Imaging description

On early post-contrast CT or MRI studies of the abdomen and pelvis, mixing artifact of unenhanced blood from the lower extremity and enhanced blood from a renal transplant (Figure 96.1) or asymmetric enhancement due to flow through collateral venous channels (Figures 96.2 and 96.3) may create the appearance of a filling defect that resembles a thrombus in an iliofemoral vein [1, 2].

Importance

Pseudothrombosis of an iliofemoral vein may be mistaken for a true thrombus, potentially resulting in inappropriate treatment or unnecessary follow-up investigation.

Typical clinical scenario

Conditions that may result in mixing of enhanced and unenhanced blood or asymmetric enhancement in an iliofemoral vein include renal transplantation or downhill venous collateral formation in subclavian vein occlusion or portosystemic collateral formation in portal hypertension.

Differential diagnosis

The primary differential is bland thrombus. Close examination of axial and reformatted CT images or delayed images to show resolution of the filling defect is usually sufficient to confirm the artifactual nature of this pseudolesion, but ultrasound or flow-sensitive MRI sequences can be used if the distinction cannot be made with certainty on CT.