May-Thurner syndrome, or MTS, is an iliac vein compression syndrome. This is where the left common iliac vein, which carries blood from the left leg, is pressed upon by the right common iliac artery, which supplies blood to the right leg. The pressure occurs at a point where the artery crosses the vein, and it causes the vein to become squashed against the bones of the spine. Scarring and narrowing of the vein occur, and symptoms of leg pain and leg swelling may be experienced. Sometimes people with May-Thurner syndrome may develop blood clots in their veins, a condition known as deep vein thrombosis, or DVT.
Women between the ages of 20 and 50 years are most likely to develop May-Thurner syndrome. In mild cases, there may be no symptoms. As the condition progresses, the left leg may become permanently swollen. If DVT occurs, the leg may also hurt, appear red and feel warm, and the veins may look more prominent than usual. It is important to treat DVT, because it can lead to a potentially fatal pulmonary embolism, where the clot breaks away and blocks the blood supply to the lungs.
The diagnosis of May-Thurner syndrome generally involves carrying out what is known as a venogram. A special dye, visible on X-ray, is injected into a vein in the foot, and travels to the common iliac vein, where it shows the flow of blood through the vein. The pressure of blood flowing on each side of the narrow section can be measured to assess the severity of the blockage.
Management of May-Thurner syndrome generally involves treating any associated DVT and widening the narrowed vein. Drugs to break up a blood clot may be delivered directly to it through a narrow tube inserted into the vein. Once any clot has been dealt with, a surgical procedure known as an angioplasty may be carried out. This involves stretching the narrowed vein by inflating a special type of balloon inside it. A tube made of mesh may then be inserted and left inside the vein to hold it open permanently.
Other possible treatments include bypassing the blocked vein or moving the right iliac artery so that it no longer causes compression. Sometimes the artery is held away from the vein using a type of sling made of body tissue. The outlook for someone with May-Thurner syndrome is usually positive if treatment is started early, before or soon after a clot has formed.