Cochlear Otosclerosis Adjacent to Round Window and Oval Window: A Histopathological Temporal Bone Study

Hypothesis: The purpose of this histopathological study is to examine temporal bones of patients with cochlear otosclerosis adjacent to the round window or adjacent to the oval window as compared with healthy controls. Background: It is unclear if the extent and site of otosclerosis affects the extent of damage to cochlear structures and hearing loss. Methods: Twelve temporal bones from 10 patients with cochlear otosclerosis adjacent to the round window, 11 temporal bones from 8 patients with cochlear otosclerosis adjacent to the oval window, and 12 bones of healthy age-matched controls were selected for study. We calculated the number of spiral ganglion cells, changes in cochlear structures, the extent and site of cochlear otosclerosis, and audiometric data. Results: The loss of spiral ganglion cells and the absence of outer hair cells in patients with cochlear otosclerosis adjacent to the round window were significantly higher than those in patients with cochlear otosclerosis adjacent to the oval window and healthy controls. The area of the spiral ligament in patients with cochlear otosclerosis adjacent to the oval window was significantly smaller than that in healthy controls. However, no significant difference was found in the spiral ligament of patients with cochlear otosclerosis adjacent to the round window and healthy controls. There was no significant difference between patients with cochlear otosclerosis and age-matched controls in audiometric data. Conclusion: Cochlear otosclerosis adjacent to the round window caused significantly more damage to spiral ganglion cells and outer hair cells than cochlear otosclerosis adjacent to the oval window without loss of spiral ligament.