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Hearing Loss

What Causes Hearing Loss?

Last modified: 
29/03/2012 - 21:08

Contributing Author: Guy Slowik FRCS

What problems can affect the outer ear?

What problems can affect the middle ear?

What problems can affect the inner ear?

What Problems Can Affect The Outer Ear?

Anything that completely blocks the ear canal can cause hearing loss. Blockage with earwax (also called cerumen) is common. A doctor can cure this easily by removing the wax either with specially designed instruments or by flushing with water. There are many over-the-counter wax control preparations that can be used at home. However, they sometimes can cause external ear infections.

Need To Know

Q: Is it a good idea to remove wax inside the ear with cotton-tipped swabs?

A: No. The ear has a natural self-cleaning mechanism. Ear skin normally sheds from the inside out. If you place a drop of ink on the eardrum and wait a few weeks, it will turn up near the opening of the ear. The ear canal is also a shaped like a funnel, with the narrow end near the eardrum. Cotton swabs generally push wax deeper into the ear than it normally is (wax forms only in the outer segment of the ear canal), and packs it into a mass. As long as there is even a pinhole opening in the packed wax, hearing is usually good. However, when the canal is completely blocked by wax, substantial hearing loss develops.

Many other problems can block the ear canal and lead to hearing loss. Such blocking causes a decrease in volume but does not generally produce distortion. These problems include:

  • Infections with swelling that shuts the ear canal
  • Foreign bodies in the ear
  • An injury
  • Birth defects
  • A growth in the ear canal

Any of these, including blockage by wax, may result inconductive hearing loss. That is, it interferes with sound conduction and is generally correctable. It causes decrease in volume but does not generally produce distortion.

What Problems Can Affect The Middle Ear?

Problems that can affect the middle ear and lead to hearing loss include:

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.

Nice To Know:

Most perforations (holes) in the eardrum heal spontaneously. When one does not, it can nearly always be repaired with surgery. The procedure is usually relatively fast, and is generally performed under local anesthesia.

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. 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 job 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.

When the condition causes frequent middle ear infections (acute otitis media) some physicians recommend the long-term use of antibiotics, although this treatment is currently controversial.

For more information about glue ear, go to Glue Ear.

For more information about middle ear infections, go to Middle Ear Infection.

Otosclerosis

Otosclerosis is a common hereditary disease in which new bone is deposited around one of the tiny bones in the middle ear, specifically around the footplate of the stapes (or 'stirrup') bone. This prevents normal bone transmission of sound from the eardrum to the inner ear, and consequently, conductive hearing loss results.

This hereditary condition is present in about 10 percent of white Americans, and it causes significant hearing loss in about one percent. It occurs less commonly in black and Asian people. Otosclerosis generally becomes apparent during early adult life, and the severity of hearing loss can be accelerated by pregnancy.

This type of hearing loss can be cured by a surgical procedure called stapedectomy, in which the stapes bone is replaced by an artificial bone. This procedure usually only takes 30 or 40 minutes, and it is performed under local anesthesia (in which the person is awake). In many cases, hearing can return to normal after surgery.

Birth defects

Various birth defects may also involve the middle ear and cause hearing loss. Some are major and cause obvious external defects. Many involve only the inner ear structures. In any case, most conductive hearing loss, in which sound waves are not transmitted effectively to the inner ear, is surgically treatable.

Tumors

Tumors of the middle ear may be responsible for hearing loss. They may be cancerous (malignant) or noncancerous (benign).

  • Examples of cancerous tumors are rhabdomyosarcoma, a very rare muscle tumor, in children or squamous cell carcinoma in adults.
  • Examples of noncancerous tumors are glomus tumors (which also cause pulsating ear noises) or neuromas of the facial nerve.
  • Cholesteatoma is a common noncancerous skin cyst that grows slowly and dissolves adjacent bone as it grows. It is a fairly common problem, especially in people who have had repeated ear infections; but it may also occur from birth. It generally requires surgery to remove the cyst.

What Problems Can Affect The Inner Ear?

There are many conditions that cause the delicate inner portion of the ear to function abnormally. They include:

Otosclerosis

Otosclerosis (the hereditary disease in which bone deposits collect around the small bone in the middle ear known as the stirrup) can also affect the cochlea (the coiled tube in the inner ear), and cause hearing loss in some people.

