Pleural effusion refers to a buildup of excess fluid between the layers of the pleura outside the lungs. The pleura is a thin membrane made up of an inner visceral pleura that covers the lungs, and an outer parietal pleura that lines the inside of the chest cavity. Between these two membranes is the pleural space, which contains a small amount of lubricating pleural fluid that allows the lungs to inflate and deflate smoothly during breathing. In pleural effusion, excess fluid accumulates in this pleural space due to an imbalance in the forces controlling pleural fluid formation and absorption. This abnormal buildup of fluid can affect normal breathing by limiting lung expansion. Pleural effusions are a common medical condition that can arise from diseases affecting many different organs.
What organs can be affected in pleural effusion?
Pleural effusions often occur secondary to underlying diseases affecting the structures in the thorax including the lungs, pleura, and heart. However, effusions can also develop from abdominal pathologies, cancers affecting distant organs, systemic processes, and injuries. Some of the major organ systems and diseases that can lead to pleural effusion include:
Lungs
The most common cause of pleural effusions is disease or injury involving the lung parenchyma. This includes:
– Pneumonia – Bacterial, viral, or fungal lung infections are a frequent cause of pleural effusions, occurring in over 40% of patients hospitalized with pneumonia. Infectious inflammation in the lungs can spread to the pleura.
– Lung cancer – Between 7-15% of lung cancers present with a pleural effusion. Malignant pleural effusions indicate metastatic spread of cancer to the pleural space.
– Pulmonary embolism – Blood clots in the pulmonary arteries can cause pleural effusion, occurring in 5-16% cases. The exact mechanism is unclear but likely involves mediastinal lymph node obstruction.
– Interstitial lung disease – Inflammatory and fibrotic conditions like asbestosis, sarcoidosis, idiopathic pulmonary fibrosis can cause pleural effusions, especially if acute exacerbations develop.
– Tuberculosis – Pleural tuberculosis develops in about 5% of patients with pulmonary TB due to direct spread from lung lesions.
– Bronchiectasis – Chronic dilatation and infection of bronchi damages local pleura resulting in effusion.
– Rare lung conditions like yellow nail syndrome and lymphangioleiomyomatosis.
Pleura
Diseases of the pleural membranes themselves can lead to fluid buildup:
– Malignant pleural mesothelioma – Cancer of the pleural mesothelial cells causes effusions in over 90% cases.
– Pleural injury – Physical trauma to the chest wall from blunt injury or surgery can disrupt the pleural space leading to leakage of fluid.
– Pleurisy – Inflammation of the parietal and visceral pleural layers from infection, connective tissue disease, drugs etc. increases capillary permeability resulting in exudative effusions.
Pericardium
The pericardium is the membrane around the heart that shares continuity with the pleural layers. Pericardial effusions can translocate fluid into the pleural space by direct spread along the reflections of serous membranes. This occurs in conditions like:
– Pericarditis – Inflammation of the pericardium from infection, autoimmune conditions, metabolic problems, radiation therapy etc.
– Post-cardiac injury syndromes – Pleural effusions can develop after myocardial infarction, heart surgeries, stab wounds due to transudative fluid tracking along the pericardial reflections.
– Urinothorax – Rarely, urine can leak from the kidney into the pleural space causing a transudative effusion.
Congestive heart failure
Impaired pumping function of the heart leads to increased back pressure in the pulmonary vessels and leakage of fluid into the pleural space. About 40% of pleural effusions are caused by congestive heart failure.
Liver disease
Advanced liver cirrhosis and portal hypertension can cause transudative pleural effusions due to decreased oncotic pressure and impaired fluid removal by the liver and lymphatics. Ascites can also shift into the pleural cavity through diaphragmatic defects.
Kidney disease
Renal failure results in fluid retention and can cause pleural effusions, especially when the glomerular filtration rate falls below 10-15 ml/min. Effusions tend to occur more often in hemodialysis patients.
Autoimmune disorders
Diseases like rheumatoid arthritis, systemic lupus erythematosus, and scleroderma can cause inflammation of the pleura leading to effusions.
