Confluent Vein-Like Structure Behind the Left Atrium in Late Gestation: A Case With False-Positive Suspicion of Anomalous Pulmonary Venous Connection.

BACKGROUND: Anomalous pulmonary venous connection, including total and partial anomalous pulmonary venous connections (TAPVC and PAPVC), represents about 1%-2% of all congenital heart diseases. Prenatal identification of these anomalies remains challenging because of the small vessel size, low flow velocity, and variable insonation angles. A confluent vein behind the left atrium has been proposed as a useful sonographic marker for TAPVC; however, normal anatomical variants may mimic this finding, leading to false-positive interpretations.

CASE PRESENTATION: A 34-year-old gravida 3 para 2 woman underwent fetal echocardiography at 36 + 4 weeks of gestation, which demonstrated a tubular vascular structure between the left atrium and the descending aorta, raising suspicion of a confluent vein. Detailed assessment suggested the presence of only two pulmonary venous inflows-one from each lung-entering the left atrium, which raised concern for a possible PAPVR, as the remaining pulmonary venous branches could not be clearly visualized. Postnatal contrast-enhanced CT revealed that all four pulmonary veins drained normally into the left atrium, confirming a false-positive prenatal suspicion. The vascular structure posterior to the left atrium was later identified as the left superior pulmonary vein.

CONCLUSION: A vascular structure observed posterior to the left atrium in late gestation may represent the left superior pulmonary vein rather than an abnormal venous confluence. Slight cranial angulation from the standard four-chamber view can help confirm the inflow of the left superior pulmonary vein into the left atrium and prevent false-positive diagnosis of anomalous pulmonary venous connection.