---

Facial Nerve (CN VII) - Complete Case-Based Learning Guide

---

Learning Objective 1: Anatomy and Functional Components of CN VII

• Motor nucleus (SVE)
• Superior salivatory nucleus (GVE)
• Nucleus of the solitary tract (SVA, GVA)
• Cummings Otolaryngology Head and Neck Surgery, p. 2451

---

Learning Objective 2: Course of the Facial Nerve - Origin to Terminal Branches

Intracranial Segment

Intratemporal Segment - The Fallopian (Facial) Canal

1. Labyrinthine segment - First, shortest, and narrowest segment (0.68 mm at meatal foramen). Travels superior to the cochlea, opens into the geniculate fossa. This is the site of injury in Bell's palsy. The geniculate ganglion here gives off the Greater Superficial Petrosal Nerve (GSPN) anteriorly and is the First Genu.
2. Tympanic (horizontal) segment - Runs along the medial wall of the middle ear, superior to the oval window niche. Ends at the Second Genu at the pyramidal eminence, giving off the nerve to stapedius.
3. Mastoid (vertical) segment - Runs inferiorly in the mastoid. Gives off the chorda tympani at a variable point. Exits through the stylomastoid foramen.

Extratemporal Segment

• Temporal
• Zygomatic
• Buccal
• Marginal mandibular
• Cervical
• Cummings Otolaryngology, p. 2451-2452

---

Learning Objective 3: Surgical Landmarks of the Facial Nerve

• Cummings Otolaryngology, p. 2452

---

Learning Objective 4: Clinical Features of Facial Nerve Palsy

• Loss of forehead wrinkling - inability to wrinkle brow
• Inability to close the eye (lagophthalmos) - risk of exposure keratitis
• Bell's phenomenon - upward and outward rolling of eye on attempted eye closure (protective reflex)
• Flattening of nasolabial fold
• Deviation of mouth to opposite side on smiling (contralateral pull)
• Drooling from corner of mouth
• Inability to puff cheeks, blow, or whistle

• Hyperacusis (if above nerve to stapedius)
• Loss of taste on anterior 2/3 tongue (if above chorda tympani)
• Decreased lacrimation (if above GSPN - geniculate ganglion)
• Pain in/around ear (otalgia)

• Cummings Otolaryngology, p. 3277-3278

---

Learning Objective 5: UMN vs. LMN Facial Palsy - Differentiation

---

Learning Objective 6: Electrodiagnostic Tests

The Four Electrodiagnostic Tests:

• Transcutaneous stimulation at stylomastoid foramen; compare threshold current to opposite side
• A difference of 2.0-3.5 mA between the two sides suggests an unfavorable prognosis
• Least precise; largely superseded

• Similar to NET but uses maximum stimulation
• Compares response on affected vs. unaffected side

• Bipolar stimulation at stylomastoid foramen; records Compound Muscle Action Potential (CMAP)
• Compares amplitude of response to normal side as a percentage
• ≥90% degeneration (i.e., CMAP amplitude ≤10% of normal side) = poor prognosis, indicates consideration of surgical decompression
• Should be performed every 1-3 days until nadir is reached
• Most clinically useful objective test

• Measures motor unit potentials (MUP) directly from facial muscles
• Useful in first 3 days (before Wallerian degeneration)
• Important 2-3 weeks after onset to assess reinnervation:
  • Fibrillation potentials = denervation (active)
  • Polyphasic potentials = reinnervation (recovery)
• If ENoG shows ≥90% degeneration and EMG shows no voluntary motor units - patient may be candidate for surgical decompression

---

Learning Objective 7: Causes of Facial Nerve Palsy

By Frequency:

• Bell's palsy (idiopathic/HSV-1) - ~70% of all facial palsy

By Location of Lesion:

• Stroke (most common)
• Brain tumor
• Multiple sclerosis
• Head trauma

• Pontine glioma
• Brainstem infarction (Millard-Gubler syndrome - ipsilateral CN VI + VII palsy with contralateral hemiplegia)
• Multiple sclerosis

