gms | German Medical Science

Objective: Navigated transcranial magnetic stimulation (nTMS) is a non-invasive examination method used in the preoperative diagnostics for patients with tumors in motor eloquent areas to localize functional areas. In addition, nTMS combined with diffusion tensor imaging (DTI) enables an improved reconstruction of the corticospinal tract (CST). The aim of our study is to examine whether the characteristics of nTMS-based motor DTI based on two different approaches are associated with patients’ clinicalfindings.

Method: Prospectively collected data of 15 patients undergoing nTMS mapping prior to surgery of motor eloquent high-grade gliomas were analyzed. The following data were scrutinized based on nTMS-based fiber tracking with a) a cubic ROI (3D) and b) a plane ROI (2D) in the anterior inferior pons: the pre- and postoperative motor status (after 7 days und 3 months), the number of fibers and aberrant fibers respectively, the fractional anisotropy (FA) and FA threshold (FAT), the apparent diffusion coefficient (ADC) and the closest distance between the tracts and the tumor.

Results: Using a plane ROI instead of a cubic ROI can reduce the occurrence of aberrant fibers from 73% to 27% in the affected hemisphere (p = 0.027) and from 40% to 13% in the healthy hemisphere (p = 0.021). Differences were observed when comparing the values of FA, FAT and ADC of the affected hemisphere with the values of the healthy hemisphere whereas no significant difference were found based on the use of a plane or cubic ROI. The average values of FA and ADC in the affected hemisphere were significantly associated with the postoperative motor outcome.

Conclusions: Use of a plane ROI in the anterior inferior pons increases DTI specificity. Moreover, impairment of diffusivity within peritumoral tracts seems to be predictive of postoperative motor deficits. Larger patient samples are needed to further characterize the impact and prognostic value of nTMS-based motor DTI.