Can Pleural Effusion Be Caused by PE?
Yes, pulmonary embolism definitively causes pleural effusion—small distal emboli create areas of alveolar hemorrhage resulting in pleuritis and pleural effusion, which is usually mild. 1
Mechanism of PE-Related Pleural Effusion
The pathophysiology is well-established by the European Society of Cardiology:
- Distal emboli cause alveolar hemorrhage that leads to pleural irritation, even when these emboli don't significantly affect hemodynamics 1
- This clinical presentation is termed "pulmonary infarction," though true histopathological infarction is uncommon—the actual correlate is alveolar hemorrhage 1, 2
- The mechanism involves increased interstitial fluid in the lungs resulting from ischemia or release of vasoactive cytokines 3
- The effusion develops from pleural irritation due to these distal emboli causing the hemorrhagic process 1
Clinical Characteristics of PE-Related Pleural Effusion
Frequency and Size
- Pleural effusion occurs in approximately 25-48% of patients with PE 4, 5
- The effusions are typically small, usually occupying less than one-third of the hemithorax 3
- Most effusions (86%) occur on the same side as the emboli 4
Fluid Characteristics
- Nearly all pleural effusions due to PE are exudates (occasionally transudative) 3, 6
- The fluid is frequently hemorrhagic with marked mesothelial hyperplasia 6
- The presence of bloody pleural fluid is not a contraindication for anticoagulation therapy 6
Associated Clinical Features
- Approximately 75% of patients with PE and pleural effusion have pleuritic chest pain 3
- Pleuritic chest pain with pleural effusion is highly suggestive of PE, particularly in patients under 40 years old where PE is the most common cause 3, 6
- Dyspnea is frequently out of proportion to the size of the pleural effusion—a key clinical clue 3
Relationship to PE Severity
Patients with pleural effusion tend to have more severe PE:
- Higher percentages of central PE (84% vs 73%) and right ventricular dilation (45% vs 36%) 5
- Pulmonary infarction is the strongest independent predictor of pleural effusion (OR 6.20) 5
- Elevated C-reactive protein levels are also independently associated with effusion development (OR 1.05) 5
- Patients are likely to have emboli in central, lobar, segmental, or subsegmental pulmonary arteries—regions detectable by spiral CT pulmonary angiography 6
Prognostic Implications
Important caveat: While pleural effusion indicates more severe PE, it carries prognostic significance:
- Pleural effusion is an independent predictor of both 30-day mortality (OR 2.154) and long-term mortality (OR 1.591) 7
- 30-day mortality is significantly higher in PE patients with effusion (23% vs 9%) 7
- However, the presence of effusion itself does not predict length of hospital stay 5
Clinical Pitfalls to Avoid
- Do not attribute large or contralateral pleural effusions to PE without excluding alternative diagnoses—PE-related effusions are typically small and ipsilateral 4
- PE is the most commonly overlooked disorder in patients with pleural effusion and should be evaluated in all patients with undiagnosed effusion 6
- The effect on gas exchange is usually mild except in patients with pre-existing cardiorespiratory disease, where it can be more significant 1
- No specific treatment is required for the pleural effusion itself—treat the underlying PE with standard anticoagulation 6