Pleural effusion

Synonyms: Water on the lungs

Medical Specialties: Cardiology, Family practice, Internal medicine

Clinical Definition

Pleural effusion is an accumulation of excess fluid between the pulmonary pleural layers. A pleural effusion can occur without symptoms; alternatively there may be symptoms including chest pain, nonproductive cough and dyspnea. This excess fluid can be described as transudative (watery) or exudative (protein-rich), which can help in determining the etiology. 

In Our Own Words

It’s normal to have a little bit of fluid outside the lungs but within the chest, to lubricate and help lung tissue expand and contract. A pleural effusion, however, is an abnormal accumulation of fluid in this space around the lungs. Infections, blood clots, and other conditions such as cancer may cause a pleural effusion. The fluid can often be seen on a chest X-ray, and doctors can take a sample using a needle, in a procedure known as thoracentesis.


A more watery (transudative) effusion is commonly associated with conditions such as heart failure, liver cirrhosis, or after open-heart surgery. Thicker, protein-rich (exudative) effusions, on the other hand, are more commonly associated with blood clots in the lung, cancer, pneumonia, kidney disease or other sources of inflammation.

Relevant Conditions
  • Cancer
  • Heart failure
  • Pneumonia
  • Pulmonary embolism
Common Types
  • Protein-rich (exudative)
  • Protein-poor (transudative)
Side Effects
  • Chest pain
  • Dry cough
  • Shortness of breath or difficult breathing
  • Inability to breathe easily unless the person is sitting up straight or standing
Share this article
  • The Cleveland Clinic. "What is pleural effusion?" Heart & Vascular Institute Overview. 2010. Accessed Oct. 2013.
  • Harvard Medical School. "Pleural Fluid Smapling (or Thoracentesis)" Diagnostic Tests. 2013. Accessed Oct. 2013.
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