Otosclerosis affects which bone?

Ans. is 'a' i.e., Stapes Types of otosclerosis Following types of otosclerosis have been described :- 1. Fenesteral or stapedial otosclerosis It is the most common type (80-90%) The lesion stas just in front of the oval window in an area called fissula ante fenestram" and causes stapes footplate fixation and conductive hearing loss. Hearing loss is purely mechanical. 2. Cochlear otosclerosis (Retrofenestral otosclerosis) When present, it is almost always associated with stapedial (fenestral) otosclerosis. It involves region of round window or other areas in the otic capsule. It causes mixed or sensorineural hearing loss which is believed to be toxic due to diffusion of cytotoxic enzymes into the fluid of the membranous labyrinth (In contrast to stapedial otosclerosis, where the deafness is purely mechanical and is conductive). Tinnitus is more common in cochlear otosclerosis. 3. Histologic otosclerosis This type of otosclerosis remains asymptomatic and causes neither conductive nor sensorineural hearing loss.