gms | German Medical Science

Objective: Presurgical functional brain mapping is crucial for treatment planning of tumors located within or close to the primary motor cortex (M1) or the pyramidal tract. In the past years, neuronavigated transcranial magnetic stimulation (nTMS) has become an alternative to functional magnetic resonance imaging (fMRI). However, both methods, being based on different approaches, may reveal discrepant results, especially when dealing with brain tumor patients. Therefore, we compared the results of fMRI and nTMS in patients with respect to the M1 representation and the function-associated fiber tracts, compared to healthy subjects.

Method: 10 healthy volunteers and, to date, 20 patients with M1-adjacent tumors were prospectively investigated by fMRI, nTMS and fiber tracking regarding the M1 representation hand, foot and tongue. In brain tumor patients monopolar direct cortical stimulation (mDCS) was performed intraoperatively. Euclidean distances (ED; in mm±SD) were computed between the local activation maxima (LAM) of the fMRI maps and the nTMS hotspots. Moreover, EDs between DCS and fMRI / nTMS coordinates were calculated. Fibers connecting the respective M1 body part representation with the brain stem were tracked.

Results: EDs between firm LAM and nTMS hotspots for patients(p)/volunteers(v) were: hand 15.8±9.3(p) vs. 14.7±2.2(v), foot 16.5±5.7(p) vs. 18.7±2.2(v) and tongue 16.4±13.5(p) vs. 18.5±3.1(v). EDs between fMRI LAM and DCS hotspots vs. nTMS and DCS hotspots were within the same range (hand: fMRI 14.2±6.4 / nTMS 13.7±6.0; foot: fMRI 11.6±9.2 / nTMS 11.6±2.9; tongue: fMRI 10.4±4.4 / nTMS 10.2±6.8). However, high variability between the patients is reflected by remarkably lower EDs when combining both presurgical mapping techniques (hand 10.9±4.9; foot 8.1±4.3; tongue: 9.2±5.4). In some cases, the location of the fMRI-based pyramidal tract differed remarkably from the nTMS-based fibers.

Conclusions: Clinical factors such as anticonvulsant drugs, motor deficits and alertness considerably affect the results of both mapping techniques and may contribute to preselection of patients of one or the other presurgical functional mapping method in the future. In average, none of the methods turned out to be clearly superior when compared to the gold standard, DCS. Further analysis and recruitment of larger patient numbers may illustrate, which presurgical functional mapping technique amounts to the highest validity in specific subsets of patients.