Porth's Essentials of Pathophysiology, 4e

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Disorders of Special Sensory Function: Vision, Hearing, and Vestibular Function

C h a p t e r 3 8

of the craniofacial base also render the tensor muscle less efficient for opening the eustachian tube in this age group. In addition, craniofacial disorders, such as a cleft palate, alter the attachment of the tensor muscle, producing functional obstruction of the eustachian tube. Mechanical obstruction results from internal obstruction or external compression of the eustachian tube (see Fig. 38-18C). Ethnic differences in the structure of the palate may increase the likelihood of obstruction. The most common internal obstruction is caused by swelling and secretions resulting from allergy and viral respiratory infections. With obstruction, air in the middle ear is absorbed, causing a negative pressure and the transudation of serous capillary fluid into the middle ear. Otitis Media O titis media (OM) refers to inflammation of the mid- dle ear without reference to etiology or pathogenesis (Fig. 38-19A). Inflammation of the middle ear may present as acute otitis media or otitis media with effusion. 50–52 Acute otitis media (AOM) refers to the rapid onset of signs and symptoms of a middle ear infection. Otitis media with effusion (OME) refers to inflammation of the middle ear with the presence of fluid in the middle ear without signs and symptoms of an acute ear infection. 53 It is important to differentiate OME from AOM to avoid unnecessary use of antimicrobial agents. Risk Factors. Otitis media may occur in any age group, but is seen most frequently in infants and young children between the ages of 3 months and 3 years, with the peak incidence between 6 and 11 months. 51 There is a second peak incidence at about 5 years of age that is believed to be associated with entrance into school. 50 Risk factors include premature birth, male gender, ethnicity (Native American, Inuit), family history of recurrent OM, presence of siblings in the household, genetic syndromes, and low socioeconomic status. 51 It is more frequent in children with orofacial abnormalities such as cleft lip and palate. The most important factor that contributes to OM is believed to be a dysfunction of the eustachian tube that allows reflux of fluid and bacteria into the middle ear from the nasopharynx. There are two reasons for the increased risk of OM in infants and young children: the eustachian tube is shorter, more horizontal, and wider in this age group than in older children and adults; and infection can spread more easily through the eustachian canal of infants who spend most of their day in the supine posi- tion. 51 Bottle-fed infants have a higher incidence of OM than breast-fed infants, probably because they are held in a more horizontal position during feeding, and swallow- ing while in the horizontal position facilitates the reflux of milk into the middle ear. Breast-feeding also provides for the transfer of protective maternal antibodies to the infant. Measures to reduce the risk for development of OM during the first 6 months of life include breast-feed- ing, avoidance or elimination of bottle propping, and reduction or elimination of pacifier use. 51 Other ways

Petrous portion of the temporal bone

Incus

Malleus

Base (footplate) of stapes occupying oval window

Stapes Tympanic cavity

Eustachian tube

External acoustic meatus

Tympanic membrane

A

Cholesteatoma

B

Otosclerosis

C

FIGURE 38-19. Disorders of the middle ear. (A) Otitis media. Otitis involves inflammation of the tympanic cavity. Infection often enters through the eustachian tube. (B) Cholesteatoma, a cystlike mass of the middle ear that often extends to involve the temporal bone. (C) Otosclerosis involving formation of new, spongy bone around the stapes and oval window.