Facial Nerve Testing

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Facial Nerve Testing

Otology/Audiology
Author Credentials 

Isaac Erbele, MD
Fellow
Otology, Neurotology, and Skull Base
Hearing and Balance Center/Louisiana State University Health Sciences Center
Baton Rouge, LA

Module Summary

Reviews pathology and differential for acute facial nerve weakness.  Reviews anatomy, technique, and application of facial nerve testing.  Identify timing of useful, actionable information.  Review role of surgery in acute facial nerve weakness.

Module Learning Objectives 
  1. Describe function of facial nerve.
  2. Compare normal and abnormal facial nerve anatomy.
  3. Detail causes of facial nerve weakness.
  4. Predict results of facial nerve testing in acute facial nerve weakness.
  5. Choose the most appropriate facial nerve tests in setting of facial nerve weakness.

Embryology

Learning Objectives 
  • Discuss embryological development of the facial nerve.
  • Identify which branchial cleft the facial nerve develops from and innervates.
  • Relate the course of the facial nerve to the stages of embryological development. 
  • Apply knowledge of the development of the temporal bone around the facial nerve after birth to post-auricular incision planning in children.
  • Relate abnormal courses of the facial nerve with congenital defects and describe possible alternative courses in these conditions:
    • Aural atresia
    • Cochlear malformations

 

References 
  1. Gulya AJ. Developmental Anatomy of the Temporal Bone and Skull Base. In: Gulya AJ, Minor LB, Glasscock ME, et al., eds. Glasscock-Shambaugh Surgery of the Ear. Shelton, Ct.: People's Medical Publishing House-USA; 2010:18-19
  2. LaRouere M, Lundy L. Anatomy and Physiology of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed. Philadelphia: Mosby; 2005:1199-1200
  3. Goldsztein H, Roberson JB, Jr. Anatomical facial nerve findings in 209 consecutive atresia cases. Otolaryngol Head Neck Surg. 2013;148(4):648-652
  4. Palabiyik FB, Hacikurt K, Yazici Z. Facial nerve anomalies in paediatric cochlear implant candidates: radiological evaluation. J Laryngol Otol. 2017;131(1):26-31

 

Anatomy

Learning Objectives 
  • Discuss course of facial nerve and branches.
  • Sketch course of innervation of facial muscle movement from cerebral cortex to muscles of facial expression.
    • Identify location of origin of movement within the cerebral cortex.
    • List brainstem nuclei associated with the facial nerve:
      • Motor nucleus
      • Tractus solitarius
      • Spinal tract
      • Nucleus of trigeminal
      • Superior salivatory and lacrimal nuclei
    • List the six segments of the facial nerve and branches at each segment:
      • Intracranial/cisternal
      • Canalicular/meatal
      • Labyrinthine
      • Temporal/horizontal segment
      • Mastoid/vertical segment
      • Extracranial/extratemporal
    • Draw relationship between facial nerve, nervus intermedius, superior vestibular nerve, inferior vestibular nerve and cochlear nerve in the root entry zone, cerebropontine angle, and internal auditory canal.
  • Describe course of parasympathic innervation related to the facial nerve from superior salivatory nucleus to end organs:
    • Lacrimal gland
    • Submandibular gland
    • Sublingual gland
  • Comprehensively describe functions of facial nerve.
    • Facial expression
      • Identify movements related to the five major branches of the facial nerve:
        • Temporal/frontal
        • Zygomatic
        • Buccal
        • Marginal mandibular
        • Cervical
    • Muscles movement unrelated to facial expression:
      • Stapedius
      • Stylohyoid
      • Posterior digastric
      • Scalp movement via posterior auricular nerve
    • Lacrimation
      • Identify ganglion related to parasympathic lacrimal gland function
    • Salivation
      • Identify ganglion related to parasympathic submandibular and sublingual gland function
    • Taste
      • Locate area of taste sensation on the tongue related to facial nerve function
    • General sensation
      • Locate area of general sensation related to the facial nerve
      • Relate geniculate ganglion function with presentation of Ramsay-Hunt syndrome
  • Apply knowledge of frequency of facial nerve dehiscences to possible iatrogenic injury from ear surgery.
  • Describe blink and stapedial reflex arcs.
References 
  1. LaRouere M, Lundy L. Anatomy and Physiology of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed. Philadelphia: Mosby; 2005:1199-1211
  2. Limb C, Niparko J. The Acute Facial Palsies. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed.: Mosby; 2005:1230-1257
  3. O’Donoghue G, Nikolopoulos T. Tumors of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby; 2005:1258-1269
  4. Francis H. Anatomy of the Temporal Bone, External Ear, and Middle Ear. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:1977-1986
  5. Ridgway J, Bhama P, Kim J. Rehabilitation of Facial Paralysis. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. . 6 ed.: Elsevier/Saunders; 2014:2643-2661

