Background: Within language function research, there is a shift of focus from cortical specialization to a more hodotopical view including subcortical fiber tracts in functional and oncologic considerations. Diffusion tensor imaging fiber tracking (DTI FT) is well established to visualize subcortical fiber tracts. Recently, a new technique has been developed using cortical regions mapped via repetitive navigated transcranial magnetic stimulation (rTMS) as seed regions. This study investigates if rTMS-based DTI FT for language pathways is also feasible postoperatively and whether preoperative versus postoperative fiber changes correlate with changes and severity of the patients' aphasia grades.
Methods: rTMS-based DTI FT was performed preoperatively and postoperatively in 24 patients with left hemispheric perisylvian tumors. Language pathways were analyzed individually preoperatively and postoperatively with 5 different settings of minimum fiber length and fractional anisotropy. Transient aphasia was defined as any new or worse language impairment caused by surgery that resolved within the regular 3-month follow-up interval. Because postoperative aphasia does not allow rTMS language mapping, preoperative rTMS data were used throughout.
Results: Patients with transient aphasia postoperatively had a significant reduction in fiber count compared with patients without deficit (321.5 ± 242.8 fibers vs. 518.0 ± 435.2 fibers; P = 0.01). Furthermore, in this patient group, the arcuate fascicle was lost postoperatively twice as often compared with patients with no deficit after surgery (52% vs. 26%; P < 0.01).
Conclusions: This study shows that rTMS-based DTI FT is feasible for postoperative examination of language pathways. Moreover, changes in preoperative versus postoperative fibers correlate well with the grade of aphasia.
Keywords: Aphasia; Diffusion tensor imaging; Fiber tracking; Language; Subcortical fiber tracts; Transcranial magnetic stimulation.
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