MECHANISM OF HEARING
The ear is comprised of three portions: an outer ear (external), a middle ear and inner ear. Each part performs an important function in the process of hearing.
The outer (external) ear consists of an auricle and ear canal. These structures gather the sound and direct it toward the ear drum (tympanic membrane).
The middle ear chamber lies between the external and inner ear. This chamber is connected to the back of the throat (pharynx) by the eustachian tube which serves as a pressure equalizing valve. The middle ear consists of an eardrum and three small ear bones (ossicles): malleus (hammer), incus (anvil) and stapes (stirrup). These structures transmit sound vibrations to the inner ear. In so doing, they act as a transformer, converting sound vibrations in the external ear canal into fluid waves in the inner ear. A disturbance of the eustachian tube, eardrum or the ear bones may result in a conductive hearing impairment. This type of impairment is usually corrected medically or surgically.
The inner ear (cochlea) contains the microscopic hearing nerve endings (hair cells) bathed in fluid. Inner ear fluid waves move the delicate nerve endings which in turn transmit sound energy to the brain by the hearing nerve, where it is interpreted into sound. A disturbance in the inner ear fluids or nerve endings may result in a sensorineural hearing impairment. Most often this type of hearing impairment is due to a hair cell loss. This type of impairment is not correctable with surgery.
FUNCTION OF THE EUSTACHIAN TUBE
The eustachian tube is a narrow channel which connects the middle ear with the nasopharynx (the upper throat area just above the palate, in back of the nose). The Eustachian tube is approximately 1 1/2 inches in length. The narrowest portion is that area near the middle ear space.
The eustachian tube functions as a pressure equalizing valve of the middle ear, which is normally filled with air. Under normal circumstances the eustachian tube opens for a fraction of a second in response to swallowing or yawning. In so doing it allows air into the middle ear to replace air that has been absorbed by the middle ear lining (mucous membrane) or to equalize pressure changes occurring with altitude changes. Anything that interferes with this periodic opening and closing of the eustachian tube may result in a hearing impairment or other ear symptoms.
Obstruction or blockage of the eustachian tube results in a negative middle ear pressure, with restraction (sucking in) of the eardrum (tympanic membrane). In an adult this is usually accompanied by some discomfort, such as a fullness or pressure feeling, and may result in a mild hearing impairment and head noise (tinnitus). In children there may be no symptoms. If the obstruction is prolonged, the fluid may be sucked in from the mucous membrane in the middle ear creating a condition called serous otitis media (fluid in the middle ear). This occurs frequently in children in connection with an upper respiratory infection or allergies and accounts for the hearing impairment associated with this condition.
On occasion just the opposite from blockage occurs; the tube remains open for a prolonged period. This is called abnormal patency of the eustachian tube (patalous eustachian tube). This is less common than serous otitis media and occurs primarily in adults. Because the tube is constantly open the patient may hear himself breathe and hears his voice reverberate in the affected ear. Fullness and a blocked feeling are not uncommon sensations experienced by the patient. Abnormal patency of the eustachian tube is annoying but does not produce a hearing impairment.
EUSTACHIAN TUBE PROBLEMS RELATED TO FLYING
Individuals with a eustachian tube problem may experience difficulty equalizing middle ear pressure when flying. When an aircraft ascends, the atmospheric pressure decreases, resulting in a relative increase in the middle ear air pressure. When the aircraft descends, just the opposite occurs; atmospheric pressure increases in the cabin of the aircraft and there is a relative decrease in the middle ear pressure. Either situation may result in discomfort in the ear due to abnormal middle ear pressure compared to the cabin pressure, if the eustachian tube is not functioning properly. Usually, this discomfort is experienced upon descent of the aircraft.
To avoid middle ear problems
associated with flying you should not fly if you have an acute upper
respiratory problem such as a common cold, allergy attack or sinus
infection. Should you have such a problem and
must fly, or should have a chronic eustachian tube problem, you may help avoid ear difficulty be observing the following recommendations:
1. Obtain from your druggist the following items: Sudafed tablets and a plastic squeeze bottle of 1/4 percent NeoSynephrine or Afrin nasal spray.
2. Following the container directions, begin taking Sudafed tablets the day before your air flight. Continue the medication for 24 hours after the flight if you have experienced any problems equalizing your middle ear pressure.
3. Following the container directions, use the nasal spray shortly before boarding the aircraft. Should your ears “plug up” upon ascent, hold your nose and swallow while attempting to force air up to the back of the throat. This will help suck excess air pressure out of the middle ear.
4. Forty five minutes before the aircraft is due to land, again use the nasal spray every five minutes for fifteen minutes. Chew gum to stimulate swallowing. Should your ear “plug up” despite this, hold your nose and blow gently toward the back of the throat while swallowing. This will blow air up the eustachian tube into the middle ear (Valsalva Maneuver).
