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Pulmonary embolism

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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Pulmonary embolus (PE) occurs when a clot from a vein, originating in the venous sinuses of the calf or the femoral vein or the pelvis, detaches and becomes lodged in the pulmonary arterial tree (1).

Occasionally the right side of the heart is a source of a pulmonary embolus.

Deep vein thrombosis (DVT) is the formation of blood clots in deep veins of the legs (1). In a majority of patients, PE is a consequence of DVT (2)

  • when sensitive diagnostic methods were used, DVT was detected in around 70% of patients with PE (2)
  • clinically important PEs originate from proximal DVT of the leg e.g. - popliteal, femoral or iliac veins (3)

Venous thromboembolism (VTE) is the term used to describe a thrombus in a vein which may detach from the site of origin and travel through blood to a distant site, a phenomenon called embolism (1). PE and DVT represent different clinical manifestations of VTE (2).

An estimated 12-36% of patients with PE are misdiagnosed during initial evaluation in emergency departments or primary care clinic (4)

Non thrombotic pulmonary emboli are rare. Causes include:

  • septic emboli
  • fat emboli
  • amniotic fluid
  • venous air embolism
  • intravascular foreign bodies
  • tumor emboli (2)

Computed tomography pulmonary angiogram (CTPA) scan

  • most common diagnostic imaging modality for PE
  • V/Q SPECT (ventilation-perfusion single photon emission CT) is a scintigraphic modality that captures three dimensional images and offers equal diagnostic accuracy as CTPA while delivering a lower absorbed dose of radiation (4)


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