Conductive hearing loss
Encyclopedia
Conductive hearing loss occurs when there is a problem conducting sound waves anywhere along the route through the outer ear
, tympanic membrane (eardrum), or middle ear
(ossicles
).
This type of hearing loss may occur in conjunction with sensorineural hearing loss
or alone.
The Weber test
, in which a tuning fork is touched to the midline of the forehead, localizes to the affected ear
in people with this condition. The Rinne test
, which tests air conduction vs. bone conduction is negative (abnormal result).
, such as allergies or tumors. Blocking of the eustachian tube leads to increased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles
and the tympanic membrane.
is carried out, sound localizes to the ear affected by the conductive loss.
A Rinne test
, in which air conduction is normally greater than bone conduction, is usually negative (abnormal – note unusual terminology here compared with other medical tests), and shows greater bone conduction than air conduction.
Table 1. A table comparing sensorineural hearing loss
to conductive
Outer ear
The outer ear is the external portion of the ear, which consists of the pinna, concha, and external auditory meatus. It gathers sound energy and focuses it on the eardrum . One consequence of the configuration of the external ear is to selectively boost the sound pressure 30- to 100-fold for...
, tympanic membrane (eardrum), or middle ear
Middle ear
The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has...
(ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
).
This type of hearing loss may occur in conjunction with sensorineural hearing loss
Sensorineural hearing loss
Sensorineural hearing loss is a type of hearing loss in which the root cause lies in the vestibulocochlear nerve , the inner ear, or central processing centers of the brain....
or alone.
The Weber test
Weber test
The Weber test is a quick screening test for hearing. It can detect unilateral conductive hearing loss and unilateral sensorineural hearing loss...
, in which a tuning fork is touched to the midline of the forehead, localizes to the affected ear
Ear
The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system....
in people with this condition. The Rinne test
Rinne test
The Rinne test is a hearing test. It compares perception of sounds transmitted by air conduction to those transmitted by bone conduction through the mastoid...
, which tests air conduction vs. bone conduction is negative (abnormal result).
Uncommon
- Foreign body in the external auditory canal (not always)
- Exostoses
- Tumour of the ear canal
- Congenital atresia
Tympanic membrane
- Tympanic membrane perforation
- Membrane tension by different pressurePressurePressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
s in the external and middle ear. This can temporarily occur, for example, by the environmental pressure changes as when shifting altitude, or inside a train going into a tunnel. It is managed by any of various methods of ear clearingEar clearingEar clearing or clearing the ears is any of various maneuvers to equalize the pressure in the middle ear with the outside pressure, by letting air enter along the Eustachian tubes, as this does not always happen automatically when the pressure in the middle ear is lower than the outside pressure...
maneuvers to equalize the pressures.
Common
Fluid accumulation is the most common cause of conductive hearing loss in the middle ear, especially in children. Major causes are ear infections or conditions that block the eustachian tubeEustachian tube
The Eustachian tube is a tube that links the nasopharynx to the middle ear. It is a part of the middle ear. In adult humans the Eustachian tube is approximately 35 mm long. It is named after the sixteenth-century anatomist Bartolomeo Eustachi...
, such as allergies or tumors. Blocking of the eustachian tube leads to increased pressure in the middle ear relative to the external ear, and this causes decreased motion of both the ossicles
Ossicles
The ossicles are the three smallest bones in the human body. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-filled labyrinth . The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss...
and the tympanic membrane.
- Acute otitis mediaOtitis mediaOtitis media is inflammation of the middle ear, or a middle ear infection.It occurs in the area between the tympanic membrane and the inner ear, including a duct known as the eustachian tube. It is one of the two categories of ear inflammation that can underlie what is commonly called an earache,...
- Serous otitis mediaOtitis mediaOtitis media is inflammation of the middle ear, or a middle ear infection.It occurs in the area between the tympanic membrane and the inner ear, including a duct known as the eustachian tube. It is one of the two categories of ear inflammation that can underlie what is commonly called an earache,...
Uncommon
- CholesteatomaCholesteatomaCholesteatoma is a destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process.-Signs and symptoms:...
- OtosclerosisOtosclerosisOtosclerosis is an abnormal growth of bone near the middle ear. It can result in hearing loss.-Clinical description:Otosclerosis can result in conductive and/or sensorineural hearing loss...
- Middle ear tumour
- Temporal boneBoneBones are rigid organs that constitute part of the endoskeleton of vertebrates. They support, and protect the various organs of the body, produce red and white blood cells and store minerals. Bone tissue is a type of dense connective tissue...
trauma
Common
Severe Otosclerosis, form of mechanical conductive hearing loss most commonly found in people who have been subjected to intense noise. Occurs when there is an obstruction in either the oval window and/or the round window. This type of hearing loss can usually be repaired by surgical opening of the blockage.Differentiating conductive and sensorineuronal hearing loss
When a Weber testWeber test
The Weber test is a quick screening test for hearing. It can detect unilateral conductive hearing loss and unilateral sensorineural hearing loss...
is carried out, sound localizes to the ear affected by the conductive loss.
A Rinne test
Rinne test
The Rinne test is a hearing test. It compares perception of sounds transmitted by air conduction to those transmitted by bone conduction through the mastoid...
, in which air conduction is normally greater than bone conduction, is usually negative (abnormal – note unusual terminology here compared with other medical tests), and shows greater bone conduction than air conduction.
Table 1. A table comparing sensorineural hearing loss
Sensorineural hearing loss
Sensorineural hearing loss is a type of hearing loss in which the root cause lies in the vestibulocochlear nerve , the inner ear, or central processing centers of the brain....
to conductive
| Criteria | Sensorineural hearing loss | Conductive hearing loss |
| Anatomical Site | Inner ear Ear The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system.... , cranial nerve VIII, or central processing centers |
Middle ear Middle ear The middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the cochlea. The mammalian middle ear contains three ossicles, which couple vibration of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear has... (ossicular chain), tympanic membrane, or inner ear Inner ear The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:... |
| Weber Test | Sound localizes to normal ear Ear The ear is the organ that detects sound. It not only receives sound, but also aids in balance and body position. The ear is part of the auditory system.... |
Sound localizes to affected ear (ear with conductive loss) |
| Rinne Test | Positive Rinne; Air conduction > Bone conduction (both air and bone conduction are decreased equally, but the difference between them is unchanged). | Negative Rinne; Bone Conduction > Air Conduction (Bone/Air Gap) |