Intraoperative neurophysiological monitoring for intradural extramedullary spinal tumors: Predictive value and relevance of D-wave amplitude on surgical outcome during a 10-year experience

OBJECTIVE The purpose of this study was to evaluate the technical feasibility, accuracy, and relevance on surgical outcome of D-wave monitoring combined with somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) during resection of intradural extramedullary (IDEM) spinal tumors. METHODS Clinical and intraoperative neurophysiological monitoring (IONM) data obtained in 108 consecutive patients who underwent surgery for IDEM tumors at the Institute for Scientific and Care Research “ASMN” of Reggio Emilia, Italy, were prospectively entered into a database and retrospectively analyzed. The IONM included SSEPs, MEPs, and—whenever possible—D-waves. All patients were evaluated using the modified McCormick Scale at admission and at 3, 6, and 12 months of follow-up . RESULTS A total of 108 patients were included in this study. A monitorable D-wave was achieved in 71 of the 77 patients harboring cervical and thoracic IDEM tumors (92.2%). Recording of D-waves in IDEM tumors was significantly associated only with a preoperative deeply compromised neurological status evaluated using the modified McCormick Scale (p = 0.04). Overall, significant IONM changes were registered in 14 (12.96%) of 108 patients and 9 of these patients (8.33%) had permanent loss of at least one of the 3 evoked potentials. In 7 patients (6.48%), the presence of an s18278 caudal D-wave was predictive of a favorable long-term motor outcome even when the MEPs and/or SSEPs were lost during IDEM tumor resection. However, in 2 cases (1.85%) the D-wave permanently decreased by approximately 50%, and surgery was definitively abandoned to prevent permanent paraplegia. Cumulatively, SSEP, MEP, and D-wave monitoring significantly predicted postoperative deficits (p = 0.0001; AUC = 0.905), with a sensitivity of 85.7% and a specificity of 97%. Comparing the area under the receiver operating characteristic curves of these tests, D-waves appeared to have a significantly greater predictive value than MEPs and especially SSEPs alone (0.992 vs 0.798 vs 0.653; p = 0.023 and p < 0.001, respectively). On multiple logistic regression, the independent risk factors associated with significant IONM changes in the entire population were age older than 65 years and an anterolateral location of the tumor (p < 0.0001). CONCLUSIONS D-wave monitoring was feasible in all patients without severe preoperative motor deficits. D-waves demonstrated a statistically significant higher ability to predict postoperative deficits compared with SSEPs and MEPs alone and allowed us to proceed with IDEM tumor resection, even in cases of SSEP and/or MEP loss. Patients older than 65 years and with anterolateral IDEM tumors can benefit most from the use of IONM.