Otosclerosis — Pathology, Signs, Tuning Fork Tests, Audiogram and Stapes Surgery

Otosclerosis is a disorder of bone remodelling in the otic capsule — the dense bone around the inner ear. Normal endochondral bone is replaced by foci of irregular, spongy bone that later hardens abnormally. When a focus involves the stapes footplate and its annular ligament at the oval window, the stapes can no longer vibrate, and sound cannot pass efficiently into the cochlea. The result is conductive hearing loss.

If the foci spread into the cochlea itself (cochlear otosclerosis), sensorineural loss is added, giving a mixed hearing loss — usually affecting the higher frequencies.

The first lesion usually appears at the fissula ante fenestram, a small area just in front of the oval window, between the oval window and the cochleariform process. From there it spreads through vascular channels to the anterior footplate and annular ligament. Active, vascular foci appear red; mature foci are sclerotic.

Many more people have otosclerotic foci than have symptoms. Clinical otosclerosis affects roughly 0.04–1% of White individuals, yet histological foci may be found in up to 10% of that group. Histological otosclerosis is less frequent in Black (about 1%) and Asian (about 5%) populations. Only foci that reach the stapes footplate or cochlea cause hearing loss.

• Slowly progressive hearing loss, bilateral in about 70% of patients.
• Tinnitus is very common — about 89% in one surgical series.
• Paracusis Willisii — the patient hears better in a noisy background. It is not pathognomonic, but it indicates a conductive loss.
• Normal tympanic membrane on otoscopy in most patients.
• Schwartze sign — a reddish blush on the cochlear promontory seen through a thin eardrum, due to increased vascularity of an active focus.

The Gellé test places a vibrating fork on the mastoid while the air pressure in the ear canal is raised. In normal ears and in sensorineural loss, canal pressure measurably shifts bone-conduction thresholds. When the stapes is fixed, nothing changes — a negative Gellé test. Gellé himself proposed it as a diagnostic criterion for otosclerosis in 1885, and a 2025 surgical series found it negative in 98.7% of ears.

• Pure tone audiometry: air-conduction loss, usually starting in the low frequencies, with an air–bone gap.
• Carhart notch: an apparent dip in the bone-conduction line of about 20–30 dB at 2,000 Hz, caused by loss of the ossicular chain's resonance — not true cochlear damage. It usually disappears after stapedectomy.
• Mixed loss: in advanced or cochlear disease, sensorineural loss is added, mainly at high frequencies.
• Tympanometry: usually normal (type A) in early otosclerosis, which helps distinguish it from ossicular discontinuity. Speech discrimination is also normal early.
• Stapedial reflexes: may still be normal in early disease.
• High-resolution CT temporal bone: foci of spongy or sclerotic bone anterior to the oval window; in cochlear otosclerosis a 'halo sign' of lucency around the cochlea.

In stapes surgery the fixed stapes superstructure is removed and a prosthesis (piston) is placed from the incus to the oval window. In stapedectomy the footplate is removed; in small-fenestra stapedotomy — now the most common operation — only a small hole is made in the footplate for the piston. Surgery can be done under local or general anaesthesia.

• Worse ear first: in bilateral disease the ear with greater loss is operated first.
• Never both ears at the same sitting — to avoid the remote risk of bilateral total sensorineural loss.
• Contraindications: the only hearing ear, active infection of the canal or middle ear, and poor general condition that prevents anaesthesia.
• Main risk: sensorineural hearing loss, up to an anacusic 'dead ear' — higher in revision surgery.
• After surgery: the Carhart notch usually disappears; some patients still need a hearing aid.