Venous dilatation seen on routine mammography: a clue to superior vena cava obstruction.

A diagnosis of superior vena cava obstruction (SVCO) generally is made on clinical grounds and can be confirmed by SVCO-specific diagnostic tests. When the obstruction is long-standing, clinical recognition may be compromised as venous drainage of the head, neck, chest, and upper extremity is diverted via collateral venous channels that bypass the obstructed superior vena cava. In such situations, only the visualization of this collateral flow will suggest the presence of SVCO. We describe a patient in whom the unanticipated diagnosis of SVCO was first suggested when routine mammography revealed grossly dilated superficial veins of both breasts, which were the result of collateral flow.