Detection of intraoperative laser injury to the facial nerve by electromyographic monitoring of facial muscles.

Injury to the facial nerve is a significant risk during resection of cerebellopontine angle tumors. To minimize the risk of facial nerve injury, intraoperative electromyographic monitoring of facial musculature is frequently used. However, the reliability of such monitoring systems for detection of thermal nerve injury resulting from the use of carbon dioxide lasers has not been systematically evaluated. We determined the sensitivity of a computerized electromyographic monitor for detection of laser facial nerve injury in an anesthetized rat model. The mandibular and buccal branches of the facial nerve were isolated in 12 rats. A carbon dioxide laser was used to create controlled sites of thermal injury to both nerves over a 3-hour period. When a laser injury was created distal to previous injury sites, electromyographic discharge was noted in 72% to 82% of injuries. Laser injury proximal to previous injury sites was detected with 33% efficiency. These detection rates did not change significantly over a 3-hour period. This preliminary data suggests that electromyographic monitoring of facial musculature allows detection of facial nerve injury caused by carbon dioxide lasers.