Chronic Otitis Media
The Middle Ear and Its Structures
The middle ear is a hollow chamber in the bone of the skull. It is separated from the outside world by a thin membrane about one half inch in diameter, the eardrum. The middle ear area is lined by the same kind of mucous membrane that lines the nose and mouth. It is connected to the back of the nose, just above the soft upper portion of the mouth, by a narrow passage called the eustachian tube.
The eustachian tube lies closed until the swallowing movement pulls it open and allows fresh air to enter the middle ear. The fresh air equalizes the middle ear pressure with the air pressure outside the head.
Suspended within the middle ear is a chain of three small bones, the ossicles that conduct sound vibrations from the eardrum across the middle ear into the fluid-filled inner ear. Inside the inner ear these vibrations are converted to nerve signals that are carried by the auditory nerve to the brain.
Definition of Chronic Otitis Media
Chronic Otitis Media (COM) is the term used to describe a variety of signs, symptoms, and physical findings that result from the long-term damage to the middle ear by infection and inflammation. This includes the following: perforation of the eardrum, scarring or erosion of the small, sound conducting bones of the middle ear, chronic or recurring infected drainage from the ear damage to surrounding structures such as the balance or hearing organs of the inner ear, the facial nerve, or the brain and its coverings, known as the meninges.
How Chronic Otitis Media Occurs
If the eustachian tube becomes blocked by swelling or congestion in the nose and throat, or by swelling of the mucous membranes in the middle ear, the air pressure in the middle ear cannot equalize properly when you swallow.
When this occurs, the mucous secretion cannot drain properly down the eustachian tube. This leads to a build-up of fluid in the middle ear, which eventually blocks sound vibrations, impairs hearing and may lead to infection if bacteria get into the fluid.
If the eustachian tube blockage is temporary, or if it can be treated with medications such as decongestants, antihistamines, or antibiotics; the accumulated middle ear fluid will drain away and normal function will return.
If the eustachian tube blockage persists, however, chronic changes in the tissues of the middle ear begin to occur. First the mucous secretions become thicker; and therefore less likely to drain, then the membranes themselves begin to thicken and become inflamed. At the same time, a vacuum develops in the middle ear due to the inability to admit fresh air through the eustachian tube, and suction from this vacuum begins to deform the eardrum. Eventually, the eardrum may become severely distorted, thinned, or even perforated.
The deformity of the eardrum, along with the inflammatory changes of the middle ear membranes, can lead to erosion of the bony structures of the ear including the ossicles and the walls of the middle and inner ear. Depending upon which bone is eroded, the patient may experience hearing loss, imbalance, or weakness of facial movement on the affected side. In rare instances, the infection may extend deeper into the head, causing meningitis or brain abscess.
Hearing in the Normal Ear
The ear is typically subdivided into three sections: the external ear, the middle ear, and the inner ear. Sound travels along the ear canal of the external ear and causes the eardrum to vibrate. The three small bones of the middle ear, called the ossicles (the malleus, incus and stapes), conduct this vibration from the eardrum to the cochlea of the inner ear via the oval window. The cochlea contains approximately 15,000 hair cells, which are connected to the thousands of nerve fibers that make up the hearing nerve. Vibration of the cochlea causes the hair cells to produce electrical signals on the nerve fibers. These signals are conducted to the brain, where they are interpreted as sound.
We hope that this information has been helpful. If you have specific questions that are not answered here, please feel free to call the General Ear, Nose, and Throat Service (link to service) at 617-573-4101. Or, if you would like to schedule an appointment for an examination by an otolaryngologist, please call our Physician Referral Service at 617-573-3954.
(Information provided by the National Institutes of Health)