Surgical opportunities on facial nerve decompression following intra-temporal facial nerve injury:an experimental study

Objective To establish animal models of intratemporal facial nerve injury and find the natural developmental features of facial nerve injury. To explore the best time to do facial nerve decompression surgeries and to discover the laws of injured facial nerve recovery after the decompression surgeries. Methods 32 200～300 g female Wister rats were used, and the tympanic segments of the bone canal of the facial nerves were compressed by minimal forceps. After making the models, rats were randomly divided into 4 equal groups which were given decompression surgery at different times: within 3 weeks group, after 4 weeks group, after 8 weeks group and the control group. In the control group nothing was done. Decompression consisted of removing the crushed bone pieces and incising the epineurial sheath at the above-mentioned times. The facial nerve threshold current was measured using the NIM-Response to observe the recovery of the facial nerve at intervals of 4 weeks. Results The complete paralysis rats had no response to the maximal current (3mA) in the first week. No significant difference was found between the control group and the group which had decompression surgery after 8 weeks(P0.05), but a difference between the other groups and the control group was found(P0.05). There were significant differences among the three surgery groups(P0.05). Conclusions Crushing the facial nerve bone canal by minimal forceps is a reasonable method to make the animal models of intratemporal facial nerve injury. Decompression of the facial nerve performed within two months resulted in a faster recovery of the threshold current. Decompression later than two months had the same recovery speed as no decompression of the facial nerve. During the first two months, the earlier the decompression of the facial nerve was performed, the faster the facial nerve recovered.