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Terms in this set (49)
2 types of conduction?
• Ossicular conduction (air conduction) is when sound is transmitted from the tympanic membrane to the ossicles and then to the oval window. This is the more powerful of the two types of sound conduction
• Bone conduction is the conduction of sound to the inner ear through the bones of the skull which results in the vibration of the fluid in the inner ear.
2 types of hearing loss?
• Conductive deafness occurs when ossicular conduction is lost but bone conduction is preserved and is more sensitive in order to compensate.
o Any disease affecting the outer or middle ear will produce a conductive deafness.
• Sensorineural deafness is when both types of conduction are impaired.
o Results from damage to the cochlea or 8th nerve.
o Common feature is loss of hair cells from the organ of Corti. These are not replaced so the deafness is usually permanent, and displays high tone loss on audiometry as the hair cells responding to high frequencies are most susceptible to damage.
Compares ossicular conduction to bone conduction in the same ear. This is to screen for a conductive cause.
• This test involves using a 512 hz tuning fork which is first pressed against the mastoid bone and then held 1 cm from the ear. Then ask the patient which of the two were louder.
• Rinne positive → sound is normally heard better by ossicular conduction
• Rinne negative → disease in the external or middle ear (producing conductive deafness) will reverse the rest result
NOTE avoid false Rinne-negative by properly masking the contralateral ear.
Compares bone conduction between two ears by placing the tuning fork on the forehead in the midline and sound waves are transmitted to both ears equally via the skull. It is more sesntitive than Rinne test.
• If the defective ear hears it louder, it would suggest conductive deafness.
• However, if it is weaker (and sound is heard on the other side), it would indicate sensorineural deafness.
Pure tone audiometry?
o Headphones deliver tones at different frequencies and strengths in a sound-proofed room.
o Pt. indicates when sound appears and disappears.
o Mastoid vibrator → bone conduction threshold.
o Threshold at different frequencies are plotted to give an audiogram
o More sophisticated
o Phonetically balanced words are presented at different sound intensities and the number of correct answers is expressed as a percentage score
o Useful for evaluating hearing aids
(measures function of tympanic membrane)
o Evaluates middle ear function and sometimes sensorineural deafness
o Impedance audiometry → varying pressure in external ear canal, the compliance of the eardrum may be calculated by the degree of sound reflected from a probe tone
o Particularly useful for middle ear effusions and for assessing Euschian tube function.
o Flat tympanogram → mid ear fluid or perforation
o Shifted tympanogram → +/- mid ear pressure
Evoked response audiometry?
o Auditory stimulus → measurement of elicited brain response by surface electrode.
o Used for neonatal screening (if otoacoustic emission testing negative) and handicaps - people to whom standard tests are not applicable as hearing thresholds are objective
o Otoacoustic emissions testing is a useful screening test for neonatal sensorineural loss where the middle ear function is normal
Hearing loss abnormality on PTA?
SNHL: ac=BC (inner ear problem)
CHL: bc<ac (middle ear problem)
Mixed HL: bc is better than ac but bc not within normal limits
Hearing loss abnormality on tympanometry?
Peaked → normal
No peak → glue ear, grommets, perforation
Peaked with negative pressure → Eustachian tube dysfunction
Hearing assessment in children?
• From birth to 6 months → gold standard is by electric response audiometry
• 6 months to 18 months → distraction test (ex. Child will turn to a noise like a rattle); performed by 2 observers and is a basic screening test
• 2 years + → conditioning or cooperation tests are employed using free field noises ex. Placing a peg in a basket after hearing the noise
• Ages 3-4 → this is when u can start using headphones to independently test each ear
Detection before 6 months improves language.
- Otoacoustic emissions
- Audiological brainste responses
NOTE: if they fail new born hearing test, more likely to be a SNHL
Risk factors for hearing loss in children?
