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Chapter 16
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The Facial Nerve andLateral Skull Base
Disorders
StanleyPelosi
Pearls
• Electroneuronography records facial muscle compound action potentials in
response to transcutaneous stimulation and may predict prognosis in patients
with acute facial paralysis.
• Skull base osteomyelitis/necrotizing otitis externa should be suspected in patients
with prolonged otalgia and otorrhea and can be diagnosed with a combination of
biopsy and nuclear imaging.
• Vestibular schwannoma is the most common neoplasm of the cerebellopontine
angle, and symptoms include asymmetric sensorineural hearing loss.
The Facial Nerve
• Facial nerve anatomy
– Segments: intracranial → meatal → fundus (narrowest portion,
0.68mm)→labyrinthine→tympanic→mastoid→extratemporal
– Extratemporal branches: temporal, zygomatic, buccal, marginal mandibular,
cervical
– Brainstem nuclei: facial motor (voluntary facial movement), superior saliva-
tory (parasympathetic efferents for tearing, salivation), nucleus of the solitary
tract (sensory afferents for taste)
– Facial nerve most commonly dehiscent in tympanic segment > geniculate
(middle fossa)>mastoid (adjacent to retrofacial cells)
S. Pelosi (*)
Long Island Jewish Medical Center, Donald and Barbara Zucker School of Medicine at
Hofstra/Northwell, New Hyde Park, NY, USA
© Springer Nature Switzerland AG 2023
F. Y. Lin, Z. M. Patel (eds.), ENT Board Prep,
https://doi.org/10.1007/978-3-031-26048-3_16
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• House–Brackmann classication
– I: Normal function
– II: Slight weakness but symmetric at rest, good forehead motion
– III: Obvious weakness but symmetric at rest, impaired forehead motion, able
to close eye, may have synkinesis, spasm, or contracture
– IV: Symmetric at rest, incomplete eye closure, no forehead motion
– V: Asymmetry at rest, barely perceptible movement
– VI: Asymmetry at rest, no movement
• Sunderland classication of nerve injuries
– Class I: Neuropraxia; compression of axon, no axonal disruption
– Class II: Axonotmesis; disruption of axon; endoneurium, perineurium, and
epineurium still intact
– Class III: Neurotmesis; disruption of endoneurium surrounding axon; peri-
neurium and endoneurium still intact, risk for synkinesis
– Class IV: Neurotmesis; disruption of perineurium and endoneurium, epineu-
rium still intact
– Class V: Neurotmesis; complete nerve disruption (endoneurium, perineurium,
epineurium)
• Facial nerve function tests
– Use to assess integrity of nerve in cases of paralysis (not necessary for paresis)
S. Pelosi
Electroneuronography (evoked electromyography)
• Records facial muscle compound action potentials in response to transcutaneous stimulation (stimulating electrode placed at angle of mandible in the region of stylomastoid foramen)
• Can provide an objective measure of action potential amplitudes from
normal and paralyzed sides
• Not useful until 2–3 days after injury; have to wait for Wallerian degeneration to occur
• Has been used to predict prognosis and determine the criteria for surgical intervention in traumatic/idiopathic causes of paralysis
– Bell’s palsy: Middle fossa decompression suggested if greater
than 90% degeneration compared to normal side within 2 weeks
– Temporal bone fracture
Electromyography (EMG): Determines the level of spontaneous muscle
activity, useful in predicting prognosis for acute or long-standing paralysis
• Fibrillation: Seen in denervated muscle ~2 weeks after injury
• Silence: Muscle atrophy (long-standing denervation)
• Polyphasic potentials → seen with muscle reinnervation ~6 weeks
after injury
• Normal voluntary action potentials indicate at least partial nerve
continuity
16 The Facial Nerve andLateral Skull Base Disorders
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Other tests (infrequently used)
• Nerve excitability test: Compare the lowest current stimulation
threshold required to cause minimal muscle contraction on each side
of the face (difference >3.5 mA considered signicant); stimulation
probe placed at angle of mandible; requires subjective observation
by tester
• Maximum stimulation test: Compare muscle movement on each side of
face in response to suprathreshold current stimulation, stimulation
probe placed in the region of nerve branch to be tested; requires subjective grading by tester
• Causes of unilateral facial nerve weakness/paralysis
– Congenital
Mobius syndrome: Unilateral/bilateral CN VII/VI palsies, club foot, mental retardation
Congenital unilateral lower lip palsy: Hypoplasia of depressor anguli oris
muscle, cardiac defects
– Acute acquired
Infectious
• Bell’s palsy
• Herpes zoster oticus/Ramsay Hunt syndrome
• Lyme disease: 10% develop ipsilateral or bilateral facial weakness/
paralysis, consider ordering Lyme titer in any patient with acute facial
