Neurophysiologic intraoperative monitoring: I. Auditory function

As a result of advances in neuro-otology and neurosurgery, surgeons often operate in the vicinity of sensitive and delicate neural structures in an attempt to restore their function, remove tumor, or alleviate distressing and disabling symptoms. Concerns about preservation of neural function during these surgical procedures have provided the need and motivation for the development and adaptation of neurophysiologic techniques designed to provide feedback about impending trauma. The most common functions that are at risk in neuro-otologic surgery are related to the auditory nerve and centers and the facial nerve. This paper deals with principles and practices of intraoperative monitoring of auditory function. The following applications are illustrated and discussed: 1) intraoperative monitoring of auditory function during posterior fossa tumor resection, 2) auditory brain stem response and VIIIth nerve monitoring during retrolabyrinthine vestibular nerve section, 3) monitoring of auditory function during microvascular decompression of cranial nerve VII, VIII, or IX, and 4) special applications related to cochlear implant surgery.