Pleural effusion causes
Reading File
Finding Sources
Finding Sources
Reading File
Reading File
Reading File
Here is a comprehensive overview of the causes of pleural effusion, organized by fluid type.
Pleural Effusion — Causes
Pleural effusions develop when fluid influx into the pleural space exceeds efflux. They are broadly classified as transudates or exudates based on Light's criteria.
TRANSUDATES
(Systemic factors alter hydrostatic/oncotic pressures; the pleura itself is normal)
| Cause | Key Mechanism |
|---|---|
| Congestive Heart Failure | Most common cause overall. Pulmonary interstitial fluid transudates across the mesothelium. Effusions are typically bilateral, right > left. ~83% of CHF exacerbations produce effusions on CT. |
| Hepatic Hydrothorax / Cirrhosis | Ascitic fluid moves via diaphragmatic defects into the pleural space. Right-sided in ~85%. Can develop without clinically apparent ascites. |
| Nephrotic Syndrome | Decreased plasma oncotic pressure + increased hydrostatic pressure from salt/water retention. Usually bilateral, often infrapulmonary. |
| Peritoneal Dialysis | Dialysate migrates from peritoneal cavity through diaphragmatic defects. ~90% right-sided. |
| Myxedema (Hypothyroidism) | Decreased lymphatic function; often coexists with pericardial effusion. Borderline transudate/exudate. |
| Hypoalbuminemia | Reduced oncotic pressure. |
| Glomerulonephritis | Volume overload and low oncotic pressure. |
| Superior Vena Cava Obstruction | Increased systemic venous pressure. |
| Pulmonary Embolism | Can be transudate or exudate (latter more common with infarction). |
EXUDATES
(Pleural/pulmonary disease disrupts local fluid dynamics — increased capillary permeability or impaired lymphatic drainage)
Infections
- Bacterial pneumonia — parapneumonic effusion (most common exudative cause overall)
- Tuberculosis — leading cause in endemic regions; lymphocyte-predominant exudate
- Lung abscess / Bronchiectasis
- Viral illness
Malignancy
- Primary lung cancer — most common cause of malignant effusion
- Breast cancer — second most common cause of malignant effusion (~7–11% of breast cancer patients)
- Mesothelioma
- Lymphoma
- Pulmonary/pleural metastases
- Meigs' syndrome — benign ovarian tumors cause ascites + pleural effusion
Connective Tissue / Autoimmune
- Rheumatoid arthritis
- Systemic lupus erythematosus (SLE)
Abdominal / Gastrointestinal Disorders
- Pancreatitis — high amylase in pleural fluid; left-sided
- Subphrenic abscess
- Esophageal rupture — rare but highly morbid; usually left-sided
- Post-abdominal surgery
Miscellaneous
- Pulmonary embolism with infarction (pulmonary infarction)
- Uremia — fibrinous pleuritis; pathogenesis unclear, possibly analogous to uremic pericarditis
- Drug reactions (e.g., amiodarone, nitrofurantoin, methotrexate) — fluid may be eosinophilic
- Chylothorax — disruption of the thoracic duct (trauma, lymphoma, surgery)
- Post-partum
- Ovarian hyperstimulation syndrome
- Dressler's syndrome (post-MI/post-cardiac injury)
Quick Mnemonics
Common causes in the US (in order of frequency):
- Congestive heart failure
- Malignancy
- Bacterial pneumonia (parapneumonic)
- Pulmonary embolism
TB remains the dominant cause in endemic regions.
Sources: ROSEN's Emergency Medicine, 10e; Murray & Nadel's Textbook of Respiratory Medicine
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