Mastoiditis

Overview
Mastoiditis is an infection of the mastoid process, the portion of the temporal bone of the skull that is behind the ear. It is usually caused by untreated acute otitis media (middle ear infection) and used to be a leading cause of child mortality. With the development of antibiotics, however, mastoiditis has become quite rare in developed countries, most likely due to antibiotic treatment of otitis media before it can spread. It is treated with medications and/or surgery. If untreated, the infection can spread to surrounding structures, including the brain, causing serious complications.

Epidemiology
In the United States and other developed countries, the incidence of mastoiditis is quite low, around 0.004%, although it is higher in developing countries. The most common ages affected are 6–13 months, as it is during that age that ear infections are most common. Males and females are equally affected.

Pathophysiology
The pathophysiology of mastoiditis is straightforward: bacteria spread from the middle ear to the mastoid air cells, where the inflammation causes damage to the bony structures. The bacteria most commonly observed to cause mastoiditis are Streptococcus pneumoniae, Streptococcus pyogenes, Staphylococcus aureus, and gram-negative bacilli. Other bacteria include Moraxella catarrhalis, Streptococcus pyogenes, and rarely, Mycobacterium species. Some mastoiditis is caused by cholesteatoma, which is a sac of keratinizing squamous epithelium in the middle ear that usually results from repeated middle-ear infections. If left untreated, the cholesteatoma can erode into the mastoid process, producing mastoiditis, as well as other complications.

Symptoms and Signs
Some common symptoms and signs of mastoiditis include pain and tenderness in the mastoid region, as well as swelling. There may be ear pain (otalgia), and the ear or mastoid region may be red (erythematous). Fever or headaches may also be present. Infants usually show nonspecific symptoms, such as anorexia, diarrhea, or irritability. Drainage from the ear occurs in more serious cases.

Diagnosis
The diagnosis of mastoiditis is clinical&mdash;based on the medical history and physical examination. Imaging studies may provide additional information; the study of choice is the CT scan, which may show focal destruction of the bone or signs of an abscess (a pocket of infection). X-rays are not as useful. If there is drainage, it is often sent for culture, although this will often be negative if the patient has begun taking antibiotics.

Treatment
The primary treatment for mastoiditis is administration of intravenous antibiotics. Initially, broad-spectrum antibiotics are given, such as Ceftriaxone (Rocephin). As culture results become available, treatment can be switched to more specific antibiotics. Long-term antibiotics may be necessary to completely eradicate the infection. If the condition does not quickly improve with antibiotics, surgical procedures may be performed (while continuing the medication). The most common procedure is a myringotomy, a small incision in the tympanic membrane (eardrum), or the insertion of a tympanostomy tube into the eardrum. These serve to drain the pus from the middle ear, helping to treat the infection. The tube is extruded spontaneously after a few weeks to months, and the incision heals naturally. If there are complications, or the mastoiditis does not respond to the above treatments, it may be necessary to perform a mastoidectomy in which a portion of the bone is removed and the infection drained.

Prognosis
With prompt treatment, it is possible to cure mastoiditis. Seeking medical care early is important. However, it is difficult for antibiotics to penetrate to the interior of the mastoid process and so it may not be easy to cure the infection; it also may recur. Mastoiditis has many possible complications, all connected to the infection spreading to surrounding structures. Hearing loss may result, or inflammation of the labyrinth of the inner ear (labyrinthitis) may occur, producing vertigo. The infection may also spread to the facial nerve (cranial nerve VII), causing facial-nerve palsy which can produce weakness or paralysis of some facial muscles on that side of the face. Other complications include Bezold's abscess, an abscess (a collection of pus surrounded by inflamed tissue) behind the sternocleidomastoid muscle in the neck, or a subperiosteal abscess, between the periosteum and mastoid bone ( resulting in the typical appearance of a protruding ear). Serious complications result if the infection spreads to the brain. These include meningitis (inflammation of the protective membranes surrounding the brain), epidural abscess (abscess between the skull and outer membrane of the brain), dural venous thrombophlebitis (inflammation of the venous structures of the brain), or brain abscess.

Prevention
In general, mastoiditis is rather simple to prevent. If the patient with an ear infection seeks treatment promptly and receives complete treatment, the antibiotics will usually cure the infection and prevent its spread. For this reason, mastoiditis is rare in developed countries.