Inside the ribcage, the lungs are surrounded by a moist, double-layered membrane called the pleura. Normally, there is a small amount of fluid which lubricates the surfaces of the pleural membranes. A pleural effusion is an abnormal accumulation of fluid between the membranes.
There are two types of effusions that can develop. Transudative effusions are caused by an underlying disease or disorder that disrupts the normal pressures in the lungs, compromising the ability of the blood vessels in the chest to remove excess fluid within the pleural space. Types of disorders that can cause transudative effusions include congestive heart failure, cirrhosis, and atelectasis. It is also associated with some medical procedures, such as peritoneal dialysis.
Exudative effusions are caused by lung diseases resulting in inflammation of the pleura due to infection or disease. Exudates occur when the pleura becomes inflamed and fluid is unable to pass through the membranes. Types of disorders that can cause exudative effusions include cancer, lymphoma, pulmonary embolism, tuberculosis, asbestos-related diseases, and trauma.
Symptoms of a pleural effusion can include shortness of breath, chest pain and cough. The physician will listen to the chest with a stethoscope for signs of decreased breath sounds or a pleural friction rub--the sound of pleura rubbing together during respiration.