Introduction: Object: To overcome the temporal and spacial limitations of classical subcortical mapping of the corticospinal tract. We evaluated the feasibility and safety of continuous and dynamic subcortical motor mapping especially at low motor thresholds.
Methods: We prospectively studied 69 patients who underwent tumor surgery adjacent to the CST with simultaneous subcortical monopolar motor mapping. Continuous (temporal coverage) and dynamic (spacial coverage) mapping was technically realized by integrating the mapping probe at the tip of a new suction device with the concept that this device will be in contact with the tissue where the resection is performed. Motor function was assessed one day after surgery, at discharge, and at 3 months.
Results: The initial evaluation in 24 patients showed a 1:1 correlation of MTs for stimulation sites simultaneously mapped with the new suction mapping device and the classic fingerstick probe (74 stimulation points, r =0.996, p<0.001). Thereafter, the fingerstick probe was no longer used and mapping was performed only using the continuous dynamic technique. All procedures were technically successful. Lowest individual motor thresholds (MTs) were as follows (MT, number of patients): >20mA, n=7; 11-20mA, n=13; 6-10mA, n=8; 4-5mA, n=17; 1-3mA, n=24. At 3 months, two patients had a persisting postoperative motor deficit (3%), both were caused by a vascular injury. There was no permanent motor deficit caused by a mechanical injury of the CST.
Conclusions: Continuous dynamic mapping was found to be a feasible and ergonomic technique of localizing the exact site and distance to the CST. The acoustic feedback and the ability to continuously stimulate the tissue exactly at the site of tissue removal improves the accuracy of mapping especially at low (<5mA) stimulation intensities. This new technique may increase the safety of motor eloquent tumor surgery.
Patient Care: This new method of mapping can increase the rate of GTR in glioma surgery and potentially prolong outcome in up to 20% of glioma patients without increasing the risk of new motor deficit.
Learning Objectives: The participants will be introduced into the limitations of subcortical mapping. They will learn about a new technique of continuous mapping and the risks and benefit of glioma resection until low mapping thresholds can be detected.