Which bone is primarily affected in otosclerosis?

Explanation

## Pathology of Otosclerosis **Key Point:** Otosclerosis is a disease of abnormal bone remodeling in the middle ear, characterized by replacement of normal bone with abnormal otosclerotic bone. ### Site of Involvement The **stapes** is the ossicle most commonly and characteristically affected in otosclerosis. The disease typically begins at the **fissula ante fenestram** (a small cleft of connective tissue anterior to the oval window) and progresses to fix the stapes footplate to the oval window. ### Pathophysiology 1. Abnormal osteoclastic and osteoblastic activity 2. Replacement of normal bone with hypervascular, disorganized otosclerotic bone 3. Stapes footplate fixation → conductive hearing loss 4. Cochlear involvement (cochlear otosclerosis) → sensorineural hearing loss ### Why Other Ossicles Are Spared While the malleus and incus may rarely be involved, they are **not** the primary site. The stapes footplate fixation is the hallmark finding that distinguishes otosclerosis from other causes of conductive hearing loss. **High-Yield:** The **oval window region and stapes footplate** are the classic sites of otosclerotic bone formation. This anatomical predilection is why otosclerosis causes progressive conductive hearing loss that may be amenable to stapedectomy. **Clinical Pearl:** Imaging (HRCT temporal bone) shows hypodense otosclerotic foci around the oval window, and the stapes footplate appears fixed on audiological testing.