The Study Of Locating Facial Nerve Precisely In Middle Ear Surgery Based On Clinical Anatomy

Cranial nerve ? is facial nerve,it is the longest nerve travels in the narrow bone canal.Which is a mixed nerve,composed of motor and sensory fibers,neural function is by these two kinds of nerve bundle of the decision.Facial nerve leaves the pontomedullary sulcus,travel through the internal acoustic meatus,cavitas tympanica,mastoid process,and pass through the parotid gland,masseter and cheek to the lateral aspect of the face after leaving skull from the stylomastoid foramen,the overall length of facial nerve is 36.0~53.0mm.There are many factors that caused injury or defect nerve in clinic,such as traumatism,inflammation,cancer,or iatrogenic reasons.The dysfunction of expression brings patients many questions of social mentality and disorder of social communication.The main clinical manifestations to facial expression muscle losing contractile function incomplete or complete,often accompanied by weakness in closing eyelids,deviation of mouth angle,sensory disturbance,slurred speech.The anatomical structures inside of temporal bone are very complex,facial nerve has strong ties to the structures surrounded by.The facial nerve is a special structure to protect in the middle ear surgery,and it is also an important sign of temporal bone-associated operation.In order to ensure the effect of operation,avoid and reduce the chance of facial nerve injury,Surgeons need to have an intimate knowledge of the anatomical structures of middle ear and positioning methods of the nerve.At present,the operator relies more on experience and preoperative imaging to locate the facial nerve in general,there is lack of an anatomical method for specifying facial nerve localization in the clinical work of middle ear surgery.Some scholars had suggested that the facial nerve can be roughly positioned by using the chorda tympani nerve,lateral chamber of the facial recess,vasa vasorum of the facial nerve.However,it is not enough to rely on these landmarks solely during surgery,and they can not achieve the purpose of specifying facial nerve.In addition,the patient's individual differences,lesion destruction and some other reasons,to some extent,also lower the clinical utility of these landmarks.Most of the researches on the localization of the facial nerve at home and abroad were based on anatomical and imaging studies,these data obtained are also limited to preoperative evaluation.The reasons,on the one hand,these studies were not conducted from the view of clinical point,the bony landmarks selected are not obvious and vulnerable to invasion and destruction of lesions,and imaging measurements can also cause error due to the artifacts,on the other hand,most of these studies were based on temporal bone dry or specimens soaked in Faure Marin,the data obtained by measurement are inevitably caused by the fixation of the specimens and the cutting of the cross section.These sign structures selected and the data obtained in these studies have limitations in locating the facial nerve in the operation of the middle ear surgery are difficult to be directly applied to the clinic.At present,there are few anatomical studies based on the fresh head specimen of Chinese people,and there are few samples in these studies.In this study,15 adult cadaveric specimens(30 sides)were selected as the research materials.Combined with surgical approach,the anatomical structures inside of the temporal bone were exposed clearly through the operation under microscope.According to the anatomical structures exposed during the operation,the anatomy of the facial nerve was studied from the view of clinical operation.The main objective of this study is to observe the shape of the facial nerve,the relative spatial position and the morphological characteristics of the structures around the facial nerve.On the basis of previous studies,some new and more reliable bone marker structures was selected to refine the localization of facial nerve in the middle ear surgery.Through the selection of the midpoint of the posterior wall of external auditory canal(annulus level),the lending edge of sigmoid sinus,the lateral margin of jugular bulb,Henle crest,the posterior of short limb of incus,the lower edge of posterior semicircular canal,the lower edge of horizontal semicircular canal,the upper edge of vestibular window as the reference structures positioning of the facial nerve,we had came up with a method for locating facial nerve precisely,which will contribute to guidance clinic work.By measuring under the microscope,we got the following data,the shortest distance from the midpoint of the posterior wall of external auditory canal(annulus level)to the vertical segment of the facial nerve was(3.37 ± 0.34)mm,the shortest distance from the leading edge of the sigmoid sinus to the vertical segment of facial nerve was(7.40 ± 0.71)mm,the shortest distance from the lateral margin of jugular bulb to the facial nerve was(5.58 ± 0.79)mm,the shortest distance from Henle crest to the pyramidal segment of facial nerve was(12.76 ± 1.24)mm,the shortest distance between the pyramidal segment of facial nerve and the posterior short limb of incus was(1.56 ±0.35)mm,the shortest distance between the pyramidal segment of facial nerve and the lower edge of posterior semicircular canal was(2.56 ± 0.41)mm,the shortest distance between the lower edge of horizontal semicircular canal and the horizontal segment of facial nerve was(1.28 ± 0.32)mm,the shortest distance between the upper edge of vestibular window and the horizontal segment of facial nerve was(0.67 ± 0.15)mm.Some suggestions were also proposed,that is Surgeons need to connect facial nerve with its surrounding anatomical structures with the idea of spatial relationship and distance.A good command of the middle ear anatomy and anatomical variation as well as careful operation and methods of locating facial nerve will provide the key to reduce the probability of iatrogenic facial nerve injury in middle ear surgery.At the same time combined with the preoperative imaging examination and intraoperative facial nerve monitoring technology can greatly improve the precise positioning of the facial nerve and shorten operation time,also can enhances the surgery success ratio and reduce postoperative complications.