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Facial Nerve Paralysis, Dynamic Reconstruction
Author: Alan Bienstock, MD, Consulting Staff, Division of Plastic and Reconstructive
Surgery, Department of Surgery, Lennox Hill Hospital, St Luke's/Roosevelt Hospital
Coauthor(s): John YS Kim, MD, Assistant Professor, Department of Surgery, Division
of Plastic Surgery, Northwestern Medical Faculty Foundation; Consulting Staff,
Northwestern Plastic Surgery;
Mary C Snyder, MD, Associate Professor, Division of
Plastic Surgery, University of Nebraska Medical Center;
Perry J Johnson, MD, Assistant
Professor, Department of Plastic and Reconstructive Surgery, University of Nebraska
Medical Center
Contributor Information and Disclosures
Introduction
Facial nerve denervation and
paralysis imposes significant psychological and functional
impairment. Facial
paralysis can inhibit and mar facial expression, communication,
symmetrical smile, eye protection, and oral competence. Myriad modalities and
stratagems exist for each patient; the physician must accurately evaluate and examine
the patient and determine the etiology, duration, and the scale of the
paralysis.
Understanding facial nerve anatomy with precise assessment of the patient's
paralysis
and health status dictates the potential for recovery and the most appropriate
reconstructive scheme.
The goals of the reconstruction in facial
paralysis include the following:
- Facial symmetry at rest
- Symmetrical smile
- Voluntary, coordinated, spontaneous facial movements
- Oral competence and eyelid closure with corneal protection
- Absence or limitation of synkinesis and mass movement
Dynamic and static procedures are employed for facial reanimation; however, dynamic
strategies tend to be more successful and fruitful and should be offered to each patient
considering reconstruction, unless health risk contraindications exist. The most common
approaches for reconstruction are direct facial nerve repair with or without grafting,
nerve transfer, cross-facial nerve grafting, and muscle transfer (either regional muscle
or free-muscle neurotized transfer).
Anatomy of the Facial Nerve
The precentral gyrus emits the voluntary motor portion of the facial nerve, where most
of these nerve fibers cross in the pontine region to approach the facial nerve nucleus in
the contralateral pons. At the cerebellopontine angle (CPA), the facial nerve is near the
nervus intermedius and the eighth cranial nerve.
Intratemporal facial nerve
The first branch of the facial nerve is the greater petrosal nerve, which departs from the
geniculate ganglion and is responsible for parasympathetic secretion of the nose, mouth,
and lacrimal gland. The nerve to the stapedius is the next branch and arises from the
proximal mastoid segment. The chorda tympani nerve emerges proximal to the
stylomastoid foramen and carries parasympathetic secretory fibers to the submandibular
and sublingual glands as well taste fibers to the anterior two thirds of the tongue.
Extratemporal facial nerve
The extratemporal branching of the facial nerve has myriad patterns and variations.
Dingman and Grabb present the largest series of the surgical anatomy of the marginal
mandibular branch,
1 while Pitanguy identifies the course of the temporal branch.
2
The facial nerve innervates a total of 23 paired muscles and the orbicular oris, but only
18 of these muscles, working in a delicate balance, produce facial animation and
expression. No current reconstructive stratagem can reproduce every facial expression and movement.
Evaluation
History
Evaluation of a patient with facial
paralysis commences with a thorough and detailed
history and physical examination. Etiology is the most important factor in determining
the timing and choice of reconstructive technique. Reconstructive efforts should not
commence prior to establishing the etiology of the
paralysis.
A thorough history includes onset, initial degree of
paralysis, duration, and associated
symptoms. These details often can help identify the etiology. Facial nerve injuries from
Bell palsy, trauma, and malignant neoplasm need to be identified. The reconstructive
efforts and interventions need to be tailored appropriately based on the etiology of the disorder.
For example, a slowly progressive
paralysis suggests malignancy, while a sudden onset
of complete
paralysis suggests Bell palsy. The workup, treatment, and prognosis of
these 2 disorders differ vastly from one another. If a tumor is suspected, proper
evaluation of the patient is of the utmost importance to appropriately treat the
malignancy and choose the best reconstructive option. If
paralysis is caused by a
malignancy or is a result of resection for a malignancy, the risk of recurrence and
prognosis may influence the choice of reconstruction. Malignancy of the posterior fossa,
temporal bone, skull base, or parotid region can present with facial
paralysis.
Bell palsy is an idiopathic form of facial
paralysis and is a diagnosis of exclusion. Trauma
is the second most common cause of facial
paralysis. Eighty percent of patients with
facial
paralysis suffer from Bell palsy. Eighty-five percent of these patients begin to
recover nerve function spontaneously within 3 weeks of onset; the other 15% do not
have any movement for 3-6 months. If the patient has Bell palsy, the potential for
complete recovery is excellent, especially in incomplete
paralysis. Peitersen found 94%
of patients with partial
paralysis completely recovered facial nerve function in 1 year
without medical or surgical intervention; of those with complete
paralysis, 71%
completely recovered.