 

Pathogenesis

Learning Objectives 
  • Discuss etiologies of facial nerve paresis.
  • Comprehensively list causes of acute facial nerve paresis.
  • Compare causes of bilateral acute facial nerve paresis to unilateral facial nerve paresis.
  • Differentiate presentation of idiopathic facial nerve paresis (Bell’s palsy) from neoplastic causes of facial nerve paresis.
  • Differentiate presentation of idiopathic facial nerve paresis (Bell’s palsy) from Ramsey-Hunt syndrome.
References 
  1. Baugh RF, Basura GJ, Ishii LE, Schwartz SR, Drumheller CM, Burkholder R, et al. Clinical practice guideline: Bell's palsy. Otolaryngol Head Neck Surg. 2013;149(3 Suppl):S1-27
  2. Limb C, Niparko J. The Acute Facial Palsies. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed.: Mosby; 2005:1230-1257
  3. O’Donoghue G, Nikolopoulos T. Tumors of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby; 2005:1258-1269
  4. Mattox DE. Clinical Disorders of the Facial Nerve. In: Flint PW, Haughey BH, Robbins KT, et al., eds. Cummings Otolaryngology - Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2617-2628
  5. Refer also to Otosource: Facial Nerve Disorders 

 

Basic Science

Learning Objectives 
  • Discuss loss and regeneration of nerve function.
  • Describe how complex action potentials are conducted via a nerve.
  • From outside-in, order the layers of a skeletal muscle nerve, and describe the function of each layer:
    • Epineurium
    • Perineurium
    • Endoneurium
    • Axon
  • Grade a nerve injury based on Sunderland’s classification.
  • Grade a nerve injury based on Seddon’s classification.
  • Weigh the clinical role of Sunderland’s classification versus Seddon’s classification.
  • Describe timing of Wallerian degeneration.
  • Compare timing of axonal regeneration and myelin degeneration.
  • Compare causes of synkinesis to hyperkinesis.
References 
  1. LaRouere M, Lundy L. Anatomy and Physiology of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed. Philadelphia: Mosby; 2005:1199-1211
  2. Adour K. Electrical testing of the facial nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby; 2005:1223-1229
  3. Seddon HJ. A Classification of Nerve Injuries. Br Med J. 1942;2(4260):237-239
  4. Sunderland S. The anatomy and physiology of nerve injury. Muscle Nerve. 1990;13(9):771-784

Incidence

Learning Objectives 
  • Discuss incidences of causes of facial nerve paresis.
  • Comprehensively list causes of acute facial nerve paresis.
  • Discuss incidence of acute facial nerve paralysis, with special attention to Bell’s palsy.
References 
  1. Baugh RF, Basura GJ, Ishii LE, Schwartz SR, Drumheller CM, Burkholder R, et al. Clinical practice guideline: Bell's palsy. Otolaryngol Head Neck Surg. 2013;149(3 Suppl):S1-27
  2. Limb C, Niparko J. The Acute Facial Palsies. In: Jackler RK, Brackmann DE, eds. Neurotology. 2 ed.: Mosby; 2005:1230-1257
  3. O’Donoghue G, Nikolopoulos T. Tumors of the Facial Nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby; 2005:1258-1269
  4. Mattox DE. Clinical Disorders of the Facial Nerve. In: Flint PW, Haughey BH, Robbins KT, et al., eds. Cummings Otolaryngology - Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2617-2628
  5. Refer also to Otosource: Facial Nerve Disorders

Patient Evaluation

Learning Objectives 
  • Apply knowledge of facial nerve anatomy to the physical exam.
  • Describe elements of the House-Brackmann scale:
    • Gross
    • At Rest
    • Motion
      • Forehead
      • Eye
      • Mouth
  • Apply House-Brackmann grade to a patient with facial nerve weakness
  • From proximal to distal, order site of facial nerve injury based on loss of function:
    • Lacrimation
    • Taste
    • Salivation
    • Stapedial reflex
    • Muscles of facial expression
  • Describe Schirmer’s test:
    • Draw the reflex arc of nerves involve
    • Define a positive test
  • Apply topognostic testing to identify site of facial nerve injury.
  • Weigh relative merits of topognostic testing with electrical testing and imaging.
References 
  1. House JW, Brackmann DE. Facial nerve grading system. Otolaryngol Head Neck Surg. 1985;93:146-147
  2. Ridgway J, Bhama P, Kim J. Rehabilitation of Facial Paralysis. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2643-2661

