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

The Ear and Disorders of Auditory Function

produces no symptoms unless it hardens and touches the tympanic membrane, or the canal becomes irritated by a buildup of hardened cerumen, causing pain, itching, and a sensation of fullness. As the canal becomes completely occluded, there may be a feeling of fullness, a conductive hearing loss, and tinnitus (i.e., ringing in the ears). In most cases, cerumen can be removed by gentle irrigation using a bulb syringe and warm tap water. Alternatively, health care professionals may remove cerumen using an otoscope for guidance along with a wire loop or plastic cerumen curette. A ceruminolytic agent is usually reserved for impacted or hardened cerumen that occurs without ear discharge, pain, rash, or irritation. Otitis Externa Otitis externa is an inflammation of the external ear that can vary in severity from mild dermatitis to severe cellulitis. 46,48 It can be caused by infectious agents, irritation (e.g., wearing hearing aids or earphones), or allergic reactions. Predisposing factors include frequent exposure to moisture in the ear canal (i.e., swimmer’s ear), trauma to the canal caused by cleaning or scratching, and allergies or skin conditions such as psoriasis. It commonly occurs in the summer and is manifested by itching, redness, tenderness, and narrowing of the ear canal because of swelling. Inflammation of the auricle or ear canal makes movement of the ear painful. There may be watery or purulent drainage and intermittent hearing loss. Treatment usually includes the use of ear drops containing an appropriate antimicrobial or antifungal agent in combination with a corticosteroid to reduce inflammation. 48 Persons with acute otitis externa (AOE) should preferably abstain from water sports, protect the

The ears are paired organs consisting of an external and middle ear, which function in capturing, transmitting, and amplifying sound; and an inner ear, which contains the receptive organs that are stimulated by sound waves (i.e., hearing) or head position and movement (i.e., balance). Disorders of the External Ear The external ear is a funnel-shaped structure that conducts sound waves to the tympanic membrane. It consists of the auricle, the external acoustic meatus (ear canal), and the lateral surface of the tympanic membrane 2,46 (Fig. 38-17). Modified sebaceous glands in the auditory canal secrete a waxlike substance called cerumen or earwax that has certain antimicrobial properties and is thought to serve a protective function. The tympanic membrane or eardrum is a thin, transparent membrane, approximately 1 cm in diameter, which separates the external ear from the middle ear. It is covered with thin skin externally and the mucous membrane of the middle ear internally. The tympanic membrane is attached in a manner that allows it to vibrate freely when audible sound waves enter the external auditory canal. Movements of the membrane are transmitted through the middle ear to the inner ear. Impacted Cerumen Although the ear normally is self-cleaning, the cerumen can accumulate in the narrow ear canal, causing reversible hearing loss. 47 Impacted cerumen usually

Inner ear

Middle ear

Cochlear portion Vestibular portion

Cranial nerve VIII

Semicircular canals

Tympanic membrane

Incus

Cochlea

Eustachian tube

Malleus

Stapes

External acoustic meatus

Auricle

Pharynx

FIGURE 38-17. External, middle, and internal subdivisions of the ear.