Table 1 The Mayo classification of macroscopic venous invasion in renal cell carcinoma

Level I

Tumor thrombus is either at the entry of renal vein or within the IVC < 2 cm from the confluence of renal vein and IVC.

Level II

Tumor thrombus extends within the IVC > 2 cm above the confluence of renal vein and IVC, but still remains below the hepatic veins.

Level III

Tumor Thrombus involves the intrahepatic IVC.

Level IV

Tumor thrombus extends above diaphragm or into the right atrium.