SVC ostium obstruction with secondary right-to-left shunt


Final diagnosis: systemic-to-pulmonary venous acquired shunt as collateral pathway.

Chronic obstruction of superior vena cava is commonly an acquired condition due to thrombus, mediastinal mass or fibrosis. Thus, bloodstream often goes through the aygos-hemiazygos pathway, or internal mammary. However, in cases of SVC's ostium obstruction or enlarged right atrium, shunting of systemic-to-pulmonary venous pathway, normally prevented by venous valves, may be observed 1.

In a patient with cardiac insufficiency symptoms with preserved contractile function, clinicians have to rule out anemia and possible shunts such as atrial septal defect (ASD), arterio-venous fistula from dialysis or other arterio-venous malformation. The first imaging needed is echocardiography. If non-contributive, consider contrast-enhanced body CT to look for shunts. 

Imaging is expected to find the location of a shunt, its primary cause, the anatomy of collateral pathways, as well as its severity in order to plan surgical treatment. The appropriate protocol could be pulmonary arterial phased acquisition as the table moves onward, followed by arterial phase acquisition as the table moves backward. Otherwise, a single acquisition with mixed phased can be performed.

Therapy consists of endovascular or surgical closure of the collateral pathways, and treatment of their primary cause.

Teaching point: In case of cardiac insufficiency with enlarged right atrium or SVC’s ostium obstruction, radiologists may find unusually shunting collateral pathways such as systemic-to-pulmonary venous pathway: bronchial plexus veins -> azygos vein -> left superior pulmonary vein.