Chapter 42 - Facial nerve Flashcards
Functions of CN VII other than motor
PNS to lacrimal, submandibular, sublingual glands, minor salivary/mucosal glands nose and palate
Taste to tongue ant 2/3, palate, tonsillar fossa
sensation from EAC, concha
sensation nasal mucosa, palate, pharynx
SNS to middle meningeal artery
When facial nerve paralysis is likely a neoplasm not Bell’s palsy
slow, progressive onset No improvement in 3 mo facial twitching recurrent episodes other CN involvement, hearing loss palpable mass in parotid or visible in middle ear Adult, unilateral middle ear effusion skin lesions suggesting skin cancer prolonged ear pain
How to treat Bell’s palsy
PO steroids within 72 hr onset
May use antivirals in combination with steroids
Eye care
Do you need imaging for Bell’s Palsy?
Not if PE/Hx consistent with it
What besides CN VII can close the upper eyelid?
Passive closure occurs by relaxation of levator palpebrae (CN III)
Where is VII most prone to entrapment with swelling?
labyrinthine segment - narrowest portion of fallopian canal
Geniculate ganglion, nerve exiting from here
junction of lab and tymp portions of VII
Special sensory cells – taste
Greater superficial petrosal nerve (first br of CN VII) with PNS to lacrimal gland branches off at anterior margin of this ganglion
Single most important factor in chances that CII will regenerate
If nerve slowly lost function over days or if it lost it immediately at time of trauma
Muscles innervated by VII
facial expression, platysma, stapedius, stylohyoid, digastric posterior belly
Anatomic segments of fallopian canal with length
Labyrinthine: IAC to gen ganglion. 3-5mm
Tympanic: GG to pyramidal process. 8-11mm. Begins at second genu (1st genu intrapontine). Bony dehiscence here.
Mastoid: pyramidal process to SMF, 10-14mm
Most common site of iatrogenic injury of CN VII during ear surgery
Tympanic segment
3 main segments of facial nerve, and their length
Intracranial (pons, CPA, IAC) 23-34mm
Intratemporal (fallopian canal) 20-30mm
Extratemporal (from SMF) 15-20mm
IAC itself is 8-10mm long
Nervus intermedius
division carrying non-motor segments
fuses with CN VII in IAC
chorda is terminal extension
Chorda tympani
PNS to submandibular, sublingual, and taste ant 2/3 tongue
Exits tympanic cavity via petrotympanic fissure
Joins lingual branch of trigeminal nerve
Muscles innervated by temporal br
frontalis, corrugator supercilii, procedrus, upper orb
Zygomatic innervates:
lower orb oculi
Buccal innervates:
zygomaticus major and minor, levator anguli oris, buccinator, upper orb oris
Marginal Mand innervates:
lower orb oris, depressor anguli oris, depressor labii inferiorlis, mentalis
Cervical innervates:
platysma
Facial nerve landmarks
Tragal pointer (triangular extension of tragus), 1cm inferior/deep
Follow posterior belly to styloid…SMF is deep, SMF 25mm deep to skin surface (in children nerve much closer to skin as mastoid underdeveloped)
6-8mm deep to end of Tympanomastoid fissure
Follow peripheral branch back
Neuropraxia
lesion stops axplasm flow.
Swelling, drug blockade
Nerve viable, returns to NL when block corrected
Electrophysiologic testing is NL
EMG doesn’t show voluntary motor action because potential don’t cross blockade
Axonotmesis
Wallerian degeneration distal to lesion
Oreservation of motor axon endoneural sheaths
Mild crush/stretch
Nerve shows rapid and complete degen, loss of voluntary motor units
Regeneration to motor end plate will occur if endoneural tubules intact
Neurotmesis
Wallerian degeneration plus endoneural tubule loss
Complete nerve degen
Regeneration dependent on endoneurium integrity, perineurium and epineurium integrity, extent of ischemia/scarring
Synkinesis
Wallerian degen –> axon regeneration –> cross wiring in which voluntary movement of one muscle induces involuntary movement of another
Facial trunk repairs usually have this
HB II
Mild dysfunction Slight weakness close inspection, normal symmetry/tone Slight asymmetry mouth Complete closure eye minimal effort Moderate to good forehead
HB III
Obvious, not disfiguring asymmetry Normal symmetry/tone Mouth: slight weak maximum effort Eye: complete closure with effort Forehead: slight to moderate
HB IV
Moderately Severe. Obvious weakness, possible dysfunction
Mouth: asymmetric maximum effort
Eye: incomplete closure
Forehead: none
HB V
Severe. Minimally perceptible motion. Asymmetry at rest
Mouth: slight
Eye: incomplete closure
Forehead: none
HB VI
No movement
Bell’s Palsy: etiology, diagnosis
Thought to be viral neuropathy from HSV
Paralysis/paresis all facial mm one side
Sudden onset
No signs of CNS disease, ear disease, parotid mass (this is a diagnosis of exclusion)
Presentation of Bells
Follows viral prodrome (3-5d) and peak in sx at 48 hr
Wide palpebral fissure, taste, chewing difficulty, hyperesthesia trigeminal, facial pain, hyperacusis
Percentage of Bells’ with FHx
14%
Percentage of Bell’s who get recurrent facial paralysis
12%, ipsi or contralat
Why we think HSV is the culprit
HSV present in geniculate ganglion of affected individuals (rare in NL pop)
Thought that it reactivated –> swell –> Bell’s
How many acute facial palsies are due to Bell’s?
