Intraoperative neuromonitoring with direct cortical stimulation motor-evoked potentials in supratentorial glioma surgeries with preoperative moderate-to-severe motor weakness.

Purpose: Intraoperative neuromonitoring (IONM) is essential for safe brain tumor surgeries. Little is known about how to assess damaged motor function. To preserve damaged motor function in these patients, we evaluated the results of direct cortical stimulation motor-evoked potential (D-MEP) monitoring in glioma surgeries performed in and near the primary motor cortex (PMC) and cortico-spinal tract (CST).

Methods: IONM using D-MEPs in patients with preoperative moderate-to-severe motor weakness was performed in 16 cases (14 patients). Before the tumor resection, a single six-contact subdural strip electrode was placed on the PMC. Muscle responses for the upper and lower extremities were confirmed during the tumor resection. Bipolar stimulation was then performed between adjacent or more distant electrodes. D-MEP monitoring was defined as successful if any D-MEP could be measured for either the upper or lower limb with Manual Muscle Test score below 3.

Results: The success rate of D-MEP monitoring in these patients was 81.2% (13/16 cases) and 50% (13/26 limbs). The baseline median intensities of stimulation for D-MEPs in the upper and lower extremities were 23.3 ± 6.1 mA and 24.7 ± 9.2 mA, respectively. The 13 cases wherein D-MEP was successfully recorded in at least in one limb with moderate-to-severe motor weakness showed no deterioration of motor function postoperatively. Among the remaining three cases with unsuccessful D-MEP measurements, one showed worsened motor weakness.

Conclusion: IONM with D-MEP-based monitoring may be a promising method for preserving damaged motor function in glioma surgeries in and near the PMC and CST.