Edema is a condition of abnormally high fluid volume in the circulatory system or in tissues between the body's cells. It is a sign of an underlying problem or problems, rather than a disease unto itself.

Normally, the body maintains a balance of fluid in tissues by ensuring that the same of amount of water entering the body also leaves it. The circulatory system transports fluid within the body via its network of blood vessels. The fluid, which contains oxygen and nutrients needed by the cells, moves from the walls of the blood vessels into the body's tissues. After its nutrients are used up, fluid moves back into the blood vessels and returns to the heart. The lymphatic system (a network of channels in the body that carries lymph, a colorless fluid containing white blood cells to fight infection) also absorbs and transports this fluid. In edema, either...