Facial Nerve Decompression

Introduction

The facial nerve is afflicted by paralysis more frequently than any other nerve in the body, most commonly in its peripheral segment as it courses through the temporal bone. The functional and cosmetic implications of facial paralysis carry the potential to significantly impact a patient’s life, with resulting psychologic damage. There are many sources of otologic facial paralysis ( Table 138.1 ), and managing facial paralysis is inevitable in the career of physicians managing otologic pathology. This chapter focuses on the role of facial nerve decompression in managing facial paralysis.

TABLE 138.1

Differential Diagnosis for Facial Paralysis

Data modified from Mary M: Differential diagnosis by history, physical findings and laboratory results. In May M (ed): The Facial Nerve. New York, Thieme-Stratton, 1986.

Birth Traumatic vaginal delivery Myotonic dystrophy Mobius’ syndrome (facial diplegia associated with other cranial nerve deficits)	Neoplastic Facial nerve neuroma Facial nerve hemangioma Vestibular schwannoma Glomus jugulare tumor Meningioma Von Recklinghausen’s disease Cholesterol granuloma Carcinoma (invasive or metastatic from the breast, kidney lung, stomach, larynx, prostate, or thyroid)
Traumatic Cortical injuries Basilar skull fractures Brainstem injuries Penetrating injury to the middle ear Facial injuries Barotrauma	Toxic Thalidomide (Miehlke’s syndrome: involvement of cranial nerves VI and VII with atretic external ears) Tetanus Diphtheria Carbon monoxide Lead intoxication
Neurologic Opercular syndrome (cortical lesion in the facial motor area) Millard-Gubler syndrome (abducens palsy with contralateral hemiplegia because of a lesion in the base of the pons involving the corticospinal tract)	Iatrogenic Mandibular block anesthesia Anti-tetanus serum Vaccine treatment of rabies Otologic, skull base, and parotid surgery Embolization
Infectious Malignant otitis externa Acute or chronic otitis media Cholesteatoma Meningitis Parotitis Chickenpox Herpes zoster oticus (Ramsay Hunt syndrome) Encephalitis Poliomyelitis (type I) Mumps Mononucleosis Leprosy Human immunodeficiency virus and acquired immunodeficiency syndrome Influenza Coxsackievirus Malaria Syphilis Tuberculosis Botulism Mucormycosis Lyme disease	Idiopathic Bell’s palsy Melkersson-Rosenthal syndrome (recurrent facial palsy, furrowed tongue, fascial labial edema) Hereditary hypertrophic neuropathy (Charcot-Marie-Tooth disease, Dejerine-Sottas disease) Autoimmune syndromes of temporal arteritis, periarteritis nodosa, and other vasculitides Guillain-Barre syndrome (ascending paralysis) Multiple sclerosis Myasthenia gravis Sarcoidosis (Heerfordt’s syndrome, uveparotid fever) Wegener’s granulomatosis Eosinophilic granuloma Amyloidosis Hyperostoses (e.g., Paget’s disease, osteopetrosis) Kawasaki disease (infantile acute febrile mucocutaneous lymph node syndrome)
Genetic and Metabolic Diabetes mellitus Hyperthyroidism Pregnancy Alcoholic neuropathy Bulbopontine paralysis Oculopharyngeal muscular dystrophy	Vascular Benign intracranial hypertension Intratemporal aneurysm of the internal carotid artery

