The Microanatomy And Clinical Application Of Masseter-to-facial Nerve Transfer

Objective:Through the detailed microdissection and data measurement to 15 cadaveric head specimens,make understanding of the segmatation, directions, length, diameters and the surrounding adjacent structures of both the facial nerve and the masseteric nerve, discuss the feasibility of masseter-to-facial nerve transfer for repair of facial nerve paralysis, sum up how to use simple surface marks accurately positioning masseter nerve, provide anatomical basis for masseter-to-facial nerve transfer. Methods:1.A total of 15 cases of cadaveric head specimens with 10% formalin fixation were dissected to reveal the course of facial nerve and masseter nerve trunk and branch, measured both the length and diameter of the masseter nerve, also the diameter of the facial nerve, summarize the classification, number of branches, relationship with surrounding tissues and the surface projection of the masseter nerve;2.Provide the evidence of the feasibility of repairing facial nerve paralysis,and provide the anatomical basis of how to effectively dissect the masseter nerve will not result in severe muscle paralysis;3.Determine the suitable segmentation of the masseter nerve for facial nerve anastomosis. Measure the distances between the anastomosis segmentation to the important surface markings to find out the surface projection of the masseter nerve, and provide the anatomical reference of looking for the masseter nerve in clinical surgery. Results:1.The anatomical structure from shallow to deep when dissect the facial nerve to masseter nerve are skin,subcutaneous fat, facial superficial muscle aponeurosis system, parotid masseter fascia, parotid gland and the masseter.2. On the basis of the branch morphology and distribution,the masseter nerve can be divided into three types: single trunk, double trunks and triple trunks.In this research, the proportion of these three types of the masseter nerve are 37%, 53% and 10% respectively.3.The length from where the masseter nerve goes through the mandibular notch to the mandibular angle(L1) is(40.6±3.8)mm; the length from the main trunk of the masseter nerve to the middle third of the masseter lower margin(L2) is(37.8±3.4)mm; and the length from the main trunk to the first third of the masseter lower margin(L3) is(26.2±2.3)mm. According to these data, we can figure out the surface topography of the masseter nerve’s path after passing through the mandibular notch.4.Counting the length and the transverse diameter of each subsection of the masseter nerve, we found that the transverse diameter of the second subsection of the main trunk(1.2±0.2)mm,the third subsection of the main trunk(0.9±0.2)mm,the first subsection of the front trunk(1.0±0.2)mm,the second subsection of the front trunk(0.8±0.1)mm are similar to the diameter of the main trunk or the main branches of the facal nerve.Besides,these subsections can detach the most sufficient nerve which can be uesed for the tension-free nerve anastomosis. On the basis of the study, we can get the conclusion that the mostly proper part of the masseter nerve for a end-to-end anastomosis to the facial nerve would be these subsections: the second and the third subsection of the main trunk, also the first and the second subsection of the front trunk.5.The vertical length from the anastomosing segment of the masseter nerve to the inferior margin of the zygomatic arch and to the tragus are respectivly(1.02±0.16) cm and(3.11±0.27)cm. According to these results, we can conclude that the anastomosing segment of the masseter nerve could be found approximately at 1cm inferior to the zygomatic arch and 3cm anterior to the tragus. Conclusion:1. Make use of simple surface markers can be accurately position the masseter nerve in the deep part of masseter, easily to search and separation in the operation;2. Highly eural efficiency, the cerebral cortex level fusion and neural peripheral parts of the transport links provide the feasibility of a certain basis for the treatment of facial nerve paralysis;3.Choose the right part of the trunk of the masseter nerve for cutting will not cause serious masseter atrophy;4.Because of being convenient for dissection,rapidly recovery of facial function after transposition and fewer complications,the masseter nerve is becoming the ideal donor resources for transposition in the treatment of facial paralysis.