A pleural effusion is an accumulation of fluid between the layers of tissue that line the lungs and chest cavity.

Your body produces pleural fluid in small amounts to lubricate the surfaces of the pleura, the thin tissue that lines the chest cavity and surrounds the lungs. A pleural effusion is an abnormal, excessive collection of this fluid.

Two different types of effusions can develop:

• Transudative pleural effusions are caused by fluid leaking into the pleural space. This is caused by elevated pressure in, or low protein content in, the blood vessels. Congestive heart failure is the most common cause.
• Exudative effusions usually result from leaky blood vessels caused by inflammation (irritation and swelling) of the pleura. This is often caused by lung disease. Examples include lung cancer, lung infections such as tuberculosis and pneumonia, drug reactions, and asbestosis.

• Chest pain, usually a sharp pain that is worse with cough or deep breaths
• Cough
• Fever
• Hiccups
• Rapid breathing
• Shortness of breath

Sometimes there are no symptoms.

During a physical examination, the doctor will listen to the sound of your breathing with a stethoscope and may tap on your chest to listen for dullness.

The following tests may help to confirm a diagnosis:

• Chest x-ray
• Pleural fluid analysis (examining the fluid under a microscope to look for bacteria, amount of protein, and presence of cancerous cells)
• Thoracentesis (a sample of fluid is removed with a needle inserted between the ribs)
• Thoracic CT
• Ultrasound of the chest

Treatment may be directed at removing the fluid, preventing it from accumulating again, or addressing the underlying cause of the fluid buildup.

Therapeutic thoracentesis may be done if the fluid collection is large and causing pressure, shortness of breath, or other breathing problems, such as low oxygen levels. Removing the fluid allows the lung to expand, making breathing easier. Treating the underlying cause of the effusion then becomes the goal.

For example, pleural effusions caused by congestive heart failure are treated with diuretics (water pills) and other medications that treat heart failure. Pleural effusions caused by infection are treated with appropriate antibiotics. In people with cancer or infections, the effusion is often treated by using a chest tube for several days to drain the fluid. Chemotherapy, radiation therapy, surgery, or instilling medication into the chest that prevents re-accumulation of fluid after drainage may be used in some cases.

The expected outcome depends upon the underlying disease.

• A lung surrounded by excess fluid for a long time may collapse.
• Pleural fluid that becomes infected may turn into an abscess, called an empyema, which requires prolonged drainage with a chest tube placed into the fluid.
• Pneumothorax (air within the chest cavity) can be a complication of the thoracentesis procedure.

Call your health care provider if you have symptoms of pleural effusion.

Call your provider or go to the emergency room if shortness of breath or difficulty breathing occurs immediately after thoracentesis.