A 62-year-old man with recently diagnosed lung cancer presents with acute dyspnea, pleuritic chest pain, and hemoptysis. CT pulmonary angiography confirms pulmonary embolism. Which is the most common source of thromboembolism in this patient?

Explanation

## Source of Pulmonary Embolism **Key Point:** The deep veins of the lower limbs (particularly the popliteal, femoral, and iliac veins) are the source of >90% of clinically significant pulmonary emboli. **High-Yield:** While upper limb, pelvic, and right heart sources exist, they account for <10% of PE cases. In this patient with malignancy (a hypercoagulable state), DVT of the legs remains the overwhelmingly common source. ### Anatomical Basis | Source | Frequency | Clinical Context | |--------|-----------|------------------| | Deep leg veins (popliteal, femoral, iliac) | >90% | Most common; associated with immobility, surgery, malignancy | | Right atrial appendage | ~5% | Atrial fibrillation, right heart strain | | Paradoxical embolism (PFO) | ~2% | Venous thrombus crosses to systemic circulation | | Cardiac mural thrombus | ~2% | Post-MI, dilated cardiomyopathy | **Clinical Pearl:** Soleal and gastrocnemius veins (calf) are the most frequent initial sites of DVT formation, but proximal DVT (popliteal and above) carries the highest risk of embolization to the lungs. **Mnemonic — DVT Risk Factors (Virchow's Triad):** **SHE** — **S**tasis (immobility, surgery), **H**ypercoagulability (malignancy, OCP, thrombophilia), **E**ndothelial injury (trauma, central lines). This patient has both stasis (post-operative or bed-bound from cancer) and hypercoagulability (malignancy). ### Why Lower Limb DVT Dominates 1. **Anatomical factors:** Large-caliber veins with slow blood flow in dependent position. 2. **Pathophysiological:** Malignancy triggers tissue factor release → hypercoagulability. 3. **Epidemiological:** 90% of PE cases originate from leg DVT; only 10% from other sources combined. [cite:Harrison 21e Ch 297]