Hearing loss Flashcards
What are the 2 functions of the inner ear?
- hearing function - via cochlear system –> transduces sound energy & converts mechanical energy to electrical
- balance - via vestibular system –> transduces motion & pull of gravity & controls balance
(all the info derived from these 2 systems is conveyed to cortex)
What is the anatomical organisation of the inner ear? What is each part responsible for?
- cochlea
- vestibule
- 3 semicircular canals
cochlea –> HEARING
vestibule w/ the 3 semicircular canals –> BALANCE
Where is the perilymph & endolymph located?
perilymph – b/w bony & membranous labyrinth
endolymph – inside membranous “
What is the cochlea?
a spiral bony canal coiled around the MODIULUS (central struc that contains Ganglion of Corti, w/ the cochlear n.)
What is found in the uncoiled cochlea?
- scala vestibuli (superior) w/ perilymph
- scala tympani (inferior) w/ perilymph
- in the middle –> cochlear duct w/ endolymph & Organ of Corti –> which is connected to the cochlear n.
Which 3 cell types make up the Organ of Corti?
- Tectorial membrane superiorly
- Basilar membrane inferiorly
- Ciliated cells (can be outer, inner or middle)
The scala tympani & vestibuli are connected in the _______, which is the apex
HELICOTREMA
Describe the auditory pathway
- activation of Organ of Corti
- activation or cochlear nerve
- cochlear n = one of branches of CN VIII
- info arrives at superior olivary nucleus
- info goes to inferior colliculus & contralateral auditory cortex
Where in the cochlea are high vs low frequency sounds perceived?
high freq –> basal portion of cochlea –> basal turn activation
low freq –> upper portion –> activates middle & apical turn
Describe the steps involved in hearing.
- sound waves collected & transmitted to tympanic membrane
- TM vibration causes middle ear ossicles to move
- movement of stapes on oval window causes movement of perilymph –> transmitted to endolymph –> to Organ of Corti
- perilymph wave induces vertical movement of basilar membr –> translated into shearing force that bends the stereo cilia of hair cells
- stereocilia bending is converted to electrical impulses –> sent to brain (& eventually auditory cortex) via cochlear n
Which sound frequencies are humans most sensitive to?
500 & 4000Hz
sounds greater than 85dB –> damage hearing apparatus/cochlea
What are the 4 main tests of hearing function?
- Pure tone audiometry - pt in room, we send sounds w/ diff frequencies & intensities
- Speech audiometry - to measure ability of pt to perceive speech signals
- Tympanometry - to study pressure in middle ear cavity
- Stapedius reflex - involuntary bilateral stapedial muscles contraction that occurs in response to high-intensity sounds
What are the main features of pure tone audiometry?
- pt in room, we send sounds w/ diff frequencies & intensities
2 diff simulations
- w/ earphones – test air conduction of external ear, middle ear & cochlea
- w/ vibrator – directly transmitted to inner ear, to test bone conduction
sensorineural hearing loss = concomitant & equal deterioration of both air & bone conduction – tested w/ earphones & vibrator (respectively)
(INNER EAR pathology)
mixed hearing loss = concomitant, summitry deterioration of air & “ “ :
- bone conduction: ≥ 25 dB in at least 1 frequency
- air: bone conduction gap ≥ 15 dB
(MIDDLE/EXTERNAL EAR pathology)
What does pure tone audiometry allow for?
- quantitatively evaluate the absolute threshold of hearing (no qualitative)
- differentiate between conductive and sensorineural hearing loss (Type)
- laterality
- subjective examination
What are the main features of speech audiometry?
- to measure ability of pt to perceive speech signals
- Speech materials (pre-recorded or read by examiner) are presented.
- The patient repeats the
speech materials to determine how well it was perceived.
QUALITATIVE test
What are the main features of tympanometry?
- to study pressure in middle ear cavity
Positive and negative pressures are applied at the level of external auditory canal and changes in
the acoustic impedance are registered.
