DISEASES OF THE INNER EAR 1.1 (AB) Flashcards
What are the two main divisions of ear diseases?
Vestibular diseases (main symptom: dizziness) and auditory diseases (main symptom: hearing loss).
Why can vestibular and auditory symptoms co-exist?
Because the membranous and bony structures of the ear are connected.
What is the primary function of the vestibular system?
To sense motion and position of the head in space and convert sensory stimuli into neural signals carried to the CNS.
What structures sense rotation in the vestibular system?
Three pairs of semicircular canals.
What structures sense linear acceleration and translation?
Otolith organs located in the utricle and saccule.
What reflex stabilizes gaze during head movement?
The vestibulo-ocular reflex (VOR).
How many vestibular afferents project from each labyrinth to the brainstem?
Almost 30,000.
What happens to afferent discharge rates during head movement?
The discharge rate increases with rotation or linear acceleration in one direction and decreases in the other.
What happens if one vestibular side is activated?
The opposite side is deactivated.
At rest, how do afferent fibers fire?
There is a balance or equal firing rate of afferent fibers going to the brain.
What happens to vestibular afferents during movement?
Excitation occurs on the side of movement, while the opposite side is inhibited.
What is the functional pair of the right anterior semicircular canal?
The left posterior semicircular canal.
What happens when the head moves in terms of fluid movement?
The fluid in the semicircular canals moves, causing hair cell deflection.
What occurs when stereocilia move toward the kinocilium?
Excitation.
What occurs when stereocilia move away from the kinocilium?
Inhibition.
Why does movement on one side of the ear affect the other?
The paired arrangement ensures an increase in firing rate on one side and a decrease on the other.
Why do otolith organs not respond exclusively to one direction?
They are curved rather than planar, allowing response to multiple acceleration directions.
What is the difference between roll tilt and interaural translation?
Both cause identical otolith afferent activity, but result in different compensatory eye movements.
How is the inner ear assessed clinically?
Through evaluation of eye movements driven by the VOR and imaging studies.
What are the two phases of VOR-driven eye movement?
Slow phase (keeps eyes on target) and quick phase (resets eye position).
What are the characteristics of nystagmus?
Can be horizontal, vertical, or torsional and consists of both slow and quick phases.
What is the purpose of Frenzel glasses?
To magnify and better observe eye movements in nystagmus.
How does nystagmus help diagnose vestibular dysfunction?
The direction of eye movement can indicate which semicircular canal is affected.
What eye movement is expected if the right semicircular canal is affected?
Horizontal eye movement.
What eye movement is expected if the superior semicircular canal is affected?
Vertical and torsional eye movement.
Which semicircular canal is most commonly affected in BPPV?
The posterior semicircular canal.
What is the expected slow-phase eye movement direction in BPPV?
Toward the axis of the affected canal.
What is the purpose of the Head Impulse Test?
To isolate the site of pathology in vestibular dysfunction.
How is the Head Impulse Test performed?
The examiner turns the patient’s head quickly while the patient maintains gaze forward.
What does a positive Head Impulse Test indicate?
A vestibular deficit on the side toward which the head was turned.
What is the main finding in a patient with left unilateral horizontal canal hypofunction during the Head Impulse Test?
A delayed catch-up saccade when turning the head to the left.
What type of hearing loss is associated with vestibular loss in Ménière’s disease?
Sensorineural hearing loss.
What test helps identify malingering in hearing loss?
Stenger test.
What type of hearing loss suggests superior canal dehiscence?
Conductive hearing loss or a suprathreshold bone line.
What imaging modality is preferred for evaluating temporal bone pathology?
High-resolution temporal bone CT.
What is the recommended CT slice thickness for temporal bone evaluation?
0.5-1 mm.
What imaging modality is used for detailed soft tissue assessment of the inner ear?
Magnetic Resonance Imaging (MRI).
What is the main problem in vestibular diseases?
