Intraoperative cranial nerve monitoring

Abstract

T HERE HAVE BEEN remarkable recent advances in surgical procedures performed on the central and peripheral nervous systems. For instance, early in this century, one of the principal concerns associated with acoustic neuroma resection was the reduction of mortality associated with this procedure. Given the surgical anatomy of the posterior fossa and the complexity of safely separating the eighth cranial nerve from tumor, there was little regard for the preservation of cranial nerve function. Subsequent understanding of the anatomic relationships of cranial nerves, as well as advances in surgical instrumentation, have greatly improved the surgical management of intracranial tumors in the posterior fossa. Decreased mortality and refinements in surgical techniques have fostered a stronger emphasis on preservation of cranial nerve function. Along with advances in surgical instrumentation and technique, the sophistication of electroneurophysiological diagnostic procedures has also contributed to the earlier diagnosis and treatment of neurological lesions. The discovery of the auditory brainstem response (ABR) by Jewett et al was a landmark contribution to this field. 1 By the late 1970s, owing to contributions by Starr and Achor 2 and by Selters and Brackmann, 3'4 the ABR was established as a valuable neurodiagnostic tool. Today, the ABR is a universally accepted diagnostic test used, among other things, for the early detection of mass lesions of the cerebellopontine angle (CPA). Electromyography of facial muscles is also rapidly gaining acceptance as a neurophysiological tool, contributing to the early diagnosis and management of