Enhancing Motor Function Preservation in Intra-axial Brain Tumor Surgery With Intraoperative Validation of Corticospinal Tractography Using Elastic Image Fusion and Direct Electrical Stimulation: A Proof-of-Concept Study and Preliminary Results

BACKGROUND AND OBJECTIVES: Accurate localization of the corticospinal tract (CST) is crucial for preserving motor function during brain tumor resection. To address the loss of tractography accuracy caused by intraoperative brain shift, this study evaluated an elastic image fusion (EIF) algorithm that deforms preoperative tractography to intraoperative anatomy. METHODS: Preoperative MRI was elastically fused with intraoperative computed tomography to generate a "virtual" intraoperative CST. Retrospective data from 80 patients were used to assess CST reconstruction after EIF. Updated CSTs were prospectively validated in 12 patients using a navigated monopolar probe by estimating probe-CST distances. Primary outcomes were feasibility and reliability (proportion of direct electrical subcortical stimulation points of ±2 mm from updated CST). Secondary measures included Dice coefficient, median CST shift, and extent of resection. RESULTS: EIF-based CST reconstruction was pursued in all 92 patients. The mean Dice coefficient was 0.71 (SD 0.15), indicating partial but not complete overlap between preoperative and "virtual" CSTs, consistent with meaningful intraoperative tract displacement. In the prospective cohort, subcortical stimulation was pursued in all 12 cases; 2 were excluded for absent motor responses at >20 mA. In the 10 analyzable cases, EIF showed a numerically higher threshold-distance matching rate than rigid fusion (40.0%, 4/10; 95% CI, 12.2%-73.8% vs 10.0%, 1/10; 95% CI, 0.3%-44.5%) and a lower mean absolute error (7.18 mm; 95% CI, 2.17-12.18 vs 10.68 mm; 95% CI, 4.99-16.36). Exploratory paired comparisons were descriptive only (exact McNemar P = .25 for concordance; Wilcoxon signed-rank P = .109). Early neurological outcomes were stable or improved in 75% (9/12) of patients. CONCLUSION: This study provides preliminary proof-of-concept evidence that an intraoperative computed tomography-based EIF algorithm can generate a "virtual" intraoperative CST and may improve agreement with intraoperative functional mapping. Larger prospective studies are required to define accuracy, generalizability, and clinical impact.