• Acoustic neuroma (vestibular schwannoma)
• Meningioma
• Cholesteatoma

• Bell's palsy (HSV-1) - commonest cause overall
• Ramsay Hunt syndrome (VZV) - vesicles in EAC, otalgia, sensorineural hearing loss
• Otitis media (acute/chronic) - cholesteatoma erosion
• Herpes zoster oticus
• Trauma - temporal bone fracture
• Tumors - facial nerve schwannoma, hemangioma, glomus tumors

• Parotid tumors (pleomorphic adenoma, mucoepidermoid carcinoma)
• Parotid surgery iatrogenic injury

• Sarcoidosis (Heerfordt syndrome - uveoparotid fever with bilateral facial palsy)
• Lyme disease (Borrelia burgdorferi)
• Guillain-Barre syndrome (bilateral)
• Melkersson-Rosenthal syndrome (recurrent facial palsy + facial edema + fissured tongue)
• Diabetes mellitus
• HIV
• Leprosy

---

Learning Objective 8: Topodiagnostic Tests for Intratemporal Lesions

• If Schirmer's abnormal → lesion at or proximal to geniculate ganglion
• If Schirmer's normal but stapedial reflex absent → lesion between geniculate and pyramidal eminence (tympanic segment)
• If stapedial reflex normal but taste abnormal → lesion between pyramidal eminence and chorda tympani takeoff
• If taste normal but motor deficit only → lesion at or distal to stylomastoid foramen

• Cummings Otolaryngology, p. 3984

---

Learning Objective 9: Management Plan for Facial Nerve Palsy

Immediate Priorities:

1. Eye care - this is the most urgent step:
   • Artificial tears (lubricating drops) during the day
   • Lubricating eye ointment at night
   • Moisture chamber / eye patch
   • Gold weight implant or tarsorrhaphy if prolonged

Medical Treatment (Bell's Palsy - start within 72 hours, effective up to 2 weeks):

• Corticosteroids (1st line): Prednisolone 1 mg/kg/day (60-80 mg/day) orally for 10 days, then taper
• Antivirals: Valacyclovir 500 mg TDS for 5-7 days (or acyclovir 400 mg 5x/day) - add to steroids given HSV-1 etiology; some controversy but minimal side effects
• Add proton pump inhibitor / H2 blocker with steroids
• Monitor blood glucose (steroids in diabetics)

Monitoring:

• If incomplete palsy at presentation - review every 2-3 days; watch for progression
• If complete palsy develops: obtain ENoG at 3 days after complete paralysis
• If ENoG shows <90% degeneration: continue medical treatment
• If ENoG ≥90% degeneration + no voluntary EMG units within 2 weeks: consider surgical decompression

Surgical Treatment:

• Middle Cranial Fossa (MCF) decompression of meatal foramen, labyrinthine segment, geniculate ganglion, and proximal tympanic segment
• Criteria: >90% neuronal degeneration on ENoG within 2 weeks of onset, patient age <65, no medical contraindications
• Transmastoid decompression does NOT adequately decompress the meatal foramen and labyrinthine segments, so has no role in Bell's palsy

If no improvement after 3 weeks: perform EMG only (ENOG unhelpful beyond 3 weeks)

• Shambaugh Surgery of the Ear, p. 650-652

---

Learning Objective 10: Complications of Facial Paralysis

Early Complications:

• Exposure keratitis / corneal ulceration - from lagophthalmos (most sight-threatening); managed with lubricants, moisture chamber, tarsorrhaphy
• Psychological distress - cosmetic disfigurement, social withdrawal

Late / Sequelae:

• Incomplete recovery - residual weakness in 15-30% of Bell's palsy patients
• Synkinesis - aberrant reinnervation causing involuntary co-contraction (e.g., eye closure when smiling); commonest long-term complication
• Crocodile tears (Bogorad syndrome) - aberrant parasympathetic reinnervation of the lacrimal gland by fibers originally destined for the salivary glands; results in lacrimation while eating
• Hemifacial spasm - involuntary unilateral facial contractions; may indicate vascular compression at the CPA
• Contracture - tightening and shortening of facial muscles; face may appear normal at rest but shows contracture on movement
• Autonomic dysfunction - gustatory sweating (Frey's syndrome - after parotid injury), abnormal salivation
• Facial pain - neuropathic pain in the distribution of CN VII/nervus intermedius

---

Case Summary

---