FV 3. Higher concordance of navigated transcranial magnetic stimulation (nTMS) than of functional MRI with intraoperative direct cortical stimulation (DCS) for delineating the primary motor area

Abstract

Objective To optimize the outcome after brain tumour surgery not only with regard to completeness of resection but also to postoperative motor functions and, thus, quality of life, individual assessment of the surgery-related functional risk is mandatory. Therefore, navigated transcranial magnetic stimulation (nTMS) has been used more and more as a reasonable alternative to functional magnetic resonance imaging (fMRI) over the last years. We compared the congruency of nTMS vs. fMRI results for non-invasively mapping the primary motor cortex (M1) prior to surgery with the gold standard method of direct cortical simulation (DCS). Methods 32 patients with intracerebral tumours underwent nTMS and fMRI prior to surgery. The cortical hotspots (HS) and Centres of Gravity (CoG) of M1 of the hand, the foot and the tongue representation were determined for each localizer technique and controlled by DCS. Euclidean distances (ED) between nTMS/fMRI and the respective DCS HS/CoG’s were computed in 3D. Moreover, nTMS, fMRI and DCS maps were projected onto the cortical surface following normalization to a standard brain. After smoothing, overlap volumes between both nTMS and fMRI with DCS functional maps (voxels) were calculated. Results CoG’s of the nTMS maps were located significantly closer to the respective DCS CoG’s as compared to fMRI ( p ± 6.0/17.3 ± 9.6 mm) and the foot (nTMS-DCS/fMRI-DCS: 16.2 ± 20/21.7 ± 17 mm) representation. However, comparison of hotspots did not reveal statistically significant differences. Regarding the overlap of entire functional maps, nTMS showed a higher agreement with DCS as compared to fMRI ( p ± 17%/57 ± 34%; p Conclusions Comparison of both M1 CoG’s and volume overlaps suggest that nTMS agrees better with the gold standard of intraoperative DCS as compared to fMRI, especially regarding the hand and the foot representation and, thus, is recommendable for presurgical M1 mapping. However, both methods should be regarded as complementary, particularly in respect of the tongue representation which is less easy to depict by nTMS.