Facial Nerve Repair Technique

Currently, no medical treatment exists for facial nerve repair. Systemic corticosteroids and/or anti-virals are advocated by some to minimize swelling of the nerve in certain cases. In animal models, the use of electrical stimulation therapy appears to be beneficial for initiating and accelerating facial nerve recovery. ^[9] A number of metabolic factors (eg, neurotrophic factors, growth factors, and stem cells) have shown some promise for facilitating nerve repair in the laboratory, although these remain in the investigational phase and results to date have been mixed.

In animal experiments, glial cell line–derived neurotrophic factors promoted facial nerve regeneration in delayed grafting but inhibited immediate nerve grafting. ^[10] In similar experiments, stem cell therapy (eg, bone marrow–derived mesenchymal stem cells in collagen) promoted excessive growth support for axon regeneration and excessive collateral nerve branching of facial motor endplates (which was not improved by manual stimulation). Current stem cell therapy requires additional study before it can be clinically useful for facial nerve repair. ^[11]

Accordingly, surgical repair is the mainstay of treatment. At present, there are 3 surgical options for repair of the facial nerve: direct repair, cable nerve grafting, and nerve substitution techniques (see below). Primary end-to-end nerve anastomosis and cable graft interposition have shown to produce better functional outcomes than nerve substitution techniques. ^[8]

Additional techniques that have been proposed as possible alternatives to suture repair include laser neurorrhaphy and tissue adhesive repair. Synthetic and biologic tubules have been created to provide a path for the regenerating axons, even spanning small gaps in the nerve. These have not yet shown any clear superiority to standard nerve grafting techniques, but they remain under investigation.

Controversies persist regarding the type (epineural versus perineural) and the timing of repair. The cross-facial nerve graft has very good results in certain reports but has not been as effective in other hands.

The facial nerve is exposed to a length sufficient to permit the exposure and mobility required for performance of the grafting procedure. A parotidectomy incision is made, and the facial nerve is identified as it exits the stylomastoid foramen by using the traditional landmarks (ie, the tragal pointer, the sternocleidomastoid, the posterior belly of the digastric, and the stylomastoid suture).

Once the nerve is identified, it is followed distally as necessary. Meticulous, gentle technique is employed, as in a parotidectomy. If the intratemporal portion of the nerve is involved or requires exposure, it is exposed via a mastoidectomy.

The key to successful nerve grafting is careful coaptation of the nerve ends without tension. Several principles apply, regardless of which specific type of procedure is chosen. The nerve tissue must be handled atraumatically with microinstruments. Magnification with an operating microscope is essential to allow meticulously precise alignment of the nerve ends. A colored background is helpful for facilitating clear visualization of the anatomy.

Typically, 2-3 sutures are carefully placed through the epineurium. Fine (8-0 to 10-0) monofilament permanent suture material is used; this minimizes tissue reactivity. Although epineurial suturing is generally considered the standard, there is some controversy on this point. Perineural and endoneurial or intrafascicular repairs have been advocated, but the data are unclear as to whether these techniques actually offer significant advantages.

The important relation to keep in mind is the size match between the endoneurial surfaces. This must be inspected with magnification; if a mismatch is evident, then one end may be trimmed in a beveled fashion to yield a better match between the surface areas of the ends to be approximated.

In some cases, a nerve segment may be unavailable for reapproximation, either because of resection of a malignancy or because of destruction by trauma. This prevents primary grafting without tension. The problem may be addressed in a number of ways. For example, if the injury site is intracranial or intratemporal, the facial nerve must be rerouted, repaired with a cable graft, or both. In this instance, one may mobilize the facial nerve from the fallopian canal by decorticating it via a transmastoid approach.

If hearing preservation is not a concern, a translabyrinthine approach allows exposure of the entire length of the nerve up to the internal auditory canal. The mastoid tip may be removed to afford the nerve greater mobility. Furthermore, the entire nerve can be rerouted by combining the mastoidectomy with a middle fossa approach, which allows grafting of the proximal portion of the nerve.

Peripheral injuries likewise may necessitate mobilization of the nerve through one of the abovementioned techniques in order to allow primary repair. Repairing the nerve with primary grafting is always preferable when feasible. If it is not feasible, then a cable graft may be used.

The great auricular nerve is found by drawing a line between the angle of the jaw and the mastoid tip. This line is bisected at a right angle by the great auricular nerve as it passes around the posterior border of the sternocleidomastoid muscle just behind the external jugular vein. The nerve is the largest of the ascending branches of the superficial cervical plexus and arises from C2-3. Extra branches can be found by following the nerve toward its origin behind the sternocleidomastoid muscle.

The sural nerve can be located between the lateral malleolus and Achilles tendon. It lies just deep or posterior to the saphenous vein. It then runs superiorly up the back of the lower leg in a subcutaneous plane until it descends between the 2 heads of the gastrocnemius toward the popliteal fossa and its origin off the tibial nerve.

