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Facial Reanimation: Evolution and Refinements
Introduction and Historic Review
Facial paralysis (FP) is a devastating condition which strips the human face from all emotional expressivity, leading to severe consequences in the quality of life, interpersonal communication, and psychological development of the afflicted patient ( Fig. 15.1 ). The most important advances in the treatment of FP during the last century included the introduction of restorative microsurgery with atraumatic manipulation of injured nerves, cross-facial nerve grafting, which allowed coordinated animation, and free muscle transfers for denervated target substitution.
Nerve Transfers
The first accessory to facial nerve anastomosis in FP was performed by Drobnick in 1897, and popularized by others. In all these cases, the entire accessory nerve was used and the function of the sternocleidomastoid and trapezius muscles was always impaired. In contrast, Terzis has always used part of the accessory nerve to the sternocleidomastoid and the trapezius (40% through a perineurial window), avoiding the functional downgrading of these muscles.
The first hypoglossal-facial transfer was performed in 1901 by Korte. In 1927, Bunnel first described end-to-end repair of the facial nerve.
Thompson in 1971, first attempted muscle to muscle neurotization of muscle autografts. Lexer and Eden first used the temporalis muscle for eye sphincter reanimation and Sir Gillies used the temporalis muscle to reanimate the oral sphincter in 1934. Conley made important contributions in extratemporal facial nerve repair, immediate reconstruction and nerve grafting techniques in 1961 and popularized the hypoglossal nerve transfer. Three years later, Kurze a neurosurgeon, and Smith a plastic surgeon, reported independently the use of the operating microscope in nerve surgery. Edgerton first transferred the anterior belly of digastric muscle to dynamically correct lower lip depression.
Fisch established the repair of the intratemporal portion of the facial nerve. In the early 1970s, working independently, Scaramella and Smith, reported the technique of cross-facial nerve grafting (CFNG) for restoration of a coordinated smile, an ingenious concept, later popularized by Anderl. Tamai transferred the first muscle in the experimental animal in 1970 and Terzis in the rabbit model showed that transferred free muscle not only survives transplantation, but it can produce useful work.
These achievements inspired Harii et al. in 1976 to transfer the first free gracilis muscle to the face; however the motor donor used was the deep temporal nerve. Three years later Terzis, introduced the pectoralis minor muscle for both eye and lower face reanimation. In 1980, O'Brien and colleagues proposed the use of CFNG as motor donor for their transferred extensor digitorum brevis muscle, however, this muscle lacked bulk for adequate smile restoration.
It was soon realized that CFNGs yielded desirable results only if preformed within 6 months from the onset of paralysis. For later cases, up to 2 years, this challenge was successfully addressed in 1984 by Terzis, who introduced the “babysitter” procedure, in which a portion (40%) of a powerful ipsilateral motor donor is used, most often the ipsilateral hypoglossal nerve, in an end-to-side manner, to reinnervate the recently denervated but electrophysiologically present facial muscles, in order to preserve the facial musculature, while CFNGs regenerate across the face. At a second stage, 9–12 months later, secondary microcoaptations take place between the CFNGs and selected branches of the affected facial nerve. In contrast, the classical hypoglossal to facial nerve transfer, popularized by Conley and Baker in 1979, had considerable undesirable sequelae, including severe synkinesis, tongue hemiatrophy, speech, mastication, and swallowing problems. Therefore, the concept of finding powerful motor donors for nerve transfer prevailed in recent years, especially in cases of bilateral FP, in which the contralateral facial nerve was also involved.
In 1989, Zuker and Manktelow proposed the use of the masseteric nerve as motor donor for free gracilis reinnervation. Terzis refined the use of the masseteric nerve as a motor donor by always performing an end-to-side coaptation to avoid downgrading the muscles of mastication. The biggest disadvantage with the use of the masseteric nerve is the difficulty in obtaining coordinated animation. In rare cases when all three nerves (hypoglossal, accessory, masseteric) are involved, Terzis has used components of the ipsilateral C7 as motor donors for facial dynamic restoration. This is a challenging procedure which involves the selective use of the anterior and posterior division fibers to the affected side. In cases of bilateral FP, similar division fibers innervate the same specific targets on each side.
Recently, the use of the masseteric nerve has gained again attention. In 2012 Biglioli et al. in a preliminary study, reported the restoration of emotional, coordinated smile in patients with long standing paralysis in a single stage using the gracilis muscle innervated by both the ipsilateral masseteric nerve and the contralateral facial nerve through a CFNG.
