Risk stratification in motor area-related glioma surgery based on navigated transcranial magnetic stimulation data

Abstract

OBJECTIVE Navigated transcranial magnetic stimulation (nTMS) is a noninvasive method for preoperatively localizing functional areas in patients with tumors in presumed motor eloquent areas. The aim of this study was to establish an nTMS-based risk stratification model by examining whether the results of nTMS mapping and its neurophysiological data predict postoperative motor outcome in glioma surgery. METHODS Included in this study were prospectively collected data for 113 patients undergoing bihemispheric nTMS examination prior to surgery for gliomas in presumed motor eloquent locations. Multiple ordinal logistic regression analysis was performed to test for any association between preoperative nTMS-related variables and postoperative motor outcome. RESULTS A new motor deficit or deterioration due to a preexisting deficit was observed in 20% of cases after 7 days and in 22% after 3 months. In terms of tumor location, no new permanent deficit was observed when the distance between tumor and corticospinal tract was greater than 8 mm and the precentral gyrus was not infiltrated (p = 0.014). New postoperative deficits on Day 7 were associated with a pathological excitability of the motor cortices (interhemispheric resting motor threshold [RMT] ratio < 90% or > 110%, p = 0.031). Interestingly, motor function never improved when the RMT was significantly higher in the tumorous hemisphere than in the healthy hemisphere (RMT ratio > 110%). CONCLUSIONS The proposed risk stratification model, based on objective functional-anatomical and neurophysiological measures, enables one to counsel patients about the risk of functional deterioration or the potential for recovery.

Keywords: CST = corticospinal tract; DTI = diffusion tensor imaging; EMG = electromyography; FAT = fractional anisotropy threshold; FDI = first dorsal interosseous; GTR = gross-total resection; IOM = intraoperative neurophysiological monitoring; IntCaps = ≤ 8 mm from CST; KPS = Karnofsky Performance Scale; M0 = neither infiltrating nor adjacent to primary motor cortex; M1 = infiltration of primary motor cortex or corticospinal tract; M2 = directly adjacent to M1; MEP = motor evoked potential; MRC = Medical Research Council; PR = partial resection; RMT = resting motor threshold; STR = subtotal resection; brain tumor surgery; diffusion tensor imaging; glioma; motor outcome; nTMS = navigated transcranial magnetic stimulation; navigated transcranial magnetic stimulation; oncology; predictive model; surgical technique.