The sural nerve may be harvested either by making a single long incision from the ankle to the popliteal fossa (depending on the length of nerve required) or a series of shorter transverse incisions. The nerve may be dissected under direct vision with the single incision or by using a fascia stripper and making the stepwise incisions.

The technique of nerve grafting is the same as for primary repair. In the case of cable grafting, obtaining enough nerve graft length to allow the graft to have some redundancy between the ends of facial nerve may be helpful. This would create a C or S shape and ensure tension-free coaptation.

Hypoglossal-facial anastomosis

A parotidectomy-type incision is made. The facial nerve is identified as it exits the stylomastoid foramen and is followed to just beyond the pes anserinus. It is sharply transected where it exits the stylomastoid foramen.

The hypoglossal nerve is then isolated in the neck. It may be identified by following the posterior belly of the digastric toward the hyoid bone. The hypoglossal nerve passes lateral to the carotid artery and medial to the internal jugular vein. The nerve may then be followed distally to gain the maximum length for anastomosis. The descendens hypoglossi is usually transected to aid in mobilization and length.

In the case of an end-to-end anastomosis, the hypoglossal nerve is transected distally and brought to meet the facial nerve by passing it either medial or lateral to the digastric muscle. The grafting of the nerve ends proceeds as previously discussed.

If a jump graft is performed, identification and transection of the facial nerve proceed in the same manner. In this case, an appropriate length of great auricular nerve is then harvested. The hypoglossal nerve is then identified, including the descendens branch. The nerve is partially incised in a beveled fashion (most authors recommending cutting one third to one half the way across). The great auricular nerve graft is anastomosed to the proximal portion of the beveled cut. The other end is grafted to the distal end of the facial nerve in a typical fashion.

Another option for preserving tongue function is the split hypoglossal nerve graft. In this technique, the hypoglossal nerve is split and dissected back to obtain a length that can be anastomosed to the facial nerve, which means that only 1 anastomosis would be required. However, given that the hypoglossal nerve also exhibits a lack of spatial orientation, with the nerve fibers interwoven randomly, some consider this approach flawed concept because splitting of the nerve any significant distance would cause significant denervation of the tongue.

Cross-facial nerve graft

Several variations of the cross-facial anastomosis have been described. These differ in terms of which donor facial nerve branches are used, how many cross-facial grafts are performed, and the path chosen to pass the graft across the face to the other side.

In each variation of the procedure, a suitable nerve to graft must be chosen. The sural nerve is most commonly used because the length of nerve required to thread across the entire face, particularly if several branches are to be anastomosed, is quite significant. Alternatively, one may perform a single graft, in which case the great auricular nerve may be sufficient.

Dissection is performed first on the paralyzed side to ensure that the distal nerve can be identified. If several branches are to be grafted, the branches may be identified by following the nerve beyond the pes anserinus and identifying the branches within or just beyond the parotid gland. The contralateral normal facial nerve is identified in the standard fashion.

The branches are individually identified. The donors are taken at the distal border of the parotid gland. A nerve stimulator is used to determine the areas innervated by the individual branches, and for each facial region, an attempt is made to find multiple nerve branches supplying a given area. This allows for the sacrifice of 1 branch with preservation of an adequate degree of function for a given anatomic region.

The sural nerve is then harvested and the branches tunneled across the face. This may be performed above and below the lip and through the neck. Passing the nerve across the forehead may have a poorer result because of the lesser blood supply to the graft lying within a relative lack of soft tissue. The nerve graft is sutured to the normal side. The graft may then be sutured to the chosen branch or branches on the paralyzed side.

Another option is to forego the anastomosis on the paralyzed side. A “babysitter” hypoglossal nerve anastomosis may be performed instead. This provides innervation to the paralyzed facial musculature and thereby prevents further degradation of the motor endplates and muscle atrophy as regeneration occurs across the considerable distance necessary for the cross-face graft.

In this situation, the Tinel sign (ie, paresthesias associated with areas of nerve regeneration) is followed across the face for several months, and the patient is returned to the operating room when this sign indicates that regeneration has completely spanned the gap. The grafts are then anastomosed to the paralyzed branches.

A simpler technique uses only the marginal mandibular branch, which is sacrificed and anastomosed to the main branch of the paralyzed nerve in a single setting. Function for each of these cases takes at least 6 months to begin to return. As with the other procedures, synkinesis is expected.

Postoperative care is similar for each of the procedures used for facial nerve repair. Meticulous hemostasis is important, with drains placed to prevent hematoma formation. Routine attention to details such as eye protection remains of paramount importance. Return of function takes months to occur.

Synkinesis is expected for all cases of facial nerve transection, regardless of the mode of repair chosen, and the best result one can hope for is a House-Brackman grade III. These consequences therefore should be viewed not as complications but as expected sequelae.

Donor-site morbidity is also expected for the hypoglossal crossover technique (tongue weakness), great auricular harvesting (ear numbness), and sural nerve harvesting (lateral leg numbness). Complications for each of the procedures include hematoma and infection.