Disclaimer: The information contained within the Grand Rounds Archive is intended for use by doctors and other health care professionals. These documents were prepared by resident physicians for presentation and discussion at a conference held at Baylor College of Medicine in Houston, Texas. No guarantees are made with respect to accuracy or timeliness of this material. This material should not be used as a basis for treatment decisions, and is not a substitute for professional consultation and/or peer-reviewed medical literature. Traumatic Injuries to the Facial Nerve Traumatic injuries to the facial nerve can be classified by site (extracranial, intratemporal, intracranial) and by the type of trauma (penetrating, non-penetrating, or iatrogenic). The general principles of management remain the same regardless of the location of the injury, but the details vary and will be presented by location. Blunt trauma to the face rarely causes significant extracranial facial nerve injury. An example is birth trauma, most often the result of a forceps delivery where the exposed facial nerve is compressed against the rigid cervical spine. Penetrating lesions of the facial nerve distal to the parotid gland and medial to the lateral canthus of the eye rarely result in severe disfigurement and most often do not require repair. Repair of the cervical or platysmal division is also usually unnecessary because of the minimal functional loss that results from transection. Lesions of the main trunk or the temporozygomatic or cervicofacial divisions should be repaired or a major deficit in facial movement will persist. Clean facial lacerations with immediate onset of facial paralysis should be promptly explored. After three days, the severed branch loses its excitability, and that can make its identification tedious and uncertain. If there is gross contamination of the wound requiring debridement, other life threatening injuries where it is not advisable to prolong anesthesia, or if there is a lack of equipment or expertise, an attempt should be made to identify the severed nerve endings and to tag them for later identification. Whenever possible, primary end-to-end anastomosis is ideal and allows the greatest functional return. Interpositional grafting is second best, but a certain percentage of regenerating axons are lost across each anastomosis. For interposition grafting, the greater auricular and sural nerves are popular largely because of the ease in which these sensory nerves are harvested. Iatrogenic injuries occur most often with extirpation of parotid malignancy where the facial nerve passes through the tumor and must be removed. In this instance, interpositional grafting is the usual procedure. Even when there is a question as to the adequacy of resection, potential long-term survival or the need for postoperative radiotherapy, grafting should be undertaken since it adds only a short time to the operation. The psychological advantages of even incomplete return of function as soon as possible after surgery should not be underestimated. In more routine parotid surgery, the facial nerve should be stimulated near the stylomastoid foramen before wound closure. If brisk facial movement occurs, subsequent facial motion will be satisfactory, even if there is paresis immediately postop. If movement does not occur in all major muscle groups, the nerve should be inspected carefully under magnification for evidence of injury, for example, ligature on the nerve, crush injury, and the like. If a crush injury is suspected it may be necessary to split the sheath to ascertain whether the fascicles are in continuity. If they are not, excision of the damaged segment and repair may be the best course of action. Temporal bone fractures are a unique form of non-penetrating injury that can cause significant damage to the intratemporal facial nerve. They may be classified as longitudinal or transverse according to the orientation of the fracture planes on high resolution CT scanning, and they may occur in a mixed form. Facial nerve injuries are more common with transverse fractures, but because the incidence of longitudinal fractures is higher, they are seen more frequently as a result of longitudinal fractures. With longitudinal fractures where the associated hearing loss is conductive in nature, exploration of the geniculate ganglion should be carried out via a middle cranial fossa approach, followed by transmastoid exploration of the tympanic and vertical segments for the occasional injury caused by fractures through the osseous canal. Transverse fractures, by virtue of the associated severe sensorineural hearing loss are explored through transmastoid and translabyrinthine approaches. Injuries in the tympanic and labyrinthine segments are easily accessible for repair via this approach. Lesions including edema, hemorrhage, contusion, and impacted bony spicules are best managed by decompression of the nerve in the fallopian canal. Transection of more than 50% of the nerve requires an interpositional graft to ensure regeneration of an adequate number of motoneurons. Penetrating injuries of the temporal bone are most often caused by gunshot wounds but can be the result of some stab wounds. If there is any suspicion of a vascular injury of the sigmoid or lateral sinus, jugular vein or carotid system, carotid arteriography is indicated. When surgery is indicated, most can be explored through standard transmastoid approaches. Primary reanastomosis of a severed nerve in the fallopian canal is rarely encountered as an option to restore continuity - Interpositional grafts are frequently necessary using the nerve's natural self-adhesiveness without the use of suture, and this may be enhanced by the application of autologous