What are some examples of results of a tympanometry?
Otitis media w/ secretions –> no response.
Perforation of TM –> no response.
Describe Type Ad & As tympanograms
Type Ad tympanogram: more flexible tympano- ossicular system (ossicular chain disarticulation)
Type As tympanogram: stiffened tympano- ossicular system (othosclerosis)
Describe the stapedius reflex and how it its tested. Describe the different findings in the 3 types of hearing loss.
= involuntary bilateral stapedial muscles contraction that occurs in response to high-intensity sounds
- If reflex present –> normal situation OR a sensorineural hearing loss
- If reflex absent –> conductive hearing loss.
> Otitis media w/ effusion –> perform otoscopy, and in the tympanogram, no response
Problem is in the middle ear, so –> conductive hearing loss.
> TM perforation –> no tympanogram, but problem is seen w/ pre tone audiometry.
> Tympanosclerosis –> absence of acoustic reflex –> means conductive hearing
How can we study the middle & inner ear?
AUDITORY BRAINSTEM RESPONSE
= a neurologic test of auditory brainstem function in response to auditory stimuli.
- Objective evaluation of afferent auditory path.
- We send a stimulus –> study the diff responses at diff levels of the auditory pathway.
(focus on diff latency among the 5 peaks to localise the problem)
- If there’s an incr in latency b/w cochlea & the pons –> suspect a tumour at this level –> e.g ACOUSTIC NEUROMA
Match the following:
A - External auditory Canal & middle ear
B - Inner ear
C - Middle & inner ear
- Sensorineural hearing loss
- Conductive hearing loss
- Mixed hearing loss
A - External auditory Canal & middle ear –> Conductive hearing loss (2)
B - Inner ear –> Sensorineural hearing loss (1)
C - Middle & inner ear –> Mixed hearing loss (3)
What is otosclerosis?
- dx of small bones of middle ear and otic capsule (bony labyrinth) of inner ear
- results in abnormal bone remodeling w/ reabsorption of bone, otospongiosis
- then replacement w/ hypercellular bone, sclerotic lesion, & blockage of the normal movements of ossicles.
How does otosclerosis manifest?
progressive conductive/mixed hearing loss and tinnitus.
What are the causes of otosclerosis?
- Familiar predisposition
- Endocrine factors
- Autoimmune disorders
Describe the ACTIVE phase of otosclerosis.
- AKA otospongiosis
- highly vascular lesions reabsorb bone surround inner ear, in a
patch pattern. - active lesions mature into calcified otosclerotic plaques –> responsible for stapes fixation.
Initially –> conductive hearing loss
Dx progresses –> mixed “ “
Describe the diagnostic steps in otosclerosis
At otoscopy the tympanic membrane is normal
- In audiometry: conductive or mixed hearing loss, worse in low frequencies sounds
- Type A tympanogram
- Absence of stapedial reflex.
Describe the treatment of otosclerosis.
- Stapedotomy (1% of risk of complete hearing loss)
1. To elevate the tympanic membrane
2. To test the ossicular chain for motion and to remove the stapes
3. To open the stapes footplace and to place a vein graft covering the footplace
4. To place the prothesis between the vein graft and the incus - Acoustic device
What is presbycusis?
- Physiologic age-related hearing loss.
- Speech discrimination is impaired in settings of high
background noise.
What is the etiopathology of presbycusis?
- Sensorineural component: hair cell loss
- Central component: loss of neurons in CNS, (related primarily to arteriosclerosis).
- Result of CNS damage = reduction in acuity & speech perception abilities –> sometimes called phonemic regression.
- In some cases it is this problem rather than a loss of hearing sensitivity that is the patient’s primary complaint.
- More frequently –> bilateral and symmetric sensorineural hearing loss, worsens on high frequencies.
What is the treatment of presbycusis?
Hearing aids (earlier the better!!)
