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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_4612_Библиотеки_им_академика_М_И_Перельмана
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Audiology Review: Preparing for the Praxis and Comprehensive Examinations
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FIGURE 7–22. Case example: Ménière disease; SHA responses.
Vestibular Schwannoma
Vestibular schwannomae (or acoustic neuromae) are slow-growing, benign neoplasms arising from
the Schwann cells of CN VIII. Nearly all arise from the vestibular nerve branch (Figure 7–23). Unilateral cases are generally sporadic and may be found incidentally. Bilateral cases are associated with
neurofibromatosis type 2 (NF2), a rare genetic disorder that leads to the formation of benign tumors,
commonly along CN VIII.
n
Most cases of vestibular schwannoma present with asymmetrical hearing loss and unilateral
tinnitus. Dizziness and vertigo are not reported as often due to the slow growth of the tumor,
allowing the vestibular system time to compensate for the gradual decline in function.
Patients may also present with facial weakness or numbness, suggesting that CN VII may
also be impaired.
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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FIGURE 7–23. A vestibular schwannoma (or acoustic neuroma) typically
arises from the superior branch of CN VIII, increasing pressure on and
displacement of the surrounding structures over time. Source: Used with
permission of Mayo Foundation for Medical Education and Research, all
rights reserved.
353
Many patients remain under observation to determine if/when intervention is warranted. If
the tumor is allowed to grow too large or within sensitive areas, it could lead to significant
brainstem compression and subsequent complications, including death.
n
In most cases, the tumor itself is not overly problematic in terms of dizziness or balance
performance, and most do not require specific management. Treatments for vestibular
schwannoma, such as surgical removal or radiation therapy (e.g., gamma knife), however, may
lead to abrupt vestibular system asymmetry.
In these cases, the patient may experience acute onset of vertigo and/or hearing loss. Vertigo
symptoms reduce over time with compensation.
Third Window Disorders
Perilymph fistula, superior semicircular canal dehiscence (SSCD), and enlarged vestibular aqueduct
syndrome (EVAS) are considered third window disorders. They act effectively as an additional “window”
into the inner ear.
Perilymph Fistula
Perilymph fistula is a disorder that occurs when perilymph leaks from the labyrinth into the middle ear
space following a tear in the round or oval window. This is most often associated with head trauma,
barotrauma, or straining but can occur idiopathically. There are no universally accepted criteria for
perilymph fistula diagnosis.
n
Symptoms include sudden unilateral hearing loss, tinnitus, aural fullness, and imbalance. Patients
with diagnosed perilymph fistula also describe acute episodes of lightheadedness, imbalance, and
motion intolerance that can be triggered by internal or external pressure changes.
Audiology Review: Preparing for the Praxis and Comprehensive Examinations
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n
Clinically, the fistula test has been used to identify a possible perilymph fistula. A positive
fistula test is the presence of nystagmus when negative pressure is applied to the external
auditory canal, such as with a tympanometer. Unfortunately, the sensitivity of the fistula
test is variable. Most often, a perilymph fistula is identified with high-resolution computed
tomography (CT) and magnetic resonance imaging (MRI) (Sarna et al., 2020).
Superior Semicircular Canal Dehiscence Syndrome (SSCD)
SSCD occurs with deterioration of the bony labyrinth covering the superior (anterior) SCC. The
dehiscence acts as a third window into the labyrinth, leading to altered transmission of sound and
pressure through the inner ear (Figure 7–24).
Patients with SSCD may describe unique symptoms, such as hearing their eyes move or experiencing vertigo in response to loud sounds (e.g., a dog bark). Overall symptoms are variable but
may include:
n
Autophony
n
Dizziness, vertigo, disequilibrium — consider Tullio phenomenon, Hennebert phenomenon,
dizziness triggered by internal/external pressure changes
n
Pulse-synchronized oscillopsia
n
Hyperacusis
n
Aural fullness
n
Pulsatile tinnitus
FIGURE 7–24. Superior semicircular canal dehiscence syndrome
(SSCD) occurs when the bone overlying the superior SSC deteriorates and creates an additional opening into the inner ear.
This can be repaired by plugging or capping the superior SCC.
Source: Used with permission of Mayo Foundation for Medical
Education and Research, all rights reserved.
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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n
Brain fog
n
Fatigue
n
Clinical signs include Tullio-/Hennebert-evoked nystagmus, exceptionally enhanced (or
augmented) VEMPs, and paradoxical (or pseudo) conductive hearing loss with present middle
ear muscle reflexes. Tullio phenomenon is defined as vertigo, dizziness, and eye movement
induced by loud sounds (think Tullio = “too loud”). Hennebert sign is nystagmus evoked by
internal or external pressure changes.
Consider this case of suspected SSCD.
The patient was a 52-year-old female reporting chronic imbalance and dizziness for several
years. She noted that she experienced aural fullness, pulsatile tinnitus, and autophony (hearing
her heartbeat, eye movements) in her right ear. She demonstrated a positive Hennebert sign,
consistent with her noted increased dizziness with barometric pressure changes.
