Comparison of anatomical-based vs. nTMS-based risk stratification model for predicting postoperative motor outcome and extent of resection in brain tumor surgery

The authors acknowledge the support of the Cluster of Excellence Matters of Activity. Image Space Material funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germanýs Excellence Strategy – EXC 2025. Dr. Rosenstock is participant in the BIH Charité Digital Clinician Scientist Program funded by the Charité – Universitätsmedizin Berlin, and the Berlin Institute of Health at Charité (BIH). Dr. Belotti received fundings from the Italian Society of Neurosurgery - “Premio Melitta Grasso Tomasello” and the Beretta Foundation for Cancer Study - “European Scholarship on Oncology”.Background: Two statistical models have been established to evaluate characteristics associated with postoperative motor outcome in patients with glioma associated to the motor cortex (M1) or the corticospinal tract (CST). One model is based on a clinicoradiological prognostic sum score (PrS) while the other one relies on navigated transcranial magnetic stimulation (nTMS) and diffusion-tensor-imaging (DTI) tractography. The objective was to compare the models regarding their prognostic value for postoperative motor outcome and extent of resection (EOR) with the aim of developing a combined, improved model. Methods: We retrospectively analyzed a consecutive prospective cohort of patients who underwent resection for motor associated glioma between 2008 and 2020, and received a preoperative nTMS motor mapping with nTMS-based diffusion tensor imaging tractography. The primary outcomes were the EOR and the motor outcome (on the day of discharge and 3 months postoperatively according to the British Medical Research Council (BMRC) grading). For the nTMS model, the infiltration of M1, tumor-tract distance (TTD), resting motor threshold (RMT) and fractional anisotropy (FA) were assesed. For the PrS score (ranging from 1 to 8, lower scores indicating a higher risk), we assessed tumor margins, volume, presence of cysts, contrast agent enhancement, MRI index (grading white matter infiltration), preoperative seizures or sensorimotor deficits. Results: Two hundred and three patients with a median age of 50 years (range: 20–81 years) were analyzed of whom 145 patients (71.4%) received a GTR. The rate of transient new motor deficits was 24.1% and of permanent new motor deficits 18.8%. The nTMS model demonstrated a good discrimination ability for the short-term motor outcome at day 7 of discharge (AUC = 0.79, 95 %CI: 0.72–0.86) and the long-term motor outcome after 3 months (AUC = 0.79, 95 %CI: 0.71–0.87). The PrS score was not capable to predict the postoperative motor outcome in this cohort but was moderately associated with the EOR (AUC = 0.64; CI 0.55–0.72). An improved, combined model was calculated to predict the EOR more accurately (AUC = 0.74, 95 %CI: 0.65–0.83). Conclusion: The nTMS model was superior to the clinicoradiological PrS model for potentially predicting the motor outcome. A combined, improved model was calculated to estimate the EOR. Thus, patient counseling and surgical planning in patients with motor-associated tumors should be performed using functional nTMS data combined with tractography.Peer Reviewe

Predicting the Extent of Resection of Motor-Eloquent Gliomas Based on TMS-Guided Fiber Tracking

Background: Surgical planning with nTMS-based tractography is proven to increase safety during surgery. A preoperative risk stratification model has been published based on the M1 infiltration, RMT ratio, and tumor to corticospinal tract distance (TTD). The correlation of TTD with corticospinal tract to resection cavity distance (TRD) and outcome is needed to further evaluate the validity of the model. Aim of the study: To use the postop MRI-derived resection cavity to measure how closely the resection cavity approximated the preoperatively calculated corticospinal tract (CST) and how this correlates with the risk model and the outcome. Methods: We included 183 patients who underwent nTMS-based DTI and surgical resection for presumed motor-eloquent gliomas. TTD, TRD, and motor outcome were recorded and tested for correlations. The intraoperative monitoring documentation was available for a subgroup of 48 patients, whose responses were correlated to TTD and TRD. Results: As expected, TTD and TRD showed a good correlation (Spearman’s ρ = 0.67, p < 0.001). Both the TTD and the TRD correlated significantly with the motor outcome at three months (Kendall’s Tau-b 0.24 for TTD, 0.31 for TRD, p < 0.001). Interestingly, the TTD and TRD correlated only slightly with residual tumor volume, and only after correction for outliers related to termination of resection due to intraoperative monitoring events or the proximity of other eloquent structures (TTD ρ = 0.32, p < 0.001; TRD ρ = 0.19, p = 0.01). This reflects the fact that intraoperative monitoring (IOM) phenomena do not always correlate with preoperative structural analysis, and that additional factors influence the intraoperative decision to abort resection, such as the adjacency of other vulnerable structures. The TTD was also significantly correlated with variations in motor evoked potential (MEP) responses (no/reversible decrease vs. irreversible decrease; p = 0.03). Conclusions: The TTD approximates the TRD well, confirming the best predictive parameter and giving strength to the nTMS-based risk stratification model. Our analysis of TRD supports the use of the nTMS-based TTD measurement to estimate the resection preoperatively, also confirming the 8 mm cutoff. Nevertheless, the TRD proved to have a slightly stronger correlation with the outcome as the surgeon’s experience, anatomofunctional knowledge, and MEP observations influence the expected EOR

Bicentric validation of the navigated transcranial magnetic stimulation motor risk stratification model.

OBJECTIVE The authors sought to validate the navigated transcranial magnetic stimulation (nTMS)-based risk stratification model. The postoperative motor outcome in glioma surgery may be preoperatively predicted based on data derived by nTMS. The tumor-to-tract distance (TTD) and the interhemispheric resting motor threshold (RMT) ratio (as a surrogate parameter for cortical excitability) emerged as major factors related to a new postoperative deficit. METHODS In this bicentric study, a consecutive prospectively collected cohort underwent nTMS mapping with diffusion tensor imaging (DTI) fiber tracking of the corticospinal tract prior to surgery of motor eloquent gliomas. The authors analyzed whether the following items were associated with the patient's outcome: patient characteristics, TTD, RMT value, and diffusivity parameters (fractional anisotropy [FA] and apparent diffusion coefficient [ADC]). The authors assessed the validity of the published risk stratification model and derived a new model. RESULTS A new postoperative motor deficit occurred in 36 of 165 patients (22%), of whom 20 patients still had a deficit after 3 months (13%; n3 months = 152). nTMS-verified infiltration of the motor cortex as well as a TTD ≤ 8 mm were confirmed as risk factors. No new postoperative motor deficit occurred in patients with TTD > 8 mm. In contrast to the previous risk stratification, the RMT ratio was not substantially correlated with the motor outcome, but high RMT values of both the tumorous and healthy hemisphere were associated with worse motor outcome. The FA value was negatively associated with worsening of motor outcome. Accuracy analysis of the final model showed a high negative predictive value (NPV), so the preoperative application may accurately predict the preservation of motor function in particular (day of discharge: sensitivity 47.2%, specificity 90.7%, positive predictive value [PPV] 58.6%, NPV 86.0%; 3 months: sensitivity 85.0%, specificity 78.8%, PPV 37.8%, NPV 97.2%). CONCLUSIONS This bicentric validation analysis further improved the model by adding the FA value of the corticospinal tract, demonstrating the relevance of nTMS/nTMS-based DTI fiber tracking for clinical decision making