Inferior Sinus Venosus Defect

BACKGROUND: Inferior sinus venosus (SV) atrial septal defect (ASD) is a rare interatrial communication, found near the inferior vena cava (IVC)-right atrial (RA) junction, that may be overlooked on transesophageal echocardiography (TEE). CASE SUMMARY: A 52-year-old woman with childhood secundum ASD closure presented with progressive right heart enlargement. Transthoracic echocardiography showed marked right-sided dilation without a detectable shunt. TEE confirmed an intact fossa ovalis patch but did not adequately visualize the IVC-RA junction. Electrocardiogram-gated cardiac computed tomography (CT) revealed an inferior SVASD with anomalous drainage of 2 right lower pulmonary veins into the RA. Intracardiac echocardiography (ICE) identified a low interatrial communication and Doppler evidence of anomalous pulmonary venous inflow. Surgical baffle repair redirected pulmonary venous return to the left atrium without complications. DISCUSSION: CT and ICE provided complementary anatomic and functional information when TEE was inconclusive. TAKE-HOME MESSAGES: TEE may not detect inferior SVASDs. CT and ICE serve as critical complementary modalities.