Definition: Inflammation within the mastoid bone.
What Is Going on in My Body? The mastoid is like a honeycomb filled with air enclosed in the bone that sits just immediately behind the outer ear. The lining of the mastoid is mucous membrane which communicates directly with the space behind the eardrum. The posterior boundary of the mastoid is formed by the lateral sinus, which drains blood from the side of the skull and brain and ultimately forms the jugular vein. The roof of the mastoid forms a portion of the floor of the brain cavity. The temporal lobe of the brain actually sits on the upper aspect of the bony roof of the mastoid. The medial part of the mastoid forms the portion of the brain cavity that houses the cerebellum. Running vertically through the mastoid is the facial nerve, which controls facial muscular movement. Also within the mastoid are the semi-circular canals which form part of the labyrinth, the portion of the inner ear responsible for detecting head rotation in horizontal, vertical, and side-to-side directions.
The function of the mastoid is not entirely understood. Since it is an air-filled region instead of solid bone, it certainly serves to lighten the skull. It also acts as an air reservoir for the air filled space behind the eardrum.
Inflammation in the mastoid itself is quite rare. It is almost always a result of inflammation or infection in the middle ear space behind the eardrum. Since there is a direct communication between the mastoid and the middle ear space (the aditus), any inflammatory process occurring in the middle ear space is directly transmitted into the mastoid. Fortunately, in most cases of acute ear infection, even though the inflammation and purulent material fill the mastoid, rarely is the mastoid itself damaged by the infection. In individuals with longstanding eustachian tube dysfunction and middle ear infections, the mastoid fails to completely enlarge, thus making the air-filled honeycomb component of it smaller than if the eustachian tube were to be functioning normally. Mastoid infections can assume two different patterns. Chronic mastoiditis is a disease process that is occurring more than three months and acute mastoiditis is occurring less than three weeks. There is acute mastoiditis, which is almost always a consequence of an acute ear infection that is not treated or is incompletely treated. In acute mastoiditis there is a direct bacterial infection in the mastoid. Often the skin overlying the mastoid directly behind the outer ear becomes inflamed and as a consequence is red and swollen. If the infection continues for more than 10 to 14 days, the small, bony walls that form the air-filled honeycomb begin to be destroyed. This bone destruction is termed coalescent mastoiditis. If the infection continues, then there can be direct pus accumulation under the skin behind the ear, with a resultant abscess. Since there are very important structures bounding the mastoid, infection can spread into the lateral sinus, causing an infected clot to form within it (lateral sinus thrombosis). Should this occur, it is characterized by high, spiking fevers with normal temperatures in between. This is often termed a picket fence pattern. The patients are usually quite ill with an elevated fever and very high white blood cell count. The infection can also extend directly inferiorly, presenting as an abscess deep to a muscle that is attached to the mastoid (sternocleidomastoid muscle). These abscesses are termed Bezold’s abscesses. In the pre-antibiotic era, acute mastoiditis was also associated with high incidence of meningitis, which is an extension of the bacterial infection from the mastoid into the lining surrounding the brain. Untreated meningitis has a very high mortality rate; and those individuals who do survive are often left with significant neurologic dysfunction. Lastly, acute mastoid infections can also create a cerebellar abscess. Since the cerebellum is involved in fine motor coordination and control of the central part of the body, especially during walking, these individuals often would lose coordination or have significant difficulties walking.
Chronic mastoiditis occurs whenever there is a chronic inflammatory process that affects the mastoid. This is usually termed chronic otitis media, where there is a perforation in the eardrum, with intermittent infected material draining through the hole in the eardrum. In chronic mastoiditis there is no bone destruction as is seen in coalescent mastoiditis. Instead the lining inside the mastoid often becomes thickened and inflamed. It may also be caused by a cholesteatoma which blocks the connection between the middle ear and mastoid. For further discussion regarding cholesteatoma, please refer to benign ear cyst or tumor.
What Are the Signs and Symptoms? The signs in acute mastoiditis are typically fever, pain behind the ear, infected drainage coming through a hole in the tympanic membrane, and swelling and redness of the skin behind the ear. As the mastoiditis progresses, there may actually develop very significant swelling behind the ear, causing it to be pushed forward, and instead of the firm bone underneath the skin, it becomes quite soft and compressible, which is indication of an abscess under the skin. Should the infection continue, more severe, ominous symptoms can ensue, such as facial paralysis, nerve deafness, vertigo, meningitis, and lateral sinus thrombosis with its resultant picket fence fever.
In chronic mastoiditis no changes exist over the bone behind the ear. There may be occasional pain, but these individuals usually are quite symptom-free except during acute flare-up of their ear disease when there then might be pain and more profuse, infected drainage coming from the ear canal. These individuals often have holes in the eardrum through which infected material can be identified. The lining in the middle ear, when examined through the perforation, is often red and swollen. There is usually some degree of hearing loss because of the hole in the eardrum or damage to the small bones for hearing.
