Intradural extramedullary tumor location in the axial view affects the alert timing of intraoperative neurophysiologic monitoring

Abstract Objective Intraoperative neurophysiologic monitoring (IONM) reportedly contributes to preventing postoperative neurological complications in high-risk spinal cord surgeries. There are both negative and positive reports about IONM for intradural extramedullary (IDEM) tumors. We investigated factors affecting alerts of IONM in IDEM tumor surgery. Methods We analyzed 39 patients with IDEM tumors who underwent surgery using IONM at our hospital between January 2014, and March 2021. Neurological symptoms were evaluated pre- and postoperatively using the manual muscle test (MMT). All patients were evaluated to ascertain the tumor level and location in the axial view, the operative time, intraoperative bleeding volume, and histological type. Additionally, the intraoperative procedure associated with significant IONM changes in transcranial electrical stimulation muscle evoked potential was investigated. Results There were 11 false-positive and 26 true-negative cases. There was one true-positive case and one false-negative case; the monitoring accuracy achieved a sensitivity of 50%, specificity of 70%, a positive predictive value of 8%, and a negative predictive value of 96%. In the analysis of 22 alert cases, if the tumor was located anterolateral in the axial view, alerts were triggered with a significant difference (p = 0.02) during tumor resection. Fifteen patients generated alerts during tumor resection; nine (60%) showed waveform improvement by intervention and were classified as rescue cases. Conclusions Alert is probably triggered during tumor resection for anterolaterally located tumors. In addition, alerts during tumor resection procedures tended to be more likely to be rescued than other procedures in IDEM tumor surgery.