Dizziness
What type of dizziness is characteristic of vestibular diseases?
Vertigo (rotatory dizziness)
What are the key features of central vertigo?
Severe imbalance, frequent neurologic symptoms, nystagmus changes direction with lateral gaze and does not change with fixation, rare hearing loss, variable nausea, slow recovery
What are the key features of peripheral vertigo?
Mild to moderate imbalance, rare neurologic symptoms, unidirectional nystagmus that decreases with fixation, frequent hearing loss, severe nausea, rapid recovery
What is the prevalence of vertigo in individuals over 40 years old?
0.07400000000000001
What percentage of individuals with an unknown cause of falls have vestibular impairment?
0.8
What percentage of individuals with vestibular impairment complain of vertigo?
0.4
What is BPPV and what are its characteristics?
Benign Paroxysmal Positional Vertigo; brief spells of severe vertigo after specific head movements, more common in women, increases with age, caused by loose otoconia from the utricle
What is the mechanism behind PC-BPPV?
Canalithiasis
What are the characteristics of PC-BPPV nystagmus?
Vertical and torsional nystagmus, fatigability, short duration
What is the classic finding in the Dix-Hallpike maneuver?
Combined upbeating and torsional nystagmus with latency of a few seconds, lasting less than one minute, fatigable
What treatment is used for BPPV?
Epley maneuver (repositioning otoconia using gravity), 80% success rate
What medications can be used to suppress vestibular symptoms?
H1 receptor agonists, antihistamines, dopamine receptor antagonists, anticholinergics, benzodiazepines
What are the key features of vestibular neuritis?
Vertigo lasting days to weeks without hearing loss, follows URTI, affects vestibular nuclei or nerve
What test can help diagnose vestibular neuritis?
Head thrust test (positive in the direction of the affected side), caloric test (warm water = same side, cold water = opposite side)
What imaging is used for vestibular neuritis?
MRI with gadolinium enhancement
What is the treatment for vestibular neuritis?
Supportive and symptomatic treatment for vertigo and vegetative symptoms
What are the key symptoms of Ménière’s disease?
Episodic vertigo (lasting minutes to hours), fluctuating low-frequency sensorineural hearing loss, tinnitus, aural fullness
What is the pathology behind Ménière’s disease?
Endolymphatic hydrops (overaccumulation of endolymph, compressing the perilymphatic space)
What dietary modification is recommended for Ménière’s disease?
Very low salt diet to reduce fluid retention
What are the diagnostic criteria for definite Ménière’s disease?
Two or more episodes of vertigo lasting at least 20 min, audiometrically documented hearing loss at least once, tinnitus or aural fullness, exclusion of other causes
What is superior semicircular canal dehiscence syndrome (SSCD)?
A condition where the superior semicircular canal has a hole in the membranous labyrinth, causing sound to exit and leading to dizziness/vertigo
What are the symptoms of SSCD?
Dizziness/vertigo triggered by straining, heavy lifting, loud sounds (typically low frequency), autophony, sensorineural hearing loss
What physical exam signs are associated with SSCD?
Hennebert’s sign (vertigo/nystagmus induced by pressure), Tullio phenomenon (vertigo/nystagmus caused by loud noise)
What is the treatment for SSCD?
Supportive management or superior canal plugging via middle cranial fossa approach
What imaging is used to diagnose SSCD?
High-resolution CT of the temporal bone
Which aminoglycosides are vestibulotoxic?
Gentamicin and Streptomycin
What is the general effect of aminoglycosides on the ear?
Ototoxicity (nausea and/or hearing loss)
What type of toxicity do gentamicin and streptomycin cause?
Vestibulotoxicity
What type of toxicity do other aminoglycosides cause?
Cochleotoxicity
Which drug causes vertigo and dysequilibrium by damaging vestibular hair cells?
Aminoglycosides, cisplatin
Which drug causes intoxication-related dizziness via CNS depression?