3 Therefore, irreversible techniques to reanimate the face may not be the best choice in these patients.
The etiology of the denervation also dictates the timing of surgical treatment, if any is
to be done. In a patient with a paralyzed face secondary to traumatic surgical disruption,
the surgeon should initiate reconstruction as soon as possible, generally within the first
month. On the other hand, a patient with an intact nerve can be monitored for recovery
for up to 12 months. The duration of the facial
paralysis is essential. The reconstructive
options for acute
paralysis,
paralysis for less than 18-24 months, and
paralysis for greater than 18-24 months differ significantly.
In addition, the surgical team must investigate previous surgical procedures for
reanimation, since these may limit reconstructive options. The patient's overall health,
psychological stability, and life expectancy are significant considerations. Patients with
significant health risks and medical problems are not appropriate candidates for invasive
reconstructive operations, the results of which do not manifest for 2-3 years
postoperatively. The patient and the surgeon should thoroughly discuss the patient's
expectations. As part of patient education, surgeons need to establish realistic
expectations and determine whether the patient is willing to expend the time and
financial resources required for a successful result.
Physical
The surgeon must perform a comprehensive physical examination of the patient with
facial
paralysis, scrutinizing the face at rest and during voluntary and reflex emotional
movement. The physician must determine the involvement of unilateral or bilateral facial
nerves, facial asymmetries, and synkinesis. The degree of brow ptosis, ectropion, lid
laxity, and oral competence must also be noted. The surgical team cannot neglect other
cranial nerve or neurologic deficits and soft tissue defects in conjunction with the
paralysis.
Diagnostic Studies
Audiometry
Audiometric testing, including acoustic reflexes and tympanometry, may be useful in
identifying the etiology of facial palsy secondary to retrocochlear pathology or mass
lesions of the middle ear.
Radiography
High-resolution CT and MRI scans are essential in the evaluation of a patient with
traumatic facial nerve palsy to delineate features of the temporal bone, which may
impact the facial nerve. Scans are also used to evaluate patients with possible parotid,
skull base, temporal bone, intracranial, or extratemporal tumors.
Electrodiagnostic tests of nerve function
Electrodiagnostic tests of facial nerve function include nerve excitability tests (NET),
electroneuronography (ENog), and electromyography (EMG). Nerve excitability testing
involves percutaneous stimulation of the facial nerve until muscle contraction is
observed. The minimal NET determines the threshold stimulation required for muscle
contraction compared to the unaffected side. Maximum stimulation test (MST) is a
modification of the NET but is a supramaximal stimulus compared to the unaffected
side, and the stimulus is increased until the patient encounters discomfort. The
subjective nature of the measurements and lack of recorded data limit both methods,
and they do not reflect denervation at the moment it is occurring.
Electroneurography (ENog) is an objective measure of facial nerve function that
measures the amplitude of evoked compound muscle action potentials (CMAP) with
electrodes over the skin of the nasolabial fold. The compound action potential is
compared between the 2 sides of the face, and the response of the affected side is
expressed as a percentage of the response of the unaffected side. A percentage of
nerve fiber degeneration is calculated. A 95% decrease in CMAP compared with the
contralateral side signifies a 50% chance that the patient will have unsatisfactory
recovery of facial nerve function. Surgery is indicated if a 90% decrease in CMAP is
reached within the initial 2 weeks of the onset of
paralysis. ENog is objective and is the
most accurate reproducible test, but it is expensive and time-consuming.
EMG is a measure of volitional muscle response unlike the other modalities. Needle
electrodes are used to monitor activity of the facial muscles. Normal muscle exhibits
activity upon needle insertion, electrical silence at rest, and diphasic or triphasic action
potentials during voluntary contraction. Fibrillation potentials are observed in the
denervated muscle, and polyphasic potentials are observed in muscle undergoing
reinnervation. Complete electrical silence is observed in denervated muscle with
significant fibrosis. EMG is useful in evaluating patients with acute or traumatic nerve
injury and in assessing the viability of the facial musculature when evaluating patients
for reinnervation procedures. EMG does not show any signs until 3 weeks after
paralysis and should not be utilized until 3 weeks after facial
paralysis without any signs of recovery.
Objective measures of facial motion
Objective measures of facial motion include digital photography and video recording of
the patient and rest and during motion. Dated visual documentation and preoperative
and postoperative facial function is salient for preoperative planning and outcome
assessment.
A recently developed method of objective measurement is the maximum static response
assay of facial motion. This method quantifies facial motion preoperatively and serially
during the postoperative period. Mark the patient's face and ask him or her to perform
region-specific movements, including brow lift, eye closure, smiling, frowning, and
whistling or puckering. The images of the face in repose and the maximum response
movements are recorded and processed for computer display. The images are calibrated
and normalized, and vectors of movement are determined and measured using a grid
and an internal facial coordinate system. Even slight improvements in facial movement
can be detected over the long recovery periods that often accompany facial reanimation procedures.
Nerve Repair
Patients desire a countenance and visage with a normal or almost normal balance
when the person's face is at rest. Objectives of treatment are corneal protection,
establishing a normal resting tone, and, most importantly, restoring a symmetrical dynamic smile.
