Background
External ear infections require otoscopic examination that must be performed in conjunction with evaluation of related structures such as the external ear and the head and neck. For example, examine the auricle for swelling, deformity, and erythema; the face for evidence of facial nerve paresis or other cranial neuropathy; and the neck for masses.
Tools
The otoscope consists of a head and a handle and is used to examine the external auditory canal (EAC), tympanic membrane, and middle ear. A magnifying lens enhances the clinician's view. One of 2 heads for the otoscope may be used. A diagnostic head is fixed to the otoscope, which does not allow use of microinstruments through the scope, while a working or operating head has a magnifying lens that can slide to the side, enabling passage of microinstruments through the speculum into the EAC and middle ear. A pneumatic attachment on the diagnostic head allows for assessment of tympanic membrane motion by generating positive pressure in the external canal, causing the tympanic membrane to deflect medially. When pressure is released, the tympanic membrane expands laterally. This technique is an important tool in the diagnosis of middle ear effusions, vascular lesions, and inner ear fistulas.
Technique
To best view the tympanic membrane in an adult, retract the auricle posteriorly and superiorly to straighten the EAC. In a child, pull the auricle posteriorly. Remove any debris or cerumen to allow for an adequate examination. Examine the external canal for masses, skin changes, and otorrhea; then, examine all parts of the tympanic membrane (eg, pars tensa, pars flaccida). Next, ascertain the motion of the tympanic membrane by pneumatic otoscopy. Lastly, attempt a thorough examination of the middle ear contents through the tympanic membrane, although this examination may be limited by the opacity of the tympanic membrane itself.
Anatomy of the external and middle ear. Pathophysiology
Anatomy
The external ear consists of the auricle and the EAC. The auricle is composed of elastic cartilage with the overlying skin attached directly to the perichondrium. The EAC has a cartilaginous framework in its outer third, while its inner two thirds is bony. The skin over the cartilaginous canal is thicker than that over the bony canal and contains apopilosebaceous units, which produce cerumen. Apopilosebaceous units are composed of both apocrine and eccrine glands that secrete their products around the base of a hair follicle. The EAC is related to the mandibular fossa anteriorly, mastoid air cells posteriorly, middle cranial fossa superiorly, and parotid gland inferiorly.
Glandular secretions from the apopilosebaceous unit combine with sloughed squamous epithelium (cerumen) to coat the external ear canal and maintain an acidic pH. This cerumen coat migrates from the isthmus of the external canal to the lateral part of the canal. Use of cotton swabs and excessive cleaning of the ear canal can disrupt this protective coating, leading to external ear infection.
Disorders of the EAC include otitis externa, otomycosis (fungal otitis externa), and eczematoid (psoriatic otitis externa). Otitis externa is a dermatitis most often caused by a bacterial pathogen, commonly a pseudomonal or staphylococcal species.
Otomycosis is most commonly due to infection with an Aspergillus species. Pseudomonal infection produces green or yellow purulent otorrhea. Aspergillus otomycosis appears as a fine white mat topped by black spheres. In addition to otorrhea, erythema and edema of the EAC are common. In severe cases, soft tissue stenosis may be present. Extension of the infection from the EAC may manifest as cellulitic skin changes involving the concha of the auricle and the tragus. In most cases, treatment consists of acidification of the ear canal with drops, with or without topical antibiotics, although systemic antibiotics may be necessary as well.
Eczematoid is somewhat different in that it is not due to an infectious pathogen. This condition often manifests as a moist, white, granular otorrhea on an erythematous base. Eczematoid often responds to topical steroid drops but may be chronic or recurrent.
Embryology
Auricle: The auricle begins to form during the sixth week of gestation by a consolidation of portions of the mesoderm of the first and second branchial arches, giving rise to the His hillocks. The first 3 hillocks are derived from the first arch, and the second 3 are from the second arch. The auricle reaches adult shape by the twentieth week of gestation, but the adult size is not reached until age 9 years.
EAC: The EAC begins to form during the eighth week of gestation, when the surface ectoderm of the first pharyngeal groove thickens and grows toward the middle ear. This core of tissue begins to resorb by the 21 weeks' gestation to form a channel that is complete by 28 weeks' gestation. The canal reaches adult size by age 9 years and ossifies completely by age 3 years.
Epidemiology
Frequency
United States
Otitis externa is a common disorder, but frequency, sex, and age predilection is unknown.
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