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Accumulation of excess fluid in body tissue

An edema will occur in specific organs as part of inflammations, tendinitis or pancreatitis, for instance. Certain organs develop edema through tissue specific mechanisms. Examples of edema in specific organs:
Peripheral edema (“dependent” edema of legs) is extracellular fluid accumulation in the lower extremities caused by the effects of gravity, and occurs when fluid pools in the lower parts of the body, including the feet, legs, or hands. This often occurs in immobile patients, such as paraplegics or quadriplegics, pregnant women, or in otherwise healthy people due to hypervolemia or maintaining a standing or seated posture for an extended period of time. It can occur due to diminished venous return of blood to the heart due to congestive heart failure or pulmonary hypertension. It can also occur in patients with increased hydrostatic venous pressure or decreased oncotic venous pressure, due to obstruction of lymphatic or venous vessels draining the lower extremity. Certain drugs (for example, amlodipine) can cause pedal edema. Cerebral edema is extracellular fluid accumulation in the brain. the latter of which are termed contact dermatitis. Another cutaneous form of edema is myxedema, which is caused by increased deposition of connective tissue. In myxedema (and a variety of other rarer conditions) edema is caused by an increased tendency of the tissue to hold water within its extracellular space. In myxedema, this is due to an increase in hydrophilic carbohydrate rich molecules (perhaps mostly hyaluronin) deposited in the tissue matrix. Edema forms more easily in dependent areas in the elderly (sitting in chairs at home or on aeroplanes) and this is not well understood. Estrogens alter body weight in part through changes in tissue water content. There may be a variety of poorly understood situations in which transfer of water from tissue matrix to lymphatics is impaired because of changes in the hydrophilicity of the tissue or failure of the 'wicking' function of terminal lymphatic capillaries. Myoedema is localized mounding of muscle tissue due to percussive pressure, such as flicking the relaxed muscle with the forefinger and thumb. It produces a mound, visible, firm and non tender at the point of tactile stimulus approximately 1 2 seconds after stimulus, subsiding back to normal after 5 10 seconds. It is a sign in hypothyroid myopathy, such as Hoffmann syndrome. In lymphedema, abnormal removal of interstitial fluid is caused by failure of the lymphatic system. This may be due to obstruction from, for example, pressure from a cancer or enlarged lymph nodes, destruction of lymph vessels by radiotherapy, or infiltration of the lymphatics by infection (such as elephantiasis). It is most commonly due to a failure of the pumping action of muscles due to immobility, most strikingly in conditions such as multiple sclerosis, or paraplegia. It has been suggested that the edema that occurs in some people following use of aspirin like cyclo oxygenase inhibitors such as ibuprofen or indomethacin may be due to inhibition of lymph heart action.

A rise in hydrostatic pressure occurs in cardiac failure. A fall in osmotic pressure occurs in nephrotic syndrome and liver failure. Causes of edema which are generalized to the whole body can cause edema in multiple organs and peripherally. For example, severe heart failure can cause pulmonary edema, pleural effusions, ascites and peripheral edema. Such severe systemic edema is called anasarca. In rare cases, a parvovirus B19 infection may cause generalized edemas. Although a low plasma oncotic pressure is widely cited for the edema of nephrotic syndrome, most physicians note that the edema may occur before there is any significant protein in the urine (proteinuria) or fall in plasma protein level. Most forms of nephrotic syndrome are due to biochemical and structural changes in the basement membrane of capillaries in the kidney glomeruli, and these changes occur, if to a lesser degree, in the vessels of most other tissues of the body. Thus the resulting increase in permeability that leads to protein in the urine can explain the edema if all other vessels are more permeable as well. As well as the previously mentioned conditions, edemas often occur during the late stages of pregnancy in some women. This is more common with those of a history of pulmonary problems or poor circulation also being intensified if arthritis is already present in that particular woman. Women who already have arthritic problems most often have to seek medical help for pain caused from over reactive swelling. Edemas that occur during pregnancy are usually found in the lower part of the leg, usually from the calf down. Hydrops fetalis is a condition in a baby characterized by an accumulation of fluid in at least two body compartments.

The pumping force of the heart should help to keep a normal pressure within the blood vessels. But if the heart begins to fail (a condition known as congestive heart failure) the pressure changes can cause very severe water retention. In this condition water retention is mostly visible in the legs, feet and ankles, but water also collects in the lungs, where it causes a chronic cough. This condition is usually treated with diuretics; otherwise, the water retention may cause breathing problems and additional stress on the heart.

Another cause of severe water retention is kidney failure, where the kidneys are no longer able to filter fluid out of the blood and turn it into urine. Kidney disease often starts with inflammation, for instance in the case of diseases such as nephrotic syndrome or lupus. This type of water retention is usually visible in the form of swollen legs and ankles.

Cirrhosis (scarring) of the liver is a common cause of edema in the legs and abdominal cavity.

Phlebetic lymphedema (or phlebolymphedema) is seen in untreated chronic venous insufficiency and is the most common type of edema (approx. 90%). It is a combination venous/lymphatic disorder that originates in defective "leaky" veins that allows the blood to back flow (venous reflux), slowing the return of the blood to the heart (venous stasis). The venous pressure in the legs changes dramatically while standing compared to lying down. How much pressure there is depends on the person's height, in the average adult person, it is 8 mm Hg while lying down and 100 mm Hg while standing. In venous insufficiency, venous stasis results in abnormally high venous pressure (venous hypertension) and greater permeability of blood capillaries (capillary hyperpermeability), to drain the blood through the lymphatic system. The lymphatic system slowly removes excess fluid and proteins from the veins in the lower legs towards the upper body; however, as it is not as efficient as an unimpaired circulatory system, swelling (edema) is visible, particularly in the ankles and lower leg. Unfortunately, the chronic increased fluid in the lymphatic system and capillary hyperpermeability causes an inflammatory response which leads to tissue fibrosis of both veins and lymphatic system, opening of arteriovenous shunts, all of which then worsens the condition in a vicious cycle. though it should always be reported to a doctor. Lack of exercise is another common cause of water retention in the legs. Exercise helps the leg veins work against gravity to return blood to the heart. If blood travels too slowly and starts to pool in the leg veins, the pressure can force too much fluid out of the leg capillaries into the tissue spaces. The capillaries may break, leaving small blood marks under the skin. The veins themselves can become swollen, painful and distorted – a condition known as varicose veins. Muscle action is needed not only to keep blood flowing through the veins but also to stimulate the lymphatic system to fulfil its "overflow" function. Long haul flights, lengthy bed rest, immobility caused by disability and so on, are all potential causes of water retention. Even very small exercises such as rotating ankles and wiggling toes can help to reduce it. Certain medications are prone to causing water retention. These include estrogens, thereby including drugs for hormone replacement therapy or the combined oral contraceptive pill, as well as non steroidal anti inflammatory drugs and beta blockers. Premenstrual water retention, causing bloating and breast tenderness, is common.

When possible, treatment involves resolving the underlying cause. Many cases of heart or kidney disease are treated with diuretics.