If discovered later –> higher risk of Alzheimer’s
What is sensorineural hearing loss?
sensorineural hearing loss = concomitant & equal deterioration of both air & bone conduction – tested w/ earphones & vibrator (respectively, using pure tone audiometry)
INNER EAR pathology
What is mixed hearing loss?
= concomitant, summitry deterioration of air & “ “ :
- bone conduction: ≥ 25 dB in at least 1 frequency
- air: bone conduction gap ≥ 15 dB
(measured using pure tone audiometry)
MIDDLE/EXTERNAL EAR pathology.
What is sudden hearing loss? Causes?
= an idiopathic sensorineural hearing loss that occurs suddenly
- usually unilateral
- requires IMMEDIATE medical referral
Causes
- vascular
- autoimmune dx
- viral infections
- 1st manifestation of cerebropontine angle (neurinoma, meningioma, hemangioma, …)
Treatment of sudden hearing loss.
- steroids
- antivirals
- neurotrophic agents
- anticoagulants
- hyperbaric oxygen therapy
32-79% –> spontaneous resolution of symptoms
Diagnostic steps for sudden hearing loss.
- otoscopy –> TM is normal
- audiometry –> unilateral sensorineural hearing loss
- MRI –> to rule out malformation
- hematological evaluation –> to rule out any thrombotic profiles
- follow-up
What is noise-induced hearing loss? What are the 2 main causes?
induced by loud sounds
- ACOUSTIC TRAUMA
- injury from brief exposure to v intense sounds (gun shots, artillery fire, explosions)
- can be severe & permanent, but recovery is common
- mono or bilateral - LONG-TERM NOISE EXPOSURE (more common)
- long term exposure to high levels of noise
- occupational settings (heavy manufacturing, agriculture)
- bilateral
What does the severity of noise-induced hearing loss depend on?
intensity of the sound and the length of exposure.
e.g. high intensities + long exposure = bad prognosis (and viceversa)
Treatment of noise-induced hearing loss.
none, just prevention
What is ototoxicity?
= sensorineural hearing loss & tinnitus caused by certain drugs
mild & temporary to severe & permanent
Which drugs may cause ototoxicity?
- loop diuretics
- antibiotics
- NSAIDs
- PDE5 inhibitors
- Platinum agents
- Others (eg quinine)
What is a 8th CN neuroma?
slow growing benign tumor that develops at pontocerebellar angle or within internal
acoustic meatus. It originates from the Schwann cells of the VIII CN.
In most of the cases, it is monolateral (bilateral in Neurofibromatosis type 2).
It presents as unilateral hearing loss, tinnitus, instability.
What are the diagnostic steps for 8th CN neuroma?
- Otoscopy –> TM is normal
- Audiometry –> unilateral sensorineural hearing loss & altered speech discrimination
- MRI w/ Gadolinium (CT is imp for the bone)
What is the treatment of 8th CN neuroma?
- conservative treatment : follow up w. MRI every 6-12months
- surgery
- radiosurgery to stop tumour growth & preserve 7th & 8th CN function
What is type 2 neurofibromatosis?
- genetic dx w/ NF2 gene mutation
- autosomal dominant
- manifests at earlier age compared to sporadic & w. bilateral tumour
What are the different types of hearing aids? Do patients benefit from them?
- non implantable
- smaller & smaller (?)
- high performance
- invisible
only 1/5 can benefit
What is a cochlear implant & when is it used?
= surgically implanted device that electrically stimulates auditory nerve fibres in inner ear
- used for ppl that don’t benefit from hearing aids
How do cochlear implants work?
external mic picks up sounds –> sends them to a processor which converts them into digital info –> sent down an electrode to cochlea
–> nerves pick up signal & are stimulated
What does the severity of noise-induced hearing loss depend on?
intensity of the sound and the length of exposure.
e.g. high intensities + long exposure = bad prognosis (and viceversa)
