Improved potential quality of intraoperative transcranial motor-evoked potentials by navigated electrode placement...

Intraoperative neurophysiological monitoring of transcranial motor-evoked potentials (tcMEPs) may fail to produce a serviceable signal due to displacements by mass lesions. We hypothesize that navigated placement of stimulation electrodes yields superior potential quality for tcMEPs compared to the conventional 10-20 placement. We prospectively included patients undergoing elective cranial surgery with intraoperative monitoring of tcMEPs. In addition to electrode placement as per the 10-20 system, an electrode pair was placed at a location corresponding to the hand knob area of the primary motor cortex (M1) for every patient, localized by a navigation system during surgical setup. Twenty-five patients undergoing elective navigated surgery for intracranial tumors (n = 23; 92%) or vascular lesions (n = 2; 8%) under intraoperative monitoring of tcMEPs were included between June and August 2019 at our department. Stimulation and recording of tcMEPs was successful in every case for the navigated electrode pair, while stimulation by 10-20 electrodes did not yield baseline tcMEPs in two cases (8%) with anatomical displacement of the M1. While there was no significant difference between baseline amplitudes, mean potential quality decreased significantly by 88.3 µV (- 13.5%) for the 10-20 electrodes (p = 0.004) after durotomy, unlike for the navigated electrodes (- 28.6 µV [- 3.1%]; p = 0.055). For patients with an anatomically displaced M1, the navigated tcMEPs declined significantly less after durotomy (- 3.6% vs. 10-20: - 23.3%; p = 0.038). Navigated placement of tcMEP electrodes accounts for interindividual anatomical variance and pathological dislocation of the M1, yielding more consistent potentials and reliable potential quality.