Thrombosis is the formation of a clot or thrombus inside a blood vessel, obstructing the flow of blood. The formation of a thrombus is usually caused by an injury to the vessel's wall, either by trauma or infection, and by the slowing or stagnation of blood flow past the point of injury. Intravascular coagulation follows, forming a structureless mass of red blood cells, leukocytes, and fibrin. There are two distinct forms of thrombosis:
- venous thrombosis
- and arterial thrombosis
Most thrombi, however, become organized into fibrous tissue, and the thrombosed vessel is gradually recanalized.