Presbycusis

The natural aging process also causes sensorineural hearing loss, in which the damage lies in the inner ear, the hearing nerve, or both. Beginning shortly after birth, we begin to lose hair cells and nerve endings within the cochlea (the region that hears very high frequencies). As this loss pattern progresses over a lifetime, sensorineural hearing loss develops.

There also are other age-related causes of hearing loss, including stiffening of portions of the cochlea and loss of nerve endings in the acoustic nerve.

Fistula

A fistula (opening) is an abnormal connection between the inner ear and middle ear. The inner ear is filled with fluid, and the middle ear is filled with air. If a fluid leak occurs from the inner ear, hearing loss and dizziness commonly result. This kind of hearing loss often is cured by surgically repairing the fistula. Such leaks are usually caused by trauma. The trauma may be direct, such as a blow to the ear or a head injury in a car accident. However, it may also be the result of air pressure changes in an airplane trip, a forceful sneeze, or lifting a heavy object.

Head injury

Direct head trauma, particularly trauma severe enough to cause unconsciousness, can cause inner ear concussions and hearing loss.

Meniere's syndrome

Meniere's syndrome is a condition characterized by fluctuating hearing loss (usually more prominent in the lower frequencies where we hear speech), dizziness, fluctuating ear pressure, and tinnitus (a noise sensation heard in one or both ears). It is due to a swelling and fluid overload of the middle compartment of the inner ear (a condition known as endolymphatic hydrops).

There are many treatable causes of Meniere's syndrome. When all tests have revealed none of the known causes, the condition is classified as Meniere's disease.

Noise

Noise is an important cause of hearing loss. An estimated 7 to 10 million people in American industry have noise-induced hearing loss, virtually all of which was preventable. In addition to industrial noise, recreational noise can damage hearing. Such noise is encountered commonly from gunfire, power tools, snow blowers, motorcycles, loud music (especially with earphones) and other causes.

In some cases, the playing of musical instruments can damage hearing. This has been reported not only with loud, electrical rock and roll instruments, but also with classical music performance such as violin playing and flute playing. One can minimize such problems by using ear protection whenever practical, such as during selected practice sessions.

Infections

Infections involving the inner ear and hearing nerve can also produce deafness. Middle ear infections can spread to the inner ear, causing loss of hearing and, usually, dizziness. Infections may also involve the hair cells or acoustic nerve, causing hearing loss and even sudden total deafness.

For more information about middle ear infections, go to Middle Ear Infection.

Sudden deafness

Sudden deafness may be caused by a variety of problems. Treatment is controversial, but there is some evidence to suggest that aggressive treatment may improve the chances for hearing recovery even after a sudden profound loss. Once the condition has been present for more than two or three weeks, even the most aggressive treatments generally do not work.

Neural problems

Neural (nerve-related) problems may also produce hearing loss. Among the more common are:

  • Acoustic neuroma, a common tumor of the acoustic nerve
  • Multiple sclerosis
  • Autoimmune sensorineural hearing loss, in which the body attacks its own ear
  • Ototoxicity, which is hearing loss caused by a substance that gets into the body; most often the substance is a medication, particularly certain antibiotics, but other toxins (such as lead) may also cause hearing loss

Need To Know:

What is an acoustic neuroma?

An acoustic neuroma is a common tumor of the acoustic nerve, the nerve responsible for hearing. It generally starts in the internal auditory canal, the bony channel through which the nerve courses as it goes from the ear to the brain. Acoustic neuromas grow, compressing the brainstem and other structures, including the facial nerve.

Ordinarily, these tumors can be cured with surgery. They are managed best by neurotologists, inner ear subspecialists with particular interest and expertise in treatment of this specific tumor. Neurotologists often work in collaboration with a neurosurgeon. In the majority of cases, it is possible to remove acoustic neuromas without serious injury and without facial paralysis. In some tumors diagnosed early, it is even possible to preserve hearing (despite the fact that the tumor has its roots in the acoustic nerve).

 

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From Andrew Maynard - Chair of the University of Michigan Department of Environmental Health Sciences, with help from David Faulkner - 2013 Master of Public Health graduate.