In atrial septal defects, which location is least commonly involved?

In atrial septal defects, which location is least commonly involved?

• A. Secundum
• B. Primum
• C. Sinus venosus
• D. Coronary sinus

Answer: (B)

Atrial septal defects show different sites along the septum, with distinct frequencies. The most common defect sits at the fossa ovalis (ostium secundum) because this area is where the septum primum fails to form a complete seal during development. Defects at the lower part of the septum (ostium primum) are less common and typically accompany endocardial cushion abnormalities. Defects near the entry of the great veins (sinus venosus) are uncommon but occur with anomalous pulmonary venous return patterns. The rarest of these locations is an ASD due to an unroofed coronary sinus. Therefore, the coronary sinus site is the least commonly involved among the listed options.

Atrial septal defects show different sites along the septum, with distinct frequencies. The most common defect sits at the fossa ovalis (ostium secundum) because this area is where the septum primum fails to form a complete seal during development. Defects at the lower part of the septum (ostium primum) are less common and typically accompany endocardial cushion abnormalities. Defects near the entry of the great veins (sinus venosus) are uncommon but occur with anomalous pulmonary venous return patterns. The rarest of these locations is an ASD due to an unroofed coronary sinus. Therefore, the coronary sinus site is the least commonly involved among the listed options.