What is a common cause of pulmonary embolism?

Pulmonary embolism occurs when an embolus, which is a substance that travels through the bloodstream, obstructs a pulmonary artery. This obstruction can be caused by various materials, such as a blood clot (thrombus), fat, air, or tumor cells. The most frequent cause is a blood clot that originates in the deep veins of the legs, a condition known as deep vein thrombosis. As the embolus travels through the circulatory system, it can become lodged in the pulmonary arteries, leading to reduced blood flow to lung tissue, impaired oxygen exchange, and potentially life-threatening complications.

Other listed options do not directly account for the mechanism of pulmonary embolism. Infection, while it can lead to complications in the lungs, does not directly cause obstruction in the pulmonary arteries in the context of embolism. Pneumothorax involves the presence of air in the pleural space and affects lung inflation, but it is not associated with embolic obstruction. Atelectasis, which refers to lung collapse, is also not an obstruction caused by emboli but rather results from various conditions affecting lung expansion. Thus, the obstruction caused by an embolus is the central mechanism leading to pulmonary embolism.