Unusual form of bilateral partial anomalous pulmonary venous drainage

A 23-year-old man with known valvular pulmonary stenosis was found to have a very unusual form of bilateral partial anomalous pulmonary venous drainage. The venous drainage from the upper parts of both lungs was anomalous, draining from the left lung via a persistent left-sided superior vena cava and from the right lung directly into the right atrial/right superior vena caval junction. The venous drainage from the lower parts of both lungs was normal. The embryological pathogenesis of the defect is discussed.