What is pulmonary embolism primarily caused by?

Pulmonary embolism is primarily caused by a blockage in the pulmonary arteries, most commonly due to a blood clot that has traveled from another part of the body, often from the legs, in a condition known as deep vein thrombosis (DVT). This blockage restricts blood flow to the lungs, leading to potentially serious complications, including damage to the lung tissues and reduced oxygen levels in the blood. The presence of a clot obstructs the necessary circulating blood, preventing it from delivering oxygen to vital organs and can cause symptoms such as shortness of breath, chest pain, and, in severe cases, cardiovascular collapse.

Other options refer to different respiratory issues: air entering the pleural cavity typically causes a pneumothorax, fluid accumulation in the lungs relates to conditions like pulmonary edema, and atelectasis refers to the collapse of lung tissue. None of these are causes of pulmonary embolism, which specifically involves a blockage due to a mass, predominantly a clot, impeding normal blood flow in the pulmonary vessels.