Early appearance of the inferior vena cava in a Tc-99m red blood cell first-pass study: a sign of superior vena cava obstruction.

A man with small-cell carcinoma of the lung underwent a Tc-99m red blood cell gastrointestinal bleeding study because he had a tarry stool. In his first-pass study, there was early filling of the radiotracer in the middle and lower portion of the inferior cava; in addition, the study revealed a distorted and distended inferior vena cava along with an abdominal aortic aneurysm. Collateral circulation of the trunk was noted in the subsequent bloodpool images. A subsequent radionuclide superior vena cava study confirmed superior vena cava obstruction just above the entrance to the right atrium. Contrast-enhanced computed tomographic scans of the chest showed that the superior vena cava was compressed completely by the mediastinal tumor mass and that collateral circulation was present. Development of collateral circulation after superior vena cava obstruction in this patient allowed venous blood to return to the right atrium through the inferior vena cava. Thus, early filling of the inferior vena cava on radionuclide first-pass studies of the abdomen may serve as a sign of superior vena cava obstruction.