What Causes Swelling In Foot With No Deep Venous Thrombosis?

Hello Dr. t, my query is about my left foot; it 's swollen since 16th of April,2011 . And I did Duplex Examination of Left Lower Limb Venous System and the report says:
*Patent left iliac veins, left formal veins, left popliteal vein and the deep vein of the left leg with no deep venous thrombosis.
*The examined veins are echofree and comressible with normal augmentation on muscular compression.
*The Doppler examination revealed average flow velocity, with normal flow direction and Doppler venous spectrum.
*Patent left great and short saphenous veins.
So I need to know, What this swelling could be?
Looking forward to hearing from you very soon.

Regards,
Reeham