What about nonvisible veins in the body? Distension backs up in veins within the liver, which enlarges, and in some cases fluid may accumulate in the abdominal cavity (ascites). The veins of the legs may not be visibly distended but the blood is under backpressure and fluid leaks out into tissues, especially when the individual stands, walks, or sits for long periods. The swelling usually occurs more frequently at the end of the day, improves after a few hours in bed, and is best in the morning. The fluid around the ankles and feet is called edema and is a hallmark of heart failure, although it can occur with obstruction of the veins from other causes. This fluid is similar to that described in the lungs, consisting of water and sodium; therefore, the legs are brine-logged not just waterlogged. The swelling usually occurs in both legs whereas in obstruction of veins it is one-sided. The accumulation of several gallons of fluid may result in very extensive involvement of the entire legs, thighs, abdomen (ascites), and lungs (pleural effusion).

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