What Is a Pleural Effusion?

A pleural effusion is an unusual amount of fluid around the lung. There are many medical conditions that can lead to it, so even though your pleural effusion may have to be drained, your doctor likely will target the treatment at whatever caused it.

The pleura is a thin membrane that lines the surface of the lungs and the inside of the chest wall outside the lungs. In pleural effusions, fluid builds up in the space between the layers of pleura.

Normally, only teaspoons of watery fluid are in the pleural space, allowing the lungs to move smoothly within the chest cavity during breathing.


A wide range of things can cause a pleural effusion. Some of the more common ones are:


You might not have any. You’re more likely to have symptoms when a pleural effusion is moderate or large-sized, or if inflammation is present.

If you do have symptoms, they may include:


Your doctor will talk to you about your symptoms and give you a physical examination. She will listen to your chest with a stethoscope and tap on your chest.


Most often, doctors will confirm pleural effusions on imaging tests. You may get:

  • Chest X-ray: Pleural effusions appear white on chest X-rays, while air space looks black. If a pleural effusion is likely, you may get more X-ray films while you lie on your side. These can show if the fluid flows freely within the pleural space.
  • Computed tomography (CT scan): A CT scanner takes many X-rays quickly, and a computer constructs images of the entire chest -- inside and out. CT scans show more detail than chest X-rays do.
  • Ultrasound: A probe on your chest will create images of the inside of your body, which show up on a video screen. It can be used to locate the fluid so your doctor can get a sample for analysis.

Also, your doctor might do something called thoracentesis. She’ll take a little bit of the fluid to test. To do this, she’ll insert a needle and a tube called a catheter between your ribs, into the pleural space.


Doctors use the terms “transudative” and “exudative” to describe the two main types of pleural effusions:

Transudative: This pleural effusion fluid is similar to the fluid you normally have in your pleural space. It forms from liquid leaking across normal pleura. This type of pleural effusion rarely needs to be drained unless they are very large. Congestive heart failure is the most common cause of this type of effusion.

Exudative: This effusion forms from excess liquid, protein, blood, inflammatory cells or sometimes bacteria leaking across damaged blood vessels into the pleura. It may need to be drained, depending on its size and how much inflammation is involved. Among its causes are pneumonia and lung cancer.


Your doctor may need to treat only the medical condition that caused the pleural effusion. You would get antibiotics for pneumonia, for instance, or diuretics for congestive heart failure.

Large, infected, or inflamed pleural effusions often need to be drained to help you feel better and to prevent more problems. Procedures for treating pleural effusions include:

  • Thoracentesis: If the effusion is large, your doctor may take more fluid than she needs for testing, just to ease your symptoms.
  • Tube thoracostomy (chest tube): The doctor makes a small cut in your chest wall, and inserts a plastic tube into your pleural space for several days.
  • Pleural drain: For pleural effusions that keep coming back, you may get a long-term catheter inserted through your skin into the pleural space. You can drain the pleural effusion at home. Your doctor will tell you how and when to do that.
  • Pleurodesis: Your doctor injects an irritating substance (such as talc or doxycycline) through a chest tube into the pleural space. The substance inflames the pleura and chest wall, which then bind tightly to each other as they heal. Pleurodesis can prevent pleural effusions from coming back, in many cases.
  • Pleural decortication: Surgeons can operate inside the pleural space, removing potentially dangerous inflammation and unhealthy tissue. To do this, your surgeon may make small cuts (thoracoscopy) or a large one (thoracotomy).
WebMD Medical Reference Reviewed by Sabrina Felson, MD on December 7, 2016



Mason, R. Murray and Nadel's Textbook of Respiratory Medicine, 5th edition, Saunders, 2010.

Lab Tests Online, “Pleural Fluid Analysis.”

National Institutes of Health, National Heart, Lung, and Blood Institute: “What Is Pulmonary Embolism?”

Mayo Clinic: “Heart failure.”

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