The facial nerve is composed of an estimated 10,000 fibers. Seventy percent are myelinated motor axons innervating the muscles of facial expression, and the remaining 3000 fibers are spread amongst general visceral efferents (salivation and lacrimation), general sensory afferents (cutaneous sensation), and special visceral afferents (taste). The extent to which facial animation is compromised is directly correlated to the fraction of injured motor fibers. The anatomy of the facial nerve is organized by distinct layers, including the endoneurium, perineurium, and epineurium ( Fig. 138.1 ). The endoneurium surrounds each nerve fiber, closely adherent to the Schwann cell layer of each axon. Individual fibers are then grouped into fascicles, and each fascicle is surrounded by perineurium. The epineurium is the outermost layer, where the vasa vasorum and lymphatics deliver oxygen and nutrients to the nerve. Sunderland described a classification system for stratifying the severity of seventh nerve injury, as outlined in Fig. 138.2 . First-degree injury is termed neuropraxia, describing a physiologic conduction block due to intraneural edema, with intact neural structure. Relief of compressive forces facilitates resolution of injury and return of function. Second-degree injury results from failure to relieve compressive forces, termed axonotmesis, resulting in injury to axons without violation of the endoneurial sheath. With relief of the pathologic process, complete recovery is anticipated. Third-degree injury indicates disruption of the endoneural tubules. Disruption of endoneurial tubules allows disorganized axonal regeneration, as each axon can enter any open endoneurial tube. This pattern of disorganized, faulty regeneration accounts for synkinesis, and recovery is anticipated to be incomplete. Fourth-degree injury is characterized by violation of the perineurium in addition to axons, myelin sheaths, and endoneurium. Attempts at regeneration are even more disorganized, with axons aberrantly entering the wrong fascicles. Fifth-degree injury is characterized by complete laceration or transection of the nerve, to include the epineurium. Recovery after fourth- and fifth-degree injury is uniformly poor. Neurotmesis includes third through fifth degree injuries.

Fig. 138.1, Cross-section schematic of nerve demonstrating endoneurium, perineurium, and epineurium.

Fig. 138.2, Classification of Degrees of Neural Injury (From Sunderland): First degree—Compression (arrow) without loss of structure; recovery is normal. Second degree—Axon degeneration: regeneration is appropriate, and recovery is satisfactory. Third degree—Loss of endoneural tubes; recovery is incomplete with synkinesis. Fourth degree—Disruption of perineurium; recovery is very poor. Fifth degree—Complete disruption; no recovery.

Key Operative Learning Points

1.
The decision as to whether facial decompression is advantageous is based upon the etiology of paralysis, duration of paralysis, and outcome of electrodiagnostic testing.
2.
Electrodiagnostic testing is necessary only in cases of complete paralysis, as the prognosis for cases of incomplete paralysis is uniformly good.
3.
Evoked electromyography (EEMG) may underestimate the extent of recovery in a regenerating nerve and should be followed by electromyography (EMG) to survey for voluntary motor unit action potentials (VUMAPs), prior to consideration of decompression.
4.
There is no consensus in the literature to support facial decompression in acute otitis media (AOM).
5.
Facial paralysis in context of chronic otitis media (COM) with cholesteatoma should be addressed operatively without delay, with goals of exploring the facial nerve and eliminating disease.
6.
Surgical decompression for Bell’s palsy must address the meatal foramen. This can be accomplished by middle fossa or translabyrinthine approaches.

Preoperative Period

History

1.
History of present illness
- a.
  How long has the paralysis been present?
- b.
  Was the paralysis abrupt or gradual in onset?
- c.
  Has this occurred previously (ipsilateral or contralateral)?
- d.
  Does the patient have hearing loss?
- e.
  Does the patient have ear pain or drainage?
- f.
  Is the patient dizzy?
- g.
  Was there associated trauma to the head?
2.
Past medical history
- a.
  Does the patient have a history of chronic ear disease?
- b.
  Has the patient been previously diagnosed with Bell’s palsy?
3.
Surgical history
- a.
  Has the patient had prior otologic surgery?
4.
Medications
- a.
  Is the patient anticoagulated?

Physical Examination

Facial examination

a.
Which branches of the facial nerve are affected?
b.
What is the extent of the weakness?

What is the House-Brackmann score? ( Table 138.2 )

TABLE 138.2

House-Brackmann Facial Nerve Grading System

Grade 1	Normal	Normal function in all areas
Grade 2	Mild dysfunction	Slight weakness noticeable on close inspection
Grade 3	Moderate dysfunction	Noticeable but not disfiguring weakness. Complete eye closure with effort. Mild synkinesis
Grade 4	Moderately severe dysfunction	Obvious weakness and/or disfiguring asymmetry. Incomplete eye closure. Normal symmetry/tone at rest
Grade 5	Severe dysfunction	Barely perceptible motion. Disfiguring asymmetry at rest
Grade 6	Total Paralysis	No movement

d.
Is there involvement of other cranial nerves?
e.
Is there or has there been a vesicular rash?

