What Is Pleural Effusion?

Pleural effusion is a buildup of excess fluid between the chest wall and the lung. A small amount of fluid normally fills the space between the two pleural layers and helps the lungs glide smoothly in the chest as we breathe.

Cancers of the chest, including mesothelioma and lung cancer, may lead to malignant pleural effusions through excess fluid production and inhibited lymphatic drainage.  

When excess fluid fills the pleural cavity, it compresses the lungs and limits their ability to move freely, making breathing more difficult. When the lung is compressed by fluid or tumors it is referred to as nonexpandable lung. A 2019 study of 229 patients with mesothelioma found 83% had pleural effusion at presentation, and nonexpandable lung was observed in 33% of this group.

On their own, uncomplicated pleural effusions are not life-threatening. They can resolve in a few months without medical intervention. However, once a person has one pleural effusion they are more likely to experience this condition again.

What is a pleural effusion?

Exudative vs. Transudative Pleural Effusion

Pleural effusions are classified into two types, known as exudative or transudative. 

Transudative pleural effusions are caused by an imbalance between the normal production of fluid and its removal. The fluid is clear and not the result of diseased pleural tissue. Heart failure is the most common cause. 

Exudative pleural effusions result from disease on the pleural tissue that produces excess fluid, blocks blood vessels and lymph vessels, and causes inflammation or infection. The fluid is cloudy and contains cells and proteins. Pneumonia and cancer are common causes. Pleural effusions caused by mesothelioma are classified as exudative effusions.

Symptoms of Pleural Effusions

Some of the most common pleural effusion symptoms and signs to watch out for are chest pain, breathlessness and cough. Symptoms of pleural effusion can vary from mild to severe. Some patients experience no symptoms at all. 

The type and severity of symptoms often correlate to the amount of fluid and any underlying breathing conditions or infections.


  • Dry cough
  • Dyspnea (shortness of breath)
  • Orthopnea (inability to breathe easily unless sitting up or standing)
  • Sharp chest pain that worsens with cough or deep breathing
  • Malaise (general feeling of discomfort)
  • Fatigue
  • Hiccups
  • Rapid, shallow breathing
  • Fever if fluid becomes infected

Many patients feel pleural effusions as pain in their chest that worsens with coughing and deep breathing. Some patients may experience back pain or shoulder pain in connection with pleural effusions.

Although pleural effusions can resolve on their own, it is best to seek treatment if you have breathing changes or a new onset of shortness of breath. The pressure from excess pleural fluid can cause a lung to collapse. If you don’t seek immediate treatment, pleural fluid may become infected. An infection of the pleural fluid is called empyema.

What Causes Pleural Effusion?

The most common causes of pleural effusion include congestive heart failure, pneumonia, cancer and pulmonary embolism. 

To identify the cause, your doctor may perform a pleural tap, called a thoracentesis, to extract pleural fluid and run tests on it. The best treatment option will vary depending on what is causing the fluid to accumulate.

Conditions that cause pleural effusion include:

  • Alcoholism
  • Asbestos exposure
  • Cancer
  • Cirrhosis
  • Heart failure 
  • High blood pressure
  • Pneumonia
  • Pulmonary embolism
  • Surgery
  • Smoking

When pneumonia causes pleural effusion, it is the result of a bacterial infection leading to an inflammatory response and the production of fluid containing inflammatory cells. 

Pleural effusions may signal a developing asbestos-related disease, such as pleural thickening, and contribute to its progression. Pleural thickening is characterized by the accumulation of scar tissue on the pleura, and it can increase and spread after each effusion episode.

How Does Mesothelioma Cause Pleural Effusion?

Mesothelioma causes pleural effusions due to cancer-induced leakage of blood, lymph and other fluid from blood vessels into the tissues around it. 

When tumors develop, they form new blood vessels that are more permeable, or leaky, than normal blood vessels. This permeability allows blood, lymph and other fluids to leak into the pleural space and accumulate.

Tumors may also block the lymphatic system that helps drain fluid from tissues throughout the body. When tumors and cancerous cells block lymph nodes, lymphatic vessels and lymphatic capillaries, it decreases their ability to drain fluids. This contributes to the accumulation of fluid between the two layers of the pleura. 

Pleural effusions do not involve fluid collection inside the lungs. When fluid builds up in the lungs it is called pulmonary edema.

Diagnosing Mesothelioma and Pleural Effusion

An X-ray is commonly used to identify this condition because a pleural effusion appears white on an X-ray while the lung’s airspace appears black. A thoracentesis or pleural tap will be performed to drain the fluid and test it for signs of disease, such as the presence of cancerous cells.

If cancerous cells are discovered, a biopsy of potentially cancerous tissue will be performed. A biopsy is the most important test to identify whether mesothelioma may be present. Pleural effusion is a common symptom of mesothelioma and other asbestos-related diseases, especially as these diseases progress.

Watch: Dr. Snehal Smart explains how pleural effusions and the color contrast of a CT-scan can lead to a mesothelioma diagnosis.

An X-ray can be used to identify pleural effusion once accumulation reaches approximately 300 milliliters, or 1.25 cups of fluid. If there is less fluid than this, the effusion may not be visible on chest X-rays.

Thoracic ultrasonography can identify as little as 5-50 milliliters of pleural fluid. CT scans can help differentiate pleural fluid and potential tumor masses and may identify signs of pleural thickening.

Pleural Effusion Treatment

Pleural effusions are treated with several options, depending upon the cause. For example, diuretics and heart failure medications are used when congestive heart failure causes pleural effusion. Malignant pleural effusions are treated with catheters, palliative thoracentesis, pleurodesis and surgery.

Palliative Thoracentesis

Patients with asbestos-related pleural effusions and those without often receive a thoracentesis to remove fluid to relieve pressure on the lungs and ease breathing.

The procedure is similar to diagnostic thoracentesis, but for palliative treatment the fluid is completely drained without saving a sample for testing.

Palliative thoracentesis does not address the cause of pleural effusion, and the fluid will collect again after the procedure. Most people need to have it repeated several times, typically when enough fluid accumulates to cause a return of symptoms.

Catheter Placement

Doctors can place a thin tube called a catheter into the pleural space, leaving one end outside the body. The catheter is then connected to a device that drains the excess fluid. Once you have this procedure, the fluid will drain regularly into a container that a medical professional is trained to empty.

Unlike undergoing repeated thoracentesis procedures, with a catheter you won’t have to return to the doctor for more procedures as fluid keeps reaccumulating. A nurse will come to your home to empty the accumulated fluid and sanitize the equipment.

Pleurectomy or Pleural Decortication 

A pleurectomy or pleural decortication removes part of the pleural lining, which eliminates the pleural space and thus prevents further fluid buildup.

These are invasive surgical procedures that are generally performed on early-stage mesothelioma patients and not as a standalone treatment for pleural effusion.


In some cases, doctors may recommend pleurodesis, a longer-term solution for recurring fluid buildup.

During pleurodesis, doctors remove excess pleural fluid by thoracentesis, then attempt to permanently close the pleural cavity to prevent further fluid accumulation. The surgeon inserts a chest tube to deliver drugs such as medical-grade talc or bleomycin, which cause inflammation that closes off the pleural space.

This procedure can have painful side effects and isn’t 100% effective. It should only be performed on people with good overall health and a life expectancy of at least several months.

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