Causes Pathophysiology

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The most common bony diseases that may cause stenosis of the external auditory canal are exostosis, osteoma, and fibrous dysplasia. Exostoses of the external canal are rounded, multiple bony outgrowths that can occur because of chronic irritation of the external canal. The most common cause of exostoses is cold-water swimming. These lesions can continue to grow even after the ear canal is no longer exposed to a cold environment. Osteomas are singular, often pedunculated, benign bony tumors arising from the osseous meatus. There is no identifiable cause for external canal osteomas. Fibrous dysplasia is a benign disease of bone characterized by the abnormal proliferation of fibro-osseous tissue within cancellous bone.

Acquired soft tissue stenosis of the external canal is due to some insult to the canal that results in cicatrix formation. The insult may be the result of recurrent/chronic inflammation (infection, dermato-logic disease), iatrogenic injuries (surgery, radiation), trauma (burns, chemical injury, repeated ear canal scratching, fracture), or neoplasm. In one large review, the leading cause of stenosis was chronic infection (54%) followed by prior ear surgery (20%).8 When surgery or trauma is the inciting event, many years may elapse before the acquired soft tissue stenosis requires surgical treatment.8

Systemic diseases of the skin (e.g., psoriasis, lupus erythematosus, scleroderma) can affect the ear canal and eventually cause external canal obstruction. One important feature of psoriasis is that mild trauma to surrounding skin induces lesions localized to the area of injury.9 Therefore, patients with psoriasis in or near the ear canal should be asked to avoid manipulation of the lesions, so as to prevent stenosis. Cutaneous (contact dermatitis) reactions to shampoos, medications, and foreign material in the ear canal can be severe and may require rapid medical attention to prevent scarring and stenosis of the soft tissue of the canal.

Acquired soft tissue stenosis of the external canal is uncommon. For postinflammatory acquired atre-sia, Becker and Tos reported an annual incidence of 0.6 per 100,000. Many other large series of acquired soft tissue stenosis report, on average, treating one case of soft tissue stenosis per year.4,11 13

Many terms have been used to describe acquired soft tissue stenosis of the external canal including medial meatal fibrosis,12 14 chronic stenosing exter nal otitis,4 and postinflammatory acquired atresia.10 The pathophysiology of acquired soft tissue canal stenosis is unknown because there are currently no experimental animal models. It is believed that the canal passes through several stages before developing the soft tissue stenosis. In the first stage of development, some type of insult (e.g., infectious, traumatic) produces granulation tissue of the ear canal, tympanic membrane, or combination of the two sites. The granulation tissue becomes infected and the tissue proliferates. This stage is considered the active or immature phase. Eventually, a mature stage ensues whereby the granulation tissue forms a well-developed fibrous plug lined by squamous epithelium. The disease process ceases to continue when the atresia reaches the lateral end of the bony canal.15

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