A new cortical electrode for neuronavigation-guided intraoperative neurophysiological monitoring: Technical note

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 s urface and allows accurate and reproducible stimulation by means of a navig ation pointer. The newly designed device consists of a monopolar electrode contact for dir ect cortical stimulation, housed in a herder which allows placement, easy r emoval, and precise repeated placement of a surgical navigation pointer. It can be used for navigation-guided, high-frequency anodal monopolar cortica l stimulation (MCS) for the mapping of eloquent cortex, and for monitoring of motor pathways. While the cortex is stimulated, compound muscle action p otentials (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 allow s repeated pinpointing and obviates the need for strip or grid electrodes i n the operative field; although such electrodes may be useful for continuou s monitoring, they often are in the surgeon's way. In addition, the primary and supplementary motor cortex can be mapped by determining the location o f the sites of stimulation on surface-projected images of the cerebral cort ex.