gms | German Medical Science

Objective: Diffusion tensor imaging fiber tracking (DTI FT) is commonly used in glioma surgery to visualize subcortical fiber tracts, especially within the neuronavigation. Yet, there is no standardized protocol at hand, which visualizes all language-involved fiber tracts reliably. Thus, this study investigates the value of using language-related cortical areas identified via repetitive navigated transcranial magnetic stimulation (rTMS) as seed regions for DTI-FT of subcortical language tracts.

Method: Language mapping by rTMS was performed in 38 patients (23 male, 15 female) with left-hemispheric perisylvian lesions from 05/2011 to 08/2014. Language positive stimulation spots were integrated in the tractography software (Brainlab, iPlanNet 3.0) as individual objects via DICOM standard and used as seed regions for DTI-FT. Deterministic tractography was then performed in each individual patient with 77 different settings of fiber lengths (40 - 100 mm) and fractional anisotropy (FA) (0.01 - 0.5) to detect language-relevant fiber tracts.

Results: By performing rTMS-based DTI-FT it was possible to identify language-related fiber tracts such as the corticonuclear tract, arcuate fascicle, uncinate fascicle, superior longitudinal fascicle, inferior longitudinal fascicle, arcuate fibers, commissural fibers, corticothalamic fibers, and frontooccipital fascicle in all 38 patients. In 33 patients every above-named fiber tract could be visualized (87%). A fiber length of 60 mm and an FA of 0.2 were proved optimal by requiring a mean of 58 ± 26 traced individual fibers for one visualized language tract.

Conclusions: With this study, we present the feasibility of rTMS-based DTI-FT for subcortical language tracts for the first time and show that it provides an easy and standardizable method for the visualization of every language tract in 87% of patients.