Pulmonary Embolism (PE): High-Yield Pathology
A pulmonary embolism is a blockage of the pulmonary artery or its branches, most commonly due to a detached thrombus (embolus) originating from the deep veins of the lower extremities.
1. Pathogenesis: Virchow’s Triad
The development of the underlying deep vein thrombosis (DVT) is classically explained by Virchow’s Triad:
- Stasis: Immobility, surgery, long travel.
- Hypercoagulability: Cancer, factor V Leiden, OCP use, pregnancy.
- Endothelial Damage: Trauma, surgery, and indwelling catheters.
2. Exam Must-Knows
| Finding | Pathological/Clinical Detail |
|---|---|
| Hampton Hump | Wedge-shaped opacity on CXR representing pulmonary infarction. |
| Westermark Sign | Focal oligemia (decreased lung markings) on CXR distal to the embolus. |
| Types of Emboli | Remember the “FAT BAT” mnemonic: Fat, Air, Thrombus, Bacteria, Amniotic fluid, Tumor. |
3. Clinical Pearl
Pathology Board Hint: Most PEs are small and clinically silent, leading to bronchial artery circulation providing dual blood supply. However, if the patient has underlying heart/lung disease, the lack of dual circulation leads to hemorrhagic (red) infarction of the lung segment.