Navigated transcranial magnetic stimulation (nTMS) in combination with diffusion tensor imaging fiber tracking (DTI FT) is increasingly used to locate subcortical language-related pathways. The aim of this study was to establish nTMS-based DTI FT for preoperative risk stratification by evaluating associations between lesion-to-tract distances (LTDs) and aphasia and by determining a cut-off LTD value to prevent surgery-related permanent aphasia.
Fifty patients with left-hemispheric, language-eloquent brain tumors underwent preoperative nTMS language mapping and nTMS-based DTI FT, followed by tumor resection. nTMS-based DTI FT was performed with a predefined fractional anisotropy (FA) of 0.10, 0.15, 50% of the individual FA threshold (FAT), and 75% FAT (minimum fiber length [FL]: 100 mm). The arcuate fascicle (AF), superior longitudinal fascicle (SLF), inferior longitudinal fascicle (ILF), uncinate fascicle (UC), and frontooccipital fascicle (FoF) were identified in nTMS-based tractography, and minimum LTDs were measured between the lesion and the AF and between the lesion and the closest other subcortical language-related pathway (SLF, ILF, UC, or FoF). LTDs were then associated with the level of aphasia (no/transient or permanent surgery-related aphasia, according to follow-up examinations).
A significant difference in LTDs was observed between patients with no or only surgery-related transient impairment and those who developed surgery-related permanent aphasia with regard to the AF (FA = 0.10, p = 0.0321; FA = 0.15, p = 0.0143; FA = 50% FAT, p = 0.0106) as well as the closest other subcortical language-related pathway (FA = 0.10, p = 0.0182; FA = 0.15, p = 0.0200; FA = 50% FAT, p = 0.0077). Patients with surgery-related permanent aphasia showed the lowest LTDs in relation to these tracts. Thus, LTDs of ≥ 8 mm (AF) and ≥ 11 mm (SLF, ILF, UC, or FoF) were determined as cut-off values for surgery-related permanent aphasia.
nTMS-based DTI FT of subcortical language-related pathways seems suitable for risk stratification and prediction in patients suffering from language-eloquent brain tumors. Thus, the current role of nTMS-based DTI FT might be expanded, going beyond the level of being a mere tool for surgical planning and resection guidance.
ABBREVIATIONSAF = arcuate fascicle; CST = corticospinal tract; DES = direct electrical stimulation; DTI = diffusion tensor imaging; DTI FT = diffusion tensor imaging fiber tracking; FA = fractional anisotropy; FAT = fractional anisotropy threshold; FL = fiber length; FLAIR = fluid attenuated inversion recovery; FoF = frontooccipital fascicle; ILF = inferior longitudinal fascicle; IONM = intraoperative neuromonitoring; LAD = lesion-to-activation distance; LED = lesion-to-eloquence distance; LTD = lesion-to-tract distance; MRI = magnetic resonance imaging; mRS = modified Rankin Scale; nTMS = navigated transcranial magnetic stimulation; rMT = resting motor threshold; ROI = region of interest; rs = Spearman correlation coefficient; SD = standard deviation; SLF = superior longitudinal fascicle; UC = uncinate fascicle.
Correspondence Sandro M. Krieg: Technische Universität München, Munich, Germany. email@example.com.
INCLUDE WHEN CITING Published online March 15, 2019; DOI: 10.3171/2018.12.JNS182988.
N.S. and A.F. contributed equally to this work.
Disclosures NS reports receipt of honoraria from Nexstim Plc. SK reports consultant relationships with Nexstim Plc and Spineart Deutschland GmbH and receipt of honoraria from Medtronic and Carl Zeiss Meditec. SK and BM report receipt of research grants from and consultant relationships with Brainlab AG. BM reports receipt of honoraria, consulting fees, and research grants from Medtronic, Icotec ag, and Relievant Medsystems Inc.; honoraria and research grants from Ulrich Medical; honoraria and consulting fees from Spineart Deutschland GmbH and DePuy Synthes; and royalties from Spineart Deutschland GmbH. However, all authors declare that they have no conflict of interest regarding the materials used or the results presented in this study.
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