Evaluation of the high-frequency monopolar stimulation technique for mapping and monitoring the corticospinal tract in patients with supratentorial gliomas. A proposal for intraoperative management based on neurophysiological data analysis in a series of ninety-two patients

Abstract

Background: Intraoperative identification and preservation of the corticospinal tract is often necessary for glioma resection. Objective: To make a proposal for intraoperative management with the high-frequency monopolar stimulation technique for monitoring the corticospinal tract. Methods: Ninety-two patients operated on with the assistance of the high-frequency monopolar stimulation. Clinical and neurophysiological data have been related with the motor status at 3 months to establish prognostic factors of motor deterioration. Results: Twenty-one patients (22.8%) presented intraoperative alterations in motor-evoked potentials (MEPs). Twelve (13%) presented an increment in the MEP threshold ≥5 mA (no deficit at 3 months). Two (2.2%) presented an MEP amplitude reduction >50% (100% deficit at 3 months). Seven (7.6%) had an intraoperative MEP loss (80% deficit at 3 months). Subcortical stimulation was positive in 75 patients (81.5%). Eighty-five patients were available for the analysis at 3 months. Fourteen presented new deficits (16.5%). Among them, 5 presented a deficit in nonmonitored muscles (5.9%) and 1 presented a new deficit not detected intraoperatively. The combination of patients with preoperative motor deficits, MEP deterioration, or loss and intensity of subcortical stimulation ≤3 mA showed the highest sensitivity and specificity in the prediction of new deficits. Conclusions: Persistent MEP loss or deterioration is associated with a high probability of new deficits. It seems recommendable to stop the subcortical resection before obtaining a subcortical MEP threshold at 3 mA especially in patients with preoperative motor deficits. A careful selection of muscles for the registration of MEPs is mandatory to avoid deficits in nonmonitored muscles.