ID 143 – Motor mapping using high-frequency cortical stimulation & EMG pickup

Abstract

Introduction We describe a cortical and subcortical mapping method for use in the OR under local or general anesthesia, as well as at the bedside in patients with implanted electrodes. The method distinguishes primary, supplementary and subcortical motor elements based on EMG responses, and does not require patient cooperation. Methods Trains of constant-current, pulses are applied via a handheld probe and/or subdural electrodes. Triggered EMG from multiple contralateral face, arm and leg are used to register motor responses. In the OR, the handheld probe is used to identify and spare cortical and subcortical motor elements, while steady-state triggered EMG via subdural electrodes is used for monitoring during resections. Results The method is simple and convenient to implement with typical intraoperative monitoring equipment, and standard disposable sterile probes and electrodes. We describe our experience with over 100 cases with significant pre-operative risk of motor function disruption. Resections were limited when MEP signal loss was observed and by the detection of low threshold MEPs in the resection margins. This led to maximal resections with minimal residual tumor, while preserving motor function. In the small number of cases with MEP signal loss at closing, the majority had transient deficits with full recovery.