F112. Continuous monitoring with direct cortical and subcortical stimulation for perirolandic tumor resection: The experience of a Brazilian group

Abstract

Introduction Tumor resection should be maximal for a longer survival and quality of life but the main concern in surgeries of the perirolandic tumors is to prevent new neurologic deficits. Neurophysiologic intraoperative techniques to continuously monitor the motor function are desired to avoid this risk. Direct cortical stimulation (DC-MEP) and subcortical (SUBC-MEP) stimulation have been successfully used for this. The aim of this paper is to present our experience with this technique. Methods We studied 36 of 45 patients with perirolandic tumors (18 female), mean age of 46.6 y (4–76 y), submitted to tumor resection under total intravenous anesthesia (TIVA) and intraoperative neuromonitoring (IONM) with our standard protocol consisting of SEP-PR, cortical motor mapping (CMM), continuous direct cortical motor evoked potential (DC-MEP) and continuous subcortical motor evoked potential (SUBC-MEP). The DC-MEP was elicited using a strip electrode placed over the hand area of the precentral gyrus (anodic stimulation) and recorded with subdermal needle electrodes placed in the contralateral hemibody muscles. SUBC-MEP was elicited through a monopolar aspirator device (cathodic stimulation) and recorded in the same muscles. A train of 4 or 5 pulses with 0,5 ms duration and inter-stimulus interval of 3 ms is applied continuously at 1 Hz alternating between cortical and subcortical. Warning criteria was 50% amplitude decrease for DC-MEP and 3–5 mA for SUBC-MEP. Results From the 45 cases, DC-MEP and SUBC-MEP were recorded in 36 patients, allowing continuous monitoring of the motor pathways. In the remaining 9 cases the surgeons decided for the use of cortical mapping only because the strip electrode positioning would disturb the tumor resection; in these patients, subcortical stimulation was performed in 5 according to the surgeon decision, but not continuously, and in two of them transitory postoperative new neurologic deficits were observed. From the 36 patients monitored with simultaneous DC-MEP and SUBC-MEP, there were no consistent amplitude decrease for DC-MEP and the threshold for SUBC-MEP was above 11 mA in 19 cases, between 6 and 10 mA in 12 and between 3 and 5 mA in 3. Only one patient with 3 mA subcortical threshold had a transitory motor deficit (less than 24 h). Our results are comparable with the previously reported in the literature. Conclusion Despite the few studied cases, it seems for us that continuous monitoring is better than cortical motor mapping alone. The DC-MEP and SUBC-MEP are precise for intraoperative diagnostic and allow a better resection with preservation of the motor pathway. In one case, SUBC-MEP showed the lowest threshold of 3 mA and was followed by a transitory deficit. Simultaneous and continuous monitoring of the cortical and subcortical MEP must be encouraged.