Embryology USMLE Step 1 Practice Question
A 4-week-old male infant presents to the pediatrician with a firm, painless midline neck mass that the parents first noticed 2 weeks ago. On examination, the mass is located between the hyoid bone and thyroid cartilage. When the infant swallows, the mass moves upward; similarly, when the tongue is protruded, the mass moves superiorly. Ultrasound shows a 1.5-cm cystic lesion with homogeneous fluid content and no internal vascularity. The infant has no fever, stridor, or dysphagia. Thyroid function tests are normal. Which of the following embryologic structures failed to regress completely, resulting in this presentation?
Answer choices
- ARemnant of the first pharyngeal pouch
- BRemnant of the second pharyngeal pouch
- CIncomplete obliteration of the thyroglossal ductCorrect answer
- DRemnant of the third pharyngeal pouch
- EEctopic thyroid tissue from aberrant descent
- FCystic hygroma derived from lymphatic tissue
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