The impact of DTI fiber tracking of the corticospinal tract based on navigated transcranial magnetic stimulation on surgery of motor-eloquent brain lesions

Introduction: Navigated transcranial magnetic stimulation (nTMS) allows for non-invasive preoperative mapping of primary motor cortex (M1). The combination with DTI fiber tracking (DTI-FT) of corticospinal tract (CST) has been described, but its impact on surgery of motor-eloquent lesions has not been definitively addressed. The aim of the present study is to analyse the impact of nTMS-based mapping on surgery of motor-eloquent lesions.Materials and methods: In this retrospective case-control study we reviewed data of patients operated for suspected motor-eloquent lesions between 2012 and 2015. Patients underwent nTMS mapping of M1 and, from 2014, nTMS-based DTI-FT of CST. The impact on preoperative risk/benefit analysis, surgical strategy, craniotomy size, extent of resection (EOR) and functional outcome (motor and seizure-free status, Karnofsky Performance Status/KPS) were compared with a historical control group.Results: We included 35 patients who underwent nTMS mapping of M1 (Group A), 35 patients who also underwent nTMS-based DTI-FT of CST (Group B), and a control group composed by 35 patients treated without nTMS (Group C). All patients underwent intraoperative neuromonitoring (IONM). Patients in group A and B received a smaller craniotomy (p=.01; p=.001), had less postoperative seizures (p=.02), better postoperative motor performance (p=.04) and KPS (p=.009) as compared to controls. Moreover, patients in Group B showed an improved risk/benefit analysis (p=.006), an increased EOR of false-eloquent lesions (p=.03), and a better motor outcome (p=.04) as compared to Group A. Conclusion: The nTMS-based motor mapping allows for a tailored surgical approach for motor-eloquent lesions. It improves risk/benefit analysis, EOR and functional outcome, especially when nTMS-based DTI-FT is performed.