What is the incidence of pulmonary embolism (PE) with untreated thrombi?

Updated: Jun 05, 2019
  • Author: Kaushal (Kevin) Patel, MD; Chief Editor: Barry E Brenner, MD, PhD, FACEP  more...
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Most small thrombi in the lower extremities tend to resolve spontaneously after surgery. In about 15% of cases, however, these thrombi may extend into the proximal femoral venous system of the leg. Untreated proximal thrombi represent a significant source of clinically significant pulmonary emboli.

In the absence of rhythmic contraction of the leg muscles, as in walking or moving, blood flow in the veins slows and even stops in some areas, predisposing patients to thrombosis. [43]

In the postoperative patient, as many as one half of all isolated calf vein thrombi resolve spontaneously within a few hours, whereas approximately 15% extend to involve the femoral vein. A many as one third of untreated symptomatic calf vein DVT extend to the proximal veins. [44] At 1-month follow-up of untreated proximal DVT, 20% regress and 25% propagate. Although calf vein thrombi are rare sources of clinically significant pulmonary embolism (PE), the incidence of PE with untreated proximal thrombi is 29-50%. [44, 45] Most PEs are first diagnosed at autopsy. [46, 47]

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