“Thrombosis” means clotting; a “thrombus” is a clot. They can rarely develop in the heart, but the vast majority occur in veins. That’s because blood in veins ekes along slowly as it returns to the heart, whereas blood in the arteries gets pumped too vigorously to stagnate and clot. If this is confusing, see Diagram: The Circulatory System. Synonyms for venous thrombosis include “thrombophlebitis,” and “venous thromboembolism”
Venous thrombosis can be superficial or deep. Superficial clots tend to hurt more, and the veins may look inflamed. But it’s in the deep larger veins where bigger clots have more potential to break loose and flow up into the lungs, causing a fatal Pulmonary Embolism.
Deep Venous Thrombosis (DVT) usually occurs in the legs or pelvis, where blood can pool. It’s possible, but much less likely, to occur in the arms. Other parts of the body that can rarely be subject to clots include the liver (Portal Vein Thrombosis), veins from the intestines (Mesenteric Venous Thrombosis), the retina of the eye, and Cavernous Venous Thrombosis in the large vein from the brain.
Thrombosis can be caused by a variety of conditions, which include:
- Immobility in the legs (from long leg casts, or general anesthesia);
- Clotting tendencies related to heredity, pregnancy, and active cancer;
- In the abdomen, various inflammatory diseases, surgery, or trauma;
- In the eye, a variety of risk factors like old age, hypertension, glaucoma, smoking, and more
- In the brain, which is rare, it mainly occurs in persons with tendencies to clot as noted above.
Many other conditions & situations can increase a person’s risk, but not by a lot. For example, we all hear about women on birth control pills or airplane passengers who die from a clot. But if you take into account all such persons, the likelihood for a given individual is very low.
Symptoms of DVT in the main leg vein (femoral vein) include new pain in the inside part of the upper thigh, or new swelling of just one lower leg. However, most people with blood clots in the leg have no symptoms, until they get short of breath from a Pulmonary Embolism. A clot in the arm causes painful swelling; in the abdomen, sudden new belly pain.
Diagnosis is easily made by Ultrasound of the leg or arm (a specially timed CT Scan is necessary fo the abdomen). Sometimes a D-dimer blood test is obtained first, because a negative result rules out DVT. Treatment for all forms of thrombosis involves anticoagulants (“blood thinners”), which prevent further clot formation, and allows the body to gradually dissolve what’s already there. Only in the most extreme of circumstances would specialists attempt to remove the clot, with medication or surgery. Without treatment, there’s risk of permanent damage to the affected organ.