Figure 7. Clinical manifestations of Abnormal Pulmonary Venous Return.

The left illustration shows a dorsal view of the cardiac venous pole. (0) Normal drainage of the pulmonary vein into the left atrium, caused by cranial separation of the pulmonary vein from the splanchnic plexus and formation of the atrium septum from the right pulmonary ridge. (1) In case of isomerism of the right atrial appendages, the atrium septum can form from the left pulmonary ridge. If this is the case, then the pulmonary vein will drain into the right atrium, as shown in the schematic section on the right. This should not be considered to be an erroneous separation of the pulmonary vein from the splanchnic plexus. Failure of such a cranial establishment of the pulmonary vein from this plexus can cause a variety of clinical manifestations of abnormal pulmonary venous return, depending on the caudal location of drainage (2, 3, and 4).