Final Subcortical Motor Mapping Threshold and Overall Survival After Motor-Eloquent Glioblastoma Resection: Exploratory Analysis of Residual Fluorescence at the Motor Boundary

Introduction: Subcortical motor mapping thresholds are routinely used during glioblastoma resection to reduce the risk of permanent neurological injury, but their association with survival is not well established. We evaluated whether the final subcortical motor mapping threshold recorded at the end of resection is associated with overall survival (OS) in patients undergoing mapping-guided resection of motor-eloquent glioblastoma, including exploratory evaluation by residual fluorescence adjacent to the motor pathway. Methods: We performed a retrospective single-center cohort study of consecutive adults with newly diagnosed IDH-wild-type glioblastoma (2018–2024) who underwent motor mapping-guided resection with a documented final subcortical stimulation threshold and received adjuvant oncological therapy. The prespecified exposure was stimulation threshold ≤ 5 mA versus >5 mA. OS was analyzed using Kaplan–Meier estimates and Cox regression. To reduce overfitting, the primary adjusted Cox model included stimulation threshold, age, and temozolomide exposure; a fully adjusted model including age, sex, extent of resection, radiotherapy regimen, and temozolomide was established for sensitivity analysis. Because proportional hazards assumptions were not fully satisfied, restricted mean survival time (RMST) differences were also estimated at prespecified horizons. Results: Among 36 patients, stimulation threshold ≤ 5 mA was associated with shorter OS compared with >5 mA (log-rank p = 0.001). In the primary adjusted Cox model, stimulation threshold > 5 mA remained associated with lower mortality risk (HR 0.35, 95% CI 0.15–0.82, p = 0.016); results were directionally consistent in the fully adjusted model (HR 0.24, 95% CI 0.089–0.643, p = 0.0046). RMST analyses favored the >5 mA group at 12, 18, and 24 months. In exploratory analyses, the association appeared most evident in patients without residual fluorescence adjacent to the motor pathway. Conclusions: Lower final subcortical stimulation thresholds were associated with shorter overall survival after mapping-guided resection of motor-eloquent glioblastoma. These findings suggest that the final intraoperative stimulation threshold was associated with overall survival in adjusted exploratory models and may provide prognostic information in addition to its established role in surgical safety; however, prospective validation in larger cohorts is warranted.