Intraoperative Monitoring of Facial and Cochlear Nerves During Acoustic Neuroma Surgery

Preservation of facial nerve function during acoustic neuroma surgery can be improved significantly by monitoring of facial electromyography (EMG) during surgery. Mechanical trauma during dissection causes EMG activity that can be played over a loudspeaker for direct feedback to the surgeon. Electrical stimulation can be used to locate the nerve even when it is out of direct view, and the threshold for stimulation provides a measure of facial (or other motor nerve) integrity. Cochlear nerve function also can be monitored by the recording of auditory brain stem responses or compound action potentials from an electrode placed on the nerve at the brain stem root entry zone.