Which of the following is a type of atrial septal defect described in the material?

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Atrial septal defects come from openings in the atrial septum, but their location tells you the subtype. The sinus venosus type sits high in the septum, at the junction where the right atrium receives the superior (and sometimes inferior) vena cava. This defect results from incomplete incorporation of the sinus venosus into the right atrium during development, creating an interatrial communication. It’s classically associated with anomalous pulmonary venous return, which helps distinguish it on imaging and clinical evaluation. The other options describe defects in different locations: an ostium primum defect is lower and linked to AV valve abnormalities; an ostium secundum defect is centered at the fossa ovalis; perimembranous is a term more often used with membranous ventricular septal defects adjacent to the valves. Thus, the sinus venosus defect is the type described here.