Venous incompetence is usually encountered in the superficial, deep and perforator veins in the lower extremities. It can occur as a result of weakness or damage of the wall of the vein or its valves, reduced external support as in obesity or increased pressure within as occurs from prolonged standing or pregnancy where the fetus presses on the abdominal veins into which the leg veins drain. Venous incompetence results in venous hypertension leading to ugly dilated tortuous veins that are prone to thrombosis, leakage or rupture.

Venous thrombosis occurs in veins as a result of either damage or irritation to the inner wall of the vein, abnormal flow states that result in stasis or an abnormality in the consistency of blood which makes it prone to clotting. The clot may occur at one spot and then migrate proximally or distally. It can also break off and embolise to the pulmonary artery. Recovery from venous thrombosis may be complicated by incompetence as a result of destruction of valves.

Venous malformations can be present from birth or can occur later on in life as a result of trauma.