Etiology of Facial Paralysis
A clinically oriented presentation of the etiology of FP includes the classification of the etiologic factors according to the location of the facial nerve damage.
Etiology and Lesion Location
The causes of the facial nerve lesion could be located at any part of three anatomically distinct portions of its pathway: the intracranial, intratemporal, and extratemporal parts ( Table 15.1 ; see Figs 10.10 , 10.11 ).
Table 15.1
Facial palsy etiology depending on the location of the lesion and the mechanism of injury
| Tumor | Trauma | Developmental | Systemic | Infectious | Iatrogenic | Idiopathic | Toxic | |
|---|---|---|---|---|---|---|---|---|
| Intra-cranial | Meningioma Acoustic neuroma Metastatic Millard–Gubler a |
Cranial base injury | Aplasia/hypoplasia/agenesis of facial nerve nuclei Moebius syndrome |
Multiple sclerosis e TTP f HIV |
Encephalitis Meningitis Syphilis m Lyme encephalopathy Gnathostomiasis m |
Embolization | ||
| Intra-temporal | Primary facial neuroma Cholesteatoma Metastatic |
Temporal bone injury Forceps delivery Neurofibromatosis |
HFM b ACF c CHARGE d Moebius syndrome |
Acute porphyria g Sarcoidosis h Temporal arteritis i Periarteritis nodosa i TTP HHN j |
External otitis Otitis media Mastoiditis CMV n Epstein–Barr n Rubella n Mumps n Tuberculosis Lyme o |
Mastoid surgery Post-immunization p |
Bell's CMT q DS r |
Thalidomide s Arsenic t Alcohol u Diphtheria v |
| Extra-temporal | Parotid gland lesions Primary facial neuroma Sarcoma Metastatic |
Head and neck injury Forceps delivery Facial injuries Neurofibromatosis |
HFM ACF CHARGE Moebius syndrome |
Sarcoidosis Temporal arteritis Periarteritis nodosa TTP HHN Dystrophia myotonica Myasthenia gravis k Diabetes mellitus l Hyper- and hypothyroidism Acute porphyria Hypertension Vitamin A deficiency |
CMV Epstein–Barr Rubella Mumps Cat scratch Tuberculosis Lyme |
Post-tonsillectomy adenoidectomy Dental local anesthesia Parotid surgery Mandibular block anesthesia Post-immunization Botulinum toxin |
Bell's CMT DS |
Alcohol Diphtheria |
a Millard–Gubler syndrome: brainstem lesion due to tumors, bleeding, and, rarely, by infarction secondary to occlusion of the basilar artery.
b HFM (Hemifacial microsomia): associated with mesodermal dysplasia, temporal bone canals atresia, and facial anatomic defects.
c ACF (Neonatal asymmetric crying faces): facial nerve compression or faulty muscle and/or nerve development.
d CHARGE: coloboma of the iris or retina, heart defects, atresia of the choanae, retardation of growth, and/or development, genitalia anomalies, ear anomalies.
e Brainstem lesions in the pontine tegmentum.
f TTP (Thrombotic thrombocytopenic purpura): bland thrombi in the microvasculature of the nerve, central nervous system involvement possible.
g Peripheral type of acute motor axonal neuropathy.
h Neurosarcoidosis: cranial nerve mononeuropathy direct nerve compression by parotid gland swelling or by a lesion within the facial canal.
i Arteritis: nerve microvascular compromise.
j HHN: hereditary hypertrophic neuropathy.
k Antibodies against nicotinic acetylcholine receptor in the motor end-plate.
l Peripheral diabetic neuropathy.
m Syphilis and gnathostomiasis: central nervous system, meningeal involvement obliterative endarteritis of terminal arterioles with resultant inflammatory and necrotic changes.
n Viral infections: antibodies against nerve, inflammation is within the fallopian canal.
o Lyme disease: peripheral neuropathy.
p Polyneuritis due to development of antibody to myelin basic protein (vaccine for rabies, anti-tetanus serum).
q Charcot–Marie–Tooth Disease (CMT): genetic defect of myelin sheath.
r Dejerine–Sottas Disease (DS): genetic defect of myelin sheath.
s Thalidomide: atresia of intratemporal canals (Miehlke syndrome).
t Arsenic intoxication: peripheral neuropathy/electrophysiological changes.
u Alcohol: Alcoholic neuropathy: axonal Wallerian degeneration, oxidative stress.
v Diphtheria: Diphtheritic neuropathy is an acute demyelinating polyneuropathy.
