Thrombosis
Thrombosis is the formation of a blood clot inside a blood vessel, obstructing the flow of blood through the circulatory system. When a blood vessel is injured, the body uses platelets 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. Thrombosis can cause serious conditions such as stroke and heart attack.
Thrombosis may occur in veins or in arteries. Venous thrombosis leads to a blood clot in the affected part of the body, while arterial thrombosis affects the blood supply and leads to damage of the tissue supplied by that artery. A piece of either an arterial or a venous thrombus can break off as an embolus, which could then 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 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.
Signs and symptoms
Thrombosis is generally defined by- the type of blood vessel affected and
- the precise location of the blood vessel or the organ supplied:
Arterial thrombosis
Stroke
A stroke is the rapid decline of brain function due to a disturbance in the supply of blood to the brain. This can be due to ischemia, thrombus, embolus or hemorrhage.In thrombotic stroke, a thrombus usually forms around atherosclerotic plaques. Since blockage of the artery is gradual, the onset of symptomatic thrombotic strokes is slower. Thrombotic stroke can be divided into two categories — large vessel disease or small vessel disease. The former affects vessels such as the internal carotids, vertebral and the circle of Willis. The latter can affect smaller vessels, such as the branches of the circle of Willis.
Myocardial infarction
Myocardial infarction, or heart attack, is caused by ischemia, which is often due to the obstruction of a coronary artery by a thrombus. This restriction gives an insufficient supply of oxygen to the heart muscle which then results in tissue death. A lesion is then formed which is the infarct. MI can quickly become fatal if emergency medical treatment is not received promptly. If diagnosed within 12 hours of the initial episode then thrombolytic therapy is initiated.Limb ischemia
An arterial thrombus or embolus can also form in the limbs, which can lead to acute limb ischemia.Other sites
usually occurs as a devastating complication after liver transplantation.Venous thrombosis
Deep vein thrombosis
Deep vein thrombosis 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.
Paget-Schroetter disease
or upper extremity DVT is the obstruction of an arm 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.Portal vein thrombosis
Portal vein thrombosis affects the hepatic portal vein, which can lead to portal hypertension and reduction of the blood supply to the liver. It usually happens in the setting of another disease such as pancreatitis, cirrhosis, diverticulitis or cholangiocarcinoma.Renal vein thrombosis
Renal vein thrombosis is the obstruction of the renal vein by a thrombus. This tends to lead to reduced drainage from the kidney.Cerebral venous sinus thrombosis
Cerebral venous sinus thrombosis 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%.Jugular vein thrombosis
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.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.Causes
Thrombosis prevention is initiated with assessing the risk for its development. Some people have a higher risk of developing thrombosis and its possible development into thromboembolism. Some of these risk factors are related to inflammation."Virchow's triad" has been suggested to describe the three factors necessary for the formation of thrombosis:
- hemodynamic changes,
- vessel wall injury/dysfunction, and
- altered blood coagulation.
| Factor | Notes | |
| Previous episodes of thrombosis | ||
| Vasoconstriction | ||
| Slow or turbulent blood flow | slow flow is modifiable with exercise | |
| Stroke | ||
| Heart failure | ||
| Sedentary life style | modifiable | |
| Plaster cast | transient | |
| Dehydration | modifiable | |
| Acute respiratory failure | ||
| Dysrhythmias | ||
| Shock | ||
| Obesity | modifiable | |
| Pregnancy and the post-partum period | ||
| Varicose veins | ||
| Surgery | ||
| Trauma | ||
| Estrogen-based oral contraceptive | discontinuation reduces risk | |
| Hormone replacement therapy | discontinuation reduces risk | |
| Ovarian hyper-stimulation therapy to treat infertility | ||
| Compression of a vein or artery by abnormality, tumor, hematoma | ||
| Long surgeries | ||
| Pacing wires | ||
| Local vein damage, incompetent valves | ||
| Central venous catheters | ||
| Dialysis catheters | ||
| Repetitive motion injury | ||
| Immobility | modifiable risk | |
| Spinal cord injury | ||
| Age | ||
| Cancers | ||
| Sepsis | ||
| Polycythemia | ||
| Protein C and/or S deficiency | congenital; associated with Warfarin necrosis | |
| Antiphospholipid antibody syndrome | altered coagulation | |
| Factor V Leiden defect | altered coagulation | |
| Prothrombin G20210A defect | altered coagulation | |
| Elevated PAI-1 | inhibits physiological breakdown of blood clots | |
| Hyperhomocysteinemia | altered coagulation | |
| Elevated factors II, VIII, IX, XI | altered coagulation | |
| Antithrombin III deficiency | altered coagulation | |
| Falls and hip fracture | related to immobility | |
| Selective estrogen-receptor modulators | ||
| Erythropoiesis-stimulating agents | ||
| Acute medical illness | ||
| Inflammatory bowel disease | ||
| Nephrotic syndrome | ||
| Myeloproliferative disorders | ||
| Paroxysmal nocturnal hemoglobinnuria | ||
| Thrombophilias | ||
| Post-menopausal hormone replacement therapy | discontinuation reduces risk | |
| Right heart failure | ||
| Venous inflammation/phlebitis | when a thrombus forms, it is thrombophlebitis | |
| Ambient air pollution | thought to be related to inflammation |