Thrombosis, deep vein

The formation of a thrombus within deep-lying veins in the leg. The cause is usually a combination of slow blood flow through 1 part of the body (such as when sitting for long periods or when the tissues are compressed, as occurs in long-haul aircraft flights) and an increase in the clotting tendency of the blood, which occurs with dehydration, after surgery or injury, during pregnancy, and in women taking oral contraceptives. Deep vein thrombosis may also be caused by polycythaemia. Deep vein thrombosis is common in people with heart failure and those who have had a stroke or who have been immobile for long periods. Clots in the leg veins may cause pain, tenderness, swelling, discoloration, and ulceration of the skin, but they can be symptomless. A deep vein thrombosis is not necessarily serious in itself, but part of the clot may break off and travel in the bloodstream to the lungs. This is known as a pulmonary embolism. A diagnosis is made by doppler ultrasound scanning. Treatment depends on the site and extent of the clots. Small clots may not need treatment if they are confined to the calf and the patient is mobile. Otherwise, anticoagulant drugs or thrombolytic drugs are given. If there is a high risk of a pulmonary embolism, thrombectomy may be performed.