A 58-year-old man with a 10-day history of immobilization following orthopedic surgery develops acute dyspnea, chest pain, and tachycardia. CT pulmonary angiography confirms bilateral pulmonary emboli. Regarding the morphologic features and risk factors of thromboembolism in this patient, all of the following are correct EXCEPT:

Explanation

## Sources and Risk Factors in Pulmonary Embolism **Key Point:** Atherosclerotic plaques in pulmonary arteries are NOT a primary source of PE. The vast majority of pulmonary emboli originate from **deep vein thrombosis (DVT) in the lower extremities**, not from in situ thrombosis of the pulmonary circulation itself. ### Source of Pulmonary Emboli | Source | Frequency | Mechanism | |--------|-----------|----------| | **DVT (lower extremity)** | 90–95% | Venous thrombi dislodge and travel to lungs | | **DVT (upper extremity)** | Rare | Catheter-related or malignancy-related | | **Right heart chambers** | Rare | Mural thrombi in atrial fibrillation or MI | | **Atherosclerotic plaques (pulmonary arteries)** | <1% | NOT a significant source | **High-Yield:** PE is almost always a consequence of **thromboembolism** (thrombus formed elsewhere, then embolized), NOT in situ thrombosis of pulmonary arteries. ### Virchow Triad in Postoperative PE All three components are present in this patient: 1. **Stasis:** Immobilization → venous stasis in lower extremity veins 2. **Endothelial injury:** Surgical trauma, vascular manipulation, catheterization 3. **Hypercoagulability:** Postoperative state → increased tissue factor, platelet activation, increased fibrinogen **Mnemonic:** **VEH** — **V**enous stasis, **E**ndothelial injury, **H**ypercoagulability ### Why DVT of Lower Extremity is the Source - Longest veins with slowest flow (popliteal, femoral, iliac) - Gravity-dependent pooling during immobilization - Surgical trauma and manipulation - Compression from swelling/casts **Clinical Pearl:** In this postoperative patient, bilateral PE suggests massive thromboembolism, likely from bilateral lower extremity DVT or a large single thrombus that fragmented. ### Other True Statements - **Virchow triad:** All three components are present in postoperative immobilization - **Lower extremity DVT source:** Correct; accounts for >90% of PE cases - **Immobilization and hypercoagulability:** Both stasis and tissue factor activation occur [cite:Robbins 10e Ch 4]