Isocitrate Dehydrogenase-1 Mutation Status and Dynamic Subcortical Motor Mapping Using Ultrasonic Aspirator...

Continuous subcortical stimulation via a cavitron ultrasonic surgical aspirator (CUSA) provides real-time functional feedback during resection, yet distance-based interpretation of subcortical motor-evoked potential (scMEP) thresholds is often limited. We compared continuous dynamic CUSA stimulation with stationary ball-tip stimulation and examined whether tumors harboring isocitrate dehydrogenase-1 (IDH1) mutation alter the relationship between preoperatively tumor to corticospinal tract (CST) distance and intraoperative minimum scMEP thresholds.

We retrospectively analyzed preoperative imaging and intraoperative electrophysiological data from 425 patients undergoing resection of intra-axial tumors adjacent to the CST. The shortest distance from the tumor margin to the CST was measured using preoperative diffusion tensor imaging-based tractography. We recorded the minimal stimulation threshold required to elicit an scMEP using either continuous dynamic CUSA stimulation or stationary ball-tip stimulation. To ensure minimal stimulation thresholds accurately reflected the minimal distance between the resection margin and the CST, only patients in whom we achieved gross total resection were included (n = 187). Correlation analyses and multivariable linear regression models were constructed.

Tumor-to-CST distance correlated with scMEP threshold across the cohort, with marked differences by IDH1 status. A stronger correlation was observed in IDH1-mutant tumors (r = 0.55, P < .001) than in IDH1-wildtype tumors (r = 0.35, P < .001). Stimulation technique demonstrated comparable overall distance to threshold behavior, with no significant difference between CUSA and ball-tip mapping (Fisher Z = 1.17; P = .24). Multivariable regression demonstrated that IDH1 mutation status significantly modified distance to threshold (distance × IDH1 interaction β = 0.30 mA/mm, P = .03).

The interpretability of distance-based subcortical motor mapping is influenced by IDH1 mutation status, whereas continuous CUSA stimulation and ball-tip stimulation show comparable overall distance-threshold behavior. Distance-based scMEP thresholds are more reliable in IDH1-mutant tumors, whereas increased variability in IDH1-wildtype tumors likely reflects greater susceptibility to intraoperative brain shift and other biological factors, supporting a biologically informed, real-time electrophysiological approach in motor-eloquent tumor resections.