A 28-year-old man presents with sudden-onset conductive hearing loss following a motor vehicle accident with temporal bone trauma. Otoscopy reveals an intact tympanic membrane. Pure-tone audiometry shows air-bone gap of 50 dB with normal bone conduction thresholds. Tympanometry is shown in the diagram. The tracing marked **C** (Type Ad) demonstrates normal middle ear pressure with markedly increased static admittance. Which of the following is the most likely diagnosis?

Question

Accepted Answer

A. Ossicular chain discontinuity with incudostapedial joint disruption. ## Why Ossicular chain discontinuity with incudostapedial joint disruption is right

The Type Ad tympanogram (marked **C**) is characterized by normal middle ear pressure (peak between −100 and +50 daPa) combined with markedly increased static admittance (peak compliance >2.0 mmho or >1.5 mL), reflecting a hypermobile middle ear system. This pattern, in the context of post-traumatic sudden conductive hearing loss with an intact tympanic membrane and large air-bone gap (50 dB), is pathognomonic for ossicular chain discontinuity. Head trauma with temporal bone fracture—particularly longitudinal fractures—is the most common cause, with the incudostapedial joint being the most vulnerable site due to weak ligamentous support. The absent acoustic reflexes (implied by the clinical presentation) further confirm ossicular disruption. Diagnosis is confirmed by high-resolution CT temporal bone. (Dhingra Diseases of Ear, Nose and Throat 8e; Cummings Otolaryngology 7e)

## Why each distractor is wrong

- **Otosclerosis with stapes footplate fixation**: This produces Type As tympanogram (shallow peak, compliance <0.3 mL), not Type Ad. The stiffened stapes system reduces compliance, whereas Type Ad reflects increased compliance from ossicular discontinuity.
- **Serous otitis media with middle ear effusion**: This produces Type B tympanogram (flat tracing with absent peak), not Type Ad. Effusion prevents normal tympanic membrane mobility and produces negative or absent pressure peaks.
- **Tympanic membrane perforation with healing**: While a healed perforation can produce Type Ad, the clinical context of acute post-traumatic loss with intact TM on otoscopy makes ossicular discontinuity far more likely. Perforation would show visible defect on examination.

**High-Yield:** Type Ad (high compliance + normal pressure) = ossicular discontinuity or hypermobile TM; Type As (low compliance + normal pressure) = otosclerosis; Type B (flat) = effusion; Type C (negative pressure) = Eustachian tube dysfunction.

[cite: Dhingra Diseases of Ear, Nose and Throat 8e; Cummings Otolaryngology 7e]

Answer

B. Tympanic membrane perforation with healing

Answer

C. Otosclerosis with stapes footplate fixation

Answer

D. Serous otitis media with middle ear effusion

Explanation

Why Ossicular chain discontinuity with incudostapedial joint disruption is right

Why each distractor is wrong

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