Otosclerosis

Otosclerosis is a disease of the bony labyrinth, which, by involvement and fixation of the s tapes footplate, leads to severe conductive hearing loss. Otosclerosis has some features of a hereditary disease, but its genetics still remain incompletely elucidated. Ultrastructural and immunohistochemical evidence for measles virus and isolation and identification of DNA and RNA sequences of that virus have been found in otosclerotic tissue [18].

Otosclerosis usually affects both ears symmetrically. The disease process is probably confined to the temporal bone. The pink swelling of otosclerosis may sometimes even be detected clinically through a particularly transparent tympanic membrane as a well-demarcated and pink focus near the promontory. A characteristic translucency of bone adjacent to the cochlea and anterior to the footplate is identified on a CT scan.

The lesion always commences in the otic capsule tissue anterior to the footplate of the stapes. In this position it does not produce symptoms. These occur when the otosclerosis invades the adjacent stapes footplate and produces fixation of that structure and thus conductive hearing loss. It later spreads widely in the otic capsule and may involve the round window ligament. Blood vessels are prominent and evenly dis-

Fig. 8.17. Radiograph of microslice of autopsy temporal bone with focus of otosclerosis. The focus is an area of mottled translu-cency in the region of the fissula ante fenestram (arrowheads). Reproduced from Michaels and Hellquist [68]

Fig. 8.18. Focus of otosclerosis involving both the anterior (upper) and posterior (lower) part of footplate of the stapes. The anterior focus has invaded onto the footplate and the anterior crus. This would have produced fixation of the stapes and its attendant conductive hearing loss. Notice that the otosclerotic foci are more darkly staining and vascular than the adjacent normal bone. Reproduced from Michaels and Hellquist [68]

Fig. 8.18. Focus of otosclerosis involving both the anterior (upper) and posterior (lower) part of footplate of the stapes. The anterior focus has invaded onto the footplate and the anterior crus. This would have produced fixation of the stapes and its attendant conductive hearing loss. Notice that the otosclerotic foci are more darkly staining and vascular than the adjacent normal bone. Reproduced from Michaels and Hellquist [68]

case, otosclerotic bone will possibly be observed in sections of the anterior part of the footplate.

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