Mastoiditis

Pathogenesis

Mastoiditis is inflammation of the mastoid air cells in the temporal bone. Knowledge of the anatomy of the middle ear and mastoid is essential to understand the clinical manifestations of mastoiditis and its complications. Fig. 31.1 shows the relationships among the eustachian tube, middle ear, and mastoid. At birth, the mastoid consists of a single air cell, the antrum, which is connected to the middle ear by a narrow channel, the aditus ad antrum. As the child grows, the mastoid bone becomes pneumatized, resulting in a series of interconnected air cells that are lined by modified respiratory epithelium.

When AOM develops as a result of eustachian tube dysfunction, there is an acute inflammatory response of the mucosa lining the middle ear and, in many cases, the mastoid. Most episodes of AOM respond to antibiotic therapy. Eustachian tube dysfunction resolves, and the mucosa of the middle ear and mastoid recovers. In rare cases of newly diagnosed AOM or in cases of inadequate or inappropriate treatment, inflammation of the middle ear and mastoid persists. Histopathologic specimens from children who undergo mastoidectomy for acute or chronic mastoiditis demonstrate similar subacute or chronic infectious changes. Serous and then purulent material accumulates within the mastoid cavities. As the pressure increases, the thin bony septa between air cells may be destroyed (i.e., acute coalescent mastoiditis). This may be followed by the formation of abscess cavities and ultimately by the dissection of pus into adjacent areas.

The direction in which purulent material dissects determines the clinical presentation and complications associated with acute mastoiditis ( Box 31.1 ). Pus traversing the aditus ad antrum reaches to the middle ear and empties through the eustachian tube (with the resolution of the process) or a perforation of the tympanic membrane. If the pus erodes the lateral cortex of the mastoid, a subperiosteal abscess is produced. The abscess results in swelling or fluctuation above the auricle in infants (when erosion comes from the zygomatic mast cells) or behind the lower earlobe over the mastoid process in older children. Rarely, erosion occurs through the medial aspect of the mastoid tip, resulting in a neck abscess beneath the attachment of the sternocleidomastoid and digastric muscles (i.e., Bezold abscess).

Pus can dissect medially to the petrous air cells (in the 20% of the population in which there is pneumatization), resulting in petrositis, or posteriorly to the occipital bone, resulting in osteomyelitis of the calvarium (i.e., Citelli abscess). Purulent material can spread to the labyrinth and facial nerve. Pus within the mastoid can dissect toward the inner cortical bone, causing suppurative complications in the central nervous system, such as meningitis; epidural, subdural, temporal lobe, or cerebellar abscesses; and venous sinus thrombosis.

Clinical Presentation

The clinical presentation of the patient with mastoiditis depends on the patient’s age and the stage of the osteitis (i.e., uncomplicated or already evolved to a subperiosteal abscess). Uncomplicated infection in a child <2 years manifests as fever, otalgia or irritability, retroauricular pain, swelling, erythema, and a downward and outward deviation of the auricle ( Fig. 31.2 ). In most cases, otorrhea or a bulging, immobile, opaque tympanic membrane is observed. There may be sagging of the posterosuperior wall of the external auditory canal. In rare instances with obstruction at the aditus ad antrum, middle ear infection clears through the eustachian tube, but the mastoid, unable to drain, continues to suppurate.

In children >2 years, the pinna usually is deviated upward and outward because the inflammatory process frequently concentrates over the mastoid process. When subperiosteal pus has accumulated, a fluctuant, erythematous, and tender mass can be found overlying the mastoid bone in all age groups.

Considerable attention has been given in the past 2 decades to the entity called masked mastoiditis or subacute mastoiditis. The patient typically has had persistent middle ear effusion or recurrent episodes of AOM without sufficient antimicrobial therapy. In either case, there is a low-grade but persistent infection in the middle ear and mastoid with osteitis. Masked mastoiditis can manifest as fever, otalgia, and an abnormal tympanic membrane or occasionally manifest with an extracranial or intracranial complication.