Experimental Model Of Facial Nerve Mechanical Injury By Compression And Histopathological Study

ObjectiveFacial palsy is very common in clinical. The causes of facial palsy include injury, infection, tumor, congenital abnormality and some primary disease. Facial palsy resulted from trauma is common in all peripheral facial paralysis, approximately account to 1/3. Facial palsy therapy is an important work of Otolaryngology doctors. Clinically, we should make sure to well know the position and the degree of injury first, then select reasonable and appropriate treatment prescription. Among these factors, the degree of injury directly correlated with the prognosis. But in clinical, we usually only through electro-neurogram (ENoG), contrast injured side and uninjured compound action potential(CAP), then to calculate the percentage of nervedegeneration. This method just presumed the quantity of injured nerve fibers. It is difficult to obtain the proof of facial nerve injury that related to histopathology, so it is impossible to make a good grasp of injure level of nerve fibre from the point of histopathology view. Because of all of above reasons, requesting us to establish a suitable animal model to comprehend injure level more precise. Previous established animal models exist a lot of flaws and shortcomings, the main point is that we can not control the value of strength/time, so it is impossible to measure the injury level. And the repeatability of experiments is not able to be satisfied, also these approaches do not allow for the application of graded pressures to the nerve, so we can not establish different degrees facial nerve injury, and it is impossible to observe the variation process of each injury degree. Some models are difficult to manipulate, the methods are complex, at the same time, confined the instrument, so the scope of research are limited. To aim directly at above, in this study we applied a new injury method to established the model of facial nerve paralysis resulted from mechanical injury by compression, in this model we overcame the shortcomings above, and is reproducible, easy to be made, accurate in pressures/times. Finally we apllied up-to-date and effective hiatopathology dyeing to dye facial nerve tissue. According to Sunderland criteria, established the experimental model of facial nerve injury with different degrees of mechanical compression injuries in rabbit, observed the changes of histopathology, then initially explored the relationship between the pressures/times value and the degree of facial nerve injury.In subsequent study, we can combine pressure/time value and electro-neurogram (ENoG) through lots of experiments, to investigate the statistical correlation of pressure/time value and certain item of ENoG, the item that is able to reflect the degree of facial nerve injury stable. Thereby, expect to establish the correspond relation between the degree of facial nerve injury and ENoG. So we can approach the relationship between the pressure/time value and the degree of facial nerve injury. To supply the evidence for diagnosis and treatment of facial palsy in clinical.Methods72 facial nerve buccal branches of 36 rabbits were compressed at different pressures/times by a novel method, and they were divided into 3 groups and 6 subgroups .Changes of histopathology were observed on 3 days and 14 days after injury.Result5cmHg～30cmHg/ 30s,5cmHg ～ 15 cmHg/60s,5cmHg/2min resulted in Sunderland I injury; 40 cmHg～55cmH g/30s,30cmHg～40cmHg/60s,15 cmHg/2min resulted in Sunderiand II injury; 75 cmHg/ 30s,55cmHg/60s,30 cmHg/2min resulted in Sunderiand injury 75cmHg/60s,40cmHg～75 cmHg/2min resulted in Sunderiand IV injury.ConclusionWe used one method that can control pressure/time value completely in this study. Established injury model were graded different degrees from light to heavy according Sunderiand criteria, the method of manipulation was easy and the process had satisfactory repeatability, the result is precise and accurate. We eliminated subjective and other adverse effect factor in this model. In the end we established Sunderiand I ～IV degree facial nerve injury animal model in rabbits. We bound three dyeing methods of histopathology of facial nerve tissue together. HE sections was used to observe the connective tissue between the nerve fiber and Schwann cell, Chromotrope 2R-Brilliant green sections was used to observe the myelin sheath, modified Bielschowsky sections was used to observe the axon.HE dyeing to periphery connective tissue of nerve fibre, chromotropic acid 2R- bright green dyeing to neural sheath , modified Bielschowsky dyeing to axon, we all observed satisfactory result. It's able to display the facial nerve pathological changes detailed and completely, and provid the foundation to further study about the damage and repair of facial nerve.