fibrin glue. The fallopian canal can be used as a sort of stent to hold the graft in place. The most common sites of inadvertent injury to the nerve in tympanomastoid surgery are in the middle ear where the tympanic segment of the nerve above the oval window is occasionally dehiscent, and in the mastoid at the second genu where it is susceptible to injury during antrotomy if the usual landmarks including the lateral semicircular canal are distorted or not recognized. If a postoperative paralysis occurs, sufficient time must elapse to ensure that the effects of any local anesthesia have worn off. If the surgeon did not identify the nerve during the operation, exploration is mandatory. If the nerve was identified and the surgeon knows it to be intact, the patient should be followed with electrodiagnostic testing. If only postoperative paresis is evident, the patient is followed closely by examination, and if the palsy becomes complete the patient should undergo electrodiagnostic testing. Injury to the intracranial segment of the facial nerve is usually iatrogenic, secondary to tumor removal, but infrequently can result from penetrating injuries or medial transverse temporal bone fracture. Collagen splints have been used for grafting in this location, but results are poor. As the quality of radiographic studies, primarily high resolution CT scan, has improved, the importance of topognostic testing has fallen off. However, although it is sometimes inaccurate and has not been shown to be of prognostic significance, they can be helpful in determining the proximal extent of injury and should not be forgotten. In the past, decisions as to surgery traditionally were based on the time of onset of complete paralysis, such that patients with immediate onset following trauma were explored and those with delayed onset were managed conservatively. Electrophysiologic testing has changed the scene quite a bit, since cases of paralysis with an immediate onset have been monitored and have had good spontaneous return of function, while delayed onset has been monitored to progress and lead to suboptimal results. In the first three days, electrical testing takes a back seat to clinical evaluation including the physical examination. Between three days and three weeks, if the patient has visible facial motion, electrical testing is not needed and will be normal if obtained. If there is paralysis, early screening with a Hilger nerve stimulator is used. If the threshold on the involved side stays less than 3.5 mAmps above the normal side, no further testing is necessary. If the threshold difference goes above 3.5 mAmps, some authors recommend exploration. However, if ENoG is available to you, it is recommended that serial examinations be performed every one or two days to follow the course of degeneration. Fisch has set up guidelines such that should degeneration, to greater than 90% of nerve fibers as calculated by ENoG, take place in the first three weeks, the prognosis is poor for spontaneous recovery and that patient should be explored. Anytime after three weeks, there is some controversy regarding the decision to explore, primarily because some nonpenetrating injuries can show spontaneous recovery. Dr. Coker and Dr. Jenkins feel that all penetrating and iatrogenic injuries with evidence of complete degeneration need exploration to document location and cause of the problem. The intact nerve can then be left alone and observed, while the severed nerve is appropriately managed. All blunt injuries outside the stylomastoid foramen can be observed for six to twelve months before intervention. The most controversy is generated over late exploration for temporal bone fractures with complete paralysis. This is because the natural course of recovery has not been established. Except by perceptible facial movement or EMG activity, there is no way of knowing whether or not regeneration is occurring across the injury site and that with time facial function could be acceptable. Some argue that bony fragments and fibrosis can impede the spontaneous regeneration at the injury site and that exploration can enhance the opportunity for regeneration. This is a difficult problem to reconcile and should be approached on a case-by-case basis with careful counseling of the patient. Should there be no return of function by twelve to eighteen months post temporal bone fracture, there is little argument that the nerve should be explored with interpositional grafting at the site of injury. The following management rationale for injuries to the facial nerve is reproduced (by permission) from the award-winning scientific exhibit presented by Dr. Newton Coker and Dr. Herman Jenkins at the 1990 American Academy of Otolaryngology - Head and Neck Surgery meeting in San Diego. Case Presentation A 54-year-old African American male was assaulted and stabbed multiple times in the back, shoulders and right face. The single facial wound was one centimeter in length and was vertically oriented 1.5 centimeters anterior to the tragus. Examination revealed complete right peripheral facial paralysis without significant edema or hematoma. Clear saliva was easily expressed from Stenson's duct. On the third day post injury, after stabilization and complete evaluation of his other injuries, he was taken to the operating room for right facial nerve exploration. The main trunk of the facial nerve was identified and found to be transected just proximal to the pes anserinus. All branches of the nerve were distally intact as demonstrated by electrical stimulation of the distal cut edge. A primary neurorrhaphy was carried out under no tension with 10-0 Prolene suture using a perineural technique.
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