Thrombosis

Thrombosis is the formation of a blood clot inside a blood vessel. This process can block the flow of blood through the circulatory system. Normally, the body uses clots to prevent blood loss during an injury. Platelets, which are small cell fragments, and fibrin, a protein, work together to seal wounds. However, thrombosis can occur even when no injury is present. This can lead to serious medical emergencies.

There are two main types of thrombosis based on the vessel involved. Venous thrombosis occurs in the veins. A common form is deep vein thrombosis, or DVT, which often affects the leg veins like the femoral vein. Arterial thrombosis occurs in the arteries. This often follows the rupture of an atheroma, which is a fat-rich deposit in the vessel wall. This specific type is called atherothrombosis.

Sometimes, a part of a clot breaks loose and travels through the bloodstream. This traveling piece is called an embolus. When an embolus lodges in a new location, it creates an embolism. This process is known as a thromboembolism. If a venous thromboembolism travels to the lungs, it is called a pulmonary embolism. An arterial embolus might travel further downstream to block other tissues. This can cause ischemia, which is a restriction in blood supply, or necrosis, which is tissue death.

Scientists use a concept called Virchow's triad to explain why clots form. This triad includes three specific factors. The first is hemodynamic changes, such as blood stasis or turbulence. Stasis is when blood flow slows down or stops. The second is endothelial injury, which is damage to the vessel wall lining. The third is hypercoagulability, or an altered ability for blood to clot. These three factors work together to trigger the formation of a thrombus.

Arterial thrombosis can lead to life-threatening events like a stroke or heart attack. A thrombotic stroke occurs when a clot forms around atherosclerotic plaques in the brain. This can affect large vessels, like the internal carotids, or small vessel disease. A myocardial infarction, or heart attack, happens when a thrombus blocks a coronary artery. This prevents oxygen from reaching the heart muscle. If a patient receives thrombolytic therapy within 12 hours, they may receive treatment.

Many different factors can increase a person's risk for thrombosis. Some risks are related to lifestyle, such as obesity or a sedentary lifestyle. Long periods of immobility, like sitting on a long airplane flight, can cause blood stasis. Other risks include surgery, trauma, or pregnancy. Certain medical conditions like cancer can also cause thrombosis. In cancer, tumors can cause stasis by pressing on vessels or secreting substances like heparanase.

Thrombosis can also affect specific organs in various ways. Budd-Chiari syndrome occurs when a hepatic vein is blocked. This can cause abdominal pain and an enlarged liver. Renal vein thrombosis affects the kidney's ability to drain blood. Cerebral venous sinus thrombosis is a rare form of stroke involving the brain's venous sinuses. This condition has a mortality rate of 4.3 percent. Understanding these different pathways helps doctors manage the risks of blood clots.