Embryology USMLE Step 1 Practice Question
A 2-day-old male infant born at 38 weeks gestation presents with excessive drooling, respiratory distress, and cyanosis that worsens with feeding attempts. His mother had polyhydramnios noted on prenatal ultrasound. Chest radiograph shows a radiopaque tube coiled in the upper mediastinum after attempted nasogastric tube placement, and air is visible in the stomach. Subsequent contrast esophagography reveals the proximal esophagus terminating in a blind pouch at the level of T4, with contrast entering the trachea. Which of the following embryologic structures failed to properly differentiate, resulting in this anomaly?
Answer choices
- ASplanchnic mesoderm of the mediastinum
- BPharyngeal arch cartilage templates (Reichert's cartilage)
- CTracheoesophageal septum derived from foregut endodermCorrect answer
- DDorsal mesentery of the esophagus
- ENeural crest cell migration to pharyngeal arches
- FIntermediate mesoderm of the thoracic region
See the full explanation
Get the correct-answer rationale, why each distractor is wrong, the underlying mechanism, and high-yield associations — plus adaptive practice that targets your weak areas — with a free MedBoardPRO account.