Hearing Loss

You may have hearing loss, and not even be aware of it. People of all ages experience gradual hearing loss, often due to the natural aging process or long exposure to loud noise. Other causes of hearing loss include viruses or bacteria, heart conditions or stroke, head injuries, tumors, and certain medications. Treatment for hearing loss will depend on your diagnosis











How does the hearing sense work?

Hearing is a complex and intricate process.The ear is made up of three sections: the outer ear, the middle ear, and the inner ear. These parts work together so you can hear and process sounds. The outer ear, or pinna (the part you can see), picks up sound waves and directs them into the outer ear canal.

These sound waves travel down the ear canal and hit the eardrum, which casuses the eardrum to vibrate. When the eardrum vibrates, it moves threee tiny bones in your middle ear. The middle ear is a small air-filled space between the eardrum and the inner ear. These bones form a chain and are called the hammer (or malleus), anvil (or incus), and stirrup (or stapes). The movement of these bonse transmits and amplifies the sound waves toward the inner ear.

The third bone in the chain, the stapes, interfaces with fluid which fills the hearing portion of the inner ear -- the cochlea. The cochlea is lined with cells that have thousands of tiny hairs on their surfaces. As the fluid wave travels through the cochlea, it causes the tiny hairs to move. The hairs change the mechanical wave into nerve signals. The nerve signals are then transmitted to your brain, which interprets the sound.

What is otitis media and ear infection?

Otitis media refers to inflammation of the middle ear. When an abrupt infection occurs, the condition is called "acute otitis media." Acute otitis media occurs when a cold, allergy, and the presence of bacteria or viruses lead to the accumulation of pus and mucus behind the eardrum, blocking the Eustachian tube. This can cause earache and fever.

When fluid sits in the middle ear for weeks, the condition is known as "otitis media with effusion" This occurs in a recovering ear infection. Fluid can remain in the ear for weeks to many months. If not treated, chronic ear infections have potentially serious consequences such as temporary hearing loss.Why do children have more ear infections than adults?

To understand earaches, and ear infections, you must first know about the Eustachian tube, a narrow channel connecting the inside of the ear to the back of the throat, just above the soft palate and uvula. The tube allows drainage of fluid from the middle ear, which prevents it from building up and bursting the thin ear drum. In a healthy ear, the fluid drains down the tube, assisted by tiny hair cells, and is swallowed.

The tube maintains middle ear pressure equal to the air outside the ear, enabling free eardrum movement. Normally, the tube is collapsed most of the time in order to prevent the many germs residing in the nose and mouth from entering the middle ear. Infection occurs when the Eustachian tube fails to do its job. When the tube becomes partially blocked, fluid accumulates in the middle ear, trapping bacteria already present, which then multiply. Additionally, as the air in the middle ear space escapes into the bloodstream, a partial vacuum is formed that absorbs more bacteria from the nose and mouth into the ear.

Children have Eustachian tubes that are shorter, more horizontal, and straighter than those of adults. These factors make the journey for the bacteria quick and relatively easy. It also makes it harder for the ears to clear the fluid, since it cannot drain with the help of gravity. A child's tube is also floppier, with a smaller opening that easily clogs.

How does otitis media affect hearing?

Most people with middle ear infection or fluid have some degree of hearing loss. The average hearing loss in ears with fluid is 24 decibels...equivalent to wearing ear plugs. (Twenty-four decibels is about the level of the very softest of whispers.) Thicker fluid can cause much more loss, up to 45 decibels (the range of conversational speech).

Types of hearing loss

Conductive hearing loss is a form of hearing impairment where the transmission of sound from the environment to the inner ear is impaired, usually from an abnormality of the external auditory canal or middle ear. This form of hearing loss can be temporary or permanent. Untreated chronic ear infections can lead to conductive hearing loss. If fluid is filling the middle ear, hearing loss can be treated by draining the middle ear and inserting a tympanostomy tube. The other form of hearing loss is sensorineural hearing loss, hearing loss due to abnormalities of the inner ear or the auditory division of the 8th cranial nerve. Historically, this condition can occur at all ages, and is usually permanent.

When should a hearing test be performed related to frequent infections or fluid?

A hearing test should be performed for children who have frequent ear infections, hearing loss that lasts more than six weeks, or fluid in the middle ear for more than three months. There are a wide range of medical devices now available to test a child's hearing, Eustachian tube function, and flexibility of the ear drum. They include the otoscopy, tympanometer, and audiometer

Do people lose their hearing for reasons other than chronic otitis media?

Children and adults can incur temporary hearing loss for other reasons than chronic middle ear infection and Eustachian tube dysfunction. They include:

  • Cerumen impaction (compressed earwax)
  • Otitis externa: Inflammation of the external auditory canal, also called swimmer's ear.
  • Cholesteatoma: A mass of horn shaped squamous cell epithelium and cholesterol in the middle ear, usually resulting from chronic otitis media.
  • Otosclerosis: This is a disease of the otic capsule (bony labyrinth) in the ear, which is more prevalent in adults and characterized by formation of soft, vascular bone leading to progressive conductive hearing loss. It occurs due to fixation of the stapes (bones in the ear). Sensorineural hearing loss may result because of involvement of the cochlear duct.
  • Trauma: A trauma to the ear or head may cause temporary or permanent hearing loss.

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Copyright 2011. American Academy of Otolaryngology - Head and Neck Surgery