Embryology USMLE Step 1 Practice Question
A 2-day-old male newborn is brought to the emergency department with severe respiratory distress, stridor, and cyanosis. Vital signs show heart rate 168 bpm, respiratory rate 70/min, blood pressure 50/26 mmHg, oxygen saturation 76% on room air. Chest X-ray reveals a well-demarcated anterior mediastinal mass causing tracheal compression. CT imaging of the neck and chest demonstrates a heterogeneous mass containing mature hair follicles, keratinous material, thyroid follicles, and bone elements. Thyroid function tests are normal. The mass is located in the midline between the thyroid gland and the hyoid bone. Which embryologic remnant most likely failed to undergo complete involution?
Answer choices
- ABranchial cleft cyst (second arch derivative)
- BThyroglossal duct cystCorrect answer
- CThymic cyst
- DUrachus
- ECystic hygroma (lymphatic malformation)
- FLaryngocele
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