A pleural effusion is the buildup of fluid between the outer lining of the lungs (visceral pleura) and the inner lining (parietal pleura) of the chest cavity. This fluid buildup has many causes, including infection, inflammation, heart failure, pancreatitis, or cancer.

A minor pleural effusion may not cause any symptoms. A large amount of fluid may prevent the complete expansion of a lung, making it hard for the person to breathe. Possible symptoms of a pleural effusion may include:

• Difficulty breathing.
• Chest pain.
• Fever.
• A cough.

A doctor may diagnose a pleural effusion during a physical exam and then confirm the diagnosis with a chest X-ray.

Small pleural effusions often heal on their own. If treatment is needed, it may involve removal of the fluid using a needle inserted through the chest wall (thoracentesis). The fluid may be sent to a lab to find out what is causing the fluid to build up.