Facial nerve palsy arises due to damage to the seventh cranial nerve. This damage may be due to injury, inflammation, infection, trauma or tumors. The resulting clinical presentation is drooping of the face or weakness of the facial muscles, that may be uni- or bilateral.
Managing facial nerve palsy may necessitate the use of pharmacotherapy, surgery and physiotherapy. There are numerous surgical options available and these include decompression of the facial nerve, facial nerve repair and muscle transfer.
Facial nerve decompression
Compression of the facial nerve against the skull is the main indication for surgical decompression. Decompression is usually performed by a craniotomy through the middle fossa and/ or behind the ear through the mastoid bone. Another approach is the translabyrinthine procedure, which is reserved for injuries along the intratemporal course of the facial nerve.
The typical patient requiring decompression has facial palsy from a facial nerve that is compressed and inflamed against a bone, but is intact. Etiologies of this condition include infection, trauma or idiopathic (i.e. Bell’s palsy).
Middle fossa decompression is done especially in cases when the injury to the facial nerve has extended into the labyrinthine segment. The vertical crest that separates the facial and superior vestibular nerves serves as a landmark for the middle fossa approach.
Other critical landmarks include the greater superficial petrosal nerve and the superior semicircular canal. The middle fossa approach can be combined in some instances with the transmastoid approach. In the transmastoid approach the injury to the facial nerve is localized mainly to the mastoid or tympanic segments of the nerve.
Facial nerve repair
There are three main options for the repair of the facial nerve: nerve substitution, cable grafting and direct repair. Direct repairs offer the best prognosis in terms of restored facial nerve function, especially if they are done tension-free, which may require mobilization of adjacent segments of the facial nerve.
When primary or direct repair of the facial nerve is not possible, then cable grafting is utilized with the use of grafts from the sural, great auricular or other cutaneous nerves. Nerve substitution may be done with hypoglossal-facial nerve anastomosis.
Muscle transfer is usually done in cases of chronic facial paralysis, where the facial muscle has atrophied. Alternative regional or free muscles are used for the re-animation of the facial muscles. The temporalis muscle with intact trigeminal nerve function is the most commonly used muscle for regional transfer in dynamic facial reanimation.
To fill the depression in the temple created by the removal of this muscle, techniques such as the use of fat grafts or alloplastic implants may be used. Eyelid weights and oculoplastic procedures are the static techniques that may be employed for facial re-animation, as enhancing factors.