In the early stage of otoscierosis (otospongiosis), the endochondral bone is replaced by foci of spongy new bone. In its late stage, the decalcified foci recalcify into a dense ossific plaque.
Fenestral otosclerosis causes a progressive conductive hearing loss, although findings on otoscopic examination will be normal; two-thirds of such patients have tinnitus during the early course of their disease. Cochlear otosclerosis causes a progressive sensorineural hearing loss. When both types exist simultaneously, as happened in the case illustrated here (figure), a mixed pattern of hearing loss can be observed.
Fenestral otoscierosis is the more common type, and it is thought to begin in the fissula ante fenestram (anterior oval window margin).' [1] In the lytic phase, the oval window can appear to be too wide on computed tomography (CT) as a result of the osteoclastic resorption of its margins (figure).
Although cochlear otoscierosis is much less common, when it is present it is invariably associated with fenestral otosclerosis. CT will show a focal lucency of the otic capsule, giving the cochlea the appearance of a double ring on axial CT. [2] On contrast-enhanced T1-weighted magnetic resonance imaging, areas of punctate enhancement in the otic capsule might be seen.
References
(1). Harnsberger HR. The temporal bone: External, middle, and inner ear segments. In: Harnsberger HR. Handbook of Head and Neck Imaging. 2nd ed. St. Louis: Mosby, 1995:426-58.
(2.) Valvassori GE. Otosclerosis and bone dystrophies. In: Valvassori GE, Mafee MF, Carter BL, eds. Imaging of the Head and Neck. New York: Thieme Medical publishers, 1995:143-56.
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COPYRIGHT 2001 Gale Group
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