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What is pleural effusion?

Pleural effusion, which some people call “water on the lungs,” is the buildup of excess fluid between the layers of the pleura outside your lungs. The pleura are thin membranes that line your lungs and the inside of your chest cavity.

Normally, everyone has a small amount of fluid in their pleura. This fluid acts as a natural lubricant and makes it easier for your lungs to move when you breathe. But with pleural effusion, you have too much fluid around your lungs. This means your body is producing too much of the fluid or not absorbing enough of the fluid it makes.

Types of pleural effusion

Healthcare providers split pleural effusion into two types, depending on the kind of fluid around your lungs.

Excess fluid may be:

• Protein-poor and watery (transudative). Fluid of this kind comes from cirrhosis or heart failure, for example. This type of pleural effusion happens when there’s an increase in pressure from the fluid.
• Protein-rich (exudative). Fluid of this kind comes from cancer or an infection, for example. This type of pleural effusion happens because too much fluid is getting through your smallest blood vessels or your lymphatic system isn’t draining enough.

Treatment varies by type and cause.

How common is pleural effusion?

Pleural effusions are very common. Healthcare providers find pleural effusions in about 1.5 million people in the United States each year.

How is pleural effusion diagnosed?

A provider will ask you about your medical history. They’ll ask what other illnesses you have and when your symptoms started. They’ll do a physical exam, which includes listening to your lungs when you breathe. Next, they’ll order tests.

What tests will be done to diagnose pleural effusion?

Healthcare providers use these tests to diagnose and evaluate pleural effusion:

• Chest X-ray.
• Computed tomography (CT) scan of your chest.
• Ultrasound of your chest.
• Thoracentesis or biopsy (inserting a needle between your ribs to remove a fluid sample).
• Pleural fluid analysis (examining the fluid from the pleural space).

If less invasive tests don’t diagnose pleural effusion, you may need a thoracoscopy. Thoracoscopy is a minimally invasive technique, also known as video-assisted thoracic surgery, or VATS. A provider performs this while you’re under general anesthesia. Thoracoscopy allows them to see and evaluate your pleura. Often, they’ll treat your effusion during the thoracoscopy.