Unexpected demonstration of superior vena caval obstruction in third trimester lung imaging

A large focus of liver activity was seen after the injection of Tc-99m macroaggregated albumin (MAA) in a pregnant patient thought to have pulmonary embolism (PE). The correct diagnosis of superior vena caval (SVC) obstruction led to an immediate cesarean section, CT of the chest and abdomen, open lung biopsy of a mediastinal mass, and radiation therapy for the lymphoma with pericardial invasion, all within 24 hours of presentation. The next day, an in vitro labeled Tc-99m red blood cell (RBC) angiogram was performed, which documented collateral flow from the SVC obstruction to the abdomen and filling of the right ventricle via the liver, presumably through reopened channels of the umbilical vein.