Abstract
BACKGROUND: The dilemma of neuro-oncological surgery involving suspected eloquent cortex is to maximize the extent of resection while minimizing neurological morbidity, referred to as the "onco-functional balance." Diffuse lower-grade gliomas are capable of infiltrating or displacing neural function within cortical regions and subcortical white matter tracts, which can render classical anatomic associations of eloquent function misleading. OBSERVATIONS: This study employed presurgical navigated transcranial magnetic stimulation (nTMS) to determine the motor eloquence of a diffuse lower-grade glioma at the superior frontal gyrus extending and intrinsic to the primary motor cortex in a 45-year-old female. Positive nTMS findings were confirmed intraoperatively with high-frequency direct cortico-subcortical stimulation (HF-DCS). Modification of the HF-DCS train count from train-of-five to train-of-two permitted resection beyond classic anatomical boundaries and conventional HF-DCS safe stopping criteria. LESSONS: Anatomical correlates of function can inaccurately inform the surgical management of diffuse lower-grade glioma, which represents the utmost opportunity for progression-free survival. Integrating an individually tailored nTMS-DCS surgical strategy contributed to complete resection, negating the requirement for adjuvant therapy. Serial nTMS follow-up may assist with the characterization of tumor-induced functional reorganization. https://thejns.org/doi/10.3171/CASE24197.