• Prematurity and low birth weight
• Intraventricular hemorrhage
• Neonatal jaundice
• Aminoglycoside administration
• Family history
History taking in hearing loss?
osnet and rate of progression, pain or discharge, tinnitus, imbalance, excessive noise exposure, drug history (ototoxic agents)
History taking in hearing loss in children?
general development and milestones, age first word uttered, extend of vocabulary, verbal comprehension, attention span, social background
Congenital causes of conductive hearing loss in children?
1) Anomalies of pinna, external auditory canal, TM or ossicles
2) Congenital cholesteatoma
Congenital causes of sensorineural hearing loss in children?
1) AD conditions
- Waardenburgs: SNHL, heterochromia + telecanthus
2) AR conditions
- Alport's: SNHL + hematuria
- Jewell-Lange-Nielson: SNHL + long QT
4) Ototoxic drugs
Perinatal cause of hearing loss in children?
2) Cerebral palsy
Acquired causes of hearing loss in children?
2) Infection: meningitis, measles, syphilis
3) Head injury, trauma, barotrauma
OME causes and presentation?
• OME is the commonest cause of acquired conductive hearing loss in children
• Peak clinical age group is 2-6 years old, where about 30% of children suffer effusions
• Associated with upper respiratory tract infections, Down's syndrome and cleft palate
• The effusion in the middle ear may be serous, mucoid or thick (glue).
• There is usually Eustachain tube dysfunction, where normal ventilation of the middle ear is disturbed
• A diagnosis of chronic otitis media with effusion is made when fluid is present behind the eardrum for 12 weeks or more
• Children usually present with hearing loss or recurrent otalgia
• Tempanometry produces a flat trace, indicating an immobile drum
Otoscopic appearance → retraction of the eardrum and yellow appearance to it due to the effusion
• There is no effective LT medical treatment for established OME
• Short term improvements with antibiotics are not sustained
• Surgery may be required to restore hearing
• Removal of the adenoids reduces the incidence of recurrent effusions
• Myringotomy → aspiration of fluid and insertion of a grommet, immediately restores hearing
o NOTE: after extrusion, it is common to see tympanosclerosis (white patches) in the eardrum, these do not impair hearing
• Long term ventilation may be necessary to prevent progressive retraction from the low middle ear pressure and subsequent development of chronic supparative otitis media with cholesteatoma
Epidemiology of hearing loss in adults?
70% of people over 70
40% of people over 50
have some form of hearing loss
List the causes of conductive hearing loss in adults
1) External canal obstruction
2) TM perforation
3) Ossicle defects
4) Inadequate eustachian tube ventilation of the middle ear
Adult conductive hearing loss - ear canal pathology
• Wax impaction is the commonest cause of hearing loss in adults
o Blind attempts to remove wax with cotton buds may result in impaction
o Wax may be properly removed by syringing the ear or with a blunt hook
o Preliminary softening can be achieved with sodium bicarcbonate or hydrogen peroxide ear drops
• Keratosis Obturans → rarely, excessive accumulations of desquamated skin and wax in the deepest part of the external meatus can expand and erode the ear canal. An anesthetic may be required for removal.
• The external canal may also be narrowed by bone exostoses predisposing to keratin accumulation
o These exostoses often occur in swimmers and don't require treatment unless they cause hearing deficits or external otitis
• Foreign body
List the sensorineural causes of adult hearing loss?
Defects of cochlea, cochlear nerve or brain.
1) Drugs: aminoglycosides, vancomycin
2) Post-infective: meningitis, measles, mumps, herpes
6) CPA lesion (acoustic neuroma)
7) B12 deficiency
9) Sudden idiopathic hearing loss
10) Noise exposure
11) Perilymph fistula
a disease where new bone growth occurs in the capsule of the inner ear, this may fix the footplate of the stapes and disrupt its normal movement in the oval window
- This characteristically develops in the young adult, F>M=2:1, AD condition
- Bilateral conductive deafness + tinnitus
- HL improved in noisy places: Willis' paracousis
- Worsened by pregnancy, menstruation and menopause
- Otoscopic appearance of the eardrum is normal
- PTA shows dip (Caharts notch) @ 2kHz
- When acoustic reflex testing is conducted, the acoustic reflex thresholds (ART) cannot be determined when attempting to measure on the affected side
- Surgery (stapedectomy with prosthesis) may restore normal hearing but also carries a small risk of total hearing loss
- Use of a hearing aid has no complications but is often refused
• This is a progressive loss of hair cells in the cochlea with age. It is common.
