Associations between clinical outcome and navigated transcranial magnetic stimulation characteristics in patients with motor-eloquent brain lesions: a combined navigated transcranial magnetic stimulation–diffusion tensor imaging fiber tracking approach

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Navigated transcranial magnetic stimulation (nTMS) and diffusion tensor imaging fiber tracking (DTI FT) based on nTMS data are increasingly used for preoperative planning and resection guidance in patients suffering from motor-eloquent brain tumors. The present study explores whether nTMS-based DTI FT can also be used for individual preoperative risk assessment regarding surgery-related motor impairment.


Data derived from preoperative nTMS motor mapping and subsequent nTMS-based tractography in 86 patients were analyzed. All patients suffered from high-grade glioma (HGG), low-grade glioma (LGG), or intracranial metastasis (MET). In this context, nTMS-based DTI FT of the corticospinal tract (CST) was performed at a range of fractional anisotropy (FA) levels based on an individualized FA threshold ([FAT]; tracking with 50%, 75%, and 100% FAT), which was defined as the highest FA value allowing for visualization of fibers (100% FAT). Minimum lesion-to-CST distances were measured, and fiber numbers of the reconstructed CST were assessed. These data were then correlated with the preoperative, postoperative, and follow-up status of motor function and the resting motor threshold (rMT).


At certain FA levels, a statistically significant difference in lesion-to-CST distances was observed between patients with HGG who had no impairment and those who developed surgery-related transient or permanent motor deficits (75% FAT: p = 0.0149; 100% FAT: p = 0.0233). In this context, no patient with a lesion-to-CST distance ≥ 12 mm suffered from any new surgery-related permanent paresis (50% FAT and 75% FAT). Furthermore, comparatively strong negative correlations were observed between the rMT and lesion-to-CST distances of patients with surgery-related transient paresis (Spearman correlation coefficient [rs]; 50% FAT: rs = –0.8660; 75% FAT: rs = –0.8660) or surgery-related permanent paresis (50% FAT: rs = –0.7656; 75% FAT: rs = –0.6763).


This is one of the first studies to show a direct correlation between imaging, clinical status, and neurophysiological markers for the integrity of the motor system in patients with brain tumors. The findings suggest that nTMS-based DTI FT might be suitable for individual risk assessment in patients with HGG, in addition to being a surgery-planning tool. Importantly, necessary data for risk assessment were obtained without significant additional efforts, making this approach potentially valuable for direct clinical use.

ABBREVIATIONS BMRC = British Medical Research Council; CST = corticospinal tract; DTI, DTI FT = diffusion tensor imaging, DTI fiber tracking; FA, FAT = fractional anisotropy, FA threshold; fMRI = functional MRI; HGG = high-grade glioma; IOM = intraoperative monitoring; LAD = lesion-to-activation distance; LGG = low-grade glioma; MEP = motor evoked potential; MET = metastasis; nTMS = navigated transcranial magnetic stimulation; rMT = resting motor threshold; ROI = region of interest; rs = Spearman correlation coefficient.

Article Information

Correspondence Sandro M. Krieg, Department of Neurosurgery, Klinikum rechts der Isar, Technische Universität München, Ismaninger Str. 22, Munich 81675, Germany. email:

INCLUDE WHEN CITING Published online March 31, 2017; DOI: 10.3171/2016.11.JNS162322.

Disclosures Dr. Krieg is a consultant for BrainLAB AG and Nexstim Plc.

© AANS, except where prohibited by US copyright law.



  • View in gallery

    Setup overview. This figure depicts the procedures performed during pre- and postoperative assessments and surgery, including nTMS for motor mapping and nTMS-based tractography of the CST. In addition, it shows the study's main approaches regarding data analyses.

  • View in gallery

    Tractography and measurement of the minimum lesion-to-CST distance. This figure visualizes DTI FT based on nTMS data for reconstruction of the CST (left). The motor-positive nTMS spots are depicted as green points, and the tumor volume is shown in orange. Furthermore, an axial MRI slice is shown, providing an example of how minimum lesion-to-CST distances were measured (right). Figure is available in color online only.


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