Embryology USMLE Step 1 Practice Question
A 3-day-old male newborn presents with severe respiratory distress and cyanosis. Vital signs: HR 165 bpm, RR 72/min, SpO2 78% on room air. Physical exam reveals a scaphoid abdomen and diminished breath sounds on the left. Chest X-ray demonstrates bowel loops in the left hemithorax with rightward mediastinal shift. Arterial blood gas shows pH 7.28. Prenatal ultrasound documented polyhydramnios. The mother denies intrauterine infections or maternal diabetes. Which embryologic defect is most likely responsible?
Answer choices
- ADefective neural crest cell migration to the foregut
- BFailure of the pleuroperitoneal membrane to fuseCorrect answer
- CFailure of the muscularization of the esophageal wall
- DDefective formation of the diaphragm from the septum transversum
- EIncomplete closure of the foramen of Morgagni
- FTracheoesophageal fistula
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