Embryology USMLE Step 1 Practice Question
A 3-day-old newborn presents with cyanosis and severe respiratory distress. Vital signs show HR 168 bpm, RR 52/min, BP 55/32 mmHg, SpO2 78% on room air, and temperature 37.2°C. Echocardiography demonstrates complete transposition of the great arteries with the aorta arising anteriorly from the right ventricle and the pulmonary artery from the left ventricle. Chest X-ray shows an "egg-on-string" appearance. There is no evidence of septal defects. Which embryologic process is most likely disrupted?
Answer choices
- AIncomplete resorption of septum primum
- BPremature closure of foramen ovale
- CAbnormal truncus arteriosus septationCorrect answer
- DDefective endocardial cushion development
- EFailure of neural crest cell migration
- FInadequate development of the bulbus cordis
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