2.
Otologic examination
- a.
  Is there suppurative drainage or cholesteatoma?
- b.
  Is there trauma to the ear canal or tympanic membrane?

Imaging

The decision as to whether imaging is necessary is guided by the etiology of the paralysis. A radiographic evaluation generally provides little information for a diagnosis of Bell’s palsy. However, a surgeon considering middle fossa decompression may obtain computed tomography (CT) to assist in identifying surgical landmarks or to facilitate intraoperative image guidance. Facial paralysis in combination with suppurative ear disease warrants imaging to evaluate the course of the facial nerve, survey for additional intratemporal or intracranial complications, and to facilitate preoperative planning and counseling.

Paralysis exceeding 6 months duration, facial twitching, slow progression of weakness over a period of weeks to months, and recurrent episodes should prompt a radiographic evaluation for neoplastic disease.

1.
Electrodiagnostic testing

Electrodiagnostic testing represents the primary diagnostic modality by which the severity of neural injury is assessed, facilitating estimations of prognosis. A finding of facial paralysis is not specific with respect to the extent of injury, as a patient with neuropraxia may demonstrate paralysis of similar severity to the patient with a transected nerve. In turn, the goal of electrodiagnostic testing is to identify the patient population sustaining injury of such severity that the chance of satisfactory, spontaneous recovery is low. This information is gathered by way of facial EMG and EEMG. Electrodiagnostic testing is necessary only in cases of complete paralysis, as the prognosis for cases of incomplete paralysis is uniformly favorable.
- a.
  Evoked electromyography
EEMG assesses the functional capacity of the nerve by measuring the amplitude and latency of a compound muscle action potential (CMAP) after neural stimulation. This is accomplished with the use of surface electrodes placed at the stylomastoid foramen for stimulation and the nasolabial fold for measurement. The CMAP of the injured side is comparatively expressed as a percentage of the normal side, that percentage representing the number of electrically excitable fibers. Because the applied stimulus cannot propagate through degenerated axons, the CMAP represents the collective stimulus of intact (neuropraxic) fibers. It should be noted that a transected facial nerve may generate a CMAP of normal amplitude until Wallerian degeneration and sufficient axonal loss have progressed beyond the intratemporal segment, past the point of the applied stimulus. This process occurs over a period of 48 to 72 hours, during which EEMG provides limited useful information. EEMG should then be performed on an every other day basis to survey for progressive axonal degeneration ( Fig. 138.3 ). Reliability of EEMG fades after a period of 2 to 3 weeks, as regenerating fibers and fibers recovering from neuropraxia fire asynchronously, yielding a disorganized, diminished response.
- b.
  Facial nerve electromyography
In contrast to EEMG, EMG measures responses that are volitional in nature. Needle electrodes are inserted into facial musculature for analysis of resulting electrical activity during insertion, rest, and volitional movement. EMG is capable of detecting VUMAPs when no facial mobility is visually evident. This feature renders EMG helpful in the setting of postoperative paralysis. If the nerve is transected, EMG will immediately show loss of VMUAP. However, loss of VMUAP is not specific to nerve transection, as neuropraxia may generate identical findings. Therefore, demonstration of VMUAP is helpful to the surgeon in that it indicates the nerve is intact. Loss of VMUAP in this setting is less helpful, given the lack of specificity in regards to severity of injury. While EMG is capable of identifying a nerve as intact in the acute period, it is incapable of confirming degeneration in this time frame. Contrarily, EMG does provide utility in detecting muscle denervation 2 to 3 weeks out from injury, as destabilized resting potentials of the muscle membrane appear graphically as fibrillation potentials. This 2- to 3-week period represents the time in which Wallerian degeneration ensues. Polyphasic action potentials n this time frame indicate muscle re-innervation. Finally, when EEMG results have progressed to thresholds indicating need for decompression, EMG should be performed to survey for early VMUAPs, which project a favorable prognosis in absence of surgical intervention. This is necessary because with early reversal of a conduction blockade, dys-synchrony of nerve firing may result in failure to generate a CMAP, yielding a false-positive result on EEMG.
2.
Audiogram

Defining auditory function will assist in reaching a diagnosis. For those patients requiring facial nerve decompression, the status of hearing is a key consideration in choosing a surgical approach.

