P166: Continuous dynamic mapping of the corticospinal tract during surgery of motor eloquent brain tumors

Abstract

Introduction The objective was to establish a mapping technique to overcome the temporal and spatial limitations of classical subcortical mapping of the corticospinal tract (CST). The feasibility and safety of continuous subcortical mapping synchronized with tissue resection was evaluated. Methods This prospective study included 69 patients who underwent tumour surgery adjacent to the CST ( 1 cm using diffusion tension imaging and fiber tracking) with simultaneous subcortical monopolar mapping (short train of 5 cathodal stimuli, inter-stimulus interval 4.0 ms, pulse duration 0.5 ms) and an acoustic motor evoked potential alarm. Continuous (temporal coverage) and dynamic (spatial coverage) mapping was technically realized by integrating the mapping probe at the tip of a 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 All procedures were technically successful. There was a 1:1 correlation of motor thresholds (MTs) for stimulation sites simultaneously mapped with the new suction mapping device and the classic fingerstick probe (24 patients, 74 stimulation points, r = 0.996, p 0.001). Lowest individual MTs were as follows (MT, number of patients): > 20 mA, n = 7; 11–20 mA, n = 13; 6–10 mA, n = 8; 4–5 mA, n = 17; 1–3 mA, n = 24. At 3 months, two patients (3%) had a persisting postoperative motor deficit, both of which were caused by a vascular injury. No patient had a permanent motor deficit caused by a mechanical injury of the CST. Conclusion Continuous dynamic mapping was found to be a feasible and ergonomic technique for localizing the CST. The acoustic feedback and the ability to continuously stimulate the tissue exactly at the site of tissue removal might improve the accuracy of mapping, especially at low stimulation intensities. This technique may increase the safety of motor eloquent tumour surgery.