A condition in which the tissues of the body contain too much body fluid. The fluid accumulation may cause swelling in the affected area. The presence of abnormally large amounts of fluid in the interstitial tissue spaces of the body. Edema fluid may accumulate in the subcutaneous tissues, peritoneal cavity (ascites), pleural cavity (hydrothorax) or pericardial sac (hydropericardium). The abnormal accumulation of fluid in a tissue or cavity. The accumulation of fluid in abnormal locations in the body.