What is the most common site for a pulmonary embolism to originate from?

• A. Artery of Left Leg
• B. Vein of Upper Extremity
• C. Vein of Left Leg
• D. Artery of Upper Extremity

Answer: (C)

Pulmonary emboli come from thrombi that form in the venous system, most often in the deep veins of the legs. When a deep vein thrombosis develops in the leg—especially in the calf and proximal leg veins—it can break free and travel to the pulmonary arteries. The left leg is a notable source because May-Thurner syndrome, where the left iliac vein is compressed by the right iliac artery, predisposes to left-sided DVT. So, among leg sites, the left leg deep veins are a common origin for emboli that reach the lungs. Arterial emboli don’t travel to the lungs, and upper-extremity DVTs are less commonly the source than leg DVTs.