A New Cortical Electrode for Neuronavigation-Guided Intraoperative Neurophysiological Monitoring: Technical Note

Abstract

Intraoperative neurophysiological mapping and monitoring of eloquent brain areas can be combined with image-guided localisation to enhance the safety and efficacy of surgical procedures in the motor cortex. We designed a new type of cortical electrode which can be repeatedly placed on the cortical surface and allows accurate and reproducible stimulation by means of a navigation pointer. The newly designed device consists of a monopolar electrode contact for direct cortical stimulation, housed in a holder which allows placement, easy removal, and precise repeated placement of a surgical navigation pointer. It can be used for navigation-guided, high-frequency anodal monopolar cortical stimulation (MCS) for the mapping of eloquent cortex, and for monitoring of motor pathways. While the cortex is stimulated, compound muscle action potentials (CMAP) are recorded from muscles of the contralateral extremities and are assessed both qualitatively and quantitatively. When the device is used in combination with intraoperative navigation, the stimulation sites may optionally be registered or displayed on the system monitor. This allows repeated pinpointing and obviates the need for strip or grid electrodes in the operative field; although such electrodes may be useful for continuous monitoring, they often are in the surgeon's way. In addition, the primary and supplementary motor cortex can be mapped by determining the location of the sites of stimulation on surface-projected images of the cerebral cortex.

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“…25,52 The reference electrode was placed at Fzp. 10 Identical stimulation parameters as described above for DCS were applied (TOF stimuli, interstimulus interval 4 msec, pulse duration 500 µsec).…”

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“…10 For a constant current with anodal stimulation, train-of-5 stimuli with an interstimulus interval of 4.0 ms and an individual impulse width of 500 microseconds were used. [7][8][9] Cortical and subcortical mapping was performed with a probe delivering a monopolar current 11 and the above-mentioned parameters under total intravenous anesthesia. 8 Motor responses were monitored by needle electrodes placed in standardized target muscles.…”

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“…The correct position of the stimulation electrode could be checked via the intraoperatively visible precentral gyrus. The position of the stimulation electrode on the motor cortex was also monitored by navigation [20]. Shifting of the stimulation electrode could thus be excluded.…”