Intracranial
The intracranial portion is subdivided into the:
- 1.
The supranuclear part which includes corticobulbar fibers from the precentral gyrus of the frontal lobe projecting to the facial nucleus
- 2.
The nuclear part comprised by the upper part, which receives corticobulbar fibers bilaterally and innervate primarily upper face muscle targets and by the lower part, consisting of crossed fibers which innervate lower face muscle targets
- 3.
The infranuclear part consisting of the rest of the intra-pontine efferent part of the nerve and the cerebellopontine angle.
Intracranial causes could be various brain tumors such as hemangioblastomas, craniopharyngiomas, choroid plexus papillomas, and vascular abnormalities and tumors. Intracranial may also be the origin of developmental anomalies, dysplasia or even total agenesis of the facial nerve nuclei. Other causes may include trauma and degenerative disease of the central nervous system.
Intratemporal
The intratemporal portion is where the facial and the intermedius nerves exit from the posterior pons acquiring a ventral direction and then enter the temporal bone along with the vestibulocochlear nerve. Their course is at the subarachnoid level and continues in the internal auditory canal along with the inferior anterior cerebellar artery and vein. In the internal auditory canal, the facial and the intermediate nerves enter the fallopian canal separating from the vestibulocochlear nerve. The first 4 mm in the fallopian canal comprise the labyrinthine segment, which is perpendicular to the temporal bone; the next 1 cm is the tympanic segment, which extends horizontally at the medial wall of the tympanic cavity; and the mastoidal segment, which runs vertically for approximately 1.5 cm.
The intratemporal causes of FP include tumors such as acoustic neuromas (also known as vestibular schwannomas), which account for approximately 80% of cerebellopontine angle tumors. Meningiomas comprise the remaining 20%. Rare cases of cholesteatoma, glomus tumors, vascular tumors, lipomas, and metastatic lesions have also been observed (<0.1%). Developmental abnormalities, trauma with or without fracture of the temporal bone and skull base may also be included in the intratemporal causes of FP. Rare intratemporal causes of FP could be various viral or bacterial infections and iatrogenic mishaps. Systemic and autoimmune diseases such as sarcoidosis, periarteritis nodosa, temporal arteritis and osteoporosis may also cause FP by impairing the blood supply and/or the normal course of the facial nerve (e.g., by being responsible for stenoses in the intratemporal canals or foramina).
Extratemporal
The extratemporal portion begins at the exit of the facial nerve through the stylomastoid foramen and includes all facial nerve branches that innervate the facial musculature. Trauma, malignant tumors of the parotid gland, skin and soft tissue tumors are included in the extratemporal causes of FP. Primary facial nerve tumors (cylindromas), intraparotid facial nerve schwannomas (0.8%) and neurofibromatosis also comprise possible FP causes. Systemic and autoimmune diseases are also present here and may cause FP in severe cases. Bell's palsy, also known as idiopathic unilateral facial nerve paralysis, is the most common extratemporal cause of FP (>80%), as it has been associated with inflammation and pressure on the facial nerve at or after its exit through the stylomastoid foramen. The aforementioned systemic (diabetes mellitus) and autoimmune (sarcoidosis) diseases, as well as certain viral infections (HSV1, VZV) have been identified as possible reasons for the acute onset of Bell's palsy and for the syndromic form of the palsy (Ramsay–Hunt syndrome), which presents also with vestibulocochlear dysfunction and herpetiform eruptions. In more than 85% of cases, Bell's palsy resolves, leaving a small degree of functional impairment (in 10% of the cases).
Overall, developmental abnormalities during the fetal period comprise the second most common cause (after Bell's palsy) followed by trauma and tumor. Apart from the isolated form of developmental FP, the broad category of developmental causes also include several syndromic presentations such as Moebius and Goldenhar syndromes.
Mechanism of Injury and Impairment
Regardless of location, tumors may impair the function of the facial nerve by compressing or distorting its course as space occupying lesions or by infiltrating it and disrupting its anatomic and/or electrophysiologic continuity. Additionally, especially when the facial nerve is infiltrated by the tumor and oncologic resection requires additional nerve length sacrifice in order to achieve tumor free margin excision, the postoperative defect may be considerably larger altering the prognosis and treatment strategy for facial nerve reconstruction.
