Fluid Around the Lungs – Types and Causes of Pleural Effusions

A pleural effusion is when fluid accumulates in the pleural space around the lungs. It is commonly referred to as fluid in the lungs or water surrounding the lungs but should not be confused with pulmonary edema which is fluid in the lungs. Depending on the severity, it may compress the lung and impair breathing. Mild effusions may be asymptomatic and only detected upon radiographic investigation (x-ray, CT scan). Drainage may be necessary if a mild effusion does not resolve spontaneously with the proper treatment. Analysis of the drained fluid may provide an indication of the exact cause of the effusion or the underlying disease process. The fluid may be a transudate or exudate.

Types and Causes of Pleural Effusions

Transudative Effusions

Transudates are indicative of a disturbance in the balance between hydrostatic and osmotic pressure and there is usually no inflammation of the pleura or injury of the pleural capillaries. It is a serous fluid that is similar in composition to normal pleural fluid but excessive. This can be unilateral or bilateral and is known as a hydrothorax.

Causes of transudative exudates includes :

  • Congestive heart failure
  • Liver failure
  • Cirrhosis
  • Kidney failure
  • Nephrotic syndrome
  • Pulmonary infarction (usually a hemorrhagic exudate)

Exudative Effusions

Exudates may be due to inflammation of the pleura or surrounding tissue and injury to the microvasculature and is often a feature of inflammatory conditions. The exudate can be serous, serofibrinous or fibrinous. A serous exudate is similar to the normal pleural fluid with minimal inflammatory infiltrate like lymphocytes. The fibrinous exudate is when the microvascular permeability is increased significantly and fibrin enters the tissue spaces. This can lead to organization and adhesions.

Causes of a exudate, usually without blood or pus, includes :

  • Systemic lupus erythematosus (SLE)
  • Rheumatoid disease
  • Tuberculosis
  • Acute pancreatitis (may also be blood-stained)

Different Types of Pleural Exudates

Puruluent exudate is pus in the pleural exudate which is known as an empyema. It occurs with infections in the pleural space, most frequently with bacteria but may also be seen with fungal infections. The pathogenic microorganisms usually spread to the pleural space from surrounding sites, particularly the lung or bronchi or it may reach the pleural space through the blood stream or lympatic system (dissemination). Purulent exudate is yellow to green in color, creamy compared to the normal thin serous fluid with a number of inflammatory cells – neutrophils and other leukocytes.

Causes of purulent exudate includes :

  • Infectious pleuritis – pyogenic bacteria, fungi
  • Pneumonia
  • Intra-abdominal / subdiaphragmatic or abscess, especially liver abscess

Hemorrhagic exudate is the presence of blood in the pleural exudate. It is not a true hemothorax where only blood fills the pleural space as is seen in chest trauma. A hemorrhagic exudate, however, may be just as serious. It is associated with severe vascular damage as blood cells are able to leak out into pleural exudate. This may be microscopic and not visible to the naked eye or can stain the exudate pink, red or darker shades with red blood cell breakdown.

Causes of hemorrhagic exudate includes :

  • Pulmonary infarction
  • Pulmonary embolism
  • Malignancy – cancer of pleura, lung, bronchi, chest wall
  • Acute pancreatitis

Chylothorax is the term for accumulation of chyle, a milky  fluid high in fats,  in  in the pleural space. It is seen with lymphatic obstruction where the drainage of pleural fluid via the lymphatic system is compromised. A chylothorax can also occur when there is a rupture of lymphatic vessels.

Causes of a chylothorax includes :

  • Thoracic duct obstruction
  • Malignancy – pleura, mediastinal carcinomatosis
  • Lymphangitis

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