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Facial Neurovascular Conflict

Summary

  • Neurovascular compression of the facial nerve (CN VII) at the root exit zone causing hemifacial spasm
  • Results from vascular loop compression, typically by anterior inferior cerebellar artery (AICA) or posterior inferior cerebellar artery (PICA)
  • High-resolution MRI with CISS/FIESTA sequences demonstrates vascular contact at the cisternal segment of CN VII1

Pathophysiology

  • Mechanism of compression
    • Arterial pulsations cause chronic irritation of facial nerve at root exit zone (REZ)
    • REZ is transition zone between central and peripheral myelin (2-3mm from brainstem)
    • Most vulnerable area due to lack of epineurium
  • Pathologic changes
    • Demyelination at compression site
    • Ephaptic transmission between adjacent nerve fibres
    • Hyperexcitability of facial nerve nucleus
  • Offending vessels
    • AICA (most common - 40-50%)
    • PICA (30-40%)
    • Vertebral artery (10%)
    • Basilar artery dolichoectasia (rare)
    • Venous compression (extremely rare)

Demographics

  • Incidence
    • 11 per 100,000 population
    • Accounts for primary hemifacial spasm in >95% of cases
  • Age
    • Peak incidence: 5th-6th decade
    • Mean age at onset: 45-50 years
    • Rare in patients <30 years
  • Gender
    • Female predominance (2:1 ratio)
  • Laterality
    • Left side more commonly affected (60%)
    • Bilateral involvement rare (<1%)

Diagnosis

  • Clinical presentation
    • Involuntary, intermittent tonic-clonic contractions of facial muscles
    • Typically begins in orbicularis oculi muscle
    • Progresses caudally to involve lower face
    • Exacerbated by stress, fatigue, voluntary facial movements
    • Persists during sleep (distinguishes from blepharospasm)
  • Electrophysiology
    • Abnormal muscle response on EMG
    • Lateral spread response on nerve conduction studies
    • Synkinesis between different facial nerve branches
  • Differential diagnosis
    • Secondary hemifacial spasm (tumour, AVM, aneurysm)
    • Facial myokymia
    • Blepharospasm
    • Facial tics
    • Post-Bell's palsy synkinesis

Imaging

  • High-resolution 3D heavily T2-weighted sequences (CISS/FIESTA), ≤1 mm, through the CPA are the mainstay
    • Show a vessel contacting, indenting or displacing CN VII at the root exit zone; perpendicular contact is most significant
  • TOF-MRA identifies the offending vessel and excludes an aneurysm or malformation
  • Contrast is used mainly to exclude an enhancing mass (schwannoma, meningioma)

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  • A patient presenting with right hemifacial spasm has an MRI showing contact between the attached segment of the facial nerve and a superiorly looping PICA.

Treatment

  • Medical therapy (carbamazepine, botulinum toxin); microvascular decompression is definitive for refractory cases

Differential diagnosis (secondary causes of hemifacial spasm at the CN VII root exit zone)

Imaging differential Differentiating feature
Facial schwannoma Enhancing fusiform mass along the nerve rather than a vascular loop
Meningioma Enhancing dural-based CPA mass with a dural tail
Epidermoid cyst Diffusion-restricting insinuating CPA lesion
Vertebrobasilar dolichoectasia / aneurysm Ectatic or aneurysmal vessel contacting the REZ

  1. Jesuthasan et al. Hemifacial spasm: an update on pathophysiology, investigations and management. 2025. Journal of neurology - Open in new tab. ↩