Neal Conway, Noémie Wildschuetz, Tobias Moser, Lucia Bulubas, Nico Sollmann, Noriko Tanigawa, Bernhard Meyer, and Sandro M. Krieg
The goal of this study was to obtain a better understanding of the mechanisms underlying cerebral plasticity. Coupled with noninvasive detection of its occurrence, such an understanding has huge potential to improve glioma therapy. The authors aimed to demonstrate the frequency of plastic reshaping, find clues to the patterns behind it, and prove that it can be recognized noninvasively using navigated transcranial magnetic stimulation (nTMS).
The authors used nTMS to map cortical motor representation in 22 patients with gliomas affecting the precentral gyrus, preoperatively and 3–42 months postoperatively. Location changes of the primary motor area, defined as hotspots and map centers of gravity, were measured.
Spatial normalization and analysis of hotspots showed an average shift of 5.1 ± 0.9 mm (mean ± SEM) on the mediolateral axis, and 10.7 ± 1.6 mm on the anteroposterior axis. Map centers of gravity were found to have shifted by 4.6 ± 0.8 mm on the mediolateral, and 8.7 ± 1.5 mm on the anteroposterior axis. Motor-eloquent points tended to shift toward the tumor by 4.5 ± 3.6 mm if the lesion was anterior to the rolandic region and by 2.6 ± 3.3 mm if it was located posterior to the rolandic region. Overall, 9 of 16 (56%) patients with high-grade glioma and 3 of 6 (50%) patients with low-grade glioma showed a functional shift > 10 mm at the cortical level.
Despite the small size of this series, analysis of these data showed that cortical functional reorganization occurs quite frequently. Moreover, nTMS was shown to detect such plastic reorganization noninvasively.
Lucia Bulubas, Jamil Sabih, Afra Wohlschlaeger, Nico Sollmann, Theresa Hauck, Sebastian Ille, Florian Ringel, Bernhard Meyer, and Sandro M. Krieg
Because of its huge clinical potential, the importance of premotor areas for motor function itself and plastic reshaping due to tumors or ischemic brain lesions has received increased attention. Thus, in this study the authors used navigated transcranial magnetic stimulation (nTMS) to investigate whether tumorous brain lesions induce a change in motor cortex localization in the human brain.
Between 2010 and 2013, nTMS motor mapping was performed in a prospective cohort of 100 patients with brain tumors in or adjacent to the rolandic cortex. Spatial data analysis was performed by normalization of the individual motor maps and creation of overlays according to tumor location. Analysis of motor evoked potential (MEP) latencies was performed regarding mean overall latencies and potentially polysynaptic latencies, defined as latencies longer than 1 SD above the mean value. Hemispheric dominance, lesion location, and motor-function deficits were also considered.
Graphical analysis showed that motor areas were not restricted to the precentral gyrus. Instead, they spread widely in the anterior-posterior direction. An analysis of MEP latency showed that mean MEP latencies were shortest in the precentral gyrus and longest in the superior and middle frontal gyri. The percentage of latencies longer than 1 SD differed widely across gyri. The dominant hemisphere showed a greater number of longer latencies than the nondominant hemisphere (p < 0.0001). Moreover, tumor location–dependent changes in distribution of polysynaptic latencies were observed (p = 0.0002). Motor-function deficit did not show any statistically significant effect.
The distribution of primary and polysynaptic motor areas changes in patients with brain tumors and highly depends on tumor location. Thus, these data should be considered for resection planning.
Nico Sollmann, Noémie Wildschuetz, Anna Kelm, Neal Conway, Tobias Moser, Lucia Bulubas, Jan S. Kirschke, Bernhard Meyer, and Sandro M. Krieg
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.