n_facialnpalsy

facial nerve palsy / Bell's palsy

patient information sheets

basic anatomy

  • cortical motor fibres
    • voluntary motor corticobulbar fibres to lower half of the face are only from the contralateral motor cortex
    • voluntary motor corticobulbar fibres to upper half of the face are from the contralateral AND ipsilateral motor cortex!
    • nerve fibers influencing emotional facial expression are thought to arise in the thalamus and globus pallidus
    • extrapyramidal fibres also have a role
    • hence, a motor cortical lesion that produces a lower facial deficit is usually associated with:
      • a motor deficit of the tongue and weakness of the thumb, fingers, or hand on the ipsilateral side
      • preservation of emotional motor responses
    • a lower midbrain lesion (above the level of facial nucleus) may cause:
      • contralateral paresis of the face and muscles of the extremities
      • ipsilateral abducens muscle paresis (due to effects on the abducens nerve)
      • ipsilateral internal strabismus
      • a peripheral type of ipsilateral facial paralysis may also occur if lesion extends far enough laterally to include the emerging facial nerve fibers
  • brainstem anatomy
    • the facial nerve is the 7th cranial nerve and its motor nuclei reside in the pons in the brainstem with its fibres looping around the 6th cranial nerve nucleus before exiting the brainstem and traversing the posterior cranial fossa joining with the intermediate nerve (sensory and parasympathetic fibres) before entering the petrous temporal bone via the internal auditory meatus.
  • bony facial canal course
    • upon exiting the internal auditory meatus, the nerve then runs a tortuous course through the facial canal, which is divided into the labyrinthine, tympanic, and mastoid segments.
    • the sensory nerve bodies are in the labyrinthine section at the geniculate ganglion where the 1st branch, the greater superficial petrosal nerve is given off, these fibres innervate the lacrimal gland.
    • in the temporal part of the facial canal, the nerve gives rise to the stapedius and chorda tympani. The chorda tympani supplies taste fibers to the anterior two thirds of the tongue, and also synapses with the submandibular ganglion. Postsynaptic fibers from the submandibular ganglion supply the sublingual and submandibular glands.
  • extracranial course
    • upon emerging from the stylomastoid foramen, the facial nerve gives rise to the posterior auricular branch and then passes through the parotid gland, which it does not innervate, to form the parotid plexus, which splits into five branches innervating the muscles of facial expression (temporal, zygomatic, buccal, marginal mandibular, cervical)

is it a peripheral facial nerve palsy or a stroke?

    • rapid onset within seconds or minutes
      • in contrast, Bell's palsy usually develops over hours or days
    • sparing of the forehead muscles
      • ask the patient to lift their forehead as if they are surprised - the brow and upper eyelid remain fully functional in stroke although the lower eyelid may be pulled down by the weight of the cheek. This happens because the cheek muscle loses its tone and strength
      • don't forget, botox injections may be causing bilateral forehead muscle paralysis which may confuse the issue.
    • a spontaneous or involuntary smile may be preserved indicating it is not a peripheral nerve palsy
    • paralysis only occurs with emotion, then a dorsolateral pons lesion such as superior cerebellar artery infarction which also causes deafness, Horner's, or reduced sweating
    • other features of stroke - see FLAWS exam in ED Mx of stroke
      • new upper or lower limb weakness or paraesthiae
      • dysphasia - inability to understand what you say or find words when talking (not just slurred speech which may also occur with facial nerve palsy)
      • acute vestibular disturbance (see vertigo - peripheral vs central)
      • new confusion or decreased mental state
  • features which may be present in Bell's palsy which are not usually indicators for CT scanning:
    • tinnitus
    • loss of taste
    • discomfort or subjective numbness to that side of the face
    • mild headache

  • if there are no clinical features of stroke as above, CT brain is NOT usually indicated, especially if they are young adults in whom risks outweigh benefits of CT scanning

if it is a LMN peripheral facial nerve palsy, can you identify a cause?

  • the vast majority are idiopathic but excluding an alternative cause is important as one would not wish to commence prednisolone for herpes zoster Ramsay Hunt Syndrome or immunocompromised states and some may require ENT intervention

    • peripheral CVII palsy + herpetic vesicles in ear canal and on tympanic membrane +/- vertigo/tinnitus
  • other causes:

or is it idiopathic facial nerve palsy? (Bell's palsy)

  • Bell's palsy is acute, idiopathic, unilateral paralysis of the facial nerve.
  • Vascular, inflammatory, and viral causes have been suggested from paired serologic analyses and studies of the cerebral ganglia, suggesting an association between herpes infection and the onset of facial paralysis.
  • Epidemiologic studies show that 11 to 40 persons per 100,000 are affected each year, most commonly between the ages of 30 and 45 years.
  • Although most patients recover well, up to 30% of patients have a poor recovery, with continuing facial disfigurement, psychological difficulties, and facial pain.

management of idiopathic facial nerve palsy

  • no evidence to support use of aciclovir
  • early prednisolone Rx within 72hrs (eg. 25mg bd for 10 days) seems to be of benefit in some
  • tape eyelids and use irrigation drops to prevent corneal ulcers.

references

n_facialnpalsy.txt · Last modified: 2019/03/16 14:02 by wh