Are pulmonary embolism and deep-vein thrombosis always one disease?

Pulmonary embolism is traditionally, since autopsy studies by Virchow in the mid 1800s, thought to originate from embolization of a deep-vein thrombosis, resulting in two clinical manifestations of one disease: venous thrombosis. The incidence of deep-vein thrombosis in the population is twice as high as the incidence of pulmonary embolism, i.e. 1 per 1000 and 0.5 per 1000 person-years respectively. The aim of this thesis was to assess whether pulmonary embolism and deep-vein thrombosis are always the same disease or not, and to answer this question with regard to etiology (genetic and acquired risk factors) and anatomical distribution of thrombi in the veins. We studied this question in two populations: the PEDLAR study and the MEGA case-control study. In the PEDLAR study we assessed the origin of pulmonary embolism using a total body Magnetic Resonance Direct Thrombus Imaging technique. We proposed several mecha nisms for the absence of deep-vein thrombi in more than half of the patients with pulmonary embolism. In addition, we investigated the effect of aging on venous valve thickness. This was performed in an ultrasonography study, with participants from 20 to 80 years old (the aging venous valves study). We hypothesized that part of the increasing incidence in venous thrombosis with age can be explained by increasing valve thickness.