A pleural effusion (say "PLER-uhl eh-FYOO-zhun") is the buildup of fluid in the pleural space. This is the space between the tissues lining the lungs and the chest wall.
Because of the fluid buildup, the lungs may not be able to expand completely. This may make it hard to breathe. Other possible symptoms include chest pain, a fever, and a cough.
A doctor may diagnose a pleural effusion during a physical exam and then confirm it with a chest X-ray.
A minor pleural effusion often goes away on its own. If treatment is needed, a doctor may remove the fluid by putting a needle in the chest (thoracentesis). The fluid may be sent to a lab to find out what is causing the buildup. There are many possible causes, including infection, inflammation, heart failure, pancreatitis, or cancer.