Little information is available on the denervation of human facial muscles. Denervated
muscles cannot be voluntarily stimulated and has no response to electrical stimulation.
A longer period of denervation translates into a lesser degree of recovery after
reinnervation. There is a decrease in efficiency of muscle reinnervation after 12-18
months of
paralysis/denervation. Muscles that are reinnervated may not undergo full
recovery nor respond to regenerated nerves.
Repair of the facial nerve is the most effective procedure to restore the function of the
face. Repair is indicated in patients who have experienced acute disruption or
transection of the nerve from an accident, trauma, resection during extirpation, or
inadvertent division during surgery.
Principles of Nerve Repair
Early identification and repair of nerve injuries
The most critical factor in achieving good postoperative facial function is early
identification and repair of nerve disruption. Several investigators have demonstrated
that earlier repair of the facial nerve produces superior results. Some authors report
function in patients who were grafted 18-36 months after injury, but superior results are
found with repairs performed within 1 year. May advocates repair within 30 days. This
recommendation is based on clinical results and neurobiologic investigations that reveal
that the regenerative process begins almost immediately following injury.
Following axotomy, the nerve cell body immediately undergoes changes in morphology
and protein synthesis to support axonal replacement. The proximal portion of the
interrupted axon transforms into a growth cone, and, within a few days, axon sprouts
push out, seeking the distal motor endplate. Neuron metabolic activity peaks
approximately 21 days after injury. The distal portion of the interrupted axon undergoes
Wallerian degeneration, and, within 2 weeks, collagen and scar tissue begin to replace
axons and myelin in the distal nerve stump.
Traumatic nerve injuries must be repaired expediently. In the instance of a grossly
contaminated wound (eg, shotgun injury), the nerve ends can be tagged and repaired at
a later date. A nerve accidentally transected during surgery (eg, facelift) should be
attacked with an end-to-end anastomosis. If the facial nerve is resected because of
tumor involvement, frozen sections of both ends can be sent for histopathologic
examination to exclude microscopic invasion before attempting repair. When margins are
clear, either end-to-end anastomosis or graft repair can be performed immediately.
Evaluation of nerve condition
The condition of the nerve at the time of injury dictates whether nerve repair is
indicated and whether it will presage functional repair. The condition of the nerve
depends on the type of injury or trauma. A patient with preoperative facial palsy
secondary to tumor involvement of the facial nerve is unlikely to experience a good
result following resection and repair. The amount of functioning nerve fibers at the time
of surgery does not increase after repair; do not expect improved postoperative facial
function over preoperative status.
A sharp facial nerve laceration from glass or a knife should be suitable for end-to-end
anastomosis. Gunshot wounds, however, either crush or avulse the nerve, which
propagates further nerve degeneration/denervation. These injuries should not be
repaired in the immediate setting until the extent of the nerve damage has declared
itself. In a delayed intervention, scar tissue and neuromas must be removed, and
unhealthy nerve ends must be excised. Identifying healthy nerve stumps may
necessitate histologic or microscopic confirmation.
Matching of endoneurial surfaces
Matching of the endoneurial surfaces is essential in promoting
neural regeneration and
is more important than a match of the total nerve diameter. The endoneurium is
examined more easily by removing the overlying perineurium at the ends of the nerve.
Occasionally, a significant mismatch between proximal and distal nerve ends requires a
double cable graft (eg, when grafting from the main facial nerve trunk to segmental branches).
Epineural versus perineural suturing
Various neurorrhaphy techniques and adjunctive measures have been investigated in
attempts to improve
neural regeneration, including epineural versus perineural sutures,
tissue adhesives, laser neurorrhaphy, tubulization, and trophic factors. However, the
most efficacious method of re-approximation remains unproven, and no specific
adjunctive measure has been found to be beneficial. A minimal number (usually 2 or 4)
of epineural or perineural sutures, using a fine monofilament suture under microscopic
vision, or loupe magnification, remains the time-tested criterion standard for nerve repair.
Tension-free anastomosis and nerve grafts
Primary neuropathy can be achieved if the proximal and distal facial nerve ends can be
approximated without tension. If tensionless nerve repair is not feasible, then a nerve
graft (usually the sural nerve) will be interposed in between the proximal trunk and
distal branches. Any tension on the ends after repair results in the formation of scar
tissue and poor
neural regeneration. Mobilization of the nerve may add up to 2 cm of
relative length but also may result in devascularization and further
neural injury. Any
defect greater than 2 cm should be tackled with a nerve graft. The surgeon must design
the nerve graft of adequate length without any tension and with a small amount of slack when bridging the defect.
Cable grafts function as conduits in which sprouting axons from the proximal nerve
stump travel to the motor endplates. The graft provides cellular and humoral promoters
for
neural growth, such as Schwann cells, extracellular matrix, and neurotrophic growth factor.