Pancreatitis
Inflammation of the pancreas allows pancreatic enzymes to leak into surrounding tissues and reach the mediastinum through openings in the diaphragm. This can cause chemical irritation leading to pleural effusion.
Gastrointestinal disorders
Any gastrointestinal disease that results in low serum albumin can cause decreased oncotic pressure and pleural effusion. This includes protein-losing enteropathies like celiac and Crohn’s disease.
Gynecological conditions
Ovarian hyperstimulation syndrome from IVF and mechanical irritation from large ovarian cysts can cause right-sided pleural effusions.
Drugs
Many prescription medications like amiodarone, nitrofurantoin, methotrexate etc. can cause drug-induced pleural disease.
Metastatic cancers
Most cancers like breast, ovarian, and gastrointestinal malignancies can metastasize and affect the pleura, even if the primary cancer did not originate in the chest.
Summary of organs affected in pleural effusion
| Organ System | Diseases Causing Pleural Effusion |
|---|---|
| Lungs | Pneumonia, lung cancer, pulmonary embolism, interstitial lung disease, tuberculosis, bronchiectasis |
| Pleura | Mesothelioma, chest trauma, pleurisy |
| Pericardium | Pericarditis, post-cardiac injury syndromes, urinothorax |
| Heart | Congestive heart failure |
| Liver | Cirrhosis, portal hypertension |
| Kidneys | Renal failure, nephrotic syndrome |
| Autoimmune system | Rheumatoid arthritis, systemic lupus erythematosus, scleroderma |
| Pancreas | Pancreatitis |
| Gastrointestinal tract | Protein-losing enteropathies |
| Gynecological | Ovarian cysts, ovarian hyperstimulation syndrome |
| Drugs | Amiodarone, nitrofurantoin, methotrexate |
| Cancer | Lung, breast, ovarian, lymphoma, gastrointestinal |
Mechanisms of pleural effusion
The underlying diseases cause pleural effusions via several mechanisms:
Increased pleural fluid formation
– Increased capillary permeability due to inflammation of the pleura allows proteins and fluid to leak out into the pleural space at an abnormally high rate. This occurs in conditions like pneumonia, pleurisy, pulmonary embolism.
– Impaired lymphatic drainage prevents efficient removal of fluid, causing it to accumulate. Lymph node obstruction from malignancy or fibrosis can result in this.
– Increased negative intrapleural pressure due to atelectasis and reduced lung volume pulls more fluid into the pleural space.
Decreased pleural fluid absorption
– Low oncotic pressure in the pleural space due to hypoalbuminemia (liver disease, kidney disease, protein-losing enteropathy) or escape of albumin through inflamed pleura reduces the normal absorption of fluid.
– Elevated hydrostatic pressure in lung capillaries due to congestive heart failure or renal failure pushes more fluid out.
– Lymphatic obstruction prevents drainage of fluid from the pleural space.
Translocation of fluid from elsewhere
– Pericardial fluid may shift into pleural space along reflections of serous membranes in pericardial effusion.
– Ascites due to liver disease transfers into pleural cavity through diaphragmatic defects.
– Pancreatic fluid collections can track into mediastinum and pleural space through esophageal or diaphragmatic openings.
Direct spread
– Infectious or inflammatory lung diseases like pneumonia and tuberculosis spread directly from lung parenchyma into pleural space.
– Malignant cancers of the lungs, pleura, chest wall, or breast metastasize and seed the pleural membranes.
Conclusion
Pleural effusions have diverse causes arising from pathology in organs throughout the body. While the lungs and pleura themselves are affected in many cases, pleural effusions also commonly develop secondary to disease processes originating in other organs like the heart, liver, kidney, pancreas, and gynecological organs. Systemic disorders like congestive heart failure, cirrhosis, autoimmunity, and cancer can result in pleural effusion even without primary lung involvement. The mechanisms include increased fluid formation, decreased absorption, translocation from other sites, and direct spread of infection or malignancy. Identifying the source of the fluid accumulation based on clinical history and investigative findings is key to target management appropriately.