Artikel
DTI Fiber tracking of clear positive speach responses of the superior parietal lobe in nTMS language mapping
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Autoren
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Gregor Durner
- Bezirkskrankenhaus Günzburg, Günzburg, Deutschland
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Aksel Ribenis
- Bezirkskrankenhaus Günzburg, Günzburg, Deutschland
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Christian Rainer Wirtz
- Bezirkskrankenhaus Günzburg, Günzburg, Deutschland
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Jan Coburger
- Neurochirurgische Klinik der Universität Ulm, Standort Günzburg, Günzburg, Deutschland
| Veröffentlicht: | 9. Juni 2017 |
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Gliederung
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Objective: Navigated transcranial magnetic stimulation (nTMS) has gained increasingly relevance for non-invasive language mapping in recent years. In our mappings, we recognized a high number of clear positive speech responses in parietal lobe, specifically in superior parietal lobe (SPL) which most authors would consider to be a non-eloquent region regarding language processing. In our current pilot study, we assessed positive nTMS responses using diffusion tensor imaging (DTI) fiber tracking.
Methods: We performed nTMS language mapping based on a standardized protocol covering both hemispheres and all superficial cortical gyri in 9 patients with left sided speech dominance using Nexstim NBS System. Positive speech responses were defined as a missing answer during the 1s stimulation interval of a picture naming task. Parietal responses were then used as a seed for DTI fiber tracking using Brainlab iPlan 3.0 software. Fractional anisotropy (FA) threshold was set to 0,2 and minimum length to 70mm.
Results: 7 out of 9 patients showed parietal nTMS responses in their dominant hemisphere. SPL responses were found in 4 patients, in 2 cases more than 1. In fMRI responses confirmed these answers in all 4 patients. When performing fiber tracking of all parietal seeds, we identified typical fibers of superior longitudinal fasciculus (SLF) in 5 patients, temporo-parietal (tp) SLF in 3 patients and 1 seed showed parieto-parietal commissural fibers. All 3 SLF-tp tracts were based on SPL seeds.
Conclusion: The detected tracts showed quite consistent results corresponding to fibers of SLF. SLF-tp fibers originated from SPL specifically. Thus, SPL should not per se be considered as a non-eloquent area in dominant hemisphere. Preoperative fMRI or nTMS testing with DTI fiber tracking seems to be valuable tools in assessment of involvement of language processing. However, future studies are needed to verify our results by awake mapping or detailed postoperative neuropsychological assessment after resection of parietal lesions.
