The External Ear
This chapter aims to provide an overview of disorders affecting the auricle and external auditory canal. The anatomy, clinical manifestations, diagnostics, and various treatment modalities available for these disorders are reviewed in this chapter. The ex
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The External Ear Aisha Larem, Adham Aljariri, and Zaid Altamimi
3.1
Introduction
The ear consists of three parts: the external, middle, and internal ear. All three parts play an essential rule in the hearing function of the ear. The auricle concentrate (collects and localizes) the sound waves from different directions and directs them to the ear canal, then into to the middle, and then into the cochlea. The external ear is the outermost part of the ear, and it is subdivided into auricle (Pinna) and the external auditory canal (EAC). The external ear is subjected to different types of disorders with a higher risk for trauma, infections, and foreign body impaction than the other parts of the ear [1]. In this chapter, the pathologies of the auricle and the EAC are discussed and divided into congenital, acquired, and inflammatory. A brief overview of the embryology, anatomy, and physiology of the external ear is discussed below.
A. Larem (*) · A. Aljariri · Z. Altamimi Hamad Medical Corporation, Doha, Qatar e-mail: [email protected]; [email protected]; [email protected]
3.1.1 Embryology The ear is originating from the three embryonic layers, ectoderm, mesoderm, and endoderm. The auricle develops from the fusion of six mesodermal hillocks which arises from the first and the second branchial arches [1]. The external ear canal is derived from the first branchial groove (cleft). EAC ends at the tympanic membrane (TM), a structure developed from the three embryonic layers. Different congenital anomalies can affect the external ear, and it includes microtia, anotia, canal atresia, prominent auricles (Bat ears), pits, or sinuses.
3.1.2 Anatomy The auricle is the visible portion of the external ear. The auricular cartilage is composed of elastic cartilage; the auricle sensory innervation is by the greater auricular, the lesser occipital nerves (branches of the cervical plexus), auriculotemporal nerve (branch of the mandibular nerve), and branches of the facial and vagus cranial nerves. The sensory nerve innervation of the auricle is demonstrated in Fig. 3.1. The external auditory canal is approximately 24 mm in length. The outer one-third (8 mm) is formed by cartilage, and the medial two-thirds are formed by bone.
© Springer Nature Switzerland AG 2021 A. Al-Qahtani et al. (eds.), Textbook of Clinical Otolaryngology, https://doi.org/10.1007/978-3-030-54088-3_3
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Auriculotemloral nerve
Lesser occipital nerve Auricular branch of vagus nerve
Greater auricluar nerve
Fig. 3.1 Schematic drawing to the auricle with sensory nerve supply
EAC is lined with stratified squamous epithelium that contains hair follicles, sebaceous glands, and special cerumen gland that secret cerumen. The sloughed epithelium along with any impacted material in the EAC is sloughed out in a centrifugal manner to expel externally.
3.1.3 Physiology The auricle and the external auditory canal work to concentrate the sounds from surroundings and lead to rising specific resonant frequencies, concha gives resonant to the
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