A fetus is found to have an atrial septal defect of the ostium secundum type. This defect results from failure of which embryological structure?

• A Failure of the septum primum to form
• B Failure of endocardial cushion fusion
• C Persistence of the interventricular foramen
• D Excessive resorption of the septum primum or inadequate formation of the septum secundum ✓

Explanation

Ostium secundum ASD results from excessive resorption of the septum primum (making the foramen ovale too large) or from inadequate development of the septum secundum so it fails to adequately cover the foramen ovale. The ostium primum defect (at the base of the atrial septum near the AV valves) is due to failure of endocardial cushion fusion. Endocardial cushion defects also cause AV canal defects. Interventricular foramen persistence causes ventricular septal defects. Ostium secundum is the commonest ASD type.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.