Functional imaging in frameless stereotactic biopsy of highly eloquent brain lesions

Introduction: In terms of diagnostics and treatment planning, intracranial mass lesions often require needle biopsies. Despite being performed with minimum invasiveness, biopsy-related functional deficits may still occur. Navigated transcranial magnetic stimulation (nTMS) enables preoperative non-invasive identification of eloquent brain areas. In addition, nTMS-based tractography can visualize eloquent white matter pathways. The aim of this study was to evaluate the usefulness and clinical impact of non-invasive cortical mapping and tractography of eloquent brain functions for trajectory planning before stereotactic biopsies.

Methods: Cortical nTMS data and nTMS-based tractography of motor and language function were integrated into the routine workflow of trajectory planning before biopsies. Intraoperative data, histopathological findings, and clinical outcomes were analyzed.

Results: Between March 2018 and March 2023, 45 cases of stereotactic frameless biopsies of eloquent brain lesions with preoperative nTMS mappings and nTMS-based tractography (16 motor / 2 language / 27 both) were analyzed. Cortical nTMS data and tractography were considered during trajectory planning in all cases. The diagnostic yield was 84.4%. Histopathological findings showed HGG in 25 (55.6%) cases, low-grade-glioma in 5 (11.1%) patients, lymphoma in 5 patients (11.1%), and reactive gliosis to rule out tumor progression in 4 cases (8.9%). Amongst cases with no clear histopathological finding, resection of the lesion was performed in four patients, while one patient underwent repeated biopsy. One case of language deterioration resolved after admission of dexamethasone and two cases of progressive motor decline related to extensive tumor progress on MRI were observed during hospitalization. Postoperative CT imaging in these three cases revealed no postoperative hemorrhage.

Conclusion : Non-invasive functional data can easily be integrated into trajectory planning workflow for frameless stereotactic biopsies. The reliable visualization of eloquent cortical and subcortical regions facilitate the planning process and might avoid surgery-related neurological deficits.