This is an advanced case of otosclerosis. There is involvement of fissula ante fenestram, oval window, round window and the otic capsules. The left side is showing both fenestral and cochlear otosclerosis.

Otosclerosis is a disease of the bony labyrinth. It starts at the fissula ante fenestram and spreads posteriorly to involve the oval window and then is called the fenestral type.

If it progresses it will involve the round window, pericochlear region and the otic capsule and then it is called the cochlear type.

This case is very advanced because the lucencies surrounding the otic capsule, and spreading to the anterior wall of the IACs. There is also bony overgrowth of the basal turn of the cochlea obliterating the round window niche.