Edema represents the accumulation of excess liquid in the interstitial (extracellular) spaces of a tissue or in pre-existing cavities. It may affect any organ, but most often it appears in : subcutaneous tissues, lung and brain.
According to the etiology, edema may be localized (in inflammation or in impaired venous drainage) or systemic (in right heart failure or in nephrotic syndrome). A generalized and severe edema is called anasarca.
Accumulation of transudate or non-inflammatory fluid (effusions) in body cavities :
- Peritoneal cavity - ascites
- Pleural cavity - hydrothorax
- Pericardial cavity - hydropericardium
Etiology of pulmonary edema : acute left heart (ventricular) failure, pulmonary failure in syndrome of adult respiratory distress, pulmonary infections and hypersensitivity reactions.
Pulmonary edema. Alveolar walls are thickened due to acute distention of capillaries and interstitial edema. Alveolar lumen is filled with transudate (pale-eosinophilic, finely granular), a liquid which replaces the air. (H&E, ob. x20)
Pulmonary edema (detail)
Pulmonary edema. (H&E, ob. x40)