Pleural effusion is the condition characterized by an abnormal
collection of uid in pleural space resulting from excess uid
production or decreased absorption(1–3). It is due to pleural uid
accumulation inside pleural space. The major mechanism include:
increased interstitial uid in the lungssecondary to increased pulmonary
capillary pressure (i.e., heart failure) or permeability (i.e., pneumonia);
decreased intrapleural pressure (i.e., atelectasis); decreased plasma
oncotic pressure (i.e., hypoalbuminemia); increased pleural membrane
permeability and obstructed lymphatic ow (e.g., pleural malignancy
or infection); diaphragmatic defects (i.e., hepatic hydrothorax); and
thoracic duct rupture (i.e., chylothorax)(4).