Though this disease is commonly described as otosclerosis - the primary abnormality is bony resorption with spongy lucent appearing bone, hence otospongiosis is a better term for this disease.
Sclerosis is a late manifestation of the disease.
The temporal bone is unique in that there is normally persistence of primary endochondral bone as the middle layer of the otic capsule. There are two varieties of otosclerosis. The more common variety is fenestral otosclerosis which involves the oval window and the stapes foot plate. This presents with primarily conductive hearing loss. This is difficult to see on CT and is usually diagnosed clinically when a patient presents with conductive hearing loss and a clean middle ear as seen through the otoscope.