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 presumed motor eloquent areas to exactly localize functional areas. The aim of our study is to examine whether the spatial data provided by nTMS and nTMS-based fiber tracking in combination with the preoperative neurophysiologic measurements provided by nTMS are predictive for postoperative motor outcome and could be utilized to stratify patients in high and low risk groups in respect to functional deterioration.

Method: Prospectively collected data of 185 patients undergoing nTMS examination of the tumorous and the healthy hemisphere prior to surgery of motor eloquent brain tumors were included. The following data were analyzed: the pre- and postoperative motor status (after 7 days und 3 months), the histology, the nTMS-data (resting motor threshold (RMT), latency, EMG amplitude), the closest distance between nTMS based DTI fiber tracts and the tumor and the spatial relation between tumor and primary motor cortex.

Results: 74% after 7 days and 63% after 3 months of the patients had no change in their motor status. Whereas none of the patients with a secondary brain tumor demonstrated deterioration of their motor system, worsening of the motor status was observed in 25% of patients with gliomas after 3 months. New postoperative deficits on day 7 correlated with an increased RMT on the tumorous hemisphere compared to the healthy hemisphere (RMT tumorous 10% higher than healthy hemisphere; p=0,035). In terms of distance between tumor and fiber tracts no functional deterioration was observed when the distance was greater than 8mm and the precentral gyrus was not infiltrated.

Conclusions: nTMS in combination with nTMS-based fiber tracking allows stratifying patients with tumors in critical motor location into a high risk (varying RMT between hemispheres and/or distance tracts to tumor < 8mm and/or infiltration of M1) and a low risk group to develop a new motor deficit postoperatively. No surgically induced functional deficits have been observed on the low risk group. Intraoperative neurophysiological monitoring is mandatory in high risk cases.