History: 50 year old male with lower extremity swelling.
This is an indirect sign of a deep vein thrombosis. Normally, flow within the deep venous system is low resistance with variation during inspiration and expiration as central venous pressure changes with the respiratory cycle and cardiac cycle (as is seen in the first image above of the right common femoral vein).
The asymmetry between the waveforms in the common femoral veins suggests obstruction closer to the heart, such as thombosis more centrally in the left common femoral vein. The inferior vena cava should be free of thrombosis in this case because the right common femoral vein waveform is within normal limits. This article shows that this does not always mean thrombosis or obstruction, as the loss of phasicity can be caused by respiratory factors. However, when respiratory factors cause loss of waveform phasicity, it is bilateral and the asymmetry seen in this case would not be present.
Here is an interesting case of superficial venous thrombosis extending to a deep venous thrombus.
Thank you Paul Murphy, M.D., Ph.D. for this great case!