Audiometric testing was abnormal for low-frequency conductive hearing loss at 250 and
500 Hz only. Note the significantly low bone-conduction threshold (<0 dB HL) (Figure 7–25).
Type A tympanograms and present ipsilateral and contralateral middle ear reflexes from 500 to
2000 Hz were documented bilaterally.
Cervical and ocular VEMPs were completed. CVEMPs were within normal limits bilaterally, with no enhancement noted. OVEMPs were significantly abnormal for the right ear, most
apparent with 89.88
oVEMP amplitude is ~5
µV interpeak amplitude noted (Figure 7–26) — remember that average
µV. Her remaining vestibular evaluation was within normal limits.
Management strategies were discussed. She was referred to ENT due to suspicion of third
window disorder in the right ear. She was counseled to expect dizziness when in significant
noise and to consider wearing an earplug in these situations. She also discussed plugging the
superior SCC as a future option with the managing otologist.
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FIGURE 7–25. Case example: SSCD; audiometric presentation.
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FIGURE 7-26. Case example: SSCD; oVEMPs.
Enlarged Vestibular Aqueduct Syndrome (EVAS)
EVAS — sometimes called large vestibular aqueduct syndrome (LVAS) — is a genetic condition associated with progressive hearing loss. EVAS can occur alone or with other conditions such as Pendred
syndrome or brachio-oto-renal (BOR) syndrome. While progressive hearing loss is a known concern
for patients with EVAS, the vestibular system may be involved in up to 70% (Berrettini et al., 2005).
It is likely that vestibular dysfunction also occurs in a progressive manner. Clinical signs of vestibular
dysfunction in patients with EVAS include:
n
Enhanced cVEMP/oVEMP responses (Zhou et al., 2017)
n
Caloric response asymmetry (Jung et al., 2017; Zhou et al., 2017)
n
Caloric response hypofunction (Jung et al., 2017; Zhou et al., 2017)
n
Abnormal vHIT possible (Jung et al., 2017)
Stroke Syndromes
Cardiovascular events are important to consider, especially in cases of sudden symptom onset. Symptom
presentation varies depending on the site of infarct (Table 7–14). For an overall labyrinthine infarction, vestibular and audiological presentation is like labyrinthitis; however, the patient may also report
headache and/or confusion. Patients reporting sudden onset of imbalance may have experienced a cerebellar infarct. Identifying other symptoms may help identify these conditions, which should prompt
urgent medical management.
Cerebellar Degeneration
Cerebellar dizziness may occur with various etiologies and accounts for approximately 10% of those
presenting to dizziness centers for evaluation (Zwergal et al., 2020). Patients generally present with
chronic, progressive signs of cerebellar involvement such as ataxia, abnormal oculomotor performance,
and down-beating nystagmus (Table 7–15).
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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TABLE 7–14. Presentation of Labyrinthine and Cerebellar Infarcts
LABYRINTHINE INFARCT CEREBELLAR INFARCT
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Timing Sudden
Symptoms last hours to days
Vertigo common
Trigger Reduced blood flow to all or part
of the labyrinth
Other symptoms Sudden sensorineural hearing loss
Headache
Disorientation
Diagnosed AICA stroke
TABLE 7–15. Etiologies Associated With Cerebellar Dizziness
TIMING CATEGORY DIAGNOSIS
Degenerative Idiopathic late-onset cerebellar
ataxia
Cerebellar ataxia
Downbeat nystagmus syndrome
CANVAS
Sudden imbalance
Spontaneous nystagmus >24 hours
Vertigo rare
Transient ischemic attack (TIA) in
the cerebellar artery
Lateropulsion
Decreased coordination
Hiccoughs
Ataxia
Genetic/hereditary Spinocerebellar ataxias
Chronic
Acquired Paraneoplastic syndrome
Infection Acute cerebellitis
Recurrent
Cerebellar stoke PICA most common
Acute
Source: Zwergal et al. (2020).
Inflammation Multiple sclerosis
Episodic ataxias
Autoimmune disorders
Toxicities (e.g., alcohol)
Vitamin deficiencies (e.g., B1,
B12, E)
Postinfection cerebellar
syndrome
Chronic cerebellar infection
Episodic ataxias
Vestibular migraine
Sarcoidosis
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Cerebellar Ataxia With Neuropathy and Vestibular Areflexia Syndrome (CANVAS)
CANVAS is a recently described disorder that illustrates the clinical presentation possible with cerebellar degeneration. Patients with CANVAS experience slowly progressive symptoms and many have a
family history positive for similar symptoms. Findings consistent with CANVAS include (Szmulewicz
et al., 2016):
n
Bilateral vestibulopathy
Decreased VOR performance: reduced caloric function, reduced SHA gain, present
saccades/low gain on vHIT
Impaired VVOR testing
Poor fixation suppression
n
Cerebellar involvement
Cerebellar atrophy specifically involving the vermis
Cerebellar dysarthria
Truncal ataxia
Dysphasia
Oculomotor abnormalities: saccadic smooth pursuit, gaze-evoked/direction-changing
nystagmus, dysmetric saccades, rebound nystagmus
n
Somatosensory impairment — neuronopathy
n
There is no significant effect on the cochlea or cochlear branch of CN VIII.
