A 28-year-old woman presents with progressive bilateral hearing loss over 2 years, worse on the left. She reports low-pitched tinnitus and notes that she can hear better in noisy environments when she raises her voice. Otoscopy shows a normal, mobile tympanic membrane. Audiometry is shown in the diagram. The pattern marked **B** shows conductive hearing loss with a characteristic notch at 2 kHz on bone conduction. Which of the following best explains the pathophysiology underlying this audiometric finding in otosclerosis?

Question

Accepted Answer

A. Loss of the natural middle ear resonance at 2 kHz due to stapes footplate fixation, creating an artifact on bone-conduction testing that resolves after stapedotomy. ## Why option 1 is correct

The Carhart notch at 2 kHz is a pathognomonic finding in otosclerosis that reflects loss of the natural middle ear resonance at 2 kHz. This is an **artifact of bone-conduction testing** caused by stapes footplate fixation, not true cochlear damage. The notch is characteristic because bone conduction normally bypasses the middle ear, but the loss of middle ear resonance (which normally amplifies bone-conducted sound at 2 kHz) creates a relative dip. Critically, this notch **resolves completely after successful stapedotomy**, confirming it is a functional artifact rather than permanent sensorineural pathology. This is the defining audiometric signature of fenestral otosclerosis and is essential for diagnosis (Dhingra ENT 8e; Cummings Otolaryngology 7e).

## Why each distractor is wrong

- **Option 2**: Cochlear otosclerosis does cause sensorineural hearing loss, but it is less common than fenestral disease and does NOT produce the characteristic Carhart notch at 2 kHz. The notch is specific to conductive loss from stapes fixation, not cochlear involvement.
- **Option 3**: Ossicular discontinuity (e.g., from trauma or chronic otitis) causes conductive loss but does not produce the pathognomonic Carhart notch at 2 kHz. The notch is unique to stapes fixation and middle ear resonance loss.
- **Option 4**: Tympanic membrane retraction causes conductive loss but would not produce a selective bone-conduction dip at 2 kHz. Retraction affects air-bone gap globally, not the specific resonance frequency.

**High-Yield:** Carhart notch at 2 kHz = stapes fixation artifact on bone conduction; resolves after stapedotomy; pathognomonic for otosclerosis.

[cite: Dhingra ENT 8e; Cummings Otolaryngology 7e]

Answer

B. Tympanic membrane retraction causing mechanical dampening of sound transmission at low frequencies

Answer

C. Sensorineural hearing loss from cochlear involvement with permanent damage to the organ of Corti at the 2 kHz frequency region

Answer

D. Conductive loss from ossicular discontinuity with secondary damage to the round window membrane

Explanation

Why option 1 is correct

Why each distractor is wrong

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