Success of a nerve graft depends on the following factors:
- The number of axons remaining in the nerve
- The potential for regeneration of axons
- The status of the facial muscles (ie, the more axons that are available, the greater chance of recovery and a satisfactory result)
Donor Nerves for Facial Nerve Grafting
The great auricular nerve and sural nerve are the most commonly selected nerves for
facial nerve grafting. Disadvantages include a sensory deficit of the earlobe when using
the great auricular nerve or of the lateral foot when using the sural nerve. The great
auricular nerve is harvested easily; since it is located near the surgical field in which the
nerve repair is taking place, it tends to be a good match in size, and its extensive
arborization allows the anastomosis of the proximal facial nerve stump to several
segmental branches. However, only 7-10 cm of the great auricular nerve can be
harvested safely, which limits its use in extensive repairs. The sural nerve is larger, with
a greater axonal volume, and up to 35 cm is harvested easily from the posterior lower
leg. It is especially useful in cross-facial grafting.
The principles and technique of graft anastomosis are identical to those of primary
repair. The patient should not expect return of facial function following nerve grafting for
4-6 months, as regenerating axons travel a distance of approximately 1 mm/d.
Improvement in function can be expected for up to 2 years. In general, results after
nerve grafting are not as good as those observed with primary repair. Spector et al
found incomplete reinnervation of facial divisions, decreased voluntary contractions, and
more severe synkinesis when comparing cable grafts to direct end-to-end anastomoses.
4
However, 92-95% of patients who undergo facial nerve grafting experience some return
of facial function, and 72-79% have good functional results.
Location of Injury
Intracranial
Intracranial nerve injury most commonly occurs during resection of an acoustic
neuroma or other tumor of the cerebellopontine angle (CPA). Prior to the advent of the
operating microscope in 1961, rates of facial palsy following acoustic neuroma removal
approached 95%. House, by implementing the use of the operating microscope,
reported a 72% rate of normal facial function in patients who underwent tumor
resection from 1961-1968.
5 More recently, a 97.7% rate of facial nerve preservation
following CPA tumor surgery was reported.
In the event of nerve injury in the CPA, immediate repair with direct anastomosis or
graft is advocated. Rerouting the tympanic and mastoid segments of the nerve may add
enough length for end-to-end anastomosis, but a graft is often required. Interposition
grafts can be placed from the intracranial nerve segment to the temporal segment or
from the intracranial nerve segment to the extracranial segment, thus bypassing the
temporal bone. These repairs are technically difficult. The proximal nerve end, as it
enters the brain stem, usually is short and has no epineurial covering. The brain stem is
pulsatile, and cerebral spinal fluid constantly flows through this area. However, despite
the difficult nature of intracranial repair of the facial nerve, it is a highly reliable
technique to restore facial function. Arriaga and Brackmann report that 87.5% of
patients who undergo this type of repair developed some degree of facial function, with
57% achieving grade IV or better.
6
Intratemporal
Intratemporal facial nerve injury is observed in patients who experienced external head
trauma or iatrogenic injury during otologic procedures. Temporal bone fracture is the
most common mechanism of facial nerve injury from external trauma. Most temporal
bone fractures result from motor vehicle accidents, and 7-10% of these fractures result
in facial nerve dysfunction. In temporal bone trauma, facial nerve injury most often
occurs in the perigeniculate and labyrinthine areas with axonal degeneration extending a variable distance, possibly involving the entire intratemporal length.
Management of facial nerve injury following temporal bone trauma remains
controversial. However, a review of the literature concludes that patients with complete
paralysis at the time of injury have a poorer prognosis than those with incomplete or
delayed
paralysis. Chang and Cass propose a reasonable algorithm for management of
intratemporal facial nerve injury, in which patients with delayed onset or incomplete
paralysis are observed. If the
paralysis progresses to complete
paralysis, perform
serial ENog.
7 In addition, monitor patients with immediate complete
paralysis with
serial ENog. If ENog shows greater than 95% degeneration in the first 14 days after
injury, offer the patient facial nerve exploration and decompression. Explore the entire
length of the nerve from the meatal foramen to the stylomastoid foramen. Perform
nerve repair via primary anastomosis or graft only if total or near-total transection is certain.
Intratemporal nerve injury occurs in 0.6-3.6% of otologic procedures. A review by Green
et al revealed mastoidectomy, with or without tympanoplasty, as the most common
otologic procedure resulting in facial nerve injury.
8 Green et al also reported injury of
the facial nerve during tympanoplasty alone and during removal of exostoses.
8 Patients
with previous surgery, infection, tumor, or congenital anomalies of the ear are at a
higher risk for inadvertent nerve injury. If the injury is recognized immediately, repair it
during the primary procedure. Explore a postoperatively recognized facial
paralysis that
does not recover over several hours. Monitor a delayed-onset
paralysis with serial ENog
and explore if more than 90% degeneration occurs within the first week. Strongly
consider nerve repair if more than 50% of the nerve is transected.
Extratemporal
Extratemporal injury to the nerve may occur during surgery of the parotid or
submandibular gland, temporomandibular joint procedures, or facelift procedures, or
from traumatic lacerations of the face.
