Pulmonary Embolism: Cause

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Cause

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 deep vein in the leg and travels to the lungs, where it becomes lodged in a smaller lung artery.

Over 95% of blood clots that cause pulmonary embolism are formed in the upper deep leg veins.¹ Clots can also form in the lower deep veins of the legs as well as in the deep veins of the arms or pelvis. However, only about 20% of blood clots in the veins of the calf will become larger and move into the upper leg or groin veins.²

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

In rare cases, pulmonary embolism may be caused by other substances, including:³

• 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.

Last updated:	February 13, 2007
Author:	Shannon Erstad, MBA/MPH
Reviewed By:	Caroline S. Rhoads, MD - Internal Medicine, Jeffrey S. Ginsberg, MD - Hematology
Editors:	Kathleen M. Ariss, MS, Pat Truman, MATC