SURG-21. Revisiting the Relationship Between Tumor-to-CST Distance and Subcortical MEP Thresholds in Brain Tumor Surgery

Abstract BACKGROUND The relationship between tumor-to-corticospinal tract (CST) distance and the subcortical motor evoked potential (scMEP) threshold remains unclear. This study examines how contrast-enhancement charecteristics influence this correlation. METHODS We retrospectively analyzed preoperative imaging and intraoperative electrophysiological data from 323 patients who underwent resection of intra-axial tumors adjacent to the CST. We recorded the shortest distance from the tumor margin to the CST (as defined by DTI-based tractography) and the lowest stimulation current required to elicit an scMEP. To ensure the lowest threshold corresponded the minimal tumor-to-CST distance, only patient underwent gross total resection were included. Correlation between tumor-to-CST distance and scMEP threshold were analyzed, stratified by contrast enhancement status. RESULTS Of the 203 patients meeting inclusion criteria, 158 had contrast-enhancing tumors. The mean preoperative tumor-to-CST distance was 9 ± 7.4 mm (range: 0–20 mm) for enhancing tumors and 7.2 ± 5.4 mm (range: 0.9–20 mm) for non-enhancing tumors. The mean lowest scMEP threshold was 7.9 ± 4.7 mA (range: 1–25 mA) for enhancing tumors and 6.5 ± 4.5 mA (range: 1–20 mA) for non-enhancing tumors. A strong correlation was observed between tumor-to-CST distance and scMEP threshold in non-enhancing tumors (r = 0.73; 95% CI: 0.54–0.85; P <.0001), whereas the correlation was weaker in enhancing tumors (r = 0.37; 95% CI: 0.21–0.51; P <.0001). CONCLUSIONS In non-enhancing tumors, preoperative tumor-to-CST distance reliably predicts the minimal current required to elicit an scMEP. However, in contrast-enhancing tumors, intraoperative scMEP mapping offers superior functional guidance, underscoring its critical role in surgical planning and decision-making.