Pathology of the otic capsule.

The otic capsule is unique in retaining calcified cartilage, known as globuli interossei, throughout life and shows changes consequently, which are peculiar to it. In Paget's disease of bone, the otic capsule appears resistant to involvement and this occurs with extensive disease at a late stage. In contrast, otosclerosis is a new bone formation of unknown cause that is limited to the otic capsule. In osteogenesis imperfecta, the poor formation of collagen leads to abnormally thin bony trabeculae with a poorly formed otic capsule. In osteopetrosis, the otic capsule is greatly expanded by increased globuli interossei, as a result of defective osteoclast function. When fractured the middle layer of the otic capsule does not form callus, but heals by fibrosis.