Direct motor evoked potentials and cortical mapping using the NIM nerve monitoring system: A technical note

Introduction: Motor evoked potentials (MEPs) are commonly used to prevent neurological injury when operating in close proximity to the motor cortex or corticospinal pathway. We report a novel application of the NIM nerve monitoring system (Medtronics@ NIM response 3.0) for intraoperative direct cortical (dc)-MEPs monitoring. Case Summary: A 69-year-old female patient presented with a 4 month history of progressive left hemiparesis resulting from a large right sided posterior frontal meningioma that abutted and compressed the motor cortex. Motor cortical mapping and MEPs were indicated. The patient was anesthetized and maintained on total intravenous anesthetics. Compound muscle action potentials (CMAP) of the right upper limb were monitored using the NIM system. After a craniotomy was performed, we first used the Ojemann stimulator (monopolar) for dc-stimulation and then switched to use the monopolar nerve stimulator probe of the NIM system. The CMAP response was successfully elicited using the NIM stimulating probe (pulse width = 250 s, train frequency = 7 pulses/s, current = 20 mA). A gross total resection of the tumor was achieved with intermittent cortical mapping of MEPs. There were no intraoperative complications and the patient’s motor function was preserved after the surgery. Conclusion: We conclude that the NIM nerve monitoring system is a feasible alternative to standard neurophysiological monitoring systems.