Pleural effusion is excess fluid that accumulates in the pleural cavity, the fluid-filled space that surrounds the lungs. Excessive amounts of such fluid can impair breathing by limiting the expansion of the lungs during inhalation.

Pleural effusion is usually diagnosed on the basis of medical history and physical exam and confirmed by chest x-ray. CT scan of chest showing left sided pleural effusion. Effusion fluid often settles at the lowest space due to gravity here at the back as the patient is lying under scanner.

Pleural fluid is drawn out of the pleural space in a process called thoracentesis. A needle is inserted through the back of the chest wall in sixth, seventh or eight intercostal space in midaxillary line, into the pleural space.

Four types of fluids can accumulate in the pleural space: serous fluid, blood, pus and chyle.

The other evaluation of pleural fluid is to determine whether the effusion is a transudate or an exudate. Transudative and exudative pleural effusions are differentiated by comparing chemistries in the pleural fluid to those in the blood.

Transudative pleural effusions are caused by systemic factors that alter the balance of the formation and absorption of pleural fluid e.g. left ventricular failure, cirrhosis and pulmonary embolism, while exudative pleural effusions are caused by alterations in local factors that influence the formation and absorption of pleural fluid e.g., bacterial pneumonia, cancer, and viral infection.

The common causes of transudative pleural effusions are left ventricular failure, pulmonary embolism, and cirrhosis causing hepatic hydrothorax, while the most common causes of exudative pleural effusions are bacterial pneumonia, cancer, viral infection, and pulmonary embolism. The other causes of pleural effusion include Tuberculosis, autoimmune disease such as systemic lupus erythematosus, bleeding & chylothorax often due to trauma and accidental infusion of fluids.

Tuberculous pleural effusion occurs in approximately 5% of patients with Mycobacterium tuberculosis infection. Pleural effusion is a secondary disease being related to tuberculosis or other lung disease because there is irritation on the lining of pleural cavity, thus altering the permeability of the membrane and decreasing the oncotic pressure needed to drain the excess fluid in the pleural space.

Pleural effusions may also occur through medical or surgical interventions, including the use of medications. Treatment depends on the underlying cause of the pleural effusion. Therapeutic aspiration may be sufficient larger effusions may require insertion of an intercostal drain either pigtail or surgical.