Deep vein thrombosis is a blood clot located within a deep vein of the body, usually in the thigh or leg. The deep veins are the main blood vessels returning blood from the tissues of the body back to the heart.
If a blood clot forms in a deep vein, it can block the flow of blood, which prevents the tissues from draining properly. This causes excess fluid accumulation, swelling, warmth and discomfort in the leg. A blood clot in a deep vein may also break off and travel back to the heart and into the lungs, causing a pulmonary embolism. Pulmonary embolism can be minor and go unnoticed, or it can be significant and cause difficulty breathing, sharp chest pain and even death. Less commonly, the clots can also travel through the heart and back to the rest of the body, including the brain. This is called paradoxical embolism. A blood clot that travels this way to the brain can be the cause of a stroke.
DVT is different from a clot in a vein close to the surface of the body, such as a vein near the skin or in the calf. These superficial clots, while often uncomfortable, are usually not dangerous. DVT is typically treated with medications that lower the chances of new clots forming and allow the body to dissolve the clot over time.