What is edema?
The definition of edema is observable swelling from fluid accumulation in body tissues. When parts of the body are affected with edema, they are considered edematous. Edema most commonly occurs in the feet, ankles, legs, and/or hands where it is referred to as peripheral edema. Edema of the foot is sometimes called pedal edema. The swelling is the result of the accumulation of excess fluid under the skin in the spaces within the tissues.
All tissues of the body are made up of cells, blood vessels, and connective tissues that hold the cells together called the interstitium. Most of the body's fluids that are found outside of the cells are normally stored in two spaces; the blood vessels (as the "liquid" or serum portion of your blood) and the interstitial spaces (not within the cells). In various diseases, excess fluid can accumulate in either one or both of these compartments.
The body's organs have interstitial spaces where fluid can accumulate, and there are a number of different types of edema. An accumulation of fluid in the interstitial tissue around the air spaces (alveoli) in the lungs occurs in a disorder called pulmonary edema. In addition, excess fluid sometimes collects in what is called the third space, which includes cavities in the abdomen (abdominal or peritoneal cavity - called "ascites") or in the chest (lung or pleural cavity - called "pleural effusion").
Anasarca, also known as extreme generalized edema is severe, widespread accumulation of fluid in the all of the tissues and cavities of the body at the same time.
This article focuses mainly on leg and feet edema (peripheral edema), but these are other forms of edema that are typically named depending on the parts of the body affected:
- Cerebral edema is an accumulation of excess fluid in the brain.
- Angioedema is swelling underneath the skin. Unlike hives, which affect the surface of the skin, angioedema affects the deeper layers of the skin and often occurs on the face.
- Hereditary angioedema is a rare genetic condition that causes the capillaries to release fluids into surrounding tissue, which results in edema.
- Papilledema is swelling of the optic nerve of the eye that is a result of pressure inside the skull and around the brain (intracranial pressure).
- Macular edema is a swelling of the portion of the eye that perceives central, detailed vision (the macula).
- Dependent edema usually is edema of the legs and lower body, which is affected by gravity and is dependent on a person's position. This edema usually occurs in the legs when a person is standing, and in the buttocks and hands if a person is lying down.
- Scrotal lymphedema is an enlargement of the scrotum due to fluid accumulation around the testes.
- Lipedema is a disorder of the fatty (adipose) tissue that causes swelling of the legs and hips, and can lead to lymphedema.