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What is carried on the nervus intermedius?
- Parasympathetic and sensory information
- Motor root joins NI in the IAC to form the common facial nerve
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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
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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
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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
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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
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What is the most common site of facial nerve dehiscence?
Tympanic segment (40-50%)
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What two nerves branch from the mastoid (vertical) segment of the facial nerve?
- Nerve to stapedius
- Chorda tympani
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What sensory fibers are transmitted with the chorda?
- Special sensory taste fibers to anterior 2/3 of tongue
- Parasympathetic to submandibular and sublingual glands
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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
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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
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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
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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
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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
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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.
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What is a Sunderland class I nerve injury?
- Neuropraxia
- Compression decreases axoplasmic flow
- Temporary conduction block
- Complete recovery anticipated
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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
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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
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What is a Sunderland class IV nerve injury?
Violates perineurium
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What is a Sunderland class V nerve injury?
- Complete transection, violates epineurium.
- Risk of neuroma
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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
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What is Hitselberer's sign?
Hypesthesia of the sensory division of the facial nerve at posterosuperior concha.
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In denervated muscle, when do fibrillations appear?
1-2 weeks
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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.
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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
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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%)
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What percentage of Bell's palsy recurs?
7-12%
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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)
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Prognosis for recovery in Ramsay-Hunt?
- 30-50% risk of residual weakness (worse that Bells)
- Worse prognosis if complete paralysis in acute phase
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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
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Facial nerve injuries medial to which structure typically recover spontaneously?
Lateral canthus
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Incomplete facial palsy after facial nerve injury can be monitored with electrodiagnostic testing at what times?
3-7 days and 3-4 weeks
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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
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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.
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