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Define embolism? 

Embolism is a process of partial or complete occlusion of the vessel by the embolus. An embolus is a detached intravascular solid mass, liquid, or gaseous mass that is carried by the blood to a distant site from its point of origin. Usually results in ischemic necrosis of the tissue supplied by the affected vessel (infarction).


  1. Thromboembolism–Based on site of origin of thromboembolic and their subsequent lodgement
    1. Pulmonary thromboembolism
    2. Systemic thromboembolism
  2. Fat and marrow embolism
  3. Air embolism
  4. Amniotic fluid embolism



Pulmonary thromboembolism

Occlusion of pulmonary vasculature by in greater than 95% of cases the venous thromboembolic (left deep vein thrombosis). Depending on the size of the embolus, occlusion can occur in the main pulmonary artery, straddle the pulmonary artery bifurcation (saddle embolus), or pass out into the smaller, branching arteries.

Pulmonary thrombo-embolism

Systemic thromboembolism

Emboli in the systemic arterial circulation. The site of origin of emboli

  • Left heart:
    • Mural thrombi in the left ventricular wall (e.g. Myocardial infarction), left atria (e.g. mitral valve disease)
    • Fragmentation of valvular vegetations
  • Thrombi from aortic aneurysms
  • Thrombi on ulcerated atherosclerotic plaques
  • Venous (Paradoxical) emboli from the right heart

Paradoxical emboli

Arise in the venous system and pass through an atrial or ventricular septal defect into the systemic circulation.


Fat and marrow embolism

Most fat emboli occur after fractures of long bones (particularly the shaft of the femur) and pelvis. Microglobules of fat from the bone marrow or surrounding fat tissue enter the circulation and lodge in the microvasculature throughout the body.


Air Embolism

Gas bubbles present within the circulation can obstruct vascular flow. Usually, a surplus (excess) of 100cc is required to have a clinical effect. A particular form of gas embolism called decompression sickness:

  • Occurs when individuals are exposed to instant changes in atmospheric pressure.
  • E.g. Sudden ascent towards the surface by the scuba (deep-sea divers).


When air is breathed at high pressure (e.g., during a deep-sea dive) and increased amounts of gas (particularly nitrogen) are dissolved in the blood and tissues. If the diver then ascends (depressurizes) too rapidly, the nitrogen comes out of the solution in the tissues and the blood.


Types of decompression syndrome

  • Bends:
    • The rapid formation of gas bubbles within skeletal muscles and supporting tissues in and about joints is responsible for this painful condition.


  • Chokes:
    • In the lungs, gas bubbles in the vasculature, causes edema, hemorrhage, & focal atelectasis or emphysema, which leads to a form of respiratory distress.
  • Caisson disease:
    • A chronic form of decompression sickness and persistence of gas emboli in the skeletal system leads to multiple foci of ischemic necrosis; sites are the femoral heads, tibia, and humeri.


Amniotic Fluid Embolism

Amniotic fluid embolism is a potential complication of difficult labor and delivery. The underlying cause is the infusion of amniotic fluid into the maternal circulation by tearing in the placental membranes & rupture of uterine veins. The results in respiratory distress, cardiovascular collapse, and bleeding.


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