Intraoperative neuroelectrophysiological monitoring for neurosurgery

Abstract

In neurosurgery, it is extremely important to try keeping the postoperative neurological functions intact. Recent advancements in neuroimaging technique, management and/or technique of the general anesthesia, surgical technique, intraoperative neuroimaging such as navigation, ultrasonogra- phy, etc. have greatly contributed to postoperative functional preservation. Furthermore, neuroelectrophysiological monitoring has a greater role on this matter. There are various modalities of neuroelectrophysiological monitoring, and they are appropriately applied according to the site of lesions and type of surgical procedures. Mapping is another important modality for identifying cranial nerves and nerve fibers, which are sometimes difficult to identify at surgery. At our institute, we conduct various monitoring methods such as motor- evoked potential (MEP), somatosensory-evoked potential, visual-evoked potential, auditory brainstem response, cochlear nerve action potential, facial nerve monitoring, abnormal muscle response for microvascular decompression of hemifacial spasm, brainstem mapping for the fourth- ventricular floor approach to identify facial colliculus, bulbocavernous reflex for lumbosacral surgery, language monitor at awake craniotomy, etc. All these monitoring methods can be stably and accurately conducted in good collaboration with anesthesiologists. A case of unruptured intracranial aneurysm located at the internal carotid artery-posterior communicating artery is shown which was safely clipped under MEP monitoring, especially at dissection of the anterior choroidal artery severely attaching the wall of the aneurysm. A case of brainstem cavernous angioma is introduced, in which various monitoring methods were used including abnormal muscle response, MEP, somatosensory-evoked potential, and brainstem mapping. A case of awake craniotomy for astrocytoma of the left frontal lobe will also be presented, in which speech function was confirmed during surgery by collaboration with anesthesiologist. How to set-up the monitoring electrodes and cords at surgery is another important issue. To set-up accurately and speedily, we use peg-screw for transcranial stimulation, and developed stapler electrodes for recording. Including other tips we are adapting, quick set-up and stable recording throughout the surgical procedure have been achieved. In summary, functional preservation can be achieved with these monitoring methods as well as with the intraoperative and perioperative managements.