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. It can occur in toxic or abnormal metabolic states and conditions such as systemic lupus or reduced oxygen at high altitudes. It causes drowsiness or loss of consciousness, leading to brain herniation and death. Pulmonary edema occurs when the pressure in blood vessels in the lung is raised because of obstruction to the removal of blood via the pulmonary veins. This is usually due to failure of the left ventricle of the heart. It can also occur in altitude sickness or on inhalation of toxic chemicals. Pulmonary edema produces shortness of breath. Pleural effusions may occur when fluid also accumulates in the pleural cavity. Edema may also be found in the cornea of the eye with glaucoma, severe conjunctivitis or keratitis or after  surgery. Affected people may perceive coloured haloes around bright lights. Edema surrounding the eyes is called periorbital edema (puffy eyes) . The periorbital tissues are most noticeably swollen immediately after waking, perhaps as a result of the gravitational redistribution of fluid in the horizontal position. Common appearances of cutaneous edema are observed with mosquito bites, spider bites, bee stings (wheal and flare), and skin contact with certain plants such as poison ivy or western poison oak, the latter of which are termed contact dermatitis.
Hydrops fetalis is a condition in a baby characterized by an accumulation of fluid in at least two body compartments. Cause
Heart
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. Kidneys
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. Protein
Protein attracts water and plays an important role in water balance. In cases of severe protein deficiency, the blood may not contain enough protein to attract water from the tissue spaces back into the capillaries. This is why starvation often shows an enlarged abdomen. The abdomen is swollen with edema or water retention caused by the lack of protein in the diet.When the capillary walls are too permeable, protein can leak out of the blood and settle in the tissue spaces.