• Roughly 1% of the cells are lost each year, and this affects the high frequency part of the inner ear first
• Clinically noticeable from the age of about 60-65, bilateral slow onset, +/- tinnitus
• Degree of loss is variable, some patients have recruitment (reduced dynamic range of hearing) which reduces effective amplification.
• The threshold for hearing and the uncomfortable level of sound are abnormally similar
• The only treatment is hearing aids
Sudden idiopathic hearing loss?
• This is rare. Cochlear failure occurs in a previously normal ear
• The patient is suddenly aware of a blockage or a rapid deterioration in hearing
• Tinnitus or vertigo may be present
• The etiology is thought to be a virus infection or vascular ischemia
• Treatment is non-specific, currently there is an interest in the role of steroids and antiviral agents
• Acoustic trauma occurs from sudden exposure (impact or blast), or from prolonged exposure (noise of heavy industrial machinery)
• Levels of 90 dB or greater require ear protection with ear defenders
• Exposure leads to initial threshold shifts, perceived as "woolly hearing" with tinnitus, and then goes on to permanent threshold shifts, usually affecting the higher frequencies
• A rupture of the labyrinthine windows (round or oval) may result in leakage of perilymph fluid and a sensorineural type hearing loss
• Mild features of imbalance or even frank vertigo may occur
• Usually preceded by a rise in intracranial pressure or a stapedecotmy operation
• Usually needs surgical treatment to seal the rupture
• The inner ear has many active metabolic processes which are susceptible to drugs
• The cochlea or labyrinth may be affected in isolation of in combination, and this can result in hearing loss and symptoms of imbalance
• Renal toxins are often also toxic to the tear (ex. Aminoglycosides, vancomycin, cytotoxic agents, MTX, furosemide)
• Salicycylates and quinines have reversible toxicity
• These are rare but treatable (benign) tumors of the vestibular element of the 8th cranial nerve (vestibular schwannoma)
• Commonest presentation is slow onset unilateral SNHLwith tinnitus and sometimes vertigo
• Also presents with headache (from high ICP), CN palsies (5,7 and 8) as well as cerebellar signs
• Acts as SOL → CPA syndrome (80% of CPA tumors)
• Associated with NF2
• MRI scanning of cerebellopontine angle is gold standard, also PTA
• DDx → meningioma, cerebellar astrocytoma, mets
• Current treatment options include serial scanning (for small tumors), surgical excision or sterotactic radiosurgery
o Risk of hearing loss with surgery
• Despite having normal thresholds some patients are still unable to hear well, especially in noisy environments
• The etiology is presumed to be a cochlear abnormality
An urgent referral to ENT should be made for patients with sudden-onset sensorineural hearing loss, middle-ear effusion, focal neurology with cholesteatoma or malignant otitis externa.
Assess and fit referral?
• The assess and fit appointment may either be a one-stop appointment where a universal hearing aid is offered, or a two-stop process where the first visit is to create an ear mould and provide information and the next is to fit the aid.
• Existing patients may also be referred to upgrade their hearing aid.
• Depending on local practices, there may be a telephone follow-up.
• Visually impaired/problems with dexterity or communication/older age group - refer for a primary assessment with audiology service (unless you think that they will manage with a simple assess and fit).
• Slight difficulty in one ear and/or unwillingness to have an aid - watchful waiting with counselling and information.
• Tinnitus that lasts for more than five minutes and doesn't simply occur after loud sounds - refer for primary assessment with the audiology services.
