Pulmonary Embolism

Pulmonary embolism is caused by a blocked artery in the lungs. The most common cause of such a blockage is a blood clot that forms in a Reference deep vein Opens New Window in the leg and travels to the lungs, where it becomes lodged in a smaller lung artery.

Almost all blood clots that cause pulmonary embolism are formed in the Reference deep leg veins. Clots also can form in the deep veins of the arms or pelvis.

Occasionally blood clots develop in Reference surface veins Opens New Window, but these clots rarely lead to pulmonary embolism.

In rare cases, pulmonary embolism may be caused by other substances, including:

• Small masses of infectious material.
• Fat, which can be released into the bloodstream after some types of bone fractures, surgery, trauma, or severe burns.
• Air bubbles from trauma, surgery, or medical procedures.
• Amniotic fluid from normal or complicated pregnancy and childbirth (very rare).
• Tumors caused by rapidly growing cancer cells.
• Foreign substances—such as a catheter that can break off during a medical procedure, talc, mercury, iodine, cotton, or the growth of tapeworm larvae.

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