Paralysis of the facial nerve following
uncomplicated parotid procedures is reported at a 20% rate of temporary palsy, with a
10% rate of permanent paresis of temporal or mandibular branches. Children are at
higher risk for facial nerve injury during parotid surgery, as are patients who undergo
total parotidectomy. Surgery of the parotid gland often is performed for benign or
malignant tumors that may involve the facial nerve. If the nerve is resected because of a tumor, histopathologic confirmation of clear margins is required prior to repair by direct anastomosis or graft.
Inadvertent transection recognized during facelift or parotid surgery warrants immediate
primary repair. Postoperative
paralysis with known facial nerve integrity usually
recovers within 6 months of the procedure. Traumatic transections, iatrogenic injuries,
and division of segmental branches proximal to the lateral canthus should be explored
and repaired. Facial nerve injury following submandibular gland surgery, which usually
involves the marginal mandibular branch of the nerve, is not uncommon. Sacrifice of this
branch may be unavoidable because of involvement by the disease process, most
commonly chronic infection or tumor. Temporomandibular joint procedures may injure
the temporal branch or, less commonly, the main trunk of the facial nerve. Facial nerve
injury during rhytidectomy is rare, usually temporary, and most often involves the segmental branches.
The surgeon is obliged to explore traumatic or iatrogenic transections that involve the
main trunk of the facial nerve and repair them as soon as they are recognized. The
surgeon should explore and repair segmental branches proximal to the lateral canthus
and nasolabial fold. Medial to the lateral canthus, extensive interconnections between
the zygomatic and buccal branches provide neurotization of denervated muscle and
satisfactory functional recovery. Nonetheless, the surgeon should also explore and repair
medial temporal and marginal branch injuries, if possible.
Nerve Substitution and
Grafting
Nerve substitution via grafting or nerve transfer should be achieved in patients with
facial
paralysis who lack the proximal nerve segment but have an intact distal
neuromuscular pathway, including an intact distal segment of nerve and facial
musculature suitable for reinnervation. A donor nerve, transferred and anastomosed to
the distal facial nerve stump, innervates the facial muscles in place of the injured
proximal facial nerve.
The spinal accessory, phrenic, and trigeminal nerves have been used in nerve transfer
procedures. However, sacrificing these nerves involves significant morbidities. Therefore,
the hypoglossal nerve transfer/graft and cross-facial grafting have remained the mainstays in treatment.
Selection of Patients
Eighteen months after the original nerve injury, the facial muscles atrophy and do not
regain any modicum of function. When the interval of facial nerve dysfunction is less
than 18 months, primary repair, nerve grafting, or nerve transfers can be explored.
Denervated facial musculature undergoes atrophy immediately after nerve injury and
takes several years to complete. If the status of the facial musculature is in question,
the team should perform electromyography (EMG), muscle biopsy, or both prior to the reinnervation procedure.
Proximal facial nerve segment
Several factors must be considered when selecting patients for nerve substitution. The
availability of the distal neuromuscular unit is the most essential requirement for this
technique. Unavailability of the proximal facial nerve segment most commonly occurs
following cerebellopontine angle (CPA) surgery, in which the nerve is resected at the
brain stem or, occasionally, following radical or ablative procedures for tumors of the parotid gland, temporal bone, or skull base.
Intact distal neuromuscular unit
The surgeon must evaluate the distal neuromuscular unit. Denervated facial
musculature undergoes atrophy and eventual fibrosis in a process that begins
immediately after nerve injury and takes several years to complete. As stated above, if
the status of the facial musculature is in question, perform EMG and muscle biopsy prior
to the reinnervation procedure. The distal nerve stump also undergoes degeneration as
previously described, and severe neurofibrosis may limit axonal regrowth.
Suitable donor nerve and loss of donor nerve function
Nerve transfer always results in either total or partial loss of function in the donor
nerve, depending on the technique used. Hypoglossal substitution results in
paralysis
or weakening of the ipsilateral tongue muscles, which may result in significant problems with speech, mastication, and swallowing.
Techniques
Direct hypoglossal-to-facial graft
Korte performed the first hypoglossal-facial nerve anastomosis in 1901.
9 May reports
improvement of tone and symmetry in more than 90% of patients who undergo this
procedure. Initial results usually are observed within 4-6 months, indicating the amount
of time necessary for axons to travel to the distal motor endplate. Voluntary movement
develops and continues to improve for up to 2-3 years.
Spontaneous, symmetric movement is unlikely following this type of procedure. Patients
must undergo biofeedback and motor sensory re-education to learn voluntary control of
movement, decrease synkinesis, and limit facial grimacing that can occur with mastication.
The team evaluates function of the facial nerve following hypoglossal-facial anastomosis
by the degrees of tone, symmetry, movement, and synkinesis exhibited rather than by
the traditional House-Brackmann scale. A review of several large series of patients
found that 42-65% experienced good-to-excellent results, which were described as the presence of tone and symmetry, with fair-to-good movement and moderate-to-mild synkinesis.
