As the use of chest CT-angiograms in emergency departments and medical wards has risen by more than tenfold, so has the discovery of small pulmonary emboli of unclear clinical significance. These PEs are often isolated to distal (subsegmental) branches of the pulmonary artery, without concurrent deep venous thrombosis (DVT). Small distal PEs may be incidentally found in an asymptomatic patient; more often, these PEs are found on CTs obtained for dyspnea, but the clots seem too small to cause significant symptoms. Should anticoagulation be prescribed to patients with subsegmental pulmonary embolism? If so, for how long? The short answer is, no one knows. Here’s why.

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