F117. Efficacy of intraoperative electrocorticography: Long-term results of surgical treatment of symptomatic epilepsy

Abstract

Electrocorticography (ECoG) is a standard procedure for the localization of the epileptogenic zone during the surgical treatment of symptomatic epilepsy. The purpose of this study was to evaluate the diagnostic efficacy of intraoperative pre- and post-resective ECoG for the localization of the epileptogenic zone in patients with symptomatic epilepsy associated with supratentorial brain tumors. Twenty-four patients (11 men) with tumor-related epilepsy and various localizations of tumors (8 persons – frontal lobe, 10 patients – temporal lobe, 2 patients – parietal lobe, 4 patients – other localization) entered this study. Patients underwent surgical treatment at the Polenov Russian Scientific Research Institute of Neurosurgery in 2013–2016. The age of the patients ranged from 22 to 66 years. Patients underwent tumor resection accompanied by neurophysiological monitoring. The ECoG was recorded intra-operatively with 2 × 4 cortical grids (Ad-Tech, USA) via the Mitsar-EEG-201 complex (Mitsar Co. Ltd., Russia). Prior to resection, registration was performed over the tumor site and adjoining cortical areas. Post-resective ECOG was performed after the removal of the tumor to assess the completeness of resection of the epileptogenic zone. In the postoperative period, the patients completed a questionnaire aimed to report the presence and severity of the postoperative seizures over a period of one to three years after the operation. The patients underwent surgical treatment with varying resection rates: gross total resection was achieved in 54% (13) patients, subtotal – in 13% (3) patients, partial – in 19% (7) patients. During the surgical treatment ECoG was performed in 62.5% (15) of the patients. In 9 out of 15 patients (60%) epileptiform activity was detected. In the long-term period, 9 patients noted the persistence of epileptic syndrome. In these 9 cases, only in 5 patients epileptic activity was registered on pre-resective ECoG, in 2 patients – on post-resective. The ECoG procedure was not performed in 9 patients due to technical challenges. In this group of patients 8 out of 9 patients reported ongoing epileptic seizures in the late postoperative period. Statistical analysis of these data shows that EcoG lacks diagnostic efficacy (χ2 = 2,27, p = 0.13). The sensitivity in this study is 50% for pre-operative ECoG and 25% for post-operative ECoG. Specificity reaches 75% for post-operative ECoG. 1. In the surgical treatment of symptomatic epilepsy associated with intracerebral neoplasm, intraoperative ECG remains a relatively effective method. 2. The effectiveness of intraoperative pre- and post-resection ECoG is affected by factors associated with the performance of neurosurgical surgery (the influence of general anesthetics, mechanical effects on the brain, repeated electrocoagulation), which significantly alter the index of epileptiform activity.