Complications following hypoglossal-to-facial anastomosis include variable degrees of
hemitongue atrophy and functional disability, including difficulty with chewing,
swallowing, and speaking. In general, these impairments improve over time, and many
patients report fewer problems chewing postoperatively than preoperatively. This likely is due to improvement of buccal tone.
Partial hypoglossal-to-facial jump graft
A partial hypoglossal-to-facial nerve transfer using a jump graft can reanimate the facial
muscles while curbing the complications of complete hypoglossal sacrifice. In this
technique, a cable graft is anastomosed in a notch in the hypoglossal nerve and
attached to the intact facial nerve stump using microsurgical principles.
May analyzed results and complications between cranial nerve XII-VII direct-transfer
and XII-VII jump-graft techniques and found that only 8% of patients undergoing jump
grafting experienced permanent tongue deficit, compared to 100% of nerve transfer
patients. Good facial movement and expression was noted in 41% of jump graft
patients, and they experienced less synkinesis than the nerve transfer patients.
10 Facial
motor function generally is not as strong following a jump graft, and recovery of facial function was found to take longer in jump grafts.
Cross-facial nerve graft
Smith and Scaramella first reported cross-facial nerve grafting in 1971. This technique
provides the potential for symmetry and involuntary mimetic function. Disadvantages
include weakening of the contralateral facial nerve and inadequate power to innervate
the ipsilateral musculature. Cross-face nerve grafting is indicated if the proximal
ipsilateral facial nerve is not available but the distal stumps are available. Outcome of
cross-nerve grafting depends on timing and technique and can provide the best facial
reanimation scheme if performed on the right patient.
The surgeon must select appropriate segmental branches of the contralateral facial
nerve as donors, with the sural nerve serving as a cable graft. Many techniques have
been described, such as a single segmental-to main trunk anastomosis and multiple
anastomoses from segmental branches to segmental branches. The grafts are tunneled
above the supraorbital ridge for the orbicularis oculi, the upper lip for the zygomatic and
buccal branches, and below the lower lip for the marginal mandibular branch.
Facial muscle movement will not emerge until 9-12 months after the procedure (ie, the
allotted time for axonal growth to cross the graft). Cross-facial nerve grafting remains
polemic, and many investigators relegate it as an adjunctive procedure in combination with other reanimation strategies.
Muscle Transposition
When facial nerve dysfunction has exceeded 18 months, dynamic slings and free
muscle transfers can be executed to restore facial and oral motor function. Severe
neurofibrosis and myofibrosis in the distal neuromuscular unit preclude successful
reinnervation. Patients with congenital facial paralyses cannot be reinnervated, since the
neuromuscular units never developed. Regional muscle transposition and free-muscle
transfer are the 2 modalities to reanimate the face in this subset of patients.
Regional muscle transfer can reanimate the lower third of the paralyzed face. This new
neuromuscular unit is composed of the transferred muscle (to its new origin) with its original nerve and vascular supply.
Temporalis
The temporalis muscle may improve the symmetry of the commissure of the mouth and
reestablish a voluntary smile. The vector of the temporalis muscle resembles that of the zygomaticus major and, thus, results in a lateral smile.
Temporalis muscle transposition can also reanimate the eyelids. Reanimation of the eye
with the temporalis transfer can produce eyelid distortion. To avoid a contour defect, do
not use the muscle anterior to the hairline. Transposition will not produce spontaneous
mimetic function. Each movement necessitates a specific volitional action, in which the
patient must consciously contract the transposed muscle in conjunction with the smiling.
Reanimation of the eye with the temporalis muscle can cause eyelid distortion.
The muscle is harvested through a vertical incision in front of the ear that extends to
the scalp. The middle section of the muscle and fascia is elevated and detached
superiorly from the skull while preserving the inferior attachments. Two tongues are
creating by bisecting the muscle, and the muscle is tunneled through a subcutaneous
pocket from the zygomatic arch to the vermillion border. The ends of the temporalis are
secured to the orbicularis and the corner of the mouth. The ends should be secured with
enough tension to create some level of overcorrection. The patient initiates a smile by consciously tensing the temporalis muscle. Patients will require therapy to master this technique.
In his study, May reports improvement in 95% of patients with temporalis transfer for
lower face reanimation and good-to-excellent results in 78% of patients. The
complication rate was 18%; the most common complications were infection and implant-
related complications. Other potential complications include failure of attachment, pulling
away of the temporalis muscle from the commissure, and overcorrection of the upper lip. The transfer may also generate excess muscle bulk and a facial deformity, particularly over the zygoma.
Masseter
The masseter muscle is another muscle used for reanimation of the commissure of the
mouth, either alone or in conjunction with the temporalis. Unlike the temporalis, the
vector of smile of the masseter muscle is in the buccinator-risorius direction, which
produces a less natural smile. This muscle is elevated by detaching the anterior portion
from its mandibular insertion. It is similarly bisected and secured to the modiolus. The
muscle is quite bulky and can create facial irregularity or surface deformity, such as a
bulge at the commissure. Postoperatively, patients must train the masseter with
aggressive physical therapy to learn how to use the transposed masseter to produce a smile.
