«Thrombosis (from Ancient Greek θρόμβωσις thrómbōsis "clotting”) is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel (a vein or an artery) is injured, the body uses platelet (thrombocytes) and fibrin to form a blood clot to prevent blood loss. Even when a blood vessel is not injured, blood clots may form in the body under certain conditions. A clot, or a piece of the clot, that breaks free and begins to travel around the body is known as an embolus.^[1][2]

Thrombosis may occur in veins (venous thrombosis) or in arteries (arterial thrombosis). Venous thrombosis lead to congestion of the affected part of the body, while arterial thrombosis (and rarely severe venous thrombosis) affects the blood supply and lead to damage of the tissue supplied by that artery (ischemia and necrosis). A piece of either an arterial or a venous thrombus can break off as an embolus which can travel through the circulation and lodge somewhere else as an embolism. This type of embolism is known as a thromboembolism. Complications can arise when a venous thromboembolism (commonly called a VTE) lodges in the lung as a pulmonary embolism. An arterial embolus may travel further down the affected blood vessel where it can lodge as an embolism.

Thrombosis is generally defined by the type of blood vessel affected (arterial or venous thrombosis) and the precise location of the blood vessel or the organ supplied by it.

Deep vein thrombosis (DVT) is the formation of a blood clot within a deep vein. It most commonly affects leg veins, such as the femoral vein. Three factors are important in the formation of a blood clot within a deep vein—these are the rate of blood flow, the thickness of the blood and qualities of the vessel wall. Classical signs of DVT include swelling, pain and redness of the affected area.^{[citation needed]}

Paget-Schroetter disease is the obstruction of an upper extremity vein (such as the axillary vein or subclavian vein) by a thrombus. The condition usually comes to light after vigorous exercise and usually presents in younger, otherwise healthy people. Men are affected more than women.

Budd-Chiari syndrome is the blockage of a hepatic vein or of the hepatic part of the inferior vena cava. This form of thrombosis presents with abdominal pain, ascites and enlarged liver. Treatment varies between therapy and surgical intervention by the use of shunts.^{[citation needed]}

Portal vein thrombosis affects the hepatic portal vein, which can lead to portal hypertension and reduction of the blood supply to the liver.^[3] It usually happens in the setting of another disease such as pancreatitis, cirrhosis, diverticulitis or cholangiocarcinoma.^{[citation needed]}

Renal vein thrombosis is the obstruction of the renal vein by a thrombus. This tends to lead to reduced drainage from the kidney.^{[citation needed]}

Cerebral venous sinus thrombosis (CVST) is a rare form of stroke which results from the blockage of the dural venous sinuses by a thrombus. Symptoms may include headache, abnormal vision, any of the symptoms of stroke such as weakness of the face and limbs on one side of the body and seizures. The diagnosis is usually made with a CT or MRI scan. The majority of persons affected make a full recovery. The mortality rate is 4.3%.^[4]

Jugular vein thrombosis is a condition that may occur due to infection, intravenous drug use or malignancy. Jugular vein thrombosis can have a varying list of complications, including: systemic sepsis, pulmonary embolism, and papilledema. Though characterized by a sharp pain at the site of the vein, it can prove difficult to diagnose, because it can occur at random.^[5]

Cavernous sinus thrombosis is a specialised form of cerebral venous sinus thrombosis, where there is thrombosis of the cavernous sinus of the basal skull dura, due to the retrograde spread of infection and endothelial damage from the danger triangle of the face. The facial veins in this area anastomose with the superior and inferior ophthalmic veins of the orbit, which drain directly posteriorly into the cavernous sinus through the superior orbital fissure. Staphyloccoal or Streptococcal infections of the face, for example nasal or upper lip pustules may thus spread directly into the cavernous sinus, causing stroke-like symptoms of double vision, squint, as well as spread of infection to cause meningitis.^{[citation needed]}

Arterial thrombosis is the formation of a thrombus within an artery. In most cases, arterial thrombosis follows rupture of atheroma (a fat-rich deposit in the blood vessel wall), and is therefore referred to as atherothrombosis. Arterial embolism occurs when clots then migrate downstream, and can affect any organ.^{[citation needed]}» (wikipedia)