In high-resolution CT of the temporal bone, which structure is identified at the cochlear promontory level that appears as a dark 'halo' around a bright dot — the 'double ring sign'?

• A Normal cochlear turns with perilymph
• B Labyrinthitis ossificans
• C Cochlear otosclerosis (retrofenestral otosclerosis) ✓
• D Superior semicircular canal dehiscence

Explanation

Retrofenestral (cochlear) otosclerosis on HRCT temporal bone shows the classic 'double ring' or 'halo' sign — a hypodense lucent halo around the cochlear capsule due to spongiotic (hypervascular) bone replacing the normal dense endochondral bone. This corresponds to the lucency seen around the cochlea and represents active otospongiosis. This sign is pathognomonic of cochlear otosclerosis and correlates with the degree of sensorineural loss.

Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.