| STAGE 0 | No compression No obstruction No collateralisation No fibrous bands/spur |
| STAGE 1 | Compression of the left common iliac vein with or without fibrous band |
| STAGE 2 | Compression of the left common iliac vein with collateralisation, with or without fibrous band, indicating obstruction |
| STAGE 3 | Compression of the left common iliac vein Fibrous bands replaced by localised occlusion With collateralisation No involvement of adjacent venous segments |
| STAGE 4a | As for STAGE 3 but with thrombotic or post-thrombotic involvement of adjacent venous segments |
| STAGE 4b | As for STAGE 4a with involvement of distal venous segments popliteal/femoral. |