Imaging description

On early post-contrast CT or MRI studies of the abdomen, the inferior vena cava just above the renal veins often appears to contain a central ill-defined and poorly enhancing filling defect that tapers and disappears more superiorly. This pseudothrombosis is due to the laminar flow of enhanced blood from the renal veins streaming parallel to the column of unopacified blood returning from the lower body (Figure 50.1) [1,2]. This pseudolesion disappears over time and is not seen on more delayed images, because the blood returning from the lower extremities through the inferior vena cava is then more opacified. Accordingly, this pseudolesion is commoner on spiral as compared to conventional CT scans [3].

Importance

Pseudothrombosis of the inferior vena cava may be mistaken for a true thrombus of the inferior vena cava, either tumor thrombus or bland thrombus, resulting in unnecessary follow-up investigations and patient anxiety.

Typical clinical scenario

Pseudothrombosis of the inferior vena cava is commonly seen on early post-contrast CT or MRI scans of the abdomen, particularly given the increasing use of spiral CT and multiphasic post-contrast imaging of the abdomen.

Differential diagnosis

Both tumor and bland thrombus can be seen in the inferior vena cava, but are typically better marginated and will not disappear on delayed post-contrast images. In addition, tumor thrombus will be contiguous with a primary tumor prone to venous invasion (such as renal cell carcinoma, adrenal cell carcinoma, or hepatocellular carcinoma) while bland thrombus will be contiguous with deep venous thrombus more inferiorly.