A fetus is found to have absence of the septum primum and septum secundum. Which cardiac malformation results, and from what embryological failure?

• A Patent foramen ovale / ASD — failure of fusion of septum primum and septum secundum after birth
• B Complete atrioventricular septal defect (AVSD) — failure of both atrial and endocardial cushion fusion
• C Ventricular septal defect — failure of the membranous ventricular septum to form
• D ASD primum (ostium primum type) — incomplete fusion of septum primum with endocardial cushions ✓

Explanation

Ostium primum ASD (ASD primum / partial AVSD) results when the septum primum fails to fuse with the endocardial cushions, leaving a persistent ostium primum at the base of the atrial septum. It is commonly associated with a cleft mitral valve. In contrast, ostium secundum ASD results from excessive resorption of the septum primum. A patent foramen ovale occurs when the foramen ovale (septum primum flap) fails to fuse with the septum secundum after birth. Complete AVSD involves both ASD primum and inlet VSD.

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

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Written and medically reviewed by the StethoPrep medical team.