None of these recommendations or precautions needs to be followed if you have a middle ear ventilation tube (PE tube) in your eardrum (tympanic membrane).
SEROUS OTITIS MEDIA
Serous otitis media is a term which is used to describe a collection of fluid in the middle ear. This may be a recent onset (acute) or may be long standing (chronic).
Serous otitis media is the most common cause of hearing loss in children. Fortunately, the hearing loss associated with this condition usually is not permanent. Proper treatment restores the hearing to a normal level and prevents secondary complications, which can give rise to a more serious problem.
In serous otitis media, the external and inner ear and hearing nerve are normal. The problem stems from inadequate function of the Eustachian tube. The tube becomes blocked and does not allow air to fill the middle ear space. Subsequently, fluid (called serous fluid) forms from the middle ear lining and collects in the space (fig. 2). The presence of this serous fluid limits or “dampens” the vibration of the eardrum and causes a mild to moderate hearing impairment. This fluid makes the ear more susceptible to recurrent ear infections in many children. The trapped fluid is an ideal place for bacteria to grow and reproduce rapidly. Therefore, bacteria entering the middle ear space easily cause a purulent infection; the pus produced then exerts pressure on the eardrum with resultant pain (earache).
However, serous otitis media may be present without recurrent ear infections and a mild hearing loss may be the only sign of its presence.
Acute serous otitis media is usually the result of blockage of the eustachian tube from an upper respiratory infection or an attack of nasal allergy. In the presence of bacteria this fluid may become infected leading to an acute suppurative otitis media (infected or abscessed middle ear).
When infection does not develop the fluid remains in the middle ear until the eustachian tube again begins to function properly, at which time the fluid is absorbed or drains down the tube into the back of the throat.Chronic serous otitis media may result from long standing eustachian tube blockage or from a thickening of the fluids so that it cannot be absorbed or drained down the tube. This chronic condition is usually associated with a hearing impairment. There may be recurrent ear pain, especially when the individual catches a cold. Serous otitis may persist for many years without producing any permanent damage to the middle ear mechanism. Presence of fluid in the middle ear, however, makes it very susceptible to recurrent acute infections. These recurrent infections may result in middle ear damage.
CAUSE OF SEROUS OTITIS MEDIA
Serous otitis media may result from any condition that interferes with the periodic opening and closing of the eustachian tube. The causes may be congenital (present at birth), may be due to infection or allergy, or may be due to mechanical blockage of the tube.
The Immature Eustachian Tube
The size and shape of the eustachian tube is different in children than in adults. This accounts for the fact that serous otitis media is more common in very young children. Some children inherit a small eustachian tube from their parents; this accounts in part for the familial tendency to middle ear infection. As the child matures, the eustachian tube usually assumes a more adult shape.
Serous otitis media is more common in the child with a cleft palate. This is due to the fact that the muscles that move the palate also open the eustachian tube. These muscles are deficient or abnormal in the cleft palate child.
The lining membrane (mucous membrane) of the middle ear and eustachian tube is connected with, and is the same as, the membrane of the nose, sinuses and throat. Infection of these areas results in the mucous membrane swelling, which in turn may result in eustachian tube obstruction.
Allergic reaction in the nose and throat result in swelling of the mucous membranes and this swelling may also affect the eustachian tube. This reaction may be acute or chronic.
ACUTE SEROUS OTITIS MEDIA
Treatment of acute serous otitis media is medical, and is directed towards treatment of the upper respiratory infection or allergy attacks. This may include antibiotics, antihistamines (anti-allergy drugs), decongestants (drugs to decrease mucous membrane swelling) and nasal sprays.
ACUTE SUPPURATIVE OTITIS MEDIA
In the presence of an upper respiratory infection, such as a cold, tonsillitis, or pharyngitis, fluid in the middle ear may become infected. This results in what is commonly called an abscessed ear or an infected middle ear.
This infected fluid (pus) in the middle ear may cause severe pain. If examination reveals that there is considerable ear pressure, a myringotomy (incision of the eardrum membrane) may be necessary to relieve the abscess, and the pain. In many instances antibiotic treatment will suffice.
Should a myringotomy be necessary, the ear may drain pus and blood for several days. The tympanic membrane then heals and the hearing usually returns to normal within three to four weeks.
Antibiotic treatment, with or without a myringotomy, usually results in normal middle ear function within three to four weeks. During this healing period there are varying degrees of ear pressure, popping, clicking and fluctuation of hearing, occasionally with shooting pains in the ear.
Resolution of the acute infection occasionally leaves the patient with uninfected fluid in the middle ear. This is called chronic serous otitis media.
CHRONIC SEROUS OTITIS MEDIA
Treatment of chronic serous otitis media may either be medical or surgical.
