Treacher Collins Bilateral Conductive Hearing Loss MCQ — NEET PG Practice Question | NEETPGAI
Treacher Collins Bilateral Conductive Hearing Loss
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ear ENT
A 6-month-old boy with bilateral microtia, micrognathia, and downslanting palpebral fissures is referred for audiologic assessment. Audiometry reveals the pattern marked **A** in the diagram — bilateral symmetric air-bone gap of 50 dB across all frequencies with normal bone conduction thresholds. Which of the following best explains the preservation of bone conduction in this patient's hearing loss?
A. Intact cochlear and inner ear function due to sparing of neural crest cell derivatives of the otic placode
B. Preserved function of the tensor tympani muscle despite middle ear ossicular malformations
C. Recruitment of the contralateral cochlea via transcranial bone vibration pathways
D. Compensatory hypertrophy of the stapes footplate to overcome ossicular fixation
Explanation
Why "Intact cochlear and inner ear function due to sparing of neural crest cell derivatives of the otic placode" is right
Treacher Collins syndrome results from TCOF1 mutations causing haploinsufficiency of treacle protein, which disrupts ribosomal RNA transcription and triggers p53-mediated apoptosis of neural crest cells migrating to the first and second pharyngeal arches (weeks 5–8 of gestation). This selective damage affects structures derived from these arches — mandible, maxilla, zygoma, external ear, middle ear ossicles, and palate — but spares the inner ear and cochlea, which develop from the otic placode (ectodermal origin, not pharyngeal arch neural crest). Therefore, bone conduction (which bypasses the external and middle ear and directly stimulates the cochlea) remains normal, producing the characteristic pure conductive loss with air-bone gap and preserved bone conduction thresholds. This is the pathophysiologic hallmark of Treacher Collins audiologic findings (Cummings Otolaryngology, 7th ed.).
Why each distractor is wrong
Compensatory hypertrophy of the stapes footplate to overcome ossicular fixation: Treacher Collins involves ossicular malformations (absent/hypoplastic incus and malleus, fused stapes), not compensatory remodeling. The stapes footplate does not hypertrophy to overcome conductive loss; bone conduction is preserved because the cochlea itself is intact, not because of ossicular compensation.
Recruitment of the contralateral cochlea via transcranial bone vibration pathways: While bone conduction does utilize transcranial vibration, this is not specific to Treacher Collins and does not explain why bone conduction is preserved in this syndrome. The key is that the cochlea is structurally and functionally normal, not that contralateral recruitment occurs.
Preserved function of the tensor tympani muscle despite middle ear ossicular malformations: The tensor tympani is a muscle of the first pharyngeal arch and would be affected by the same neural crest cell apoptosis that damages the ossicles. Moreover, tensor tympani function does not determine bone conduction thresholds; the cochlea does.
High-YieldNEET PG
Treacher Collins = pure conductive loss + normal bone conduction + normal cochlea → first-line hearing aid is bone-conduction device (softband initially, BAHA at age 4–5).
Cummings Otolaryngology, 7th ed.; pathogenesis of Treacher Collins syndrome and audiologic findings in craniofacial dysostosis
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