Bell’s Palsy


KEY FACTS

Terminology

  • Bell's palsy (BP): Herpetic peripheral facial nerve paralysis secondary to herpes simplex virus

Imaging

  • T1WI C+ fat-saturated MR: Fundal “tuft” and labyrinthine segment CN7 show intense asymmetric enhancement

    • Entire intratemporal CN7 may enhance

  • Imaging note: Classic rapid-onset BP requires no imaging in initial stages

  • If atypical Bell's palsy , search with imaging for underlying lesion

Top Differential Diagnoses

  • Normal enhancement of intratemporal CN7

  • Ramsay Hunt syndrome

  • Lyme disease

  • Facial nerve schwannoma

  • Facial nerve venous malformation (hemangioma)

  • Perineural tumor from parotid

Pathology

  • Etiology-pathogenesis (current hypothesis)

    • Latent herpes simplex infection of geniculate ganglion with reactivation and spread of inflammatory process along proximal and distal intratemporal facial nerve fibers

Clinical Issues

  • Classic clinical presentation

    • Acute-onset peripheral CN7 paralysis (36-hour onset)

  • Medical therapy for BP

    • Tapering course of prednisone; begin within 3 days of symptoms for best result

    • Antiviral agents no longer used

  • Surgical therapy for BP is controversial

    • Profound denervation (> 95%) treated with facial nerve decompression from internal auditory canal fundus to stylomastoid foramen

Axial T1WI C+ FS MR shows classic findings of Bell's palsy with an internal auditory canal fundal “tuft” of enhancement
. The labyrinthine
and tympanic
facial nerve segments also enhance.

Slightly lower axial T1WI C+ FS MR in the same patient again shows the internal auditory canal fundal “tuft” sign
and tympanic segment of the facial nerve enhancement
. Remember that the geniculate ganglion and posterior genu/upper mastoid segment of the facial nerve may normally enhance.

Axial T1WI C+ FS MR in the same patient through the stylomastoid foramen demonstrates an enhancing, slightly enlarged facial nerve
. Swelling of the facial nerve is possible outside the bony facial nerve canal within the temporal bone.

Coronal T1WI C+ FS MR in the same patient reveals avid enhancement in the mastoid
, stylomastoid
, and extracranial facial nerve
in this patient with typical Bell's palsy.

TERMINOLOGY

Abbreviations

  • Bell's palsy (BP)

Synonyms

  • Herpetic facial paralysis

Definitions

  • BP (original definition): Idiopathic acute onset of lower motor neuron facial paralysis

  • BP (modern definition): Herpetic facial paralysis secondary to herpes simplex virus

Other Facts

  • Named after Sir Charles Bell (1774-1842), who 1st described BP syndrome

IMAGING

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