HYDROTHORAX

accumulation of watery fluid in the pleural cavity, between the membrane lining the thoracic cage and the membrane covering the lung. Hydrothorax occurs most commonly when fluid seeps from congested lungs into the pleural cavity as a result of impaired circulation of blood in the lungs, a complication of chronic heart failure. Hydropneumothorax denotes the presence of both fluid and air in the pleural cavity.