Blood Clot
Blood Clot. Callista Images/Getty Images

Definition: An embolus is a particle or mass that travels through the bloodstream, that may subsequently lodge in a blood vessel, producing blockage and causing organ damage. The plural of embolus is emboli. Organ damage caused by an embolus is often called an embolic event.

An embolus may consist of a blood clot, fat, air, pus, cholesterol, amniotic fluid, or a foreign body.

Embolus vs. Thrombus vs. Thromboembolus

The terms embolus and thrombus are often confused.

A thrombus is a blood clot that forms within the vascular system. If that blood clot breaks free and travels through the bloodstream, it has become an embolus.

An embolus that consists of a thrombus that has detached from its site of origin is sometimes called a thromboembolism.

Examples of Embolic Disease

  • A pulmonary embolus is an embolus (most typically, a blood clot) that travels to the lungs and produces lung damage. Pulmonary embolus is most often caused by deep venous thrombosis in the legs.
  • A cerebral embolus is an embolus that lodges in an artery supplying the brain, producing a stroke. A common cause of cerebral emboli is atrial fibrillation. In fact, a major goal in treating atrial fibrillation is to prevent embolic stroke.
  • A fat embolus can occur when the fracture of a long bone releases droplets of fat into the bloodstream. Fat emboli most often travel to the lungs or to the brain, producing pulmonary embolus or stroke.
  • A septic embolus is a mass of bacteria-containing tissue or pus that enters the bloodstream from a site of infection. Causes of septic embolus include infectious endocarditis, or an infection at the site of an intravenous catheter.
  • An air embolus is caused by small amounts of air that can get into the circulation during a medical procedure (such as surgery or a catheterization procedure).
  • A cholesterol embolus is caused by the release of cholesterol crystals from an atherosclerotic plaque. These crystals can lodge in an artery downstream from the plaque and cause tissue damage. Cholesterol emboli most commonly occur with peripheral artery disease, and the damage they cause depends on the location of the plaque. Manifestations may include painful blue toes, gangrene of the lower extremities, skin discoloration, kidney failure, abdominal pain, intestinal bleeding, stroke, or peripheral nerve disease.
  • An amniotic fluid embolus is a rare emergency associated with childbirth. It is caused by amniotic fluid, or cells shed from the baby, entering the mother’s circulation through the placental bed. The damage done to the mother with an amniotic fluid embolus is usually not caused by the embolus lodging in a particular location, but rather, is caused by a general, often overwhelming, allergic reaction to “foreign” tissue. An amniotic fluid embolus is an extremely dangerous event which is often fatal.
  • A foreign body embolus is another rare event, usually associated with a medical procedure. For instance, talc entering the bloodstream can become an embolus.
  • A “paradoxical” embolus is an embolus originating in a vein that ends up lodging in an artery. A paradoxical embolus requires a pathway from the right side of the heart to the left; for instance, via a patent foramen ovale.


Lin HJ, Wolf PA, Kelly-Hayes M, et al. Stroke Severity in Atrial Fibrillation. The Framingham Study. Stroke 1996; 27:1760.

Norgren L, Hiatt WR, Dormandy JA, et al. Inter-Society Consensus for the Management of Peripheral Arterial Disease (TASC II). J Vasc Surg 2007; 45 Suppl S:S5.

Tagalakis V, Patenaude V, Kahn SR, et al. Incidence of and Mortality from Venous Thromboembolism in a Real-world Population: the Q-VTE Study Cohort. Am J Med 2013; 126:832.e13.

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