What Are the Causes and Risks? The main cause of acute mastoiditis is untreated or incompletely treated acute otitis media. The risks have already been mentioned above but for acute mastoiditis include infected material under the skin behind the ear, lateral sinus thrombosis, meningitis, cerebellar abscess, brain abscess, facial nerve paralysis, nerve deafness, and vertigo. The main cause of chronic mastoiditis is a perforated tympanic membrane with persistent inflammatory or infectious disease within the middle ear and mastoid. Cholesteatomas (benign ear cysts) are also frequent causes.
How to Prevent the Disease: Fortunately, with the advent of antibiotics, antibiotic management of acute otitis media and the placement of ventilation tubes to bypass a poorly functioning eustachian tube, there has been an overall decline in the frequency of acute and chronic mastoiditis. In the child with acute otitis media, appropriate antibiotic therapy will often prevent it from occurring. It is crucial to make sure that the patient completes their course of antibiotics. Attention to persistent ear disease, whether it is chronic or recurrent acute, should help prevent the formation of chronic mastoiditis and cholesteatoma.
How Is It Diagnosed? In the individual with acute mastoiditis, on physical examination the eardrum is often reddened. Behind the eardrum is clearly infected material. If the acute mastoiditis is early, then there may be some tenderness, mild swelling, and redness in the skin behind the ear. If a coalescent mastoiditis is beginning, then plain x-rays or CT scans will show destruction of the small, bony walls forming the air-filled honeycomb in the mastoid cavity. The mastoid will also not be filled with air as it is normally, but instead will be filled with material consistent with thickened lining or pus. Chronic mastoiditis is diagnosed by noticing a hole in the tympanic membrane or a cholesteatoma. A CT scan is often helpful in the diagnosis of chronic mastoiditis, particularly if there is cholesteatoma involvement. Whereas in chronic mastoiditis no bone destruction is usually present, when there is cholesteatoma, because of the expanding nature of the skin cyst, bone destruction will often be present.
What Are the Long-Term Effects? The long-term effects of acute mastoiditis could be its conversion to chronic mastoiditis and the other abnormalities mentioned before, such as facial paralysis, deafness, vertigo, meningitis, and brain abscess and their resultant morbidities. The main long-term effect in chronic mastoiditis without cholesteatoma would be a conductive hearing loss and progressive scarring of the mucous membrane of the mastoid and middle ear. The long-term effects from cholesteatoma relate to its continued enlargement. As the cholesteatoma erodes bony structures, such complications as facial paralysis, vertigo, deafness, labyrinthitis, meningitis, and brain abscess could occur.
Am I Putting Others at Risk? No.
What Are the Treatments? The mainstay of management of acute mastoiditis is placement of a pressure equalization tube or an incision in the eardrum to allow the infected material to drain out along with antibiotics directed against the particular bacteria present in the purulent material. If the mastoiditis has become coalescent, then a tube placed in the eardrum followed by a limited mastoidectomy to drain out the infection along with appropriate antibiotics will resolve the difficulty. For chronic mastoiditis attempts to clear it with oral or topical antibiotic therapy are first performed. If the infection continues and is not responding to therapy, then surgery to remove the diseased mastoid lining, establish a communication between the mastoid and the middle ear, and repair the tympanic membrane is required. If a cholesteatoma exists, the cholesteatoma itself must be removed, the eardrum reconstructed, and if there has been damage to the bones of the middle ear, then middle ear reconstruction can be performed. In the process of removing the cholesteatoma the mastoid is often also opened up to facilitate its extraction.
What Are the Side Effects to the Treatments? The side effects to treatment would be that common to ventilation tube placement, such as perforation (3%), ear drainage (10%), and rarely deafness. The potential side effects from mastoidectomy really relate to the structures that could be injured during the mastoidectomy. If the facial nerve was injured, facial paralysis could result. If the bones for hearing were damaged, then a conductive hearing loss could occur. If there is damage to the balance system or the inner ear, then vertigo or nerve deafness would result. The side effects to the treatments for chronic mastoiditis would be identical to that of acute mastoiditis.
What Happens After Treatment? In acute uncomplicated mastoiditis, once the ventilating tube is placed and appropriate antibiotic therapy administered, the infection usually resolves without complication. The tube is left in until it extrudes, which usually occurs in six to 12 months after placement. This would also be true if surgery for acute complicated mastoiditis would have to be performed. If the procedure is successful for chronic mastoiditis, then the eardrum perforation will not reform, the hearing will recover to what the nerve is capable of doing, and the ear will no longer drain.
How Do I Monitor the Disease? Acute mastoiditis with or without abscess is a medical emergency, and home monitoring is totally inappropriate. As far as chronic mastoiditis is concerned, the individual who has a recurrently draining ear with hearing loss that has not responded to therapy, such as antibiotic ear drops and medications, needs to be seen by an ear specialist.