Digastric
The smile is one of the most important facial expressions, and facial
paralysis can
debilitate an individual. Conley developed the modern method of transposing the tendon
of the digastric muscle to the orbicularis of the lower lip. The blood supply and nerve to
the anterior belly remains intact, and dynamic depression of the lower lip border is
achieved. Of 36 patients treated in this manner by Conley, 33 were reported to have
satisfactory results. This method is ideal for isolated palsy of the marginal mandibular
nerve only, since it can create oral incompetence in patients with more extensive palsy of the lower face.
Depressor muscle function is important to dentured smile as well as to expressions of
sadness, anger, and sorrow. The lower lip is animated by interactions of the orbicularis
ori, depressor labii inferioris, depressor anguli oris, mentalis, and platysma. Terzis
describes a technique to improve this type of smile by transfer either of the anterior
belly of the digastric tenor or of the platysma.
11 Other authors argue that this
symmetrical smile could be achieved with less invasive approaches, including
BOTOX® injections or myectomy of the depressor labii inferioris.
Regional muscle transposition is limited by anatomic constraints of size and vectors and
often produces results slightly better than static strategies. Regional muscle procedures
are appropriate in patients who are in poor health or who will not survive beyond the 12-
24 month period of neurotization of a free muscle transfer. Such procedures provide
immediate reanimation and are technically less demanding than cross-facial nerve grafting with free muscle transfer.
Principles of Free-Muscle Transfer
Cross-facial nerve grafting with microneurovascular muscle transfer is the best strategy
for facial reanimation when a patient has long-established facial
paralysis (>24 mo).
Other approaches leave residual asymmetry, an unnatural appearance, and unwanted
facial movements while eating. The advent of microsurgical technique and free-muscle
transfer ignited a new epoch for facial reconstruction in patients with chronic facial
palsy. Free-muscle transfer supplies a new neuromuscular unit to the face via a free-
muscle flap and a grafted donor cranial nerve, usually a cross-facial nerve graft. This
modality establishes more precise vectors in addition to spontaneous mimetic facial
expression. Most commonly, the surgeon executes a 2-stage technique of cross-facial
nerve graft followed by a delayed free-muscle transfer. The rationale for the delay is to
prevent atrophy of the muscle graft while waiting for axons to travel the length of the nerve graft.
Cross-facial nerve graft
Occasionally, the proximal segment of the ipsilateral facial nerve is available for grafting
to innervate a free-muscle transfer. This situation most commonly occurs in the event of
a failed interposition nerve graft, resulting in facial musculature that no longer can be reinnervated.
The contralateral facial nerve is chosen as the donor nerve, and a redundant
zygomaticus branch is selected for grafting. The hypoglossal nerve also can act as a
donor, either by a direct or jump graft alone or in conjunction with a cross-facial graft.
The sural nerve is anastomosed to the contralateral facial nerve or substituted cranial
nerve and tunneled subcutaneously from the donor nerve to the planned site of free-
muscle transfer and the distal segment of the graft is tagged. The ideal time for the
muscle transfer occurs when a Tinel sign is detected in the distal nerve end, indicating completion of axon growth.
Muscles suitable for transfer
Free-muscle transfer is usually performed 9-12 months after nerve graft. A plethora of
muscles have been assiduously investigated for free transfer to the paralyzed face,
including the gracilis, serratus, pectoralis minor, latissimus dorsi, platysma, rectus abdominis, rectus femoris, and extensor digitorum brevis.
The original report by Harii in 1976 of free-muscle transfer for facial paralysis described
use of the gracilis muscle.
12 It remains the muscle of choice because of its relative ease
of dissection, adequate neurovascular pedicle, and muscle fiber length, which
corresponds to the action of the zygomaticus major muscle. The vascular pedicle is
derived from the medial femoral circumflex artery and provides up to 8 cm of length.
Innervation of the gracilis is provided by the anterior branch of the obturator nerve, which can be dissected to a length of 10-12 cm.
During the second-stage procedure, the surgeon must identify the distal end of the
nerve graft and send a frozen section for confirmation of viable axons. The muscle flap
is harvested and transferred to the face. The flap is secured to the periosteum of the
zygomatic arch and the modiolus in a vector that corresponds to the smile on the
contralateral face. Subsequently, the microanastomosis between the flap and recipient
vessels is executed, followed by the nerve anastomosis as close to the muscle as
possible. Movement can be expected in 6-9 months, with improvement over the following 2-3 years.
Lifchez and Gasparri endorse the serratus anterior for free-muscle transfer based on their
anatomical findings.
13 Each serratus slip, divided along fascial planes, can generate a
distinct force vector for facial reanimation with a total of 5 slips and 10 subslips. This
serratus anterior can, therefore, be used as a single donor muscle with multiple vectors
of action and multiple functions (eg, restoration of a symmetric smile with simultaneous but independent eyelid closure).
Terzis and Noah found no significant effect of age, gender, or ischemia time on outcome
in their series of 100 free-muscle transfers.
14 They report moderate or better results in
80% of patients undergoing free-muscle transfer, based on a 5-step scale of judgment.
