Deafness in Adults Flashcards
conductive deafness
There is impaired sound transmission via the external canal and middle ear ossicles to the front of the stapes through a variety of causes.
causes of conductive deafness
- fluid eg blood, effusion, CSF
- external canal obstruction
- TM perforation
- inadequate Eustachian tube ventilation of middle ear
- problems with ossicular chain eg trumatic, erosion, otosclerosis
imaging of conductive deafness
CT
otosclerosis
can cause conductive deafness - abnormal growth on bone which can cause the stapes to fixate to the oval window
which ossicular chain bone is the most common site of injury
incus
sensorineural deafness
Results from defects central to oval window in cochlea, cochlear nerve or, rarely, more central pathways
which type of deafness is permanent
sensorineural
causes of sensorineural deafness
- drugs
- post infective
- cochlear vascular disease
- ménière’s
- trauma
- presbycusis
imaging of sensorineural deafness
MRI
Weber’s test: sensorineural deafness
sound is heard louder on side of intact ear
Weber’s test: conductive deafness
Sound is heard louder on affected side as BC > AC
- This is because the ear with the conductive hearing loss is only receiving input from bone conduction, and no air conduction.
- Conduction problem of middle ear masks ambient noise of the room, while the well-functioning inner ear picks the sound up via the bones of the skull
what tuning fork is used for Weber test
512Hz
Rinne’s test: normal
air conduction> bone conduction
Rinne’s positive
Rinne’s test: sensorineural deafness
AC > BC as both are equally diminished
Rinne’s test: air conductive deafness
BC>AC
normal range of hearing
20dB or quieter
moderate hearing loss
can hear between 40 and 60 dB
what is considered symmetrical hearing loss
if the points for each ear occur within 10dB of each other
Presbycusis
sensorineural hearing loss due to natural ageing of auditory system
occurs gradually and affects ability to hear high pitched sounds
presbycusis
noise induced hearing loss
conductive hearing loss (bone conduction is represented by blue triangles)
sensorineural hearing loss
tympanometry: when does peak compliance occur
when the middle ear pressure is equal to that of the ear canal pressure
tympanogram type AD
high compliance - due to disruption of the ossicles, or if part of the drum is flaccid
tympanogram type B and B high
Type B - middle ear involvement from fluid, making drum stiff. ear canal volume is normal
Type B high - suggests middle ear involvement from a perforation/patent grommet, equivalent ear canal volume exceeds normal limits
tympanogram type C
shift in peak curve to left results when there is negative ear pressure (Eustachian tube dysfunction)
