Description

Types: transudate (low protein/low specific gravity) and exudate (high protein and cellular debris); transudate: commonly caused by congestive heart failure (CHF): 40%; exudates: pneumonia 25%, malignancy 15%, and pulmonary embolism (PE) 10%

Epidemiology

Incidence
Estimated 1.5 million cases per year in the United States; CHF: 500,000; pneumonia: 300,000; malignancy: 150,000; PE: 150,000; cirrhosis: 150,000; tuberculosis (TB): 2,500; pancreatitis: 20,000; collagen vascular disease: 6,000

Prevalence
Estimated 320 cases per 100,000 people in industrialized countries; in hospitalized patients with AIDS, prevalence is 7–27%; no gender predilection: ~2/3 of malignant pleural effusions occur in women.

Etiology and Pathophysiology

• Imbalance between pleural fluid formation and pleural fluid absorption due to and imbalance between oncotic and hydrostatic pressures between the vascular and pleural space
  • Favors pleural effusion: hydrostatic pressure in vessel greater than pleural space, oncotic pressure vessel less than pleural space, elevated capillary permeability from baseline
  • Favors fluid retention in the vessel: hydrostatic pressure in vessel less than pleural space, oncotic pressure vessel greater than pleural space, decreased capillary permeability from baseline
• Transudates: pleural fluid migration that results from imbalances in hydrostatic/oncotic forces, increase in capillary permeability, lymphatic obstruction/impaired drainage, translocation of fluid from another compartment (e.g., peritoneal or retroperitoneal)
• Transudates: CHF: 40% of transudative effusions; 80% bilateral; constrictive pericarditis, atelectasis; superior vena cava syndrome.; cirrhosis (hepatic hydrothorax), nephrotic syndrome, hypoalbuminemia; myxedema; urinothorax, central line misplacement; peritoneal dialysis; Dressler syndrome (postmyocardial infarction syndrome); yellow nail syndrome: yellow nails, lymphedema, and pleural effusion; SARS-CoV-2
• Exudates: lung parenchyma infection: bacterial (parapneumonic, tuberculous pleurisy), fungal, viral, parasitic (amebiasis, Echinococcus granulosus); cancer: lung cancer, metastases (breast, lymphoma, ovaries), mesothelioma; PE: 25% of PEs are transudate; collagen vascular disease: rheumatoid arthritis, systemic lupus erythematosus (SLE), Wegener granulomatosis, sarcoidosis, Churg-Strauss syndrome, Sjogren syndrome, granulomatosis with polyangitis; GI: pancreatitis, esophageal rupture, abdominal abscess, after liver transplant; chylothorax: thoracic duct tear, malignancy; hemothorax: trauma, PE, malignancy, coagulopathy, aortic aneurysm; others: after coronary artery bypass graft, uremia, asbestos exposure, radiation, drugs; drugs: nitrofurantoin, bromocriptine, amiodarone, procarbazine, hydralazine, procainamide, quinidine, methotrexate, methysergide, interleukin-2, mitomycin, practolol, minoxidil, bleomycin, cyclophosphamide, procarbazine, imatinib, all-trans retinoic acid, gemcitabine, dantrolene, valproic acid, sulfasalazine, minocycline, acebutolol, phenytoin, practolol, minoxidil, methysergide, L-tryptophan, dasatinib, docetaxel, filgrastim, ergot alkaloids
  • Meigs syndrome; yellow nail syndrome; ovarian stimulation syndrome; lymphangiomatosis; acute respiratory distress syndrome (ARDS); chylothorax: thoracic duct tear, malignancy, associated with lymphoma
  • Pleural effusions of extravascular origin (PEEVO)
  • Transudative PEEVO: hepatic hydrothorax, peritoneal dialysis, urinothorax, extravascular migration of central venous catheter, duropleural fistula, ventriculoperitoneal and ventriculopleural shunts, glycinothorax
  • Exudative PEEVO: esophageal or gastric perforation, misplaced enteral feeding tube, pancreaticopleural fistula and pancreatic pseudocyst, bilothorax

Risk Factors

Occupational exposures/drugs; PE, TB, bacterial pneumonias; opportunistic infections (in HIV patients when CD4 count is <150 cells/μL)

Commonly Associated Conditions

Hypoproteinemia, heart failure, cirrhosis, kidney disease