Measurement of Functional Status

Learning Objectives 
  • Determine role of electrical facial nerve testing in presence of:
    • Incomplete facial nerve weakness
    • Complete facial nerve weakness
  • Predict optimal timing of electrical facial nerve testing for complete facial nerve weakness.
  • Define denervation.
  • Report timing of electrical changes when testing distal to the site of facial nerve injury:
    • Define deblocking and how soon after injury it occurs
    • Describe fibrillation potentials and report when they are likely to first appear
  • Define the three components of stimulatory nerve testing that predict denervation and prognosis:
    • Level of stimulation
    • Magnitude of compound muscle action potential
    • Latency between stimulation and muscle action potential
  • Compare location of stimulation, amount of stimulation, method of grading, findings in normal facial nerve exam, and limitations of:
    • Minimal nerve excitability testing (NET)
    • Maximal nerve excitability testing (MST)
    • Electroneurography (ENoG)
    • Electromyography (EMG)
  • Describe trigeminal nerve artifact and predict which tests are most likely to produce it.
  • Determine which electrical test should be used to identify a fibrillation potential.
  • Estimate likelihood return of facial nerve function after Bell’s palsy based on MST.
  • Describe role of intraoperative EMG:
    • Compare active and passive monitoring
    • Compare information gained from a nerve “train” versus “burst”
    • Discuss role of artifacts on monitoring the facial nerve
      • Depth of anesthesia
      • Trigeminal stimulation
    • Troubleshoot lack of EMG response to facial nerve stimulation
References 
  1. Diaz R, Poti S, Dobie R. Tests of facial nerve function. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2604-2616
  2. Adour K. Electrical testing of the facial nerve. In: Jackler RK, Brackmann DE, eds. Neurotology. Mosby; 2005:1223-1229
  3. Baugh RF, Basura GJ, Ishii LE, Schwartz SR, Drumheller CM, Burkholder R, et al. Clinical practice guideline: Bell's palsy. Otolaryngol Head Neck Surg. 2013;149(3 Suppl):S1-27

Imaging

Learning Objectives 
  • Choose the most appropriate imaging for:
    • Temporal bone trauma
    • Non-traumatic acute facial nerve paresis
References 
  1. Diaz R, Poti S, Dobie R. Tests of facial nerve function. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2604-2616

Pathology

References 
  1. Refer to Otosource: Facial Nerve Disorders

Treatment

References 
  1. Refer to Otosource: Facial Nerve Disorders and Facial Nerve Surgery

Medical Therapies

References 
  1. Refer to Otosource: Facial Nerve Disorders and Facial Nerve Surgery

Surgical Therapies

Learning Objectives 
  • Describe indications and timing of facial nerve decompression.
  • Describe findings on ENoG that would prompt consideration for facial nerve decompression in complete facial nerve weakness.
  • Identify location of pathology most likely to be involved with Bell’s palsy and with facial trauma.
  • Support role of mastoid segment exploration in facial nerve decompression.
  • Compare supralabyrinthine approach to middle cranial fossa approach to perform facial nerve decompression.
  • Detail the surgical technique for middle fossa facial nerve decompression.
  • Discuss timing of facial reanimation.
References 
  1. Gantz BJ, Roche JP, Redleaf MI, Perry BP, Gubbels SP. Management of Bell's Palsy and Ramsey Hunt Syndrome. In: Brackmann DE, Shelton C, Arriaga MA, eds. Otologic surgery. 4th ed. Philadelphia: Elsevier, Inc; 2016:287-298
  2. Lupo JE, Jenkins HA. Traumatic Facial Paralysis. In: Brackmann DE, Shelton C, Arriaga MA, eds. Otologic surgery. 4th ed. Philadelphia: Elsevier, Inc; 2016:299-313
  3. Refer also to Otosource: Facial Nerve Surgery

Rehabilitation

References 
  1. Refer to Otosource: Facial Nerve Disorders and Facial Nerve Surgery

Case Studies

Case 1

A 45 year old female patient presents to you with a 3 day history of facial nerve weakness on the right.  It was progressive over that period.  The weakness is obvious, but at rest, her face appears symmetric.  She cannot move her forehead or completely close her eye.  She has asymmetric movement of the mouth with smiling.  The rest of her history and exam is unremarkable.