Consider this case of suspected CANVAS.
Patient was a 67-year-old female presenting for >10-year history of imbalance. She
reported neuronopathy in her hands and feet, as well as chronic throat spasms, chronic cough,
and dysarthria. MRI noted mild atrophy of the vermis. The patient reported significant family
history of similar symptoms, including in her brother, mother, maternal grandmother, and
maternal aunt.
Oculomotor testing was significantly abnormal. Saccade testing demonstrated significantly
prolonged latencies and reduced peak velocity. Optokinetic nystagmus was absent. Smooth
pursuit was significantly saccadic (Figure 7–27).
VOR testing was consistent with significant vestibular dysfunction. She demonstrated
bilateral caloric areflexia (TES = 0°/second). VHIT responses demonstrated significantly
reduced gain bilaterally with significant overt and covert saccades (Figure 7–28).
SHA testing demonstrated significantly reduced gain from 0.02 to 0.32 Hz. Phase and
asymmetry could not be calculated due to the low gain. VVOR response (*) at 0.16 Hz
remained reduced, consistent with central bilateral vestibulopathy (Figure 7–29).
The patient demonstrated significant functional impairment. She was unable to complete
SOT Conditions 3 to 6 without falling, suggesting a severe balance impairment and high fall
risk. DVAT was attempted but could not be completed at the maximum logMAR level with
head movement, suggesting severe deficits in the VOR pathway. These results were consistent
with the significant vestibular impairment documented on testing.
The patient returned to her managing neurologist and was subsequently diagnosed with
CANVAS. Unfortunately, CANVAS is a slowly progressive disorder with no noted therapies.
She was encouraged to continue balance therapy to develop strategies for reducing fall risk.
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FIGURE 7–27. Case example: CANVAS; smooth pursuit.
FIGURE 7–28. Case example: CANVAS; vHIT.
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FIGURE 7–29. Case example: CANVAS; SHA responses.
Traumatic Brain Injury
Posttraumatic dizziness and imbalance are common. Patients may demonstrate increased motion sensitivity, imbalance, and dizziness with head movements and when in busy visual environments. Various
underlying conditions may be associated with posttraumatic dizziness:
n
Peripheral etiologies
Direct end-organ injury
BPPV
Labyrinthine concussion
Posttraumatic endolymphatic hydrops
SSCD
Otolith dysfunction
Medication side effects
n
Central etiologies
Concomitant injury
Diffuse axonal injury
Postconcussion migraine
Cervical dizziness
Vestibulo-autonomic reflex impairment
Clinical presentation for acute posttraumatic dizziness should include vestibular and balance testing.
These metrics can be used to direct rehabilitation strategies and monitor recovery (Ellis et al., 2017;
Zhou & Brodsky, 2015).
Vestibular Migraine
Vestibular migraine is one of the most common disorders associated with dizziness. Most associate
migraine with headache, but other sensory integration abnormalities, such as vision distortions, hyper-
CHAPTER 7 Vestibular Assessment and Differential Diagnosis
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sensitivity to sensory stimuli, and paresthesias, are common. Patients with vestibular migraine describe
a range of dizziness and balance concerns, and often report current or childhood history of motion
sensitivity. There is no specific migraine test and laboratory findings vary. Vestibular migraine is diagnosed using International Headache Society classification criteria (IHS, 2018):
n
At least five episodes of vestibular symptoms of moderate or severe intensity, lasting between
5minutes and 72 hours
n
Current or previous history of migraine with or without aura
n
One or more migraine features with at least 50% of vestibular episodes
Headache with at least two of the following characteristics: unilateral location, pulsating
quality, moderate or severe intensity, aggravated by routine physical activity
Photophobia, phonophobia
Visual aura
n
Not better accounted for by another vestibular or headache diagnosis
Consider this case of suspected vestibular migraine.
The patient was a 37-year-old male presenting with 1 month of dizziness symptoms. He
described a sense of “rocking” as if he were “on a boat.” Dizziness symptoms increased in busy
visual environments and with quick head movement. The patient noted longstanding motion
sensitivity and migraine diagnosis at 18 years old. He reported no other otologic concerns.
VNG testing was within normal limits for all subtests. Balance performance was well
within normal limits (SOT composite score = 89). Otolith reflexes were abnormal. CVEMP
responses were present, but not as robust as expected (Figure 7–30), and oVEMP responses
were absent bilaterally (Figure 7–31).
Functional VOR performance was significantly abnormal. The patient demonstrated 0.32
logMAR loss for leftward and 0.48 logMAR loss for rightward head movements. Atypical
functional VOR presentation has been reported in those with vestibular migraine (Baker et
al., 2013a, 2013b) and may prove to be a useful tool in describing the clinical presentation of
this cohort.
FIGURE 7–30. Case example: vestibular migraine; cVEMPs.
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