The Role Of Great Auricular-facial Nerve Neurorrhaphy In Facial Nerve Damage

Background:Due to the superficial position, facial nerve is easy to be damaged by trauma, inflammation and surgery. And facial nerve lesions always combine with a significant loss of function, such as corneal exposure, epiphora, and brow ptosis, as well as external nasal valve collapse, oral incompetence, and loss of smile ability, which will lead to devastating consequences for patients. Thus, the improvement of facial nerve function after injury is of the utmost importance to both patients and the physicians who treat them. Although many strategies have been used to improve the recovery of facial function after facial nerve damage like neurotrophic factors, electrical stimulation, and stem cells, peripheral motor nerve regeneration and functional recovery in humans is not robust, due to that facial nerve lesion lacks of valid spontaneous regeneration in the distal nerve stump in certain situations. Thus, nerve end to end anastomosis and graft is becoming one of the treatment guidelines for facial nerve neurotmesis.Nerve grafts, which remove nerve segments from other part of the body, are used most commonly in facial nerve repair. In the past twenty years, most clinicians utilized accessory nerve, lingual nerve, sural nerve and great auricular nerve for facial nerve injury repair. Unfortunately, in some cases, patients with severe and complicated facial nerve damage did not have the condition for grafts or end to end anastomosis, because of complicated anatomy of temporal bones, hardly exposed of proximal facial nerve and the severity condition of patients who couldn’t undergo a so complicated and time-long surgery. In these respects, facial nerve foster with other nerves was becoming an alternative solution to delay the amyotrophy of these patients. Great auricular nerve, compared with other nerves, is neighborhoodly with facial nerve in anatomical position which provides great auricular-facial nerve neurorrhaphy within a smaller surgical filed in facial nerve repair surgery. What’s more, their section areas of great auricular nerve and facial nerve are similar which may lead to the facial-great auricular nerve neurorrhaphy more efficiently than other potentially replaceable nerves. In virtue of these advantages, facial-great auricular nerve neurorrhaphy attracted increasingly attention to the surgeon.However, there is few published report about whether the mechanism of functional recovery, nerve regeneration and innervation of facial-great auricular nerve neurorrhaphy in facial nerve repair has a connection with acetylcholine receptors (AChR) and neuromuscular junction (NMJ). As in recent presented studies, it was well recognized that maintenance of a high density of AChRs at the postsynaptic membrane of NMJ is essential for the effectiveness of synaptic impulse transmission. NMJs are assembled on the muscle fibers at very precise locations called end plates (EP) where AChR is required for an accurate synaptic transmission.In our present studies, we established a rat model for facial nerve injury and facial-great auricular nerve neurorrhaphy for the first time to measure the functional recovery and the nerve regeneration about great auricular nerve graft in facial nerve repair. Methods:Rat models of facial nerve cut (FC), facial nerve end to end anastomosis (FF), facial-great auricular nerve neurorrhaphy (FG), and control (Ctrl) were established. Then all the rats were feed in a same environment. After operation 8 weeks and 12 weeks, Apex nasi amesiality observation, vibrissae movement test and blink reflex test were carried out to evaluate the function recovery of facial nerve. Furthermore, electrophysiology and immunofluorescence assays were employed to investigate the mechanism of facial nerve function recovery.Results:All rats are alive and well after operation. In apex nasi amesiality observation, it was found apex nasi amesiality of FG group was partly recovered. While, in vibrissae movement test and blink reflex test, there is no obvious recovery of FG group compared with FF group and Ctrl group. Additionally, electrophysiology and immunofluorescence assays revealed that facial-great auricular neurorrhaphy could transfer nerve impulse and express AChR which was better than facial nerve cut and worse than facial nerve end to end anastomosis.Conclusions:The present study indicated that facial-great auricular nerve neurorrhaphy is a substantial solution for facial lesion repair which should be preferred in those that end to end anastomosis is hardly accepted as facial nerve is badly destroyed. Facial-great auricular nerve neurorrhaphy is efficiently preventing facial muscles atrophy by AchR, but never promoting the movements of facial muscles.