Y. Saptanaga Kumar1 , N. B. S. Parimala2

Normal pleural space between visceral and parietal pleura is lined by thin film of fluid, but excess fluid accumulation in pleural space under certain pathological condition is termed pleural effusion.1 Pleural effusions is common occurrence in both medical and surgical patients. The prevalence of pleural effusion is estimated to be slightly in excess of 400/100000 population.2 Pleural effusion is an indicator of an underlying disease process that may be pulmonary or non-pulmonary in origin and may be acute or chronic. The most common types of fluid in pleural effusion include transudates and exudates, though there can be blood or pus also in pleural effusion. However, mechanisms leading to pleural effusion are different. (Box 1) These may differ in different etiologies, and include: increased hydrostatic pulmonary pressure in heart failure, increased capillary permeability in pneumonia, decreased oncotic pressure in hypoalbuminemia, decreased intrapleural pressure in atelectasis, obstructed lymph flow and increased pleural membrane permeability in pleural malignancy/infection, and diaphragmatic defects in hepatic hydrothorax. Rupture of thoracic duct is involved in chylothorax.3