An embolus is a particle that moves about in our blood vessels, in either the veins or arteries. Most emboli are composed of clotted blood cells. A blood clot is called a thrombus and a moving blood clot is called a thromboembolus.
As an embolus moves through the body's blood vessels, it's likely to come to a passage it can't fit through. It lodges there, backing up blood behind it. The cells that normally get their blood supply via this passage are starved of oxygen (ischemia) and die. This condition is called an embolism.
Types of embolism
- pulmonary embolism: An embolus, usually formed in the leg (sometimes known as a deep vein thrombosis or DVT), lodges in one of the arteries of the lungs. Many emboli are broken down by the body and go away by themselves. However, serious pulmonary embolism may cause death.
- brain embolism: If a blood clot travels to the brain, this causes an ischemic stroke or TIA (transient ischemic attack).
- retinal embolism: Small clots that wouldn't block a major artery can block the smaller blood vessels feeding the retina at the back of the eye. The result is usually sudden blindness in one eye.
- septic embolism: This occurs when particles created by infection in the body reach the bloodstream and block blood vessels.
- amniotic embolism: Not all emboli are made of clotted blood. In pregnancy, the womb is filled with amniotic fluid, which protects the fetus. Amniotic fluid can embolize and reach the mother's lungs, causing pulmonary amniotic embolism.
- air embolism: Scuba divers who rise to the surface too rapidly can generate air embolism, bubbles in the blood that can block arterial blood flow.
- fat embolism: If fat or bone marrow particles are introduced into the blood circulation, they may block blood vessels the way a blood clot or air bubble can.
Most embolisms happen to people who have risk factors for blood clot formation, such as smoking and heart disease. Other risk factors for other types of emboli include high blood pressure, atherosclerosis (buildup of fatty plaque in the blood vessels), and high cholesterol.
The primary cause of most pulmonary embolisms is deep vein thrombosis (DVT). This is a condition in which the veins of the legs develop clots. Natural agents in the blood often dissolve small clots without causing any effects of blockage. Some clots are too big to dissolve and are big enough to block major blood vessels in the lungs or in the brain.
Factors that slow blood flow in the legs may promote clotting. People can develop a DVT or pulmonary emboli after sitting still on long flights or after immobilization of the leg in a cast, or after prolonged bed rest without moving the legs. Other factors associated with DVT or pulmonary embolism include cancer, previous surgery, a broken leg or hip, and genetic conditions affecting the blood cells that increase the chance of blood clot formation.