Dynamic Reanimation for Facial Paralysis 

Facial paralysis severely hinders mastication, speech production, and eye protection. Numerous reanimation techniques are available to restore function and are based on the cause of the facial paralysis, type of injury and its location, and the anticipated duration. These methods are broadly classified into 4 types as follows: (1) neural methods, (2) musculofascial transpositions, (3) facial plastic procedures, and (4) prosthetics.

The most desirable procedures to reestablish the mimetic control of the face generally are based on a sequence of operations that start with the most favorable operation to produce the best results, both functional and cosmetic.

The procedures for total unilateral facial paralysis are as follows:

• Direct facial nerve anastomosis
• Interpositional grafts
• Anastomosis to other motor nerves
• Dynamic musculofascial transpositions
• Static musculofascial transpositions
• Facial plastic procedures

The first 4 are dynamic procedures that restore some voluntary movement and, thus, are more desirable. The latter procedures are reserved for patients in whom the motor end plates are not viable. Combinations of the above procedures may be appropriate depending on the circumstances.

An image depicting the facial nerve can be seen below.

Attempts to correct facial paralysis date back to 200 AD, when Galen actually discussed the possibility of nerve regeneration. However, the first documented suture repair of a nerve is attributed to Paul of Argina in 600 AD. A. Waller, who recognized that peripheral nerves could regenerate, rediscovered this work in the 1850s.

With experience from World War II, H.J. Seddon is credited with introducing the use of cable grafts after it was noted that the primary repair would lead to unacceptable tension and poor results. With the introduction of magnification, including the operating microscope and loupes in peripheral nerve repair, results greatly improved. Evidence of this improvement was reflected in many other papers published after this time.

As early as the turn of the century, Alexer in Eden recognized the transposition of muscles in lieu of primary nerve anastomosis. Reuben, Baker, and Connelly repopularized this intervention in the late 1970s by using either the temporalis or masseter muscle.

Techniques for facial reanimation have a long and protracted history, but it was not until the modern era with the advent of finer sutures, magnification, and better understanding of physiology that results from reanimation techniques dramatically improved.

Total disruption of the facial nerve does not permit restoration to complete normalcy. Therefore, realistic expectations must be established at the initial encounter and candidly discussed between the physician and the patient.

If the duration of the paralysis is less than 24 months and no chance of recovery exists, attempt a neural procedure. If the motor end plates are not viable, or immediate restoration of some movement is desirable, a muscle transposition technique may be used. For a description of this procedure, see the Techniques section.

To perform the reanimation procedures, the surgeon must have a thorough knowledge of the anatomy of the facial nerve.

The facial nerve originates within the pons and exits between the olive and inferior cerebellar peduncle. At this location, the nerve forms a 12-14 mm intracranial portion within the cerebellopontine angle, as shown below.

The facial nerve then enters the temporal bone, where it is confined within a bony conduit. As it enters the internal meatus, the nerve lies medial to cranial nerve VIII. The nerve travels about 10 mm before reaching the lateral end of the meatus superior to the crista transversalis and anterior to the vertical crista (Bill's bar). Exiting the internal auditory canal, the nerve gradually curves anteriorly around the basal turn of the cochlea where it enters the infratemporal portion and travels 2-4 mm (the narrowest portion).

The greater petrosal nerve arises from the facial nerve at the geniculate ganglion. At the geniculate ganglion, the greater superficial petrosal nerve leaves anteriorly, while the facial nerve itself makes a 40-80° turn (the external or first genu). The facial nerve courses posteriorly and slightly inferiorly, traveling 11 mm across the tympanic cavity. This horizontal course lies superior to the fossula at the vestibular fenestra (oval window). The nerve makes its second genu as it leaves the oval window niche, passing anteriorly and caudal to the lateral semicircular canal. It then passes lateral to the sinus tympani and the stapedius muscle to form the vertical (mastoid) portion within the temporal bone.

At the end of this 13-mm segment, the facial nerve exits from the stylomastoid foramen, where it becomes the extracranial segment. The nerve first innervates the posterior belly of the digastric muscle and then travels 15-20 mm to enter the parotid gland. In the parotid gland, it divides at the pes anserinus into 2 main branches, namely, the temporofacial and cervicofacial. Terminal ramifications of these branches to the temporal, zygomatic, buccal, mandibular, and cervical regions are variable. Terminal branches of the facial nerve are depicted below.

The nerve fibers travel in groups called fascicles, which vary according to the level. The fibers are surrounded by 3 types of connective tissue, namely, the endoneurium, perineurium, and epineurium. The structure of the fascicles varies considerably throughout the course of the nerve. For this reason, direct repair of the fascicles is not feasible and may be counterproductive.

No contraindications exist for restoring facial reanimation in a patient, except inability to tolerate general anesthesia; however, specific guidelines must be followed. If the possibility of spontaneous facial nerve recovery exists, then any procedure that involves transsection of the nerve must be avoided until lack of recovery is a certainty.

Any attempt to restore facial function by reestablishing nerve continuity requires intact motor end plates. Nerve continuity can be re-established by direct facial nerve anastomosis, interpositional grafts, or anastomosis to other cranial nerves. Selection of these procedures cannot be considered after 3 years following the original insult. The possibility still exists for motor end plates to survive from 1-3 years after the original insult. An EMG can be obtained to determine viability of the motor end plates.

Crossover technique cannot be used if the donor nerve is essential to the overall function of the patient.