Conductive hearing loss

Conductive Hearing LossHadi Nafisi (birjand university of medical sciences)

Hearing loss is a common problem that everyone experiences from time to time. Most commonly it occurs when flying or traveling up a mountain.

Diminished hearing also may occur during an ear infection. These causes of hearing loss are usually short-lived. The other extreme is the permanent sensorineural hearing loss that occurs with aging, which we will all experience to some degree.

  EPIDEMIOLOGY :

 Hearing loss is a common chronic impairment, particularly for older adults. In the Beaver Dam cohort in the United States, the prevalence of hearing loss, defined by audiometry, increased steadily with age :

● 3 percent ages 21 to 34 ● 6 percent ages 35 to 44 ● 11 percent ages 45 to 54 ● 25 percent ages 55 to 64● 43 percent ages 65 to 84

Worldwide, estimates from the World Health Organization are that hearing loss affects 538 million people

CLASSIFICATION :

 Hearing loss may be classified into three types:

● Sensorineural

● Conductive

● Mixed loss

Conductive Hearing Loss :

involving any cause that in some way limits the amount of external sound from gaining access to the inner ear. Examples include cerumen impaction, middle ear fluid, or ossicular chain fixation (lack of movement of the small bones of the ear).

Causes of Conductive hearing loss : Outer-ear causes Congenital microtia or atresia External otitis Trauma Squamous cell carcinoma Exostosis Osteoma Psoriasis Cerumen

Middle-ear causes Congenital atresia or ossicular chain malformation Otitis media Cholesteatoma Otosclerosis Tympanic membrane perforation Temporal bone trauma Glomus tumors

OUTER EAR CAUSES :

Congenital : The external auditory canal (EAC) develops from the 8th to the 28th week of gestation; problems can occur anytime during this developmental phase. Such as: microtia ,atresia,…

Infection :Infections may lead to blockage of the EAC due to the accumulation of debris, edema, or inflammation.

OUTER EAR CAUSES :

Trauma :Penetrating trauma to the external auditory canal or meatus due to a bullet, knife, or fracture may cause mild or profound conductive hearing loss, depending upon the degree of EAC occlusion.Tumor : The most common malignant tumor of the EAC is squamous cell carcinoma. This and other tumors of the EAC, such as basal cell carcinoma and melanoma, typically cause conductive hearing loss due to occlusion of the canal.

OUTER EAR CAUSES :Exostosis :Exostosis or multiple benign bony growths of the EAC most commonly occur in individuals who have had repeated exposure to cold water.

Osteoma : Osteoma is a solitary bony growth that is most commonly attached to the tympanosquamous suture line.

Similar to exostoses, osteomas are not treated until they become so large that they affect hearing by occlusion or repeated infections because debris cannot exit the EAC.

OUTER EAR CAUSES :Benign polyps : Benign polyps may occur as a result of other otologic conditions, such as chronic ear infections or cholesteatoma.

Systemic disease :Diabetes mellitus and other immunocompromised states can predispose to developing necrotizing otitis externa, which in turn can cause conductive hearing loss.

OUTER EAR CAUSES :

Dermatologic :

 Certain skin diseases, such as psoriasis, may cause scaling and edema of the EAC and meatus. Treatment is usually with steroid ointments or creams.

Cerumen :

Some patients are not able to clear cerumen on their own or use Q-tips that push the cerumen down the ear canal. These individuals may need periodic cleaning of the cerumen to enhance their auditory capabilities.

Middle-ear causes :Congenital : Atresia or malformation of the ossicular chain can cause conductive hearing loss.

Eustachian tube dysfunction :Eustachian tube dysfunction occurs commonly in the setting of a viral upper respiratory infection (URI) or sinusitis, and it can also occur with allergies.

Infection :Otitis media (OM) is a common childhood disorder that also frequently occurs in adults

Middle-ear causes :

Tumors : Malignant tumors such as Langerhans cell histiocytosis (including the Letterer-Siwe variant) or squamous cell carcinoma may cause conductive hearing loss.

Cholesteatoma : Cholesteatoma is a growth of desquamated, stratified,squamous epithelium within the middle ear space.

Middle-ear causes :

Otosclerosis : Otosclerosis is a bony overgrowth that involves the footplate of the stapes.

Tympanic membrane perforation :Conductive hearing loss due to TM perforation is common. The degree of conductive hearing loss depends upon the size and location of the perforation. Small perforations and those located in the anterior/inferior quadrant cause the least amount of conductive hearing loss.

Middle ear barotrauma :Barotrauma occurs when a patient is exposed to a sudden, large change in ambient pressure, often during diving or flying.

Diagnostic tests

Weber and Rinne tests

Interpreting Weber and Rinne tests: Conductive versus sensorineural hearing loss

  Weber lateralizes Rinne testConductive loss

Good ear   AC > BC

Bad ear To bad ear BC > AC

Sensorineural lossGood ear To good ear AC > BC

Bad ear   AC > BC

Pneumoscopy :

 Pneumoscopy is also performed to evaluate mobility of the TM.

●A nonmobile TM may occur because of fluid in the middle ear cavity, a mass in the middle ear cavity, or a stiff or sclerotic TM.

●A hypermobile TM may indicate ossicular chain disruption. ●The TM may only move with negative pressure ;

this can be caused by retraction of the TM or middle ear with a blocked eustachian tube, resulting in negative middle ear pressure.

Pure tone, air, and bone conduction testing :

 Pure tone testing is commonly known as the audiogram. Hearing is tested with both air and bone conduction.

Any difference between air and bone

conduction thresholds is known as an air/bone gap;

a gap is consistent with conductive hearing loss

Tympanometry :

It is an objective measure of the changes in the acoustic impedance of the middle ear system in response to changes in air pressure.

:Five types of tympanograms can be seen

1. Type A: Normal tympanic membrane (TM) mobility.2. Type B: Flat tympanogram associated with fluid or

perforation (will have large volume). 3. Type C: Negative middle ear pressure such as from a

retracted TM. 4. Type AS: Very stiff noncompliant TM associated with TM

sclerosis or otosclerosis. 5. Type AD: Hypermobile usually associated with ossicular

discontinuity.