Reviewed by Brian R. Robinson, MD
Varicose veins are distended, visible, superficial veins on the legs. In most cases, incompetent valves within the venous system of the leg cause them. When one or more of these valves fails to function correctly, or leaks, some blood flows back down into the leg, in the wrong direction.
In normally functioning veins, there are valves that work like trap doors, closing completely at periodic intervals to prevent the backflow of blood. In patients with varicose veins (also called varicosities), valves are damaged or do not work properly, the blood tends to flow backwards and overfill veins. It also distends branches of superficial veins under the skin. Over time, this additional pressure of blood causes the veins to stretch, bulge, and become visible. At the same time, tiny capillary branches of the veins also overfill with blood and produce multiple spider veins and purple discoloration.
Leaky venous valves can occur anywhere in the leg, but faulty valves in the groin or behind the knee cause most varicose veins. Both these sites act as a major junction at which superficial veins (those subject to varicose veins) flow into the important deep veins of the leg, with a one-way valve to control flow at the junction. Some people may inherit a weakness of these valves; obesity and pregnancy may also cause valves stretch and leak.
Varicosities resulting from congenitally defective valves may develop early in life. Thrombophlebitis may also lead to the formation of varicose veins by destroying venous valves and causing venous obstruction. Pregnancy, abdominal tumor, excessive weight or height, and prolonged weight bearing are all considered accelerating factors because they cause increased pressure on the legs.
Varicose veins are considered very common and appear in about 30% of women and 20% of men.