Fig. 1.

The Mayo classification of venous invasion in renal cell carcinoma [24]. Level I: Tumor thrombus is either at the entry of the renal vein or within the inferior vena cava (IVC) < 2 cm from the confluence of the renal vein and the IVC. Level II: Thrombus extends within the IVC > 2 cm above the confluence of the renal vein and IVC but still remains below the hepatic veins. Level III: Thrombus involves the intrahepatic IVC. The size of the thrombus ranges from a narrow tail that extends into the IVC to one that fills the lumen and enlarges the IVC. Level IV: Thrombus extends above the diaphragm or into the right atrium