Embryology USMLE Step 1 Practice Question
A 2-year-old child presents with a midline neck mass. Vital signs show HR 98/min, RR 22/min, BP 95/62 mmHg, temperature 37.2°C, SpO2 98% on room air. Physical examination reveals thyroid tissue extending from the base of the tongue to the lower neck along the midline, with a normally located thyroid gland. Thyroid ultrasound confirms ectopic thyroid tissue. The child denies dysphagia. Which embryologic structure failed to involute properly during development?
Answer choices
- AFourth pharyngeal pouch
- BThyroglossal ductCorrect answer
- CThird branchial arch cartilage
- DFirst branchial cleft
- ESecond pharyngeal pouch
- FUltimobranchial body
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