Treatment

The management of a facial nerve injury is largely dependent on its anticipated return of function. Electrophysiologic testing, such as electroneurography (ENoG), can be helpful in predicting the ultimate prognosis for facial nerve recovery. Electrophysiologic testing is never relevant for paresis, but if the nerve is paralyzed it can be a valuable tool for predicting prognosis for recovery. Care must be taken to time the evaluation appropriately, as a test before Wallerian degeneration has occurred (approximately 72 hours after injury) will be erroneous. Optimal timing is approximately one week after the injury and must be completed within two to three weeks of the injury. The ENoG test uses a stimulating electric current over the peripheral facial nerve branches with the response measured by an electrode placed within the muscles of facial expression. The normal side is evaluated and a comparison between the responses of the two sides is reported. The amplitude of the response measured by the electrode is directly proportional to the number of intact motor

INI-"

STYLO/

INI-"

STYLO/

. MASTOID {VERTICAL)

PONTINE

MEATAL

LABYHINTHINE

TYMPANIC (HORIZONTAL)

. MASTOID {VERTICAL)

PONTINE

MEATAL

LABYHINTHINE

TYMPANIC (HORIZONTAL)

FIGURE 1 Facial nerve segments. Source: Courtesy of W. R. Wilson, Parthenon Publishing Group, Boca Raton, FL, U.S.A.

axons. Greater than 90% degeneration within 10 days of paralysis is associated with a 50% chance of poor prognosis (1).

Whether or not recovery is anticipated, management should focus on eye protection. Taping the eye closed at night in addition to frequent eye lubrication is critical to avoiding exposure keratitis and visual loss. Patients often experience increased tearing with facial paralysis, a result of the loss of the pumping action afforded by eyelid closure into the lacrimal canaliculus. If a longer or indefinite period of facial nerve dysfunction is anticipated, reversible therapy such as a gold weight will aid the patient in achieving complete lid closure for as long as needed.

Specific therapy depends on the mechanism of facial nerve injury. If the nerve remains in continuity and the injury is secondary to compression from traumatic, neoplastic, or infectious etiologies, anti-inflammatory medications such as corticosteroids or decompressive surgery may be employed. Antiviral medications are often dispensed in treating Bell's palsy but remain controversial in their efficacy. Decompression of the entire facial nerve can be accomplished with a combined transmastoid and middle cranial fossa approach. If the patient has no usable hearing, a translabyrinthine approach could also be used for complete nerve decompression.

If the nerve has been severed, the first treatment should be direct anastomosis. This is often difficult, given the bony course of the nerve, and defects greater than 1 cm cannot usually be reapproximated even with rerouting maneuvers. If direct anastomosis cannot be completed, cable grafting is the next appropriate step. The greater auricular nerve is an excellent donor nerve, providing up to 10 cm of length. Alternatively, if a longer segment is required, the sural nerve provides up to 25 cm of available length. Occasionally, the proximal end of the nerve is no longer viable or usable; this precludes any attempts at anastomotic reconstruction. In this scenario, the patient may benefit from a hypoglossal to facial nerve anastomosis. Facial crossover grafts from the uninvolved facial nerve to the contralateral involved facial nerve have also been described.

The above techniques all attempt to regain dynamic facial nerve function, but static rehabilitation is also used in facial nerve rehabilitation. Static surgical therapy usually involves rehabilitating the lower face (mouth) or rehabilitating the upper face (eye). Techniques used for lower facial rehabilitation include facial slings, temporalis or masseter muscle transfer, and lip wedge resections. Eyelid rehabilitation is usually focused on eyelid closure and can be accomplished with a gold weight placement or a palpebral spring. Any ectropion that forms due to loss of innervation to the periorbital musculature can be addressed with a canthopexy or lateral canthotomy.

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