In the pathogenesis of otosclerosis, the disease process starts in:
Otic capsule (also called bony labyrinth) has three layers: outer periosteal, inner endosteal and the middle bony. The bony layer which develops from cartilage and for some unknown reason bone of the otic capsule is absorbed and replaced by spongy vascular bone which later becomes sclerotic due to deposition of calcium.
Periosteal layer of otic capsule
Endosteal layer of otic capsule
Bone of otic capsule which develops from cartilage
Mucoperiosteum of the promontory
Ear