Anembolism is the lodging of anembolus, a blockage-causing piece of material, inside ablood vessel.^[1] The embolus may be a blood clot (thrombus), a fat globule (fat embolism), a bubble of air or other gas (gas embolism),amniotic fluid (amniotic fluid embolism), orforeign material.

Embolism
Micrograph of embolic material in the artery of a kidney. The kidney was surgically removed because ofcancer.H&E stain.
Specialty	Vascular surgery

An embolism can cause partial or total blockage ofblood flow in the affected vessel.^[2] Such a blockage (vascular occlusion) may affect a part of the body distant from the origin of the embolus. An embolism in which the embolus is a piece of thrombus is called athromboembolism.

An embolism is usually a pathological event, caused by illness or injury. Sometimes it is created intentionally for a therapeutic reason, such as tostop bleeding or to kill a cancerous tumor by stopping its blood supply. Such therapy is calledembolization.

There are different types of embolism, some of which are listed below.

Embolism can be classified based on where it enters the circulation, either inarteries or inveins. Arterial embolism are those that follow and, if not dissolved on the way, lodge in a more distal part of thesystemic circulation. Sometimes, multiple classifications apply; for instance apulmonary embolism is classified as an arterial embolism as well,^[3] because the clot follows thepulmonary artery carrying deoxygenated blood away from the heart. However, pulmonary embolism is generally classified as a form of venous embolism, because the embolus forms in veins, e.g.deep vein thrombosis.^{[citation needed]}

Arterial embolism can cause occlusion in any part of the body. It is a major cause ofinfarction (tissue death from blockage of the blood supply).^[4]

An embolus lodging in the brain from either theheart or acarotid artery will most likely be the cause of astroke due toischemia.^[5]

An arterial embolus might originate in the heart (from a thrombus in theleft atrium, followingatrial fibrillation or be a septic embolus resulting fromendocarditis). Emboli ofcardiac origin are frequently encountered in clinical practice. Thrombus formation within the atrium occurs mainly in patients withmitral valve disease, and especially in those withmitral valvestenosis (narrowing), withatrial fibrillation (AF). In the absence of AF, pure mitral regurgitation has a low incidence ofthromboembolism.^{[citation needed]}

The risk of emboli forming in AF depends on other risk factors such as age,hypertension,diabetes, recent heart failure, or previous stroke.Thrombus formation can also take place within theventricles, and it occurs in approximately 30% of anterior-wallmyocardial infarctions, compared with only 5% of inferior ones. Some other risk factors are poor ejection fraction (<35%), size of infarct, and the presence of AF. In the first three months after infarction, left-ventricleaneurysms have a 10% risk of emboli forming. Patients withprosthetic valves also carry a significant increase in risk of thromboembolism. Risk varies, based on the valve type (bioprosthetic or mechanical); the position (mitral or aortic); and the presence of other factors such as AF, left-ventricular dysfunction, and previous emboli^{[citation needed]}.

Emboli often have more serious consequences when they occur in the so-called "end circulation": areas of the body that have no redundant blood supply, such as the brain andheart.^{[citation needed]}

Assuming a normal circulation, an embolus formed in a systemicvein will always impact in the lungs, after passing through the right side of the heart. This will form apulmonary embolism that will result in a blockage of themain artery of the lung and can be a complication ofdeep-vein thrombosis. The most common sites of origin of pulmonary emboli are thefemoral veins. The deep veins of the calf are the most common sites of actual thrombi.^{[citation needed]}

In paradoxical embolism, also known as crossed embolism, an embolus from the veins crosses to the arterial blood system. This is generally found only with heart problems such as septal defects (holes in the cardiac septum) between the atria or ventricles. The most common such abnormality ispatent foramen ovale, occurring in about 25% of the adult population, but here the defect functions as a valve which is normally closed, because pressure is slightly higher in the left side of the heart. Sometimes, for example if a patient coughs just when an embolus is passing, it might cross to the arterial system.^{[citation needed]}

The direction of the embolus can be one of two types:^{[citation needed]}

• Anterograde
• Retrograde

In anterograde embolism, the movement of emboli is in the direction of blood flow. In retrograde embolism, the emboli move in opposition to the blood flow direction; this is usually significant only in blood vessels with low pressure (veins) or with emboli of high weight.^{[citation needed]}

The wordembolism comes from the Greek ἐμβολισμός, meaning "interpressure".^{[citation needed]}

• Embolectomy

• MR of Fat Embolism Brain Injury from Fat Embolism