Indications

1.
Bell’s palsy

Bell’s palsy is a diagnosis of exclusion, presenting as an acute hemifacial weakness in the absence of further symptomatology. Weakness is global in distribution, and sparing of the forehead suggests a central etiology. Bell’s palsy is by far the most common of the acute facial palsies, accounting for 75% of cases, at an estimated incidence of 30 to 40 cases per 100,000 people annually. Reviews of the natural history demonstrate satisfactory recovery in greater than 80%, and 85% of patients will demonstrate improvement within 3 weeks of onset. Timing to onset of recovery and completeness of the palsy are the two most significant prognostic indicators.

Electrodiagnostic studies have localized the conduction blockade in Bell’s palsy to the meatal foramen, which is the entry location of the facial nerve into the temporal bone, forming the labyrinthine segment. This is the narrowest segment of the canal, estimated at 0.68 mm in diameter. The anatomy of the meatal foramen is characterized by a confluence of Bill’s Bar and the falciform (transverse) crest with dense periotic bone laterally in the internal auditory canal (IAC). The nerve is devoid of epineurium, and is instead ensheathed by a band of periosteum that seals the entry site into the fallopian canal, resulting in potential for entrapment in situations of neurogenic edema ( Fig. 138.4 ).

The mainstay of the patient’s evaluation in Bell’s palsy is electrodiagnostic testing. Audiometry demonstrates symmetric function, with the exception of an absent acoustic reflex on the involved side, and routine use of imaging is unnecessary. Facial nerve decompression is indicated for patients demonstrating CMAP reduction of 90% or greater, with confirmed lack of motor activity on voluntary facial EMG. These criteria are based upon the observation that approximately one half of this patient population will sustain permanent, unsatisfactory recovery in the absence of decompression. If 90% degeneration is not documented within 2 weeks of onset, further electrodiagnostic testing is unnecessary, and prognosis for recovery is good.

Review of the literature demonstrates that pharmacologic treatment of Bell’s palsy is a subject of considerable debate. However, guidelines support the use of combined systemic steroid (prednisone 1 mg/kg per day + taper) and antiviral therapy (valacyclovir 500 mg tid × 10 days) in patients presenting within 3 days of onset of paralysis, and common practice supports initiation of therapy in patients presenting within 7 days.
2.
Chronic otitis media

Paralysis of the facial nerve due to COM is a known complication of advanced disease, generally related to the effects of chronic suppuration and cholesteatoma. Authors have proposed various mechanisms, including chronic osteitis, bone erosion, nerve edema and inflammation, neural compression, and ischemia. Disruption of the nerve is most common in its horizontal course. Onset of facial palsy in COM may be abrupt or gradual. A palsy of abrupt onset is commonly due to acute infection superimposed on the presence of cholesteatoma. Such an occurrence should serve as a reminder that not all paralysis of acute onset is due to Bell’s palsy. There is little controversy regarding treatment for facial paralysis associated with COM. Careful management with early surgical intervention has proven its efficacy in supporting neural recovery, and antibiotics and steroids are considered important adjunctive measures. The timing of surgery in relation to the onset of facial palsy is paramount. Patients should be taken to the operating room without delay, regardless of the extent of paralysis or the duration of time since onset. The goals of surgery are to eradicate all cholesteatoma and infection and to explore the facial nerve, which may require facial decompression. No consensus has been reached regarding the necessary extent of decompression at the time of surgery. Regardless of the specifics of surgical methodology, complete eradication of disease in a single procedure should be the operative goal for patients with facial paralysis due to COM.
3.
Iatrogenic facial nerve injury

