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Infection of the middle ear, or otitis media (OM), includes acute, nonacute, and chronic types of infections. Acute otitis media (AOM) is defined as an acute illness marked by the presence of middle ear fluid and inflammation of the mucosa that lines the middle ear space. Otitis media with effusion (OME) is defined by the presence of middle ear fluid without signs of acute illness and usually follows AOM but may also occur as a result of viral upper respiratory tract infection (URTI), allergy, or barotrauma. Synonyms for OME include serous otitis, secretory otitis, and glue ear. Less common chronic variations of OM include permanent perforation of the tympanic membrane (TM) and perforation or retraction of the TM with trapped epithelium that is unable to spontaneously clear desquamated debris, forming a cholesteatoma. Both perforations and cholesteatoma may be associated with recurrent foul-smelling otorrhea, termed chronic suppurative otitis media (CSOM). CSOM occurs more commonly after repeated and untreated AOM in low- and middle-income countries. Infection may spread from the middle ear space to contiguous structures such as the inner ear, mastoid air cells, petrous bone, and intracranial structures, leading to infection of the central nervous system.
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PATHOGENESIS AND EPIDEMIOLOGY
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The middle ear system includes the nasopharynx, the eustachian tube (ET), the middle ear space, and the adjacent structures, including the mastoid air cells and inner ear. The middle ear is an air-filled space between the TM and the inner ear. It has a mucosal lining of respiratory epithelium and contains 3 bony ossicles—malleus, incus, and stapes—that form a lever mechanism important for the conduction of sound. The size of the middle ear cavity and the ossicles is the same at birth as in the adult. The ET originates in the anterior middle ear space and courses anteriorly to empty into the lateral nasopharynx. The normal physiologic functions of the ET include: pressure regulation or ventilation of the middle ear, which equilibrates gas pressure in the middle ear with atmospheric pressure; protection of the middle ear by anatomic, immunologic, and mucociliary defenses; and clearance or drainage of secretions produced within the middle ear via mucociliary activity and muscular clearance. In infancy, the ET is short, wide, and in a straight position, permitting easy access of nasopharyngeal flora into the middle ear space. With increasing age, the ET elongates, narrows, and assumes an oblique position, corresponding to a decrease in the incidence of OM as age increases.
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AOM usually occurs concurrently or just after URTI; more than 90% of children with AOM have concurrent URTI symptoms. The 3 most common bacterial otopathogens include Streptococcus pneumoniae, nontypeable Haemophilus influenzae, and Moraxella catarrhalis. These organisms colonize the infant’s nasopharynx from early age and do not infect the respiratory tract or cause symptoms until viral URTI (nasopharyngitis) occurs, causing changes in the nasopharyngeal milieu. Steps in the pathogenesis of AOM are outlined in ...