Uncommon findings in Tc-99m macroaggregated albumin venography in distal inferior vena cava obstruction.

In inferior vena cava obstruction, collateral pathways allow the retrograde flow of venous blood from the lower part of the body. Unanticipated findings of Tc-99m macroaggregated albumin (MAA) venography in 3 cases with deep vein thrombosis of the legs and infrarenal inferior vena cava obstruction are presented. Apart from extensive collateral networks in the legs and the abdomen, the visualization of the liver indicates a shunt of the systemic venous blood flow through the paraumbilical vein to the portal vein. The visualization of lumbar and thoracic vertebrae is attributed to venous flow through a dilated vertebral plexus, resulting in trapping of tracer in the neighboring bone marrow.