Comparison of extratemporal and intratemporal facial nerve injury models

Abstract

The purpose of this study was to compare functional recovery and motor nerve conduction following a distal extratemporal crush injury of the facial nerve to a more proximal intratemporal crush injury. Prospective, controlled animal study. Adult male Sprague-Dawley rats were divided into four experimental groups: 1) extratemporal crush, 2) extratemporal sham-operated, 3) intratemporal crush, and 4) intratemporal sham-operated. Each group had an n of 4-9. The facial nerve was crushed near its exit from the stylomastoid foramen for extratemporal facial nerve injuries and within the facial canal in the temporal bone for intratemporal facial nerve injuries. Recovery times for the return of facial nerve functional parameters were compared between the two injury models. Motor nerve conduction studies were also done weekly to quantify the changes in peak amplitude and latency of evoked response. Rats receiving the extratemporal facial nerve injury recovered full facial function by approximately 2 weeks postoperative (wpo) and displayed normal peak amplitude and latency recordings by 4 wpo. In comparison, rats receiving the intratemporal facial nerve injury failed to reach complete functional recovery at the end of 8 wpo. Although latency of evoked response returned to normal by 2 weeks following the intratemporal injury, peak amplitude remained approximately 70% below normal at the end of 8 wpo. An intratemporal crush of the facial nerve leads to significantly delayed functional recovery and decreased motor nerve conduction as compared to an extratemporal crush, indicating that the location of injury strongly influences the recovery outcome.