gms | German Medical Science

Objective: A mapping technique comparable to a “cortico-spinal tract (CST) radar” was applied to overcome the temporal and spatial limitations of classical subcortical mapping. The feasibility and safety of continuous dynamic subcortical motor mapping (at the site of and synchronized with tissue resection) was evaluated in patients with intra-axial brain tumors.

Method: We prospectively studied 182 patients who underwent surgery of intra-axial brain tumors adjacent to the CST (defined as <1 cm distance using diffusion tension imaging fiber tracking) with simultaneous subcortical monopolar motor mapping (cathodal stimulation, train of 5 stimuli, inter-stimulus interval 4.0 ms, pulse duration 0.5 ms) and a new acoustic motor evoked potential alarm. Temporal and spatial coverage was technically realized by integrating the mapping probe at the tip of a new suction device. Motor function was assessed using MRC scale for muscle strength one day after surgery, at discharge, and at 3 months.

Results: All procedures were technically successful. Lowest individual motor thresholds were as follows (MT, number of patients): >20 mA, n=21; 11-20 mA, n=35; 6-10 mA, n=31; 4-5 mA, n=37; 1-3 mA, n=58. At 3 months, 6 patients (3%) had persisting postoperative motor deficits, 3 of them were caused by vascular injury, 2 by mechanical injury of the CST and one was unclear. MRCS grades deficits at 3 months caused by vascular injury were 0.5, 1 and 3, by mechanical injury 0.5 and 2 and in the unclear case 1.

Conclusions: Continuous dynamic mapping was found to be a feasible and ergonomic technique for localizing the distance of 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 (<5 mA) stimulation intensities. This new technique may increase the safety of motor eloquent tumor surgery.