Evaluating postoperative motor function using postoperative navigated transcranial magnetic stimulation motor mapping

Objective

Navigated transcranial magnetic stimulation (nTMS) motor mapping has been established in the preoperative workflow of brain tumor patients. This study aimed to evaluate the use of postoperative nTMS motor mapping, which has been rarely performed to evaluate surgery-associated corticospinal tract injuries and functional outcome.

Methods

Patients undergoing resection of brain tumors, who received pre- and postoperative nTMS motor mapping were retrospectively evaluated. Further inclusion criteria were postoperative deterioration in motor function or the presence of a preoperative motor deficit MRC ≤3/5 without significant improvement after surgery. Postoperative nTMS was conducted within 14 days after tumor surgery. Corticospinal tracts (CST) were visualized using pre- and postoperative diffusion tensor imaging (DTI). Distances between the tumor and the CST as well as the resection cavity and the CST were measured. Primary outcome was a functionally adequate (MRC ≥4/5) motoric status after 3 months.

Results

Seventeen patients were included, mean age was 59.5 ± 14.9 years. Motor evoked potentials (MEP) of at least one extremity were recorded in 14 cases (82.4 %). The positive predictive value (PPV) for motor recovery of postoperative nTMS mapping was 90.5 %, the negative predictive value (NPV) was 38.5 %. Motor thresholds of the operated hemisphere increased significantly after surgery (p = 0.008), whereas the motor thresholds of the contralateral hemisphere remained stable (p = 0.11). Pre- and postoperative CST-visualizations did not differ concerning the distance between CST and lesion or resection cavity.

Conclusion

nTMS potentially predicts functional recovery of transient postoperative motor deficits. Further studies are warranted to prove this effect. Motor deficits significantly improved if it was possible to elicit MEPs with nTMS postoperatively.