Comparison of hemispheric dominance and correlation of evoked speech responses between functional magnetic resonance imaging and navigated transcranial magnetic stimulation in language mapping.

BACKGROUND

Non-invasive language mapping is commonly facilitated via two different approaches, functional magnetic resonance imaging (fMRI) and navigated transcranial magnetic stimulation (nTMS). The aim of our examination was to compare both methods regarding hemispheric dominance and detection of involved cortex in speech-processing.

METHODS

Since 2015, patients with language eloquent tumors received both fMRI and nTMS language mapping in our facility. Hemispheric dominance for fMRI (word pairing task) and nTMS (picture naming) was defined according to activation/response predominance between hemispheres. For a detailed comparison of methods, we used a cortical parcellation system and correlated activations of each gyrus. Statistical analysis was performed using Sign test, Spearman's rank correlation coefficient and Mann-Whitney-U test.

RESULTS

Twenty-three patients with predominantly frontal and temporal tumors were enrolled. fMRI and nTMS predicted the same hemispheric dominance in 67% of examinations. No significant difference was found between the tests (P=0.63). When examining the correlation of anatomical areas with speech relevance between the two methods, we found significant differences in activation patterns of language relevant areas when comparing patients inter-individually. Using 2/3 rule for evoked language errors in nTMS improved congruence in perisylvian regions.

CONCLUSIONS

fMRI and nTMS lead to comparable results in determining hemispheric dominance, however they show significantly different results in predicting language relevant areas. We recommend using 2/3 rule for nTMS to improve congruence. Both tools seem to be valuable methods for preoperative planning. However, surgical decision making concerning resectability of language eloquent lesions should be based on awake craniotomy, furthermore.