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.