Pulmonary venous collaterals secondary to superior vena cava stenosis: a rare cause of right-to-left shunting following repair of a sinus venosus atrial septal defect.

We describe a case of unusual pulmonary vein-to-vein collateral formation leading to systemic desaturation years following surgical repair of a sinus venosus atrial septal defect and partial anomalous pulmonary venous return from the right lung. At surgery, a single right upper lobe pulmonary vein branch was left draining high into the superior vena cava (SVC), resulting in a small left-to-right shunt. SVC obstruction developed at the site of the ASD repair and elevated venous pressure above the obstruction caused retrograde flow into the unincorporated pulmonary vein. Pulmonary vein-to-vein collaterals formed between this unincorporated vein and an adjacent pulmonary vein that had been surgically diverted to drain into the left atrium, resulting in a right-to-left shunt within the right lung. Normal pulmonary veins drain multiple bronchopulmonary segments, thus providing potential collateral pathways. Balloon angioplasty of the SVC stenosis successfully relieved the obstruction and abolished the right-to-left intrapulmonary shunt.