As the acute upper respiratory infection subsides, it may leave the patient with a persistent eustachian tube blockage. Antibiotic treatment may be indicated.
Allergy is often a major factor in the development or persistence of serous otitis media. Mild cases can be treated with antihistaminic drugs. More persistent cases may require allergic evaluation and treatment, including injection treatment.
In connection with medical treatment, often eustachian tube inflation is recommended. This is done by closing the nostrils with your fingers and blowing air toward the back of the throat while swallowing. This air goes up the eustachian tube and re-establishes the middle ear air. Children often cannot do this but often can achieve the same results by blowing balloons.
The primary objective of surgical treatment of chronic serous otitis media is to re-establish ventilation of the middle ear, or equalize pressure of the middle ear with that in the ear canal. This keeps the hearing at a normal level and prevents recurring infections that might damage the tympanic membrane and middle ear bones. This involves a myringotomy with aspiration of fluid and insertion of a ventilation tube.
A myringotomy (incision in the eardrum) is performed to remove the middle ear fluid. A hollow plastic tube or metal tube (ventilation tube) is inserted to prevent the incision from healing and to insure middle ear ventilation. The ventilation tube temporarily takes the place of the eustachian tube in equalizing middle ear pressure. This tube usually remains in place for six to nine months, during which time the eustachian tube blockage should subside. The tubes can be removed at a later date, but most of the time it is preferable to let the tubes work their way out of the eardrum. When the tube dislodges, the eardrum heals: the eustachian tube then resumes its normal pressure equalizing function. In rare instances (less than 5% of cases) the eardrum membrane does not heal following extrusion of the tube. The perforation may be repaired at a later date if this occurs. Usually this small perforation poses no problem, as it also would act as a ventilation tube.
In adults, a myringotomy and insertion of a ventilation tube is usually performed in the office under local anesthesia, with the use of a topical solution placed on top of the tympanic membrane. In children, general anesthesia is required.
Most often when the ventilation tube is extruded there is no further middle ear ventilation problem. Should recurrent serous otitis media occur, reinsertion of a tube may be necessary. In some difficult cases it is necessary to insert a more permanent type of tube.
When a ventilation tube is in place, a patient may carry on normal activities with the exception that no water must enter the ear canal. Often this can be prevented with vaseline on a cotton ball or Silly Putty can be used to provide occlusion of the ear canal. In addition a custom made earmold will often prevent water from entering the ear canal.
One should be reminded that the purpose of a ventilation tube is not to drain the fluid in the middle ear space. This fluid is drained at the time of the surgery. The purpose of a tube is to equalize the pressures across the eardrum. This prevents the reoccurrence of fluid in the middle ear and re-establishes normal middle ear function.
CHRONIC SEROUS MASTOIDITIS AND IDIOPATHIC HEMOTYMPANUM
Chronic serous mastoiditis and idiopathic hemotympanm are uncommon conditions which have the same symptoms as chronic serous otitis media. They differ in that the middle ear fluid continues to form, either draining out the ventilation tube or blocking it completely so that the tube may become dislodged shortly after surgery. This persistent fluid formation is due to changes in the mucous membrane of the middle ear and mastoid.
In both of the above conditions, mastoid surgery may be necessary to control the problem and reestablish a normal middle ear mechanism.
THE ABNORMALLY PATENT EUSTACHIAN TUBE
Abnormal patency of the eustachian tube is a condition occurring primarily in adults, in which the eustachian tube remains “open” for a prolonged period. This abnormality may produce many distressing symptoms such as ear fullness and blockage, a hollow feeling in the ear, hearing one’s own breathing and voice reverberation in the ear. It does not produce a hearing impairment although most patients will feel that they cannot hear as well in that ear.
The exact cause of an abnormally patent eustachian tube is often difficult to determine. At times it develops following a loss in weight or may develop during pregnancy. It may also occur while taking oral contraceptives or other hormones.
Treatment of this harmless condition is often difficult. Medical or surgical treatment is often directed towards causing mechanical obstruction of the eustachian tube or creating a less functional eustachian tube.
Palatal myoclonus is a rare condition in which the muscles of the palate (back of the mouth) twitch rhythmically many times a minute. The cause of this harmless muscle spasm is unknown. Often it is triggered with eating some foods or drinking hot or cold liquids.
The patient may experience a rhythmic clicking or snapping sound in the ear as the eustachian tube opens and closes. On occasion, this snapping sound is caused by a simultaneous spasm of a muscle in the middle ear attached to the ear bones.
A muscle relaxant is often effective in controlling the symptoms. When they persist and if they continue to pose a problem for the patient, surgery is sometimes recommended. Cutting the muscle in the middle ear usually relieves the symptoms.
If surgical treatment is necessary, it is performed under local anesthesia through the ear canal. Hospitalization is necessary for one night following surgery, and the patient may return to his usual activities in several days.