137 Utility of Intraoperative Neuromonitoring for Predicting Motor Deficits After Intramedullary Spinal Cord Tumor Resection

INTRODUCTION: Intramedullary spinal cord tumors (IMSCTs) are treated by maximal safe surgical resection, during which neurosurgeons often rely on motor-evoked potentials (MEPs) and direct wave (D-wave) neuromonitoring. However, the predictive value of changes in neuromonitoring for detecting motor outcomes is unclear. METHODS: All patients undergoing resection of a primary IMSCT with MEP neuromonitoring from 2003-2023 at a tertiary care hospital were retrospectively identified. Pre- and post-operative characteristics were compared between patients who had D-wave monitoring in addition to MEPs and patients with MEPs alone using T-tests, chi-squared tests, and Fisher’s exact tests. Sensitivity, specificity, and positive and negative predictive values (PPV, NPV) were calculated. RESULTS: The cohort included 213 patients, 174 with MEPs only and 39 with both MEPs and D-waves. Most tumors were ependymomas (45.1%) or astrocytomas (35.2%) and were WHO grade II (60.8%). Patients with and without D-waves had similar pre-operative presentations, surgical approaches, adjuvant therapy, gross total resection rate, and post-operative outcomes. Local recurrence of the tumor, changes in neurologic function, and modified McCormick score did not differ between patients depending on D-wave use. All patients had 1-month follow-up, and the mean follow-up length was 49.1 months. At 1-month follow-up, D-waves performed slightly better than MEPs at detecting motor deficits in terms of sensitivity (66.7% vs 55.6%), specificity (86.7% vs 83.3%), PPV (60.0% vs 50.0%), and NPV (89.7% vs 86.2%). D-waves alone had better specificity, PPV, and NPV than combination neuromonitoring. D-wave sensitivity increased to 80.0% at 6 months and 83.3% at last follow-up, while specificity remained similar at 90.3% at 6 months and 84.8% at last follow-up. CONCLUSIONS: D-waves perform better than MEPs or combination neuromonitoring at detecting motor deficits after resection of IMSCTs, and sensitivity increases for long-term deficits.