Deep venous thrombosis: rate of spontaneous lysis and thrombus extension.

Although recanalization occurs after an episode of venous thrombosis, the exact timing for this process, the rate of clearing at the different venous segments and the nature of the mechanisms involved and their progression are not well known. Recognition of these competing events is important in understanding the natural history and the mechanisms responsible for lysis of the thrombus and for the development of the post-thrombotic syndromeDuring the course of 5 consecutive years, 110 patients (126 legs) with deep vein thrombosis (DVT) were prospectively followed using ultrasonic duplex. Follow-up studies were performed at intervals of 1 and 7 days, 1 month, every 3 months for the 1(st) year, and yearly thereafter. Mean duration of follow-up was 329 days.When only legs with initial complete occlusion are considered, the prevalence of occlusion progressively decreases to 33% after 6 months, 17% after the 1(st) year, and 0% after 3 years. Recanalization of individual segments occurred even more rapidly. After 3 months, recanalization of completely occluded segments was present in 93% of common femoral veins, 79% of superficial femoral veins (proximal segment), 84% of popliteal veins, and 72% of posterior tibial veins. The rate of recanalization was highest for multisegmental disease. Propagation of thrombi to adjacent venous segments occurred in 15% of the limbs. Propagation was usually limited to 1 or 2 adjacent segments.Lysis occurred early and was progressive. After 1 year most legs have recanalized. After 3 years recanalization occurred in all legs although residual thrombosis (partial obstruction) was still present in 50% of the limbs. Propagation of the thrombus was a limited process.