palsy; treat with antibiotic
• HIV
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Traumatic: Temporal bone fracture
– Chronic acquired
Neoplastic: Schwannoma, glomus, parotid tumor
Infectious: Cholesteatoma
Autoimmune/unknown: Melkerson–Rosenthal syndrome manifesting with
recurrent facial edema, recurrent facial weakness (unilateral or bilateral),
recurrent ssured tongue; begins in childhood, treat with steroids
• Bell’s palsy
– Most common cause of unilateral facial weakness/paralysis, idiopathic but
viral etiology suspected
– Risk factors: Diabetes, pregnancy, prior history (10% recur)
– Clinical ndings
Acute unilateral weakness or paralysis developing within 48h
May have viral prodrome, hyperacusis, decreased tearing, numbness/pain
of ear/face/neck, taste changes
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– Work-up for unilateral facial nerve weakness/paralysis
MRI with contrast evaluates full course of facial nerve (brain/internal auditory canal/neck)
Audiogram
Lyme titer
Electroneuronography can be considered for patients who develop complete paralysis, can be used to determine candidacy for surgical intervention
AAO-HNS clinical practice guidelines (CPG): do not routinely perform
imaging or laboratory studies for new-onset Bell’s palsy, electrodiagnostic
testing may be offered in complete facial paralysis
– Treatment
Medical
• High-dose steroids (prednisone 1mg/kg) shown to increase the rate of
recovery, antivirals may have a modest benet
• AAO-HNS CPG strongly recommends oral steroids within 72 h of
onset; antivirals are an option if given along with oral steroids
• Eye care if difculty with eye closure to prevent exposure keratitis
(saline drops, lacrilube ointment, eye bubble)
Surgical
S. Pelosi
• Middle fossa decompression for patients under 65 with >90% neuronal
degeneration within 2 weeks of onset increased chances of good facial
nerve recovery, surgery should ideally be performed within 2 weeks
Poor prognosis with advanced age, complete paralysis
• Herpes zoster oticus/Ramsay Hunt syndrome
– Herpes zoster oticus: Reactivation of herpes zoster virus (normally dormant
in geniculate ganglion) with cutaneous lesions in distribution of nervus intermedius (CN VII)
– Ramsay Hunt syndrome: Herpes zoster oticus + facial paralysis, 18% of adult
facial palsies
– Increased risk of residual facial weakness compared to Bell’s palsy
– Clinical: Vesicular rash in distribution of tympanic membrane, external audi-
tory canal, pinna, anterior two-third of tongue, soft palate; facial paresis/
paralysis with Ramsey Hunt syndrome, may have associated hearing loss
(50% of patients, due to involvement of CN VIII), also tinnitus, vertigo/
disequilibrium
– Diagnosis: Audiogram may show sensorineural hearing loss; MRI to evaluate
the course of facial nerve
– Treatment
High-dose steroids, antivirals, eye care for difculty with eye closure
Consider anticonvulsants (carbamazepine, gabapentin, Lyrica) for postherpetic neuralgia
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• Temporal bone fractures
– Caused by blunt trauma
– Several different classication schemes
Longitudinal versus transverse
• Longitudinal caused by lateral blow, fracture runs anteromedial to otic
capsule; associated with external auditory canal laceration, tympanic
membrane perforation, bloody otorrhea, ossicle disruption, conductive
hearing loss
• Transverse caused by occipital or frontal trauma, causes hemotympanum, sensorineural hearing loss, higher risk of facial nerve injury
• Majority of fractures have mixed components of longitudinal and transverse fractures
Otic capsule sparing versus otic capsule involvement
– Clinical: Hearing loss (conductive, sensorineural, or mixed), facial nerve
weakness/paralysis (most commonly injured at perigeniculate region), cerebrospinal uid leak (otorrhea with longitudinal fracture, rhinorrhea with
transverse), dizziness (labyrinthine concussion or otic capsule fracture)
– Diagnosis: CT of the temporal bones, beta-2 transferrin if suspect cerebrospi-
nal uid leak
– Management
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Hearing loss: Middle ear exploration at a later date for conductive
hearing loss
Facial paralysis: Management analogous to Bell’s palsy
– Medical: High-dose steroids (prednisone 1mg/kg)
– Surgical
Consider decompression for patients with immediate complete paralysis
and >90% neuronal degeneration on electroneuronography within 2 weeks
of onset (similar to Bell’s palsy indications)
If no hearing, perform translabyrinthine exploration; if hearing still present, combined middle fossa/transmastoid exploration
– Penetrating temporal bone trauma causing paralysis (gunshots, knives): High
risk of nerve transection, should proceed with urgent surgical exploration
and repair
– Iatrogenic facial paralysis: Wait for local anesthetic to wear off, then explore
