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ANATOMY

Morphology

The pinnae of the external ear are funnel-shaped cartilaginous structures that aid in focusing and localizing sound. Each pinna is anchored to the cranium by skin, cartilage extension into the external auditory canal cartilage, auricular musculature, and extrinsic ligaments. The anatomy of the pinna is illustrated in Figure 49–1.

The external auditory canal (EAC) is typically 24 mm in length with a volume of 1 to 2 mL. The lateral third of the canal is made of fibrocartilage, whereas the medial two-thirds are osseous. During early childhood, the canal is straight, but takes on an S shape by the age of 9 years. The narrowest point is at the bony-cartilaginous junction. The EAC also has an important relationship with the mastoid segment of the facial nerve, which lies posterior to the EAC as it descends toward the stylomastoid foramen. The temporomandibular joint is anterior to the EAC, and disease processes affecting this joint may present with otalgia.

Skin

The EAC is lined by stratified squamous epithelium that is continuous with the skin of the pinna and the epithelium of the tympanic membrane. The subcutaneous layer of the cartilaginous portion of the canal contains hair follicles, sebaceous glands, and ceruminous glands, and is up to 1 mm thick. The immobile skin of the osseous canal does not have subcutaneous elements. It is only 0.2 mm thick and is directly adherent to periosteum (Figure 49–2). The epithelium of the EAC migrates laterally from the tympanic membrane, combines with glandular secretions, and is extruded as cerumen.

Figure 49–2

Coronal section of the ear canal. The skin of the cartilaginous and osseous canals is magnified. (Reproduced, with permission, from Lucente F, ed. The External Ear. Copyright Elsevier, 1995.)

The ceruminous glands are modified apocrine sweat glands surrounded by myoepithelial cells and are organized into apopilosebaceous units. These empty into a follicular canal surrounding each hair follicle, providing glandular secretions that combine with sloughed epithelium to create cerumen (Figure 49–3). Cerumen prevents canal maceration, is hydrophobic, and has a slightly acidic pH, all of which contribute to the antibacterial effects of cerumen.

Figure 49–3

Skin of the cartilaginous portion of the external auditory canal depicting apopilosebaceous units. (Reproduced, with permission, from Main T, Lim D. The human external auditory canal: an ultrastructural study. Laryngoscope. 1976;86:1164. Copyright LWW.)

Innervation

The pinna is innervated laterally, inferiorly, and posteriorly by the great auricular nerve (cervical plexus). Arnold’s nerve (a branch of the vagus nerve) innervates the inferior bony canal, ...

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