Factors which predispose a patient to iatrogenic injury can challenge even the most accomplished of surgeons, include variable landmarks and distorted tissue planes in revision surgery, inflammatory disease altering the course of the nerve, congenital structural anomalies, and errors in microsurgical technique. Second to hearing loss, facial paralysis is the most common reason for malpractice lawsuits in otologic surgery today. If upon the patient’s waking the surgeon is confronted with an immediate, complete paralysis, several issues deserve consideration. Use of a local anesthetic is a known source of temporary paralysis. If the surgeon identified the nerve and is confident of its integrity, patience should be all that is necessary for return of facial function. Similarly, use of packing material may inflict undue stress and compression of the facial nerve. Consideration of more invasive management options begins when palsy persists despite removal of packing, and the waning effects of local anesthesia have passed. If the status of the facial nerve is unknown or if it was aggressively instrumented, one should proceed with exploration. However, if the surgeon is confident the nerve is intact despite gentle manipulation, observation may be appropriate.

As previously discussed, EMG may serve as a diagnostic adjunct in the acute setting for aiding in the decision to explore or observe. Demonstration of VMUAP indicates that the nerve is intact, eliminating the immediate need for exploration. Loss of VMUAP in this setting is less helpful, as this may indicate injury as mild as neuropraxia or as advanced as transection. If palsy is complete and early exploration is deferred, serial electrodiagnostic testing with EEMG is indicated after 48 to 72 hours have passed. Reduction in the EEMG response to less than 10% of the normal side within 5 days of injury is indicative of severe injury and potentially transection. EMG should then be utilized to survey for VMUAP’s. If no volitional activity is noted on EMG, the patient should be taken for re-exploration. The quality of the outcome declines dramatically when surgery is delayed beyond 30 days post injury, and when repair is delayed past 1 year, results are uniformly poor. Patients with delayed onset facial palsy, even when it progresses to a complete palsy, generally achieve satisfactory recovery.

Facial paralysis associated with noniatrogenic trauma may merit decompression, which is discussed in Chapter 145 .

Contraindications

1.
Herpes zoster oticus/Ramsay Hunt

The symptomatic combination of otalgia and a herpetic, vesicular eruption of the ear and face is known as herpes zoster oticus. The addition of facial paralysis is referred to as Ramsay Hunt syndrome. Symptoms result from reactivation of varicella zoster virus, previously quiescent in the geniculate ganglion. The frequency of complete paralysis is significantly higher, and the likelihood of satisfactory recovery is substantially reduced. Symptoms are generally more severe, and the patient may demonstrate involvement of multiple cranial nerves. Accompanying auditory and vestibular symptoms confer an even worse prognosis. Radiographic workup is of limited utility, and in contrast to Bell’s palsy, electrodiagnostic testing has proven unreliable. Early administration of combined systemic steroid and antiviral therapy is paramount, and the role of surgical decompression is limited.
2.
Facial paralysis associated with acute otitis media

The advent of antibiotics has dramatically reduced rates of peripheral facial palsy complicating AOM. Facial paralysis in this setting is a phenomenon observed nearly exclusively in children. The care of these patients should be considered urgent, and include myringotomy and aggressive use of topical and systemic antimicrobials. Tympanostomy tube placement permits ongoing egress of inflammatory fluid as well as established access to the middle ear for administration of topical medication. Mastoidectomy is indicated in the case of associated coalescing mastoiditis or intracranial extension, but facial nerve decompression cannot be recommended for facial paralysis due to AOM.
3.
Facial paralysis in the only hearing ear
4.
Unfit for general anesthesia due to overall health status.

Preoperative Preparation

1.
Review the history and assumed source of facial paralysis.
2.
Review the audiogram to assess the hearing status of the ipsilateral and contralateral ears.
3.
Review imaging, if obtained.
4.
In cases where electric diagnostic testing was performed review the EEMG and EMG.

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