Trauma may include direct facial nerve disruption by the induced mechanical forces or by fragments of bone resulting from local fractures which may cut, or entrap the facial nerve in their new position. Additionally, trauma may cause extended vascular damage leading to the formation of large hematomas, aneurysmal dilatation and peripheral ischemia, which could be detrimental to the anatomic and functional integrity of the facial nerve. Intoxication caused by chemical factors primarily affect cellular metabolism at the molecular level and affect the physiology of nerve conduction. Idiopathic causes include conditions of multifactorial or inconclusive origin, genetic predisposition or of unknown etiology. Iatrogenic mishaps are caused by medication or the interventions of a physician surgical or non-surgical ( Table 15.1 ).
Clinical Presentation
The functional problems that emerge in the paralytic face greatly affect facial emotional expressivity, interpersonal interaction, verbal and non-verbal communication, and psychological development of the patient. Emotions can only be expressed by coordinated movements from all constituent parts of the face. A unilateral insult to the facial nerve disrupts this functional and aesthetic symmetry.
This loss of facial symmetry at rest and during voluntary motion could further impair the socialization of the patient by increasing distress and fear of embarrassment. The severity of FP, therefore, depends on its extent (e.g., partial or complete, uni- or bilateral). Consequently, it has been shown that the clinical and behavioral importance of the eye sphincter, levator anguli oris, oral sphincter, and depressor complex function determines the severity and prognosis of FP.
Upper Face
Frontalis Muscle
This muscle is actually the frontal belly (in some patients two separate bellies) of the occipitofrontalis muscle, which extends over the forehead area from the anterior aspect of galea aponeurotica down to the orbicularis oculi muscles (OOM) where it inserts. By wrinkling the forehead and raising the eyebrows it participates in the broad spectrum of facial emotional expressivity. Additionally, at rest, the frontalis muscle stabilizes the eyebrows and the supraorbital area by antagonizing the action of the eyebrow depressors (corrugators, procerus, lateral/vertical segment of the OOM). This ability is lost in patients with FP.
Eye Sphincter
Major aspects of clinical presentation include the inability to voluntary close the eyelids, the absence of blink, and the decreased tear production. Impaired eye closure (lagophthalmos) and the lack of the protective role of blinking and tear production result in dryness of the cornea and conjunctiva and subsequent inflammation. Corneal infections are due to the lack of the antimicrobial properties of the tears. Corneal opacity and ulcer formation have also been observed. The loss of tone of the OOM leads to ectropion, epiphora, and chronic conjunctivitis. In severe cases, where the nasociliary branch of the ophthalmic division of the trigeminal nerve is involved, corneal sensibility is decreased or absent leading to neurotrophic keratopathy and amblyopia. Cornea without sensibility is susceptible to injury while the reparative and healing mechanism is impaired. Therefore, substituting the function of the eye sphincter aims at protecting the eye and preserving vision, as well as restoring the behavioral role of eye closure and blink (emotional expressivity).
Normal Blink Reflex
Stimuli from the upper eyelid, the forehead, and periorbital area are carried by supraorbital and supratrochlear nerves to the trigeminal ganglion. Similarly, stimuli from the sclera and the cornea are carried to the trigeminal ganglion via the short and long ciliary nerves. From the trigeminal ganglion, two internucleus neuronal pathways begin. The first carries signals via the trigeminal motor nucleus to the facial nucleus and is responsible for the initiation of the ipsilateral blink due to OOM contraction. This is an oligosynaptic pathway and initiates the early, ipsilateral R1 response at about 10 ms. The second pathway carries signals via the spinal trigeminal tract to the contralateral facial nucleus, which initiates the contralateral blink. This is a polysynaptic pathway, responsible for the bilateral delayed R2 response at about 30 ms. There is also an internucleus pathway between the facial and oculomotor nuclei, which mediates the initial relaxation of the levator palpebrae superioris muscle via the oculomotor nerve, before the initiation of OOM contraction.
