In cochlear (histologic) otosclerosis extending to the otic capsule around the scala vestibuli, the sensorineural component of hearing loss results from:
- A Direct compression of the organ of Corti by bony overgrowth
- B Obstruction of the endolymphatic duct
- C Diffusion of proteolytic enzymes from the active focus into perilymph ✓
- D Ischaemia of the spiral ganglion cells
Correct answer: C. Diffusion of proteolytic enzymes from the active focus into perilymph
Explanation
Active otosclerotic foci release hydrolytic enzymes that diffuse through the annular ligament into the perilymph of the scala vestibuli, poisoning the organ of Corti and producing a sensorineural loss. This gives a mixed hearing loss on audiometry. Bony encroachment rarely compresses neural structures directly, and endolymphatic flow is unaffected, so options A and B are incorrect mechanisms.
Reference: Cummings Otolaryngology: Head and Neck Surgery, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.