Commonest site of otosclerosis is
The most common type of otosclerosis is stapedial otosclerosis. Stapedial otosclerosis causes stapes fixation and conductive deafness is the most common variety. Here the lesion mainly stas just in front of the oval window in an area called "fissula ante fenestram". This is the site of predilection( anterior focus). The lesion may sta behind the oval window(posterior focus), around the margin of the stapes footplate( circumferential), in the footplate but annular ligament being free (biscuit type). Sometimes, it may completely obliterate the oval window. ( obliterate type) (Ref: Diseases of EAR, NOSE and THROAT by PL Dhingra; 7th Edition; Page no.95.)
Round window
Oval window
Utricle
Ossicles
Ear