Malignant Neoplasms

Fig. 8.6. Exostosis of the deep external canal. Note thin epidermal layer on the exostosis and canal skin and their proximity to the bone. Reproduced from Michaels and Hellquist [68]

periosteum merge to form a thin layer. The distance between the epidermal surface and underlying bone is consequently small. This explains the propensity towards exostoses of the tympanic bone to develop in this region in those who swim frequently in cold water. It seems likely that the water, after dribbling into the deep external auditory canal, exerts a cooling effect on the bone surface and stimulates it to produce new bone. Unlike osteoma (Fig. 8.5) the bone formations of exostosis are said not to possess any marrow spaces (Fig. 8.6).

Osteoma and exostosis are often associated with infection of the external canal on their tympanic membrane side and surgical removal may be required to enhance drainage as well as to relieve the conductive hearing loss.

Five cases of a benign circumscribed bony lesion of the external auditory canal distinct from exostosis and osteoma have recently been described [91]. They all showed a hard, round, unilateral, skin-covered mass occluding the superficial external auditory canal with no relationship to the cartilaginous tissue or to the bony structure surrounding that canal. Histologically, the lesion displayed an osteoma-like bone formation with sparse osteoblastic areas; mature lamellar bone was observed some cases, and also bone marrow containing adipose tissue and hematopoietic remnants. The bone showed irregular trabeculae, bordered by osteoid osteo-blasts.

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