postoperative follow-up We used Engel classification 1A as indicator of successful surgery outcome.Results: Eleven patients (6 females) were included in this study. The mean age of patients at epilepsy surgery was 28.1 years (range, 20-37); mean duration of epilepsy was 153.82 months (range, 60-372) and the mean follow-up duration was 44.8 months (range, 12-72). Nine patients underwent anterior mesial temporal lobectomy (5 in the left and 4 in the right) while two patients underwent left posterior quadrant tailored resection. Ictal scalp EEG showed unilateral abnormalities in 6 patients, multifocal in 3 patients; and two patients had normal or obscured ictal EEG changes. MRI of the brain was abnormal in 8 patients (72.2%). Ictal SDE-EEG localized a single focus in all patients and was concordant to the MRI abnormality in all patients with a reported lesion. The pathology showed findings consistent with mesial temporal sclerosis in 6 patients (54.5 %), ischemic changes in 3 patients (27.3 %) while two patients had non-specific changes. Class 1A Engle classification was achieved in 5 patients (45.5%), of which 2 patients underwent right, and 2 left anterior temporal lobectomy, and one underwent left posterior quadrant tailored resection. Two out of 3 patients with normal MRI and all patients with ischemic changes on pathology had a class 2 or more in Engel classification, which indicate bad outcome.Conclusions: Although the number of patients in our study is low, we found that Intracranial SDE-EEG helps to localize the ictal onset zone when the non-invasive evaluation is inconclusive. Concordance of Ictal SDE-EEG to the MRI abnormality and pathological findings of mesial temporal sclerosis are good prognostic signs for surgical outcome after epilepsy surgery.