deep vein thrombosis
Meaning of deep vein thrombosis: A clot lodged in a leg vein matters less for the leg than for what happens if a piece of it breaks loose.
Definition of deep vein thrombosis
Deep vein thrombosis is a blood clot that forms inside one of the deep veins, most often in the calf, thigh or pelvis. Those veins run between the muscles rather than under the skin, and they carry most of the blood returning from the leg. The clot obstructs that return, and part of it can break away and travel to the lungs.
Why does a clot form in a vein?
Three conditions favor it, and most cases involve more than one. Blood that moves slowly clots more readily, so long immobility from surgery, a cast, a hospital stay or a long journey sets the stage. Damage to the vein lining, from injury, a catheter or an operation nearby, gives a clot somewhere to anchor. And the blood itself can be more prone to clotting than usual, whether from cancer, from pregnancy and the weeks after it, from estrogen-containing medication, from an inherited clotting tendency, or from a previous clot. Leg veins are the usual site because blood there travels uphill and depends on the calf muscles squeezing it along.
What does the leg look like?
| Condition | Typical picture |
|---|---|
| Deep vein clot | One leg swollen, aching and warm, with a tight calf |
| Cellulitis | Spreading redness with a defined edge, fever, and tender skin |
| Superficial clot | A hard tender cord felt just under the skin |
| Ruptured knee cyst | Sudden calf pain and swelling after a pop behind the knee |
None of these can be told apart reliably by looking, which is why an ultrasound of the leg veins is what settles the question. The examination misleads in both directions: many swollen painful legs turn out to have another cause entirely, and a clot large enough to matter can produce almost nothing in the leg.
Where does the real danger lie?
Not in the leg but in the lungs. A fragment breaking off travels up the veins, through the right side of the heart and into the lung arteries, where it wedges. That is a pulmonary embolism, and a large one can be fatal within minutes. Sudden breathlessness, chest pain that sharpens on breathing in, a racing pulse, coughing up blood or collapse are its recognized features. Treatment of the clot rests on an anticoagulant, which does not dissolve what is already there but stops it enlarging while the body breaks it down. Damage to the vein valves can leave lasting swelling and skin changes long afterward, and DVT is the abbreviation used in most records.
Also known as
Used in a sentence
Deep vein thrombosis of the left femoral vein was confirmed on ultrasound.
Good to know
Examination of the leg is unreliable in both directions, since many swollen painful legs have another cause and a clot large enough to travel to the lungs may produce little in the leg, so imaging rather than appearance establishes the diagnosis.
Word origin
Where “deep vein thrombosis” comes from
Thrombosis comes from the Greek thrombos, meaning a lump or clot.