Differential diagnosis for unilateral, left leg edema
I saw a 53-year-old female today for left ankle pain and chronic left leg swelling. The swelling was pitting, meaning that with digital pressure to the skin, when you pull away, your finger leaves a divot, or pit in the skin. Pitting edema classically describes fluid retention in the legs, commonly called venous stasis. But this case was unusual. The swelling was only in the left leg.
What is the significance of unilateral vs. bilateral edema? Bilateral edema is by far more common and signifies a fluid overload of the body. With standing or dependency of the legs, the legs will swell with fluid edema. An important characteristic of fluid retention and lower extremity swelling is the fact that the edema is found in both legs.
What could cause unilateral swelling of the left leg? Fortunately, this patient was familiar with her diagnosis and has been thoroughly evaluated by vascular medicine specialists. This patient presented with May-Thurner Syndrome which is a compression syndrome of the iliac vein. The iliac 
vein is found in the lower pelvis and is the final vein of the lower extremity that feeds into the vena cava, the primary vein that returns blood to the heart. In cases of May-Thurner Syndrome, swelling of the legs is exclusive to the left leg due to the unique anatomical, arterial-venous complex found in the lower abdomen. May-Thurner Syndrome is caused by compression of the left iliac vein by the right common iliac artery.
It’s interesting to note that May-Thurner Syndrome is due to the alignment of the vena cava (venous return to the heart) and aorta (arterial supply to the legs). You can see from the attached picture how the anatomical arrangement of the arterial tree is superficial to the venous return.
Treatment of May-Thurner syndrome is primarily fluid management with diuretics, compression hose and venous ablation of the superficial veins of the left leg.
Jeff
Medical Advisor
Myfootshop.com
Updated 12/24/2019
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