Tranquilizers
Which drug causes dysequilibrium due to cerebellar toxicity?
Antiepileptics
Which drug causes near syncope due to postural hypotension and reduced cerebral blood flow?
Antihypertensives, diuretics
Which drug causes dysequilibrium and oscillopsia by an unknown mechanism?
Amiodarone
Which drug causes intoxication, disequilibrium, and positional vertigo by CNS depression, cerebellar toxicity, and altering cupular and endolymphatic specific gravity?
Alcohol
Which drug causes dysequilibrium due to brainstem and cerebellar toxicity?
Methotrexate
Which drug causes vertigo due to hemorrhage into the inner ear or brain?
Anticoagulants
What are the key symptoms of Cogan syndrome?
Interstitial keratitis, Ménière-like hearing loss, vestibular symptoms
How is Cogan syndrome treated?
Systemic corticosteroids (prednisone 1 mg/kg/day with slow taper), infliximab
What are the key features of otosyphilis?
Dizziness and/or hearing loss, occurs in 30% of congenital syphilis and 80% of symptomatic neurosyphilis cases
How does early otosyphilis present?
Sudden hearing loss
How does late otosyphilis present?
Similar to Ménière’s disease with episodes of vertigo, progressive hearing loss, and tinnitus
What are the diagnostic tests for otosyphilis?
Positive VDRL and rapid plasma reagin (nontreponemal tests)
What is the treatment for otosyphilis?
Penicillin + Steroids + IDS management
What is a perilymph fistula?
An abnormal communication between the labyrinth and surrounding structures
What are the three main causes of perilymph fistula?
- Leakage of perilymph due to trauma, 2. Disruption of the bony labyrinth (e.g., cholesteatoma), 3. Idiopathic bony dehiscence (e.g., superior semicircular canal dehiscence)
What are two clinical signs of perilymph fistula?
Hennebert phenomenon (vertigo/nystagmus induced by pressure), Tullio phenomenon (vertigo/nystagmus caused by loud noise)
What imaging finding suggests a perilymph fistula?
Pneumolabyrinth on CT
What is the treatment for perilymph fistula?
Conservative management or surgical patching with a tissue graft (by an otosurgeon)
What is labyrinthine concussion?
A labyrinth injury due to blunt trauma that does not violate the otic capsule or intralabyrinthine membranes
What is the typical nystagmus pattern in labyrinthine concussion?
Initially beats toward the lesion acutely, then contralateral beating nystagmus
What hearing loss pattern is associated with labyrinthine concussion?
Similar to noise-induced hearing loss, with loss most apparent at 4 kHz
What percentage of blast trauma patients experience dizziness?
0.15
What is the nystagmus pattern in penetrating trauma?
Beats toward the healthy ear due to acute loss on the affected side
What are the symptoms of penetrating trauma?
Nystagmus, vertigo, vegetative symptoms (nausea, vomiting), gradual resolution over days to weeks
What is the cause of enlarged vestibular aqueduct?
Dilation of the endolymphatic duct during embryogenesis
When does hearing loss occur in patients with enlarged vestibular aqueduct?
Early childhood, often progressive with minor head trauma
When do vestibular symptoms appear in enlarged vestibular aqueduct?
Often delayed until adulthood
What is the risk of BPPV in patients with enlarged vestibular aqueduct?
Higher than normal
What is the key CT finding in enlarged vestibular aqueduct?
Vestibular aqueduct > 1.5 mm at the midpoint (same width as horizontal semicircular canal)
What is the management for enlarged vestibular aqueduct?
Symptomatic and supportive management
What are the three main types of central vestibular disorders?
Vestibular migraine, vascular disorders, neoplasms
What dietary restrictions help with vestibular migraine?
Low-tyramine diet (avoid cold cuts, banana, avocado, grapes, dairy products)
What is the essential non-dietary treatment for vestibular migraine?
Quality sleep to allow fluid balance recovery