surgically if still present
• Cerebrospinal uid leak
– Temporal bone fractures are the most common cause of otogenic leaks; others
include iatrogenic (mastoid surgery, often associated with encephalocele),
erosive (cholesteatoma), congenital (inner ear malformations), spontaneous
(risk in obese patients with intracranial hypertension)
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– Majority of leaks caused by temporal bone fractures close within 1–2 weeks,
initially bed rest, head of bed elevation, avoid straining, acetazolamide
– Give prophylactic antibiotics if leak present >1 week (increased meningitis
risk); consider surgical closure if leak present beyond this time
– Iatrogenic and spontaneous leaks unlikely to close, require surgical
intervention
– Surgical approaches
Single defect, <1cm: consider transmastoid repair
Large defects, multiple, involving tegmen tympani (difcult to plug from
below due to the presence of ossicles): consider middle fossa or combined
approach
• Causes of bilateral facial nerve weakness/paralysis
– Guillain–Barré syndrome
– Sarcoidosis
– Infectious: Lyme disease (most common infectious cause), HIV, syphilis,
meningitis/encephalitis
– Melkersson–Rosenthal syndrome
– Diabetes mellitus
– Intrapontine/prepontine tumors
• Facial nerve reanimation strategies
S. Pelosi
– <1 year from the time of injury (EMG must still show evidence of muscle
activity)
Primary anastomosis: best outcome, involves microsurgical anastomosis
of epineurium
Cable (interposition) graft
• Greater auricular nerve if need <10 cm, sural nerve if >10 cm (graft
multiple nerve branches)
CN XII-VII nerve transfer
• End-to-end connection of hypoglossal nerve to distal segment of
facial nerve
• Indicated when proximal stump unavailable but distal segment intact
• Sacrices ipsilateral hypoglossal function
• Requires physical therapy to reduce synkinesis
CN XII-VII neurorrhaphy using interpositional graft
• End-to-side anastomosis of hypoglossal nerve to interpositional nerve
graft that connects to distal segment of facial nerve
• Preserves ipsilateral hypoglossal function
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CN XII-V nerve transfer
• End-to-end anastomosis of CN V (nerve to masseter) to CN VII distal segment
• Minimal donor morbidity
Facial nerve crossover graft: Use graft to connect branches of opposite
facial nerve to distal segment of injured nerve
– >1–2 years from the time of injury (employ if EMG shows facial muscle
atrophy)
Static procedures
• Gold weight, lateral canthoplasty, brow lift
• Alloderm or tensor fascia lata graft
Dynamic procedures
• Temporalis or masseter muscle transposition
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The Lateral Skull Base
• Differential diagnosis of external auditory canal lesions
• Cerumen impaction
• Otitis externa (including necrotizing)
• Osteoma/exostosis
• Neoplasm: Cutaneous malignancy, glandular neoplasm
• Canal cholesteatoma
• Keratosis obturans
• Diffuse temporal bone lesions: Eosinophilic granuloma, plasmacytoma
• Cerumen impaction
• Accumulation of cerumen in external ear canal
• Predisposing factors include narrowed external auditory canals (congenital, iatrogenic, or idiopathic stenosis), bony ear canal growths (osteoma, exostosis),
dermatologic disease (eczema), blockage of epithelial migration (hearing aids,
q-tips, excessive ear canal hair), aging (harder cerumen, migrates slower)
• Clinical: Aural fullness, hearing loss (can be up to 10dB conductive hearing
loss), pruritis
• Treatment: For symptomatic patients
– Manual removal
– Cerumenolytics (use for 3–5 days)
Hydrogen peroxide, carbamide peroxide (debrox); available over
the counter
Mineral oil (over the counter), colace: Better for dry/eczematous skin
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– Irrigation: Less favored due to risk of external auditory canal and tympanic
membrane injury, but accepted method
– AAO-HNS CPG recommends against use of ear candling
• Otitis externa
– Acute inammation of external ear canal
– May be precipitated by swimming (“swimmer’s ear”), ear trauma (q-tips,
hearing aids, foreign body in external auditory canal), dermatologic condi-
tions (eczema, psoriasis, contact dermatitis)
– Most commonly caused by pseudomonas, also S. aureus
– Clinical: Otalgia, otorrhea
– Diagnosis: Purulent otorrhea with external auditory canal edema, may have
surrounding cellulitis; consider CT if infection not resolving with conven-
tional treatment and risk factors for necrotizing otitis externa (see below)
are present
– Treatment
Antibiotic drops
• Fluoroquinolones: Ciprodex, oxin cover gram± organisms, twicedaily dosing, no systemic absorption (can use for peds), no ototoxicity risk
• Neomycin/gentamicin; often combined with polymyxin (increases
pseudomonas coverage) and steroid (decrease edema); ototoxic, AAOHNS CPG does not recommend if perforation present; aminoglycosides
