gms | German Medical Science

Objective: Repetitive navigated transcranial magnetic stimulation (rTMS) is frequently used for preoperative language mapping especially in patients with eloquent glioma. Since language positive areas are found by rTMS on both hemispheres we raised the question if subcortical interhemispheral connectivity can be shown using rTMS-based DTI-fibertracking (DTI-FT) which has shown reliable results tracking subcortical language related fibers in previous studies. Moreover, its correlation with preoperative aphasia should be investigated.

Method: 34 patients with left-sided perisylvian lesions underwent language mapping by rTMS on both hemispheres. DTI FT was performed with a deterministic tractography software (iPlanNet 3.0, Brainlab) using rTMS-positive language areas of the left and the right hemisphere as seed regions. The fiber length was set to 40 mm and two settings of fractional anisotropy were chosen (FA 0.01 and 0.1). All patients were evaluated concerning fluent or non-fluent aphasia at the time of rTMS mapping.

Results: In 12 patients commissural fibers connecting TMS language positive areas of the right and the left hemisphere could be visualized performing DTI FT using a setting of 40 mm fiber length and FA of 0.01 (by increasing the FA to 0.1 10 patients showed interhemispherical connectivity). 50% of these patients presented with preoperative aphasia. In the patients were no interhemispheral connectivity could be shown 27% suffered from preoperative aphasia.

Conclusions: In this study interhemispherical connectivity using DTI-FT could be observed in 35% of the patients. In the patient group with interhemispherical connectivity the percentage of aphasia was higher (50%) than in the patients were no commissural fibers could be visualized (27%), leading to the question if increased interhemispherical connectivity is triggered by tumor-associated alteration of left hemisphere language function.