The term edema refers to the accumulation of an excessive amount of fluid in cells, tissues and organs and is clinically characterized by 'swelling'. A wide variety of conditions can result in edema including chronic venous insufficiency, infection and injury. Lymphedema can be defined as "swelling" of the subcutaneous tissues as a result of obstruction of the lymphatic vessels or lymph nodes resulting in a large amount of lymph accumulating in the area.
Any condition that interferes with the normal mechanical process by which the lymphatic system collects, filters, and returns lymph fluid to the circulatory system can result in excessive accumulation of lymph fluid. The ability of the lymphatic system to pump excess fluid away from the body's tissues is reduced or disrupted. Since the arterial capillaries continue to transport fluid to the tissues, the fluid volume increases significantly until the venous capillaries are no longer able to compensate for the dysfunction of the lymphatic vessels. At this point when the pumping is reduced by 80% or more the symptoms of lymphedema become visible .