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The Facial Nerve (CN VII): ENT Perspective

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1. Anatomy and Course

Intratemporal Course — Segments of the Fallopian Canal

Key Vulnerabilities

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2. Grading Facial Nerve Dysfunction

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3. Electrodiagnostic Testing

• Electroneurography (ENoG): Measures amplitude of compound action potential (CAP). Degeneration >90% = poor prognosis. Useful from day 3 onward (requires Wallerian degeneration to reach facial surface).
• Electromyography (EMG): Detects voluntary motor units; fibrillation potentials appear 10–14 days after complete degeneration. Maintains prognostic value when ENoG is severely depressed.
• Combined ENoG + EMG: Patients with preserved voluntary EMG potentials despite low CAP have excellent prognoses.
• Salivary flow test: Reduced flow (<25% contralateral) or abnormal scintigraphy by day 14 predicts incomplete recovery.

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4. Bell's Palsy

Definition

Pathophysiology

1. Latent HSV-1 reactivates in the geniculate ganglion
2. Viral replication triggers perineural inflammation and edema
3. Because the labyrinthine segment is the narrowest and has no epineurium, swelling in this confined bony canal leads to ischemic compression
4. Wallerian degeneration of varying severity follows

Clinical Features

• Sudden-onset unilateral LMN facial weakness (forehead involved — distinguishes from UMN palsy)
• Prodrome: retroauricular/mastoid pain
• Taste disturbance (chorda tympani involvement)
• Hyperacusis (stapedius involvement)
• Reduced lacrimation (GSPN involvement)
• Eye: incomplete closure → exposure keratopathy risk

Prognosis

• 80–90% recover completely without treatment
• Incomplete paralysis: 95–100% full recovery
• Complete paralysis: higher risk of sequelae (synkinesis, contracture, hemifacial spasm)
• Poor prognostic factors: complete paralysis, hyperacusis, decreased tearing, age >60, diabetes mellitus, hypertension, severe pain at onset
• Recovery by 6 months; if not, reconsider the diagnosis

Management

• Prednisone 1 mg/kg/day (up to 60–80 mg/day) × 10 days, initiated within 48–72 hours
• Meta-analyses show ~17% better chance of complete recovery vs placebo
• Reduces synkinesis and contracture

• Role is controversial; the American Academy of Neurology (2012) found antivirals add at most a modest (≤7%) additional benefit
• Some guidelines still recommend combining them with steroids in severe (HB IV–VI) palsy, particularly given the risk of missing zoster sine herpete

• Lubricating drops, nocturnal taping/ointment, moisture chamber
• Ophthalmology referral for lagophthalmos

• Transmastoid decompression of tympanic/mastoid segments: abandoned — randomized trials showed no benefit; the lesion is in the proximal labyrinthine segment, inaccessible via this route
• Middle fossa approach decompression of the meatal foramen and labyrinthine segment in patients with ENoG >90% degeneration within 14 days: some evidence of benefit but difficult to accumulate sufficient trial data

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5. Ramsay Hunt Syndrome (Herpes Zoster Oticus)

Definition

1. Peripheral facial palsy (LMN, CN VII)
2. Otalgia (severe ear pain)
3. Vesicular eruption — on the auricle (concha, EAC), retroauricular area, face, or oral mucosa

Pathophysiology

Features Distinguishing from Bell's Palsy

Zoster Sine Herpete

Ophthalmic Complications

Management

• Corticosteroids (prednisone): relieve acute pain, reduce vertigo, decrease postherpetic neuralgia
• Acyclovir/valacyclovir: DNA polymerase inhibition, preferentially taken up by VZV-infected cells; started early (within 72 hours of rash onset)
• Combination therapy is standard
• Eye care mandatory (lagophthalmos risk)
• Vaccine (Shingrix) — highly recommended for prevention in >50 years old

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6. Other ENT-Related Causes of Facial Nerve Palsy

Otitis Media — Acute (AOM)

• Facial palsy via congenital dehiscence of the fallopian canal adjacent to the stapes
• Management: systemic antibiotics + myringotomy; complete paralysis in AOM children rarely lasts >3 weeks
• AOM palsy is often incomplete

Chronic Otitis Media (COM) — Without Cholesteatoma

• Affects horizontal tympanic segment near stapes
• Gradual progression from mild weakness to full palsy
• Management: control the infection; surgical decompression if needed

Cholesteatoma

• Most common COM-related cause of facial palsy
• Erodes the horizontal fallopian canal (especially proximal to 2nd genu); can expose the nerve anywhere in the temporal bone
• Onset is typically gradual (slow progressive palsy over months)
• Management: mastoidectomy + careful dissection of cholesteatoma matrix from the nerve; outcomes depend on whether complete nerve degeneration has occurred before surgery (decompression within 1 week of onset significantly improves outcome)

Facial Nerve Tumors

• Gradual-onset facial paresis + hearing loss (most common presentation)
• Expansile, smooth, enhancing mass along any segment of the fallopian canal on MRI
• HRCT shows enlargement of the bony facial canal
• Slowly progressive facial paralysis is NOT Bell's palsy — always suspect tumor

• Usually at geniculate ganglion; honeycomb calcification on CT; early surgical intervention recommended to preserve nerve function

• Adenoid cystic carcinoma most notorious; facial weakness with parotid mass mandates imaging from parotid to brainstem

Traumatic Facial Paralysis

• Temporal bone fractures (most common intratemporal cause)
  • Longitudinal fractures: often incomplete palsy, delayed onset → neurapraxia → good prognosis
  • Transverse fractures: complete palsy, immediate onset → high risk of degeneration
• Penetrating injuries (gunshot)
• Iatrogenic: parotidectomy, mastoidectomy, middle fossa surgery

Lyme Disease (Borrelia burgdorferi)

• Most common infectious cause of bilateral facial palsy in endemic areas
• Can be unilateral; tested with serology; treated with doxycycline or amoxicillin
• Part of the workup for bilateral facial palsy

Malignancy/Neoplastic

• Parotid malignancies, squamous cell carcinoma of the temporal bone, metastases (breast, lung, kidney, prostate, melanoma)
• Progressive facial paralysis is the red flag for neoplasm

Bilateral Facial Palsy — Differential Diagnosis

Melkersson-Rosenthal Syndrome

• Rare; triad of recurrent facial palsy + facial edema + fissured tongue (lingua plicata)
• Cause unknown; may respond to steroids

Möbius Syndrome

• Congenital bilateral CN VI and VII palsy; spectrum ranges to multiple CN palsies
• Evidence suggests rhombencephalon developmental disorder, not primary muscle defect
• Lower face often more spared than upper face

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7. Localization of the Lesion by Clinical Findings

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8. Imaging

• MRI with gadolinium: Enhancement of the facial nerve is normal in healthy people; most consistent abnormal enhancement in Bell's/herpetic palsy is at the distal IAC and labyrinthine segment. MRI not routinely required for typical Bell's palsy — reserve for atypical presentations (recurrent ipsilateral palsy, twitching, no recovery by 6 months).
• HRCT temporal bone: Evaluates bony fallopian canal, cholesteatoma erosion, fracture lines, tumor-related canal expansion.
• Both modalities are complementary when evaluating facial nerve tumors — MRI from brainstem to parotid gland is required.

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Summary Table: ENT Causes of Facial Palsy

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Recent evidence note (PMID 39627559, Sys Rev 2024): A systematic review of photobiomodulation therapy for Bell's palsy suggests potential benefit in symptom recovery, though the evidence base remains limited and this is not yet standard of care.