The lungs are covered on the outer surface by a smooth thin membrane called visceral pleura which is continuous with a similar membrane – the parietal pleura which lines the inner surface of the chest wall. The space between the parietal and the visceral pleura is called the pleural cavity which in normal circumstances is a potential space only. The opposing surfaces of both the pleural membranes on the inside of the pleural cavity are moist so as to allow the smooth expansion of the lungs during breathing.
The pleural cavity is frequently involved in various diseases in which the fluid can accumulate and thus cause compression of the lungs. While dry inflammation of the pleurae is called ‘dry pleurisy’, it is most commonly the ‘wet pleurisy’ or pleurisy with effusion which happens in different diseases. The fluid accumulation in the pleural cavity is called ‘pleural effusion’.
Pleural effusion presents with a sense of heaviness in the chest or chest pain and breathlessness. The degree of breathlessness is directly related to the amount of the fluid in the cavity – the larger the amount, the greater the breathlessness. There may occur other symptoms such as fever, general fatigue and malaise etc.
Pleural effusion can occur in several systemic diseases such as the congestive heart-failure, liver failure due to cirrhosis or chronic kidney failure. Low serum albumin levels due to malnutrition or other diseases can also be responsible for pleural effusion. This type of effusion is generally called ‘transudative’ and often responds to the treatment of the underlying disease. If massive, the fluid may require to be removed.
Pleural effusion due to diseases of the pleura and the lungs is generally ‘exudative’. In India, tuberculosis is the most important cause of pleural effusion. Other lung infections particularly the pneumonias can also cause pleural effusion. Pleural effusion can also occur in various tumours/malignancies of the lungs and/or pleurae. Some other important causes include the connective tissue disorders such as systemic lupus erythematosis and rheumatoid arthritis. Pulmonary thromboembolism i.e. blood clots in the pulmonary arteries can also cause pleural effusion.
Pleural effusion due to malignancies, thromboembolism and occasionally due to other causes may frequently contain blood. Trauma to the chest can also cause bloody pleural effusion i. e. haemothorax. Pus in the pleural cavity called pyothorax (or empyema) can occur following pneumonias or lung abscess.
Diagnosis of pleural effusion, suspected on clinical examination, is confirmed on chest x-ray and/or ultrasound examination. Chest CT scan is required to look into the details of pleural cavity and the lungs for the underlying cause. Fluid aspiration is almost always essential. The various pleural fluid investigations will help to find the cause of effusion.
Management of pleural effusion consists of fluid aspiration and treatment for the underlying cause (such as tuberculosis or malignancies). Management of emphysema requires chest-tube drainage and a relatively prolonged antibiotic therapy. Complicated effusions require to be handled by specialists with skill and expertise. Thoracoscopic and surgical intervention may be required for both the diagnosis and the therapy.