Embryology USMLE Step 1 Practice Question
A 3-year-old boy presents with a midline neck mass that elevates with swallowing and tongue protrusion. Vital signs show BP 100/65, HR 98, RR 22, Temp 37°C, SpO2 98%. Physical examination reveals a smooth, painless 2-cm nodule. Ultrasound demonstrates a cystic lesion at the base of the tongue with clear fluid content. There is no fever, dysphagia, or respiratory distress. Which embryologic structure failed to involute completely?
Answer choices
- AFirst pharyngeal pouch
- BThyroglossal ductCorrect answer
- CNotochord remnant
- DSecond pharyngeal pouch
- EMeckel's cartilage
- FForamen cecum patent with ectopic thyroid tissue
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