• Other problems reported and/or aged under 50 years - refer to the medical consultant-led ENT/audio-vestibular medicine outpatient service.
• Sudden hearing loss - refer to the emergency ENT/audio-vestibular medicine outpatient service.
Note: if unilateral and sensorineural MRI
Other considerations for referral?
• Patients presenting with asymmetric sensorineural hearing loss.
• Patients with recurrent acute otitis media (more than three episodes in six months or four episodes in one year), chronic middle-ear effusions (more than three months in duration), or significant hearing impairment (greater than 30 dB along with an effusion) should be referred to consider the possibility of surgical drainage using myringotomy tubes.
• Tympanic membrane perforations that are >2 mm, where a full view of the problem is not possible, where associated injury is suspected or in patients where the perforation or hearing loss lasts more than two months.
• Suspicion of a tumour either in the external auditory canal or more central tumours such as an acoustic neuroma.
Electronic hearing aids
• Consists of an earpiece, amplifier, and a microphone.
• There is a volume control and many hearing aids are fitted with a T setting that allows the use of electromagnetic induction waves to provide sound and cut out extraneous background noise
• The majority of patients will be fitted with a post-auricular hearing aid which is relatively unobtrusive
• However, severe hearing loss may only be assisted by BW (body worn) aids
• It is possible to incorporate the aid into a spectacle frame if desired
• Miniaturized aids can also be worn in the ear or inserted into the ear canal
• Fitting aids to both ears is preferable in most patients
• It is vital to tell patients that discrimination may not necessarily be improved, but that amplification can provide benefit by better recognition of rhythms and phrases
o This produces the familiar high-pitched whistle, and is particularly seen in patients who require high amplification and in whom the ear mould allows sound to escape into the microphone
o A similar event will occur if the mould is incorrectly inserted, as is frequently seen in elderly patients with hand arthritis
o Alternative non-allergenic material can be employed
o In some patients this is ineffective, and in others continued insertion of a mould produces otitis externa or a discharge from a mastoid cavity
o Such cases may benefit from a bone conducting aids
Bone conducting aids
• These are anchored in the temporal bone or worn as a headband with the microphone abutting firmly onto the mastoid (this is more commonly used in children)
• The external stimulator sets the aid in vibration either across the intervening skin or by a direct percutaneous attachement facility
• Such aids do not suffer the feedback problems of air conduction aids, and have the advantage of greatly reduced background nois
dead battery or blocked tube
patients with conductive hearing losses have better results with aids than those with sensorineural losses, this is due to the fact that many of the latter losses are associated with a phenomenum called recruitment, where loud sounds are heard exceptionally loudly so that the amplification from a hearing aid may be uncomfortable to the patient
ADV of electronic aids
• Digital signal processing allows closer match to patients hearing loss
• Multiple programs (ie patient can change it according to environment)
• Directional microphones
• Feedback suppression
• Noise reduction
• Doorbells may be changed to buzzers or flashing lights
• Telephones can be fitted with volume controls and be converted to be used with the T induction aid in a hearing aid
• This is a device used in patients with a non-functioning cochlea but who have a normal cochlear nerve
• Unaidable bilateral sensorineural deafness is the main criterion for potential implantation
• The nerve can be stimulated by placing an electrode into the cochlea
• A processor convers speech into electrical signals that are transmitted to the electrode
• The cochlear nerve is stimulated, giving clues to frequencies and cadences
• With modern sound processors a severe deafened individual can be trained to communicate with a high degree of success
Lip reading and manual communication
• Most patients with hearing loss requiring aiding will benefit from the development of lipreading skills
• These are essential in any severe or progressive hearing loss
• Special classes are run by most hearing aid departments
• If at all possible, normal speech and language development in children with severe hearing loss should be encouraged by amplification of any residual hearing
• This oral method is preferred to the manual communication skills using sign language, as the latter requires determination and repeated practice to acquire, and can only be used with others who have similar skills.
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