A 58-year-old woman with a 10-year history of deep vein thrombosis and pulmonary embolism undergoes autopsy. Histological examination reveals a thrombus in the pulmonary artery. Which is the most common site of origin for pulmonary emboli?

Explanation

## Most Common Source of Pulmonary Emboli **Key Point:** The deep veins of the lower extremities (DVT) are the source of >90% of clinically significant pulmonary emboli. The popliteal, femoral, and iliac veins are the most common sites. ### Pathophysiology of PE from Lower Extremity DVT 1. **Venous stasis** in lower extremities (immobility, surgery, trauma) 2. **Endothelial injury** from catheterization or inflammation 3. **Hypercoagulability** (malignancy, thrombophilia, pregnancy) 4. Thrombus forms in deep veins → fragment detaches → travels to right heart → lodges in pulmonary arteries ### Comparison of PE Source Sites | Site | Frequency as PE Source | Clinical Significance | Notes | |------|------------------------|----------------------|-------| | Deep leg veins (popliteal, femoral, iliac) | >90% | Most clinically significant | Largest thrombi, high embolic risk | | Pelvic veins | 5–10% | Moderate; associated with malignancy | Often missed on lower extremity imaging | | Right atrial appendage | <1% | Rare; associated with AF or RV infarction | Cardiac source, not venous | | Superficial leg veins | <1% | Minimal; rarely cause PE | Small thrombi, usually contained | **High-Yield:** Proximal DVT (popliteal vein and above) has ~40% risk of PE if untreated; distal DVT risk is much lower (~5–10%). This distinction guides clinical management. **Clinical Pearl:** Patients with unprovoked DVT/PE should be screened for occult malignancy and thrombophilia. Recurrent thromboembolism suggests underlying hypercoagulable state. **Mnemonic:** **LEG-PE** — Lower Extremity Graves (DVT) → Pulmonary Embolism.