Superior caval to pulmonary venous fistula--the progenitor of the sinus venosus defect?

An infant with surgically corrected complete transposition of the arteries with intact ventricular septum, a superior caval (sinus venosus) defect, and partially anomalous pulmonary venous connection is described. The morphology of the sinus venosus defect is unusual because the pulmonary to systemic communication is a well-formed extracardiac vein that probably represents a persistence of one of the venous connections normally found in the fetus. This case complements the existing beliefs to how sinus venosus defects are formed and endorses why describing them as atrial septal defects is incorrect.