Pleural effusion, also known as fluidothorax, means a presence of fluid in chest cavity. It is not a disease, but merely a symptom of many pathological conditions. Before we focus on its causes, it is appropriate to know more about basic anatomy of the chest.
Heart is located in the middle of chest behind the breastbone. Behind heart there are trachea, esophagus and aorta. On both sides of the heart there is a lung. Each of two lungs is located in pleural cavity. The inside lining of pleural cavity is made up from a thin membrane called pleura. There is only little free space in pleural cavity around the lung tissue. This space contains only vacuum. Vacuum maintains negative pressure and it enables dilation of lungs during inspiration. However, if fluid appears in this space, we talk about pleural effusion.
Note: Fluidothorax is only a medical professional term that doesn’t specify composition of the present fluid. So we use term “hemothorax” when the fluid contains blood, “chylothorax” if it contains lymph and term “pleural empyema” or “pyothorax” when it contains bacteria and pus.
If heart ceases to maintain its function as a pump and heart failure emerges, there begins accumulation of fluid in blood vessels before the heart including lung vessels. This is connected to local elevation of blood pressure and filtering of blood fluid outside vessels. When blood filters into alveoli, we speak about pulmonary edema (“swelling of lungs”), when it filters into pleural cavity, pleural effusion arises. The liquid is in this case usually located in both pleural cavities, it is low on proteins; it has limpid yellowish color and contains no tumor cells or bacteria.
Pneumonia and pleurisy is often accompanied by formation of fluid in the pleural cavity. General symptoms of pneumonia or pleurisy (fever, cough with expectoration of phlegm, chest pain, pain during breathing) may accompanied by shortness of breath caused by oppression of the lung with fluid. In this case pleural effusion contains more protein and white blood cells. Microbial examination of fluid’s sample can detect the presence of bacteria.
Lung cancer and mesothelioma (pleural cancer) can also cause pleural effusion. When tumor cells are in close contact with pleural cavity, its lining may start to secrete fluid. This fluid is rich in proteins and sometimes it contains blood. Fine needle aspiration cytology can prove presence of cancer cells in the. Cytology, however, is not completely reliable and its negative finding does not rule out a tumor presence.
In developed countries this is not so typical cause of pleural effusion. By malnutrition in blood stream there is a lack of proteins that help keep the blood fluid inside blood vessels. With low protein levels blood fluid begins to leak outside the vessels into tissue and body cavities including pleural cavities. It causes body parts swelling, pleural effusion and ascites formation. Malnutrition is caused by poor intake of nutrients or by problems with their digestion and absorption.
Some kidney diseases cause a high protein loss in urine. It is a similar condition to that of severe malnutrition (see above).
This disease is caused by asbestos crystals. These extremely sharp microscopic particles can be inhaled and through the lung tissue they get into the pleural cavity and there irritate pleural cells causing fluid production. Long-term irritation by asbestos is related to higher risk of mesothelioma development.
Chest injury may cause bleeding into the pleural cavity, or lymph leakage from ruptured large thoracic lymphatic ducts.
The mere presence of fluid around the lungs may not be reflected in any way and thus it may be just an incidental finding. Otherwise it manifests itself quite logically by shortness of breath. Affected lung is compressed by fluid and this worsens lung dilation during inspiration.
The presence of fluid around the lungs can be easily deduced from physical examination –breathing of affected side, when listening with a stethoscope, is weakened or practically inaudible. The diagnosis is done by chest X-ray that shows the fluid level, diagnosis can be confirmed by computed tomography or by chest ultrasound. Ultrasound helps to determine the amount of fluid and identify suitable location for puncture (see treatment).
Sometimes when the cause of pleural effusion is uncertain, it is advisable to aspirate a sample by needle and send this sample for cytological, biochemical and microbiological examination. With knowledge of chemical, cellular and microbial composition of the fluid, we may estimate the causative factor of pleural effusion.
The principle of therapy is to treat the underlying cause of pleural effusion. In addition, symptomatic therapy is focused on removing fluid to bring the patient relief. Fluid is removed by one-time needle aspiration or by longer-term drainage. Aspiration of fluid has usually an immediate positive effect on clinical condition of the patient, who is relieved and by performing it we also obtain fluid samples for examination.