Hearing Flashcards
Hair cells detect sound.
There are 2 types. What are they and what is their function?
Where are they found?
How are they arranged?
Outer hair cells receive and detect sound
Inner hair cells Transmit sounds to the brain (mechanical -> electrical)
Hair cells are arranged tonotopically (like a piano) with the highest frequencies, highest pitch at the base and lower frequencies in the deeper parts. (based on low frequency => greater wavelength)
Sound is a longitudinal mechanical energy wave. Explain how sound is heard.
Sound causes vibration of the tympanic membrane => vibration of ossicles => oval window => vibration of hair cells (outer -> inner -> cochlear nerve -> brain)
Pathology in the external ear is likely to cause which type of hearing loss
Conductive hearing loss
Pathology in the middle ear is likely to cause which type of hearing loss
Conductive hearing loss
Pathology in the inner ear is likely to cause which type of hearing loss?
Sensorineural hearing loss
Quick! Relevant information from patient with regards to Hx of hearing loss
Temporal features: Acute vs chronic, Onset sudden vs gradual, progressive vs fluctuating
Associated sx: Vertigo, tinnitus, otalgia, otorrhea
Level of handicap: How does it affect QoL
Once history of hearing loss is complete, what is the workup?
Clinical exam including otoscopy, Rinne, Weber, and whisper test
Then Pure Tone Audiometry +/- Tympanometry
What is Pure Tone Audiometry? Define it as best you can
Pure Tone Audiometry tests all parts of the auditory system by asessing air conduction using headphones and speaker as well as bone conduction via oscillator on mastoid bone to generate an audiogram.
What is the normal range of hearing loss what is negligible on pure tone audiometry
0-20dB
What is the characteristic finding on Pure tone audiometry of a patient with conductive hearing loss?
Air Bone Gap showing that B>A of a difference >5-10dB. 25-40dB in this image
What would be expected on the audiogram of a patient with sensorineural hearing loss
You would expect both BC and AC to be reduced at certain frequencies.
What would be expected on the audiogram of a patient with mixed hearing loss
Air bone gape >5-10db at certain frequencies and both reduced and usually higher frequencies
How does a hearing aid work?
A hearing aid amplifies frequencies that have proven hearing loss as to prevent noise-induced hearing loss from amplifying frequencies with normal hearing
Is audiometry a subjective or objective measurement?
Pure tone audiometry is subjective as it relies on patient input => not typically done in kids <4yo
What would you use to objectively assess a patient’s hearing?
How does it work?
Tympanometry
Probe inserted into ear canal containing speaker, microphone, and pump. Speaker will deliver frequencies into ear while pump changes pressure within the sealed canal. The probe will measure the flexibility of the TM at different pressure. This is used to detect middle ear fluid when the physical exam is unclear
What does tympanometry objectively measure?
Tympanometry measures the compliance or flexibility of the tympanic membrane (eardrum) as air pressure in the ear canal is varied.
You are examining a patient with suspected hearing loss. You conduct tympanometry and obtain a Graph type A as seen in the image. What does this indicate?
Note: the shaded part is the outer ear pressure and line indicates middle ear pressure
Normal compliance
You are examining a patient with suspected hearing loss. You conduct tympanometry and obtain a Graph type As. What does this indicate?
reduced compliance => TympanoSclerosis
You are examining a patient with suspected hearing loss. You conduct tympanometry and obtain a Graph type Ad. What does this indicate?
Increased compliance => Disarticulation of ossicles, Monomeric TM
You are examining a patient with suspected hearing loss. You conduct tympanometry and obtain a Graph type B. What does this indicate? There are 3 variations of this graph. What are they and what does each indicate?
Flat => no compliance.
Remember that they all have the same graph because tympanometry does not measure the volume but the compliance.
Normal volume => Middle ear fluid
Reduced volume => wax, stenosis, exostosis (something reducing volume of ear canal)
Increased volume => Perforated TM
You are examining a patient with suspected hearing loss. You conduct tympanometry and obtain a Graph type C. What does this indicate?
Excessive -ve middle ear pressure with normal or reduced compliance and normal volume. => ET dysfunction (retraction), initiation/resolution of AOM (only ET dysfunction with bulging TM but in the beginning and end it’ll be retracted), sniffling children
List the causes of conductive hearing loss
What is the general approach to managing conductive hearing loss
Categorize!
External Ear: Otitis externa, Atresia (congenital), stenosis (exostosis), trauma (auricular hematoma/cauliflower ear)
Middle Ear: Acute Otitis Media, ET dysfunction (Glue ear, CSOM w/out cholesteatoma) + Congenital (Cleft palate, trisomies), TM perforation, Otosclerosis, neoplastic (tumour in middle ear), Trauma (Battle’s sign, temporal fracture),
Approach: Hearing aid, treat underlying cause
What is Otosclerosis?