may cause skin rash/irritation
• Antifungals: Clotrimazole otic, tolnaftate (tinactin)
S. Pelosi
Other topical treatments
• Acids: Boric acid, acetic acid (vosol, domeboro), alcohol/vinegar (5%
acetic acid) mix
• All work by creating acidic environment to limit bacterial and fungal
growth (vosol often used for fungal infection)
• Can be painful to use, may have ototoxicity potential
• Gentian violet: Dye with antiseptic/antifungal properties
Give oral antibiotics if cellulitis/chondritis are also present
Use temporary wick if cannot visualize tympanic membrane (remove after
2–3 days)
Maintain dry ear precautions
Frequent ear cleanings
• Skull base osteomyelitis/necrotizing otitis externa
– Risk factors: Diabetes, immunosuppression, advanced age
– Clinical ndings
Prolonged otalgia (>1 month), otorrhea with granulation
Cranial nerve involvement: CN VII > CN X > CN XI
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– Diagnosis
Biopsy to exclude external auditory canal malignancy (symptoms overlap)
Imaging
• Technetium-99 scan for diagnosis of osteomyelitis, high sensitivity
• Gallium scan to follow resolution of disease during treatment
• CT temporal bone with/without contrast: Can detect bony erosion, less
sensitivity for early disease
– Treatment
Initiate treatment with oral ciprooxacin
Intravenous ceftazidime if uoroquinolone resistant, progression on
oral cipro
Gallium scan every 4–6 weeks, continue treatment until resolution (average length ~9 weeks)
Hyperbaric oxygen has been used as adjunct
– Worse prognosis with cranial nerve involvement
• Canal cholesteatoma versus keratosis obturans
– Canal cholesteatoma
Invasion of squamous tissue into localized area of canal wall with periostitis and focal bony erosion
Occurs in older patients, presents as dull chronic pain with purulent
otorrhea
Treatment: Biopsy to rule out malignancy; ofce versus operating room
debridement
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– Keratosis obturans
Accumulation of desquamated keratin in the external auditory canal
Keratin is shed from the entire surface of ear canal, can cause circumferential bony widening
Occurs in younger patients, presents as acute severe ear pain, may be
bilateral
Treatment: Biopsy to rule out malignancy, topical steroids, ofce versus
operating room debridement, canalplasty may help
• Osteoma versus exostosis
– Osteoma: Solitary, pedunculated, related to suture lines; histology—lamellar
bone around trabecular cancellous bone
– Exostosis: Multiple, can be bilateral, broad-based, medial external auditory
canal; associated with cold water exposure; histology—dense lamellar bone
parallel to periosteum, poorly developed trabeculations
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• External ear canal neoplasm
– Most common are cutaneous malignancies such as basal cell carcinoma,
squamous cell carcinoma
– See Head and Neck section for diagnosis/management
• Differential diagnosis of middle ear masses
– Cholesteatoma (acquired or congenital)
– Glomus tympanicum/jugulare
– Schwannoma (facial most common)
– Middle ear adenoma: Range from epithelial (adenoma) to neuroendocrine
(carcinoid) differentiation; presents as nonspecic middle ear soft tissue
mass, difcult to differentiate from chronic otitis media until the time
of surgery
– Vascular: Hemangioma (facial), aberrant carotid artery, persistent stapedial
artery, high-riding jugular bulb
• Paraganglioma
– Most common types: Carotid body (65%), glomus tympanicum, glomus jugu-
lare, glomus vagale
– Rule of 10s: 10% familial, 5–10% of patients have multiple lesions (in famil-
ial cases, this may be 25%)
– 1–3% active secretors causing ushing, diarrhea, palpitations, hypertension,
palpitations, headache
– Malignant in 3–5%
– Clinical
S. Pelosi
Hearing loss, dizziness, cranial nerve decits (IV–XII, 10%), otorrhea
Brown’s sign (10–30%): Reddish-blue hue of glomus tympanicum behind
intact eardrum, blanches on pneumatic otoscopy
– Labs: If suspect secreting tumor, can obtain 24-h urine catecholamines (vanil-
lylmandelic acid, metanephrine) or plasma-free metanephrines (most sensi-
tive, but high false positives); order abdominal CT for positive lab tests to rule
out pheochromocytoma
– Histology: Neuroendocrine cells from parasympathetic ganglia; chief cells
arranged in “zellballen”
– Imaging
Temporal bone CT: Glomus tympanicum: enhancing mass in middle ear/
mastoid/hypotympanum overlying cochlear promontory; for glomus jugulare look for destruction of bone overlying jugular bulb and/or carotid
canal, can have “moth-eaten” appearance
MRI: T1 with contrast shows enhancement, “salt and pepper” appearance
from ow voids, also perform neck imaging to look for multicentricity
Angiography: Not routinely employed preop for diagnosis, but may be
used for preoperative embolization
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