Comparison of bipolar versus monopolar extraoperative electrical cortical stimulation mapping in patients with focal epilepsy

OBJECTIVE Extraoperative cortical stimulation (CS) for mapping of eloquent cortex in patients prior to epilepsy surgery is not standardized across centres. Two different techniques are in use, referred to as bipolar and monopolar CS. We compared the ability of bipolar versus monopolar CS to identify eloquent cortex and their safety profile in patients undergoing subdural EEG recordings. METHODS Five patients undergoing intracranial EEG recordings and extraoperative CS. Systematic comparison of stimulus parameters, clinical signs and afterdischarges of bipolar versus monopolar CS. RESULTS Bipolar CS requires less stimulation current but is more time consuming and more likely to produce afterdischarges when compared to monopolar CS. None of the stimulations elicited seizures. The area defined as eloquent by either bipolar or monopolar CS reveals only minor discordances, involving mainly the outer row and edge of the electrode array producing clinical signs with monopolar CS only. Qualitatively, bi- and monopolar CS reproduced similar movements and types of muscle contractions. CONCLUSIONS Bipolar and monopolar CS are safe procedures identifying similar cortical areas as eloquent, although monopolar cortical stimulation is less time consuming. SIGNIFICANCE Findings advocate the use of monopolar CS in a clinical setting.