Introduction
Venous thrombosis occurs in about 1 per 1,000 individuals per year.1,2 It usually affects the deep veins of the leg, but may occur in other sites, such
as the upper extremities, cerebral sinus, liver and portal veins, or retinal veins.
It also may occur in the superficial veins, usually in the leg. The predilection of
thrombosis occurring in the leg is the result of the upright position of man, with
the resulting slow antigravitational flow of blood in the veins of the leg. Embolization
occurs when parts of the clot dislodge and are transported by the blood flow, usually
through the heart to the vasculature of the lungs.3
Thrombosis is a serious disorder. It may be fatal by pulmonary embolism, although
this is rare (case fatality rate of venous thrombosis is estimated at 1% to 2%). A
common, and often disabling, consequence of deep vein thrombosis is postthrombotic
syndrome, with symptoms ranging from discoloration to pain and ulceration.4 Because thrombosis is not very rare and often has serious consequences, prophylactic
treatment is focussed on preventing first events and recurrences through adequate
knowledge about risks and risk factors.5
