Facial Nerve

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Facial Nerve
2013-08-11 21:53:32
Facial Nerve

Facial Nerve
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  1. What is carried on the nervus intermedius?
    • Parasympathetic and sensory information
    • Motor root joins NI in the IAC to form the common facial nerve
  2. 5 segments of the facial nerve before stylomastoid foramen
    • Intracranial
    • Meatal: porous acousticus to fundus
    • Labarynthine: fundus to geniculate (narrowest segment, 0.68 mm)
    • Tympanic (horizontal): geniculate to the second genu (above oval window/stapes)
    • Mastoid (vertical): second genu to stylomastoid foramen
  3. What quadrant of the IAC houses the facial nerve. What separates it from the other quadrants?
    • Anterior superior quadrant
    • Falciform crest separates it from cochlear nerve inferiorly
    • Bills bar from the superior vestibular nerve posteriorly
  4. Where is the geniculate ganglion located? What sensations are mediated at this site?
    • At first genu
    • Sensory and taste cells to palate and anterior 2/3 of tongue
  5. Where does the greater (superficial) petrosal nerve branch from and what sensation does it mediate?
    • First branch of the facial nerve comes from the geniculate ganglion
    • Carries preganglionic parasympathetic fibers to the lacrimal gland
  6. What is the most common site of facial nerve dehiscence?
    Tympanic segment (40-50%)
  7. What two nerves branch from the mastoid (vertical) segment of the facial nerve?
    • Nerve to stapedius
    • Chorda tympani
  8. What sensory fibers are transmitted with the chorda?
    • Special sensory taste fibers to anterior 2/3 of tongue
    • Parasympathetic to submandibular and sublingual glands
  9. 3 branches of the extratemporal facial nerve before the pes anserinus?
    • Posterior auricular nerve: to posterior auricular and occipitofrontalis muscle
    • Nerve to style hyoid
    • Nerve to posterior belly of digastric
  10. Describe the 3 nerve fiber components
    • Endoneurium surrounds each axon. Provides endoneural tube for regeneration
    • Perineurium surrounds endoneural tubules. Provides tensile strength, protects from infection, maintains intrafunicular pressure
    • Epineurium is the outer layer. Contains vasa nervorum for nutrition
  11. How are parasympathetics supplied to the lacrimal gland?
    Superior salivatory nucleus (pons) -> nervus intermedius -> GSPN -> through facial hiatus through middle cranial fossa -> joins deep petrosal nerve (carrying sympathetic fibers from cervical plexus) -> through pterygoid canal (becomes vidian nerve) ->through pterygopalatine fossa -> pteryopalatine ganglion -> joins V2 (as the zygomaticoteoral nerve) -> lacrimal gland
  12. The facial nerve receives sensation to which parts of the ear? Where are these cell bodies found?
    • Auricular concha, postauricular skin, wall of the EAC, part of the TM
    • Housed in geniculate ganglion with cell bodies for taste
  13. Describe parasympathetic supply to sublingual and submaxillary gland
    Superior salivatory nucleus -> nervus intermedius -> chorda -> on lingual nerve to submandibular ganglion -> postganglionic fibers to sublingual and submaxillary glands
  14. On what neural pathway is taste transmitted?
    Anterior 2/3 of the tongue, hard and soft palate via lingual nerve -> chorda -> geniculate ganglion -> nervus intermedius -> tractus solitarius -> nucleus solitarius -> bilateral postcentral gyrus.
  15. What is a Sunderland class I nerve injury?
    • Neuropraxia
    • Compression decreases axoplasmic flow
    • Temporary conduction block
    • Complete recovery anticipated
  16. What is a Sunderland class II nerve injury?
    • Axonotmesis
    • Axon transected, endoneurium preserved
    • Wallerian degeneration distal to site of injury
    • Will regenerate (1 mm/day)
    • Complete recovery anticipated
  17. What is a Sunderland class III nerve injury?
    • Neurotmesis
    • Neural tube (axon, myelin, endoneurium transected)
    • Wallerian degeneration occurs
    • High risk of synkinesis
    • Recovery is unpredictable
  18. What is a Sunderland class IV nerve injury?
    Violates perineurium
  19. What is a Sunderland class V nerve injury?
    • Complete transection, violates epineurium.
    • Risk of neuroma
  20. Describe the House-Brackmann scale
    • Grade I: normal
    • Grade II: weakness on close inspection. No synkinesis. Normal symmetry and tone at rest.
    • Grade III: obvious weakness with movement. Synkinesis. Normal symmetry and tone at rest. Complete eye closure with effort.
    • Grade IV: Incomplete eye closure with maximal effort. Normal symmetry and tone at rest.
    • Grade V: barely perceptible motion. Asymmetry at rest.
    • Grade VI: total paralysis
  21. What is Hitselberer's sign?
    Hypesthesia of the sensory division of the facial nerve at posterosuperior concha.
  22. In denervated muscle, when do fibrillations appear?
    1-2 weeks
  23. What is the difference between EMG and electroneurography (ENoG)?
    • ENoG is an evoked EMG
    • Until wallerian degeneration occurs (day 3-5) neither can distinguish axonotmesis from neurotmesis. After day 5, ENoG can make this distinction by failing to stimulate distal to the site of injury.
    • ENoG can compare action potentials amplitudes between normal and affected sides.
  24. What is the nerve excitability test (NET)
    • Determines threshold for muscle twitch. Difference between affected and unaffected side of >3.5 mA is suggestive of degeneration.
    • Rarely used
  25. Most common congenital cause of facial nerve palsy is associated with what other deficit?
    Asymmetric Crying Facies (congenital unilateral lower lip palsy) is assoc with cardiac defects (10%)
  26. What percentage of Bell's palsy recurs?
  27. Prognosis for recovery in bells palsy?
    • 70-85% have full recovery by 6 months
    • 15-30% have incomplete recovery
    • Poorer prognosis assoc with complete paralysis (ENoG >90% weakness)
  28. Prognosis for recovery in Ramsay-Hunt?
    • 30-50% risk of residual weakness (worse that Bells)
    • Worse prognosis if complete paralysis in acute phase
  29. Chronic or recurrent facial edema with facial nerve dysfunction. Symptoms present since childhood. Diagnosis?
    • Melkersson-Rosenthal Syndrome
    • Unknown etiology
    • Path: dilated lymphatics, granulomatous changes, giant cells
  30. Facial nerve injuries medial to which structure typically recover spontaneously?
    Lateral canthus
  31. Incomplete facial palsy after facial nerve injury can be monitored with electrodiagnostic testing at what times?
    3-7 days and 3-4 weeks
  32. At what point after facial nerve paralysis due to injury do muscle atrophy and loss of motor end plates eliminate the options of nerve grafting or anastomoses?
    • 12-18 months
    • Consider musculofascial transpositions, static procedures, gold weight, spring implant
  33. Why are free nerve and muscle grafts for facial paralysis done as a staged procedure? How long between stages?
    • After nerve anastomoses, must wait 6-12 months for nerve regrowth
    • If muscle transferred at time of nerve graft, muscle would atrophy while nerve regenerates.