70%
Causes of facial paralysis: Congenital
Mobius syndrome, congenital unilateral lower lip paralysis, Melkersson-Rosenthal syndrome, dystrophic myotonia
Causes of facial paralysis: Traumatic
T bone fx, intrauterine compression, birth trauma/forceps delivery, facial contusions or lacerations, penetrating wounds to face or ear, iatrogenic injury, embolization for epistaxis, mandibular block anesthesia
Causes of facial paralysis: Infection
Bell’s, herpes zoster oticus, OME, acute mastoiditis, MOE, TB, Lyme, HIV, mono, flu, encephalitis, malaria, syphilis, botulism
Causes of facial paralysis: Idiopathic
Recurrent facial palsy
Causes of facial paralysis: Neoplasia
cholesteatoma, carcinoma, acoustic neuroma, meningioma, facial neuroma, glomus jugulare/tympanicum, leukemia, hemangioblastoma, osteopetrosis, histiocytosis, rhabdomyosarcoma
Causes of facial paralysis: Metabolic/systemic
DM, hyperthyroid, pregnant, autoimmune disorders, sarcoid, HTN
Causes of facial paralysis: Neurologic
Guillan-Barre, MS, Millard-Gubler syndrome
Central vs peripheral facial paralysis
Central (supranuclear) will spare the upper face on the side of the paralysis
Other signs of central: no emotional facial movement, decreased lacrimation, taste, salivation, tongue/hand dysfunction
When to get MRI vs CT for facial paralysis
MRI w gad: inflammatory, neoplastic, non-traumatic
CT: traumatic paralysis, T-bone etiology (cholesteatoma)
Schirmer’s test
Assess greater superficial petrosal innervation of lacrimal gland (PNS)
Filter paper strips in conj fornix, compare length of paper moistened over 5 minute period
Abnormal: <15mm lacrimation or 25% less than other eye
Nerve Excitability Test: accurate at first?
Electrical impulse - muscle response to look for difference between sides. Not accurate in first 72 hours after onset since takes 3d for Wallerian degeneration to occur
Maximal Stimulation Test
maximal rather than minimal stimulation
Becomes abnormal before the NET, but lack of objectivity, as measured by subjective facial muscle movement
Electroneuronography (ENoG)
amplitudes of muscle summation potentials when supramaximal level of current applied
number of intact motor neurons determines result
Summation potential of 5-10% = 90% degenerated
Predicts who may benefit from decompression
Only accurate after 72 hours, but within 2wk to predict who will benefit from compression
Electromyography
Eliminates False + results from other tests
Determines activity of muscle rather than nerve
Detects reinnervation potentials 6-12 wk before return of facial muscle function clinically evidenc
Cannot assess degeneration degree or recovery prognosis
Audiometry for facial paralysis
Should be performed
CHL consistent with middle ear cause of paralysis
SNHL consistent with neoplasm ie acoustic neuroma, meningioma, facial nerve neuroma, affecting nerve at CPA or IAC
Most important complication of CN VII paralysis
Exposure keratitis
Can lead to vision loss
Due to paralysis with inability to close eye completely, diminished tearing, loss of corneal sensitivity if coexistent CN V dysfunction
Red, itch, foreign body sensation, visual blurring
How to avoid exposure keratitis
artificial tears 4-5x/d
ophthalmic lubricant before sleep, tape eyelid shut
Protect eye from wind, foreign body, drying (use glasses or moisture chamber)
Gold weight in eyelid if complete paralysis
Crocodile tears
Fibers normally innervating salivary glands regenrate to innervate lacrimal gland
Gustatory tearing
Approach to decompress CN VII at labyrinthine segment
middle fossa craniotomy
When to consider surgery for VII paralysis
ENoG shows <10% # of motor fibers, tested prior to day 14
Surgeries for different etiologies: trauma, acute OM, chronic OM, iatrogenic, idiopathic
Trauma/iatrogenic: decomp, anastamosis
Acute OM: Myringotomy
Chronic OM: Decomp, mastoidectomy
idiopathic: Decomp
Can facial nerve be repaired if transected?
Yes, if >50% is transected, it should be repaired
Repair perineurium, exact end to end approximation
8-0 suture monofilament without tension
may graft with great auric or sural nerve
May jump graft from XII if proximal nerve absent
May cross graft from contralateral nerve
How many T bone fxs are longitudinal? How many of these will involve facial nerve injury?
80-90% are longitudinal (parallel to petrous bone)
20% of these will have CN VII injury
How many T bone fxs are transverse? How many of these have VII injury?
15% transverse
50% of these will injure VII
With non-penetrating trauma, do you decompress or wait?
If paralysis is immediately following trauma, then likely laceration or impingement, so you may want to decompress
If paralysis develops in delayed fashion, medical management with steroids and electrophysiologic studies
Two most common facial nerve tumors
facial neuroma (schwannoma) geniculate ganglion hemangioma (plexus surrounding ganglion)
Herpes Zoster Oticus and Ramsay Hunt
intense ear pain, vesicles on EAC and concha
Reactivation of dormant herpes zoster in afferent sensory neurons of facial nerve
May progress to involve efferent motor axons of facial nerve –> facial palsy. This is called Ramsay Hunt
May have hearing loss/vertigo
Treatment of HZO
steroids, acyclovir, pain meds, eye care
