Intraoperative electrophysiologic identification of the nervus intermedius

• Published in: Otology & neurotology Vol. 26; no. 2; pp. 274 - 279
• Main Authors: Ashram, Yasmine A, Jackler, Robert K, Pitts, Lawrence H, Yingling, Charles D
• Format: Journal Article
• Language: English
• Published: United States 01-03-2005
• Subjects: Adolescent; Adult; Afferent Pathways - physiopathology; Aged; Ageusia - diagnosis; Ageusia - physiopathology; Ageusia - prevention & control; Blinking - physiology; Child; Chorda Tympani Nerve - physiopathology; Cranial Nerve Injuries - physiopathology; Cranial Nerve Injuries - prevention & control; Cranial Nerves - physiopathology; Ear - innervation; Electrodiagnosis; Electromyography; Facial Nerve - physiopathology; Facial Nerve Injuries - physiopathology; Facial Nerve Injuries - prevention & control; Facial Paralysis - diagnosis; Facial Paralysis - physiopathology; Facial Paralysis - prevention & control; Female; Humans; Male; Middle Aged; Monitoring, Intraoperative; Nasolacrimal Duct - innervation; Neuroma, Acoustic - surgery; Postoperative Complications - diagnosis; Postoperative Complications - physiopathology; Postoperative Complications - prevention & control; Prognosis; Reaction Time - physiology; Retrospective Studies; Sensory Thresholds - physiology; Tears - secretion
• ISSN: 1531-7129
• DOI: 10.1097/00129492-200503000-00026

Although enormous attention has been directed to the localization and preservation of the facial nerve in acoustic neuroma surgery, the nervus intermedius has largely been ignored. In this article, we describe a method for intraoperative electrophysiologic identification of the nervus intermedius.
Retrospective case review.
University hospital (tertiary care center).
Thirty-three patients who underwent intraoperative facial nerve monitoring for various cerebellopontine angle procedures. Recording electrodes were placed in the orbicularis oculi and orbicularis oris muscles. A constant-voltage stimulator was used to stimulate both the facial nerve and the nervus intermedius.
None.
Electrophysiologic response after stimulation of the nervus intermedius.
Stimulation of the nervus intermedius produced long-latency, low-amplitude response recorded only on the orbicularis oris channel. The response had a mean threshold 0.4 V, a mean latency of 11.1 ms, and a mean amplitude of 11.1 microV, all significantly different from responses to stimulation the facial nerve.
Knowledge of electrophysiologic features of nervus intermedius stimulation can help protect the facial nerve during cerebellopontine angle surgery. The surgeon must recognize that stimulation of the nervus intermedius can cause electromyographic activity in the facial nerve monitoring channels, but the main trunk of the facial nerve may lie in entirely different location in the cerebellopontine angle.