Facial nerve trauma: evaluation and considerations in management

Abstract

The management of facial paralysis continues to evolve. Understanding the facial nerve anatomy and the different methods of evaluating the degree of facial nerve injury are crucial for successful management. When the facial nerve is transected, direct coaptation leads to the best outcome, followed by interpositional nerve grafting. In cases where motor end plates are still intact but a primary repair or graft is not feasible, a nerve transfer should be employed. When complete muscle atrophy has occurred, regional muscle transfer or free flap reconstruction is an option. When dynamic reanimation cannot be undertaken, static procedures offer some benefit. Adjunctive tools such as botulinum toxin injection and biofeedback can be helpful. Several new treatment modalities lie on the horizon which hold potential to alter the current treatment algorithm.

Keywords: facial nerve injury; facial paralysis rehabilitation; facial reanimation; facial sling; free tissue transfer; hypoglossal-facial nerve transfer; intratemporal facial nerve trauma; temporalis tendon transposition.

Fig. 1

Temporal bone anatomy and intratemporal facial nerve segments.

Fig. 2

Extratemporal facial nerve branches (temporal, zygomatic, buccal, marginal mandibular and cervical branches). Facial nerve branches generally innervate deep to the facial muscles with the exceptions of levator anguli oris, buccinators, and mentalis muscles.

Fig. 3

Demonstration of gold/platinum weight being secured to upper eyelid tarsus.

Fig. 4

An inferior displacement of the affected oral commissure, oral incompetence, upper and lower lip asymmetry are commonly seen with facial paralysis. Upper lip philtral ridge is also commonly displaced to the unaffected side. Static suspension of lower lip can be used to address gross lip asymmetry, drooling and oral incompetence. Fascia lata, Gore-Tex and Alloderm can be used to suspend in a superoposterior vector as seen in the right image.

Fig. 5

Split hypoglossal nerve to facial nerve transfer. Either superior or inferior half of the hypoglossal nerve can be transferred. Less tongue morbidity is noted with this technique compared to classic hypoglossal nerve to facial nerve transfer in which the entire hypoglossal nerve is transferred.

Fig. 6

Dynamic temporalis muscle transfer can be performed by releasing the temporalis muscle tendon from the coronoid process using either a transcutaneous approach (as seen in the diagram) or a transoral approach. Once the temporalis tendon is released from the coronoid process, it can be secured to paralyzed oral commissure. This technique avoids excess tissue bulk noted over the zygomatic arch and temporal hallowing that can result from classic temporalis muscle transfer technique.