Middle Face
Levator Muscles of the Upper Lip and Orbicularis Oris (OOrM)
This group of muscles are primarily responsible for the elevation of the upper lip (levator labii superioris, zygomaticus minor) and the corner of the mouth (levator anguli oris, zygomaticus major) which play a central role in smiling. Levator muscles are functionally and anatomically linked with the OOrM participating in basic functions such as speaking, kissing, lip puckering, and other oral movements and expressions. The zygomatic and buccal branches of the facial nerve provide innervation. The constellation of symptoms that follows paralysis of these muscles include an inability to articulate phonemes (dysarthria) and speak properly, to smile, to kiss, and produce the plethora of perioral movements, such as whistling, sucking a straw or blowing. Additionally, oral incontinence characterized by drooling and inability to keep food in the mouth may be present. In cases where the ipsilateral antagonists (depressor complex) retain their function, drop of the corner of the mouth may be observed. In unilateral FP, mild to severe mouth asymmetry may be noted due to the prevailing function of the muscles on the unaffected side.
The restoration of a symmetric, natural, voluntary smile depends on the functional restoration or substitution of this group of muscles. According to Rubin, smile is classified as the: (a) “Mona Lisa” type, where the direction of the smile is along the zygomaticus major; (b) “canine” type, where the levator labii superioris dominates in the production of the smile; and (c) “full denture” dominant smile. The last category of smile requires also restoration of the depressor complex.
Lower Face
Depressor Complex
This group of muscles depresses the lower lip and modiolus and participates along with the levators and the orbicularis oris in the perioral movements, in speaking and retaining oral continence. The primary goal of reanimating this group of muscles aims at the restoration of a full denture smile, expressing disappointment, sadness, disgust, doubt, disdain, irony, anger, or rage. Voluntary lip depression, involves the downward motion of the lower lip for about 5.6 mm and the inversion of the vermillion border; both disappear with injury of the marginal mandibular branch. Consequently, the affected lower lip stays elevated and flattened, while the normal side remains depressed.
Platysma
Although no critical facial function is associated with the platysma, it plays a significant role in swallowing and commissure depression. Platysma is innervated by the cervical branches of the facial nerve and involvement of these branches may lead to the obliteration of neck rhytides or vertical platysma bands, and to neck skin shagging and flattening.
Additional Symptoms
The nerve to the stapedius muscle, which dampens the sound vibrations to the inner ear, a posterior auricular sensory branch, and the chorda tympani, which provides taste sensation to the anterior two-thirds of the tongue and parasympathetic innervation to the submandibular and sublingual glands are all branches originating from the mastoid segment of the facial nerve. Lesions result in intolerance to high-pitched or loud noises, loss of taste over the front of the tongue, and decrease in salivary secretion.
Salivary secretion may also be affected in lesions of the lesser petrosal nerve, a branch from the geniculate ganglion which innervates the parotid gland. Lesions of the greater petrosal nerve, the first branch from the geniculate ganglion which innervates the lacrimal gland, result in decreased tear production which, in combination with the inability for eye closure and blink, may lead to neurotrophic keratopathy and ultimately loss of vision.
Patient Examination
Physical Examination
The diagnostic approach of patients with FP includes the detailed investigation of medical, surgical, and obstetric history; of the onset and the etiology of the paralysis (e.g., injury, tumor, developmental); as well as the meticulous documentation and analysis of the clinical presentation. Full neurologic assessment of all cranial nerves and any previous treatments should be included. The goal of the meticulous initial assessment is to pinpoint the prognosis and to provide an individualized treatment plan for the patient. Specific imaging and electrophysiological studies precede the examination with the specialist.
Imaging Studies
In the early 1980s, bilateral temporal bones tomograms were used for all developmental and traumatic (intratemporal) cases. This technique was also used if there was suspicion of facial nerve neuroma, which remains a diagnostic challenge. The systematic use of bilateral computed tomography (CT) scans of the temporal bones started in the mid-1990s, along with the occasional use of magnetic resonance imaging (MRI) in cases of possible central nervous system tumors.
Polytomograms and CT scans of bilateral temporal bones could greatly aid the investigation of facial nerve lesions, primarily due to abnormalities of the adjacent osseous structures including middle and inner ear developmental craniofacial malformations, internal auditory canal stenosis, cranial deformities, and syndromic anomalies such as in hemifacial microsomia, CHARGE, Treacher–Collins, and Goldenhar syndrome.
Imaging studies have greatly contributed to the identification and differential diagnosis of developmental facial paralysis. Some of the signs may include dysmorphic, smaller temporal bone, constricted fallopian canal, absent or shorter vertical and/or mastoid segment or fallopian canal ending at a blind pocket in the mastoid process on the affected side. These signs along with the absence of generalized craniofacial malformations, inner ear deformities and multiple cranial nerve involvement more likely indicate simple rather than syndromic developmental mishap.
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