  1. What is the most likely diagnosis?
  • Bell’s palsy
  1. What House-Brackmann grade would you give her?
  • House-Brackmann IV
  1. What imaging study would you consider ordering?
  • If there is diagnostic uncertainty, it may be reasonable to perform an MRI of the internal auditory canal.  Otherwise, the AAO’s 2013 clinical practice guideline on Bell’s palsy recommends against routine imaging for new-onset Bell’s palsy.
  1. According to the AAO’s 2013 clinical practice guideline on Bell’s palsy, is there a role for electrical testing?
  • No.

You decide to have her return 4 days later, after starting steroids, valcyclovir, and eye care.  Her MRI showed perigeniculate enhancement but was otherwise unremarkable.  Her facial nerve function has deteriorated, and she now has no movement.

  1. What House-Brackmann grade would you give her?
  • House-Brackmann VI
  1. According to the AAO’s 2013 clinical practice guideline on Bell’s palsy, is there a role for electrical testing now?
  • Electrical facial nerve testing is an option.  There can be a role for determining if the patient still has incomplete paralysis, with implications on prognosis.  Testing at this point may also have a role to determine candidacy for facial nerve decompression
  1. If the patient has complete facial nerve weakness, what result on EMG would be expected?  Would fibrillation potentials be present at this time?
  • No compound muscle action potentials.  No fibrillation potentials would be present.  These typically present 14-21 days after Wallerian degeneration occurs.
  1. At what percent difference in ENoG would you consider performing a facial nerve decompression?
  • Greater than 90%

Case 2

You are consulted regarding a 26 year old male in the ICU after a motor vehicle accident for a left facial nerve weakness.  The patient is now awake after losing consciousness for 24 hours, and the status of his facial nerve function immediately after the accident is unknown.  He does not appear to have any movement on the left side of the face.  You do note that he is tearing on that side.

  1. What House-Brackmann grade would you give him?
  • House-Brackmann VI
  1. Can you guess where his facial nerve injury is?
  • Topognostic testing is unreliable, however, the injury is likely distal to the geniculate ganglion, since lacrimation (via innervation from the greater superficial petrosal nerve) appears to be preserved. 
  1. What test do you order?
  • You order a CT of the temporal bone
  1. What changes would be expected on NET?  How about MST or ENoG?
  • Nothing predictable 1 day after the injury.  Changes on these electrical tests are not seen until Wallerian degeneration begins.
  1. CT imaging suggests a bony spicule in the mastoid segment of the facial nerve.  Would there be any advantages to operating emergently, if he is otherwise stable?
  • There is some evidence to support better prognosis in early intervention.  Also, if performed within 48 hours, intraoperative EMG may potentially be used.  Stimulation of the severed nerve is possible and may help identify it.

Complications

Learning Objectives 
  • Describe ocular sequalae of facial nerve paresis.
  • Discuss how concomitant trigeminal injuries can worsen ocular complications in facial nerve paresis
  • Compare goals of short- and long- term eye care in setting of facial paresis.
  • Apply knowledge of facial nerve re-innervation to weigh role of early versus late definitive eye care.
References 
  1. Ridgway J, Bhama P, Kim J. Rehabilitation of Facial Paralysis. In: Flint PW, Haughey BH, Lund VJ, et al., eds. Cummings Otolaryngology: Head and Neck Surgery. 6 ed.: Elsevier/Saunders; 2014:2643-2661
  2. Refer also to Otosource: Facial Nerve Disorders and Facial Nerve Surgery

 

Review

Review Questions 
  1. What functions does the facial nerve have?
  • Innervation of the muscles of facial expression
  • Taste to the anterior two-thirds of the tongue
  • Sensation to the concha
  • Parasympathetics to lacrimal gland
  • Parasympathetics to sublingual and submandibular glands
  1. Name the four electrical tests used to measure facial weakness
  • Minimal nerve excitability testing (NET)
  • Maximal nerve excitability testing (MST)
  • Electroneurography (ENoG)
  • Electromyography (EMG)
  1. What clinical factors may suggest that a facial nerve paresis is due to cancer?
  • Setting of previous cancers, parotid mass, slowly progressive weakness, unresolving weakness
Resources 

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