When someone notices that the same leg always swells, almost always the left one, with no obvious cause, it’s worth considering May-Thurner syndrome. It’s a little-known venous compression that can go unnoticed for years.
What May-Thurner syndrome is
It is the compression of the left iliac vein, which as it passes through the pelvis becomes trapped between the right iliac artery in front and a lumbar vertebra behind. That pressure narrows the vein and hinders the return of blood from the left leg to the heart.
It is more common in young women. Many people have it without symptoms; the problem appears when the compression is significant or when it favors the formation of a clot.
Symptoms
Symptoms are concentrated in the left leg:
- Swelling (edema), heaviness and a feeling of congestion.
- Pain, especially at the end of the day or after standing for a long time.
- Varicose veins, sometimes in unusual areas.
- In some cases, a venous thrombosis in that leg.
If you notice sudden swelling in a single leg with pain or warmth, see a doctor soon: it could be a venous thrombosis.
When I see a young patient with a thrombosis in the left leg or swelling that is always on the same side, May-Thurner syndrome is one of the first things I rule out.
How it is diagnosed
The first step is a Doppler ultrasound, which assesses blood flow in the leg veins. To precisely see the compression in the pelvis, CT angiography or MR angiography is used, and when treatment is being considered, a venogram confirms the diagnosis and enables treatment.
Treatment
Not all cases need treatment. When it causes significant symptoms or has led to a thrombosis, the usual approach is endovascular: through catheterization, the compressed vein is reopened and a stent is placed to keep it open. If there is a clot, the thrombosis is treated first.
Details on this and other conditions can be found on the vascular compression syndromes page.
In summary
May-Thurner syndrome compresses the left iliac vein and explains many cases of swelling or thrombosis that consistently affect that leg. When it causes symptoms, stent treatment usually resolves the problem. If your left leg swells repeatedly or you’ve had a thrombosis in it, a vascular assessment is worthwhile.