O'Brien et al report good-to-excellent results in 51% of 47 patients treated by
microvascular free-muscle transfer; the surgeons most commonly used cross-facial nerve grafts and gracilis muscle transfers in their technique.
15
One-stage free muscle transfer
In their study of 25 patients, Kumar and Hassan compared single-stage versus dual-
stage free tissue transfer for facial reconstruction.
16 The gracilis obdurator nerve branch
can yield a length of 12 cm, which allows primary anastamosis of this nerve to the
contralateral facial nerve. However, this technique produces an additional scar on the
cheek. The single-stage transfer has fewer complications and a reduced recovery time with decreased rehabilitation, but the dual-stage approach has overall better symmetry.
In their investigation of 166 free gracilis transfers, Manktelow and Zuker explored
muscle transfer with cross-facial nerve graft versus single-stage transfer to the
masseter nerve. The excursion of the free gracilis innervated by the masseter nerves is
greater than that of the cross-facial nerve graft. This is probably attributable to the
different motor nerve used to reinnervate the muscle. The cross-face nerve graft
provides improved spontaneity in terms of movement, which is vital to a normal smile in
children. This is a more important characteristic than degree of excursion. Their future
studies will explore the nature of spontaneity in their muscle transfers utilizing the masseter nerve as a donor.
Although use of the masseter nerve with free tissue transfer was previously explored and
considered only in the setting of
M ö bius syndrome, bilateral facial paralysis, and facial
paralysis not suitable for cross-facial nerve grafting, the masseter nerves applicability
and role has been recently extended to patients with unilateral facial palsy. This one-
stage strategy, incorporating the masseter nerve with free tissue transfer, has become a
reasonable alternative (and may become the criterion standard) to the dual-stage
approach with cross-facial nerve grafting. The enormous advantage of the masseter
nerve-free tissue transfer technique is that, unlike the cross-facial nerve, the masseter
nerve donor produces a movement and muscle excursion (in relation to smile and
commissure excursion) in normal range with consistent movement. Also, this technique obviates the need for a second operation.
Mobius Syndrome
Mobius syndrome involves bilateral facial nerve paralysis and can often attack cranial
nerves VI, III, and XII. The syndrome generates psychological disability due to lack of
facial animation and lack of emotional expression. Patients with immobile faces cannot use their faces to show happiness, sadness, or anger.
The surgical goals for patients with Mobius syndrome are far more modest than and
differ from the goals for patients who have unilateral developmental facial paralysis.
The restoration of a true smile in these mask-like faces is impossible. Movement can
only be restored along one vector. A detailed neurological evaluation can identify
possible motor donors or residual function, which can be used for additional dynamic
restorations. Because of cranial nerve involvement, a thorough clinical and electrophysiological examination is obligatory.
Most frequently, the reconstructive surgeon performs free tissue transfers with bilateral
gracilis muscles anastamosed to the masseter nerves on both sides in order to achieve smile restoration.
Follow-up
Rehabilitation
After surgery, the rehabilitation of patients with facial paralysis necessitates
electromyography (EMG) protocols, behavioral modification, and patient exercises. The
patient needs to obtain voluntary control of facial regions. Another adjuvant therapy is the use of percutaneous electrical stimulation to stimulate motor function.
Revisions
In their patient population of 486 patients and 183 revisions, Takushima and Harii
analyzed excessive muscle bulk and dislocation of the transferred free muscle.
17 They
determined that predicting muscle bulkiness to obtain symmetry of facial contour is
difficult during the initial free-muscle transfer. Their study illustrates the wide gamut of
revisions, including muscle debulking of cheek, adjusting tension and attachments of transferred free muscle, and lipoinjection to the cheek for better volume symmetry.
Summary
The patient with facial paralysis presents a daunting challenge to the reconstructive
surgeon. A thorough evaluation, including complete history and careful physical
examination, directs the surgeon to the appropriate treatment modality. Dynamic
reanimation involves nerve repair, nerve transfer, regional muscle transfer, or free-
muscle transfer. None of the procedures can restore all of the complex vectors and
balance of facial movement and expression. However, dynamic reconstructive
techniques can yield improved facial symmetry, spontaneous and symmetric smile, eye
closure and protection, and oral competence, all of which refurbish patients' emotional, psychological, and cosmetic state and disabilities.
Keywords
facial nerve paralysis, facial paralysis, Bells palsy, Bell palsy, facial denervation, facial
reinnervation, dynamic reinnervation, paralyzed face, facial symmetry, facial movement,
facial expression, synkinesis, facial nerve symmetry, masseter nerve, single-stage, dual-
stage, mobius syndrome, Mobius syndrome, facial nerve, symmetrical smile, facial
malignancy, progressive paralysis, progressive facial paralysis, sudden facial paralysis,
intracranial nerve, masseter muscle, intratemporal nerve, extratemporal nerve, cross
facial nerve graft, facial nerve graft, crossfacial nerve graft, cross-facial nerve graft
Source:
Facial Nerve Paralysis, Dynamic Reconstruction: eMedicine Plastic Surgery