10189- STMO-12 INTRAOPERATIVE NEUROMONITORING FOR THE LOWER-EXTREMITY REGION USING MOTOR-EVOKED POTENTIAL WITH DIRECT CORTICAL STIMULATION IN BRAIN TUMOR SURGERIES

Abstract PURPOSE To evaluate the motor function of the lower extremity (LE), we used direct cortical stimulation motor-evoked potential (D-MEP) monitoring with a single six-contact subdural strip electrode placed in the interhemispheric fissure. METHODS Intraoperative neuromonitoring using D-MEPs in the LE was performed in 18 cases (16 patients) for brain tumor surgery with a follow-up period of at least 3 months from December 2018 to April 2023. After dural opening, a single six-contact subdural strip electrode was placed inside the interhemispheric fissure. To identify the central sulcus, phase reversal was recorded using SSEPs. Next, direct cortical stimulation was applied to the PMC. The baseline waveform was defined as a reproducible waveform of 30 μV or higher, and a significant decrease of >50% in the amplitude resulted in a warning during surgery. RESULTS The success rate of central sulcus identification in the LE was 66.7% (12/18 cases). D-MEP monitoring could record stable contralateral MEPs of the tibialis anterior, gastrocnemius, and abductor hallucis in 16 of 18 cases (88.9%). The mean intensity of stimulation for D-MEPs was 20.5 ± 9.9 mA, and the 16 cases showed no significant reduction in amplitude. Seventeen cases showed no deterioration of motor function of the LE at 1 and 3 months postoperatively. In the remaining case with unsuccessful D-MEP, paralysis of the LE worsened at 1 and 3months postoperatively. CONCLUSION The placement of electrodes in the interhemispheric fissure on the PMC of the LE enabled motor-function monitoring in the LE with D-MEPs, suggesting that D-MEP-based monitoring may be a reliable approach.