Conductive Hearing Loss
The Outer ear consists of:
- The Pinna
- The ear canal
- The eardrum
1. The ‘Pinna’, also known as the ‘auricle’ or ‘earlobe’:
The pinna can be the cause of a conductive hearing loss due to Atresia, the absence of a normal opening to the ear canal.
Surface anatomy of the Pinna
2. Ear canal:
The ear canal is a tube, about 1 inch long, between the outer ear and the ear drum. It directs sound waves through the skull to the ear drum. The ear canal has hairs near the outer end to keep foreign objects, such as dust or flies, out of the ear. Special oil glands also make ear wax.
2.1. Factors relating to the ear canal that can cause conductive hearing loss:
- Stenosis of the ear canal is when the canal leading from the pinna to the eardrum is abnormally narrow. This can lead to complication like abnormal appearance of the visible ear and a tendency for the ear canal to become easily clogged. In some cases, the stenotic ear canal becomes so narrow that it can cause hearing loss.
- Foreign objects in the ear canal
- Impacted wax in the ear canal
- Infections with swelling that shuts the ear canal
- An injury
- A growth in the ear canal
3. Tympanic Membrane or better known as the ‘eardrum’
The eardrum is the thin translucent oval membrane separating the outer ear from the middle ear and carries sound waves as vibrations to the chain of tiny bones in the middle ear. Conductive loss can result from damage to the eardrum.
The middle ear is an air-
- The Ossicles
- The Eustachian Tube
1. The Ossicles:
The ossicles are the three smallest bones in the human body, the malleus, the incus, and the stapes. They are contained within the middle ear space and serve to transmit sounds from the air to the fluid-
As sound waves vibrate the eardrum, it in turn moves the nearest ossicle, the malleus, to which it is attached. The malleus transmits the vibrations, via the incus, to the stapes and ultimately to the opening to the vestibule of the inner ear.
Sound traveling through the air is mostly reflected when it comes into contact with a liquid medium; only about 1/30 of the sound energy moving through the air would be transferred into the liquid. Think about the abrupt cessation of sound that occurs on a busy summer’s day at the pool when you submerge your head underwater. This is because the relative incompressibility of liquids confers resistance to the force of the sound waves traveling through the air. The ossicles give the eardrum mechanical advantage via lever action and a reduction in the area of force distribution; the resulting vibrations would be much smaller if the sound waves were transmitted directly from the outer ear to the oval window. This increase in pressure can compress the fluid found in the cochlea and thus transmits the stimulus. Thus, the use of the ossicles to concentrate the force of the vibrations improves the quality of sound.
The absence of the auditory ossicles would constitute a moderate-
1.1. Other factors caused by the middle ear resulting in conductive hearing loss include:
- Middle ear infections/Otitis Media
- Birth defects
- Damage to the ossicles
1.2. Further description of Ear Infections:
Temporary hearing loss is commonly caused by ear infections. Middle ear infections cause swelling of the lining in the middle ear, and often an accumulation of fluid (such as pus). When there is fluid behind the eardrum and surrounding the ossicles (the three small bones in the ear), these structures cannot work properly, and hearing loss results.
Infections are usually treated with antibiotics, sometimes with decongestants, and occasionally with drainage by placing a small hole in the eardrum (a procedure called myringotomy). If infections are severe or inadequately treated, they may cause permanent hearing loss by damaging the ossicles or perforating the eardrum.
1.3. Glue Ear:
Ear fluid not caused by infection accumulates commonly in children, and sometimes in adults. The condition is known as glue ear, or chronic otitis media with effusion (OME). It sometimes requires drainage through a myringotomy or with the placement of ear tubes/grommets. This ordinarily eliminates the hearing loss almost instantly.
Fluid in the ear usually is due to malfunction of the eustachian tube, which connects the ear with the back of the throat. The function of the eustachian tube is to keep the pressure in the middle ear approximately the same as that in the ear canal and outside world.
- The eustachian tube does this by opening momentarily when we swallow or yawn.
- If it fails to open because of swelling, allergy, or other reasons, the air already in the middle ear becomes trapped.
- Gradually, this air is absorbed into the bloodstream. The middle ear space is bony except for the eardrum. As absorption occurs and less and less air is present, its disappearance creates a vacuum (negative pressure), which sucks the eardrum toward the middle ear (retracted ear drum).
- When the negative pressure is great enough, it causes fluid to seep out of the blood vessels that line the middle ear. This is the fluid that constitutes glue ear.
The presence of fluid causes hearing loss, and sometimes frequently recurring ear infections. In some cases, the eustachian tube starts to work again spontaneously and the condition resolves. In others, decongestants may be helpful. When allergy is the cause, allergy treatments may improve the problem.
Grommet inserted inside an ear drum
2. Eustachian Tube:
A passage linking the nasal cavity and the middle ear cavity, which helps to balance the air pressure on both sides of the eardrum and to drain the middle ear cavity of any gathering fluid or mucus.
Eustachian tube dysfunction (ETD) occurs when the tube fails to open during swallowing or yawning. This results in a difference between the air pressure inside and outside the middle ear.
ETD is caused by poor function or blockage of the eustachian tube, including:
Inability of the tiny hairs inside the ear to remove fluid and infection Poor squeezing function within the eustachian tube Narrow eustachian tube –
Symptoms can include:
- Feeling of fullness or clogging in the ear
- Discomfort or pain in the ear
- Hearing loss
- Ringing in the ear
- A sensation of spinning known as vertigo
- Symptoms that cannot be relieved by swallowing, yawning, or chewing
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