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 ce ll gastrointestinal bleeding study because he had a tarry stool. In his fir st-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 dist orted and distended inferior vena cava along with an abdominal aortic aneur ysm. Collateral circulation of the trunk was noted in the subsequent blood- pool images. A subsequent radionuclide superior vena cava study confirmed s uperior vena cava obstruction just above the entrance to the right atrium. Contrast-enhanced computed tomographic scans of the chest showed that the s uperior vena cava was compressed completely by the mediastinal tumor mass a nd that collateral circulation was present. Development of collateral circu lation after superior vena cava obstruction in this patient allowed venous blood to return to the right atrium through the inferior vena cava. Thus, e arly filling of the inferior vena cava on radionuclide first-pass studies o f the abdomen may serve as a sign of superior vena cava obstruction.