How does it present?
How would you treat the patient conservatively and surgically?
Otosclerosis is a rare congenital disease causing fixation of the stapes footplate on the oval window leading to early !progressive! (vs fluctuating in meniere’s) conductive hearing loss.
Typically F>M, 20-30yo presenting with progressive unilateral/bilateral (70%) hearing loss + Vertigo + Tinnitus. May later affect cochlea leading to sensorineural hearing loss
Conductive hearing loss approach
Conservatively: Hearing aid
Surgically: Stapedotomy or BAHA (Bone Anchored Hearing Aid)
What is a Stapedotomy
It is a surgical treatment for otosclerosis which involves replacing the stapes with a prosthetic one. It is a very complex surgery with high risk of dead ear.
What is BAHA or Bone Anchored Hearing Aid?
When is it indicated?
What are the contraindications to this?
What are the 2 main complications of this procedure?
It is a titanium screw inserted in skull to directly stimulate the cochlea via bone conduction of sound
Indications
a) Conductive hearing loss where BC hearing loss <65 (obviously because you’re relying on bone conduction to deliver the sound)
b) Cannot use normal hearing aid as amplification does not bypass problem => Otosclerosis, atresia, meatal stenosis, recurrent mastoiditis/otitis
Contraindications:
Scalp conditions such as seborrheic dermatitis, atopic dermatitis (eczema), Psoriasis
Complications: Infection/granulation tissue, failure to Osseo integrate
List the causes of sensorineural hearing loss
What is the general approach to managing sensorineural hearing loss
Categorize!!!
ENT:
Unilateral (local causes): All need MRI
Acoustic neuroma/Vestibular Schwannoma
Meniere’s Disease (fluctuating)
Late Otosclerosis (progressive)
Trauma (sudden)
Idiopathic (sudden)
Stroke/TIA
Bilateral:
Presbycusis
Noise-induced -occupation
Ototoxicity
Late Otosclerosis (genetic)
Congenital
Infection (viral and bacterial)
Granulomatosis with polyangitis/Wegner’s Granulomatosis
Stroke/TIA
Multiple Sclerosis
Approach: Hearing aids followed by cochlear implants + treat underlying cause
1) State the causes of sudden hearing loss. Which cause is by far the most common?
2) Give the full list of investigations you would like to order if a patient presents with sudden sensorineural hearing loss
3) What is the empiric treatment given to all these patients (not antibiotics lol)
1) (vast vast majority sensorineural)
Idiopathic: By far most common
Infection (viral or bacterial)
Autoimmune: Wegner’s Granulomatosis/Granulomatosis with polyangitis, Polyarteritis nodosum, relapsing polychondritis, SLE
Neurological (MS, Stroke)
Trauma (Temporal bone)
Noise-induced
Iatrogenic
Neoplastic (Vestibular schwannoma)
Autoimmune
2) Investigations:
Bloods: FBC, ESR, Glucose, Cholesterol, TFTs
Serology: , ANCA, Auto-antibodies, Syphilis serology
Imagine: MRI IAM (vestibular schwannoma)
3) Treatment: Prednisolone 1mg/kg, reducing over 10-14 days for all patients with sudden sensorineural hearing loss
Every patient with unilateral sensorineural hearing loss should be referred for what investigation?
MRI IAM
Define Presbycusis
Describe the typical pure tone audiometry of a patient with presbycusis
How would you manage this patient?
Presbycusis is the normal age-related hearing loss due to a reduction is ganglion and hair cells. It typically affects the higher frequencies first (base of cochlea) => Should have ski-slope appearance on pure tone audiometry with bilateral and symmetrical reduction at higher frequencies.
Tx of sensorineural hearing loss (not sudden) => Hearing aid then Cochlear implants
What would be required to cause noise-induced hearing loss?
Describe the typical pure tone audiogram of a patient who has suffered from noise-induced hearing loss (e.g. Construction, airport, power tools, target shooting)
> 8 hours of >85 dB or single sound of >180dB
Audiogram shows symmetrical noise-dip at 4,000Hz with gradual spread to speech Hz (500-2000)
List drugs that are considered to be ototoxic (good to include type of drug)
Gentamicin (+nephrotoxic)
Furosemide (loop diuretic)
Aspirin (salicylate)
Propranolol (non-selective beta blocker)
Cisplatin (chemotherapy drug)
Quinine (malaria)
Non-paeds drugs (Vancomycin, erythromycin)
