From WikiVet English
Jump to navigation Jump to search


  • An embolus is a detached intravascular mass that is carried by the blood to a site distant from its point of origin.
    • May be solid or gaseous.
  • Emboli will lodge in a vessel too small to permit further passage.
    • Results in occlusion.

Types of Embolism


  • These are pieces of thrombi that have broken away from their primary site.
  • The most common cause of embolism.

Air embolism

  • Caused by accidental injection of air from a badly filled hypodermic syringe.
  • Small air bubbles may occlude the blood vessels of the brain and cause severe ischaemic necrosis.

Fat embolism

  • Pieces of adipose tissue from the bone marrow cavity may enter the blood stream following fracture.

Fibrocartilagenous embolus

  • Seen in the dog.
  • Thought to arise from a damaged intervertebral disc.
  • Cause occlusion of spinal blood vessels.
    • Results in:
      • Spinal cord necrosis.
      • Severe sudden paralysis.

Tumour emboli

Sarcoma embolus (dog). Courtesy of T. Scase
  • Otherwise known as metastasis.
  • Small groups of tumour cells may break off and be carried in vessels to reach another site

in the body.

  • May use the lymphatic or blood vessels.

Bacterial emboli

  • Some bacteria travel in colonies.
    • Come to rest in small capillaries and incite an inflammatory response.

The results of Embolism

  • The results of embolism depend on several factors.
    1. The extent of the occlusion and the availability of an adequate collateral circulation.
      • Some emboli may be irregularly shaped, allowing blood to flow around them.
    2. Duration for which the embolus blocks a vessel.
      • Some small thrombi may undergo lysis and quickly disappear.
    3. Nature of the embolus.
      • Bacterial emboli will incite an extensive inflammatory reaction.
      • Tumour emboli will multiply and grow into tumour masses.
    4. The site at which the embolus comes to rest.
      • There are two main considerations here.
        • The type of tissue supplied.
          • The brain and heart are quickly affected by anoxia.
        • The type of blood supply to the tissue.
          • Occlusion of vessels to a tissue with an end arterial supply will cause ischaemic necrosis or infarction.


  • This is the local reduction of blood flow to an area.
    • Usually refers to the arterial flow.
  • Ischaemia may be partial.
    • Results in hypoxia and atrophy of the tissue supplied.


  • Blockage of an end artery results in acute ischaemic coagulation necrosis, or infarction.
  • Some end arteries and their branches are of particluar importance.
    • The renal artery.
    • The splenic artery.
    • The coronary arteries.
    • Some cerebral and spinal cord arteries.
    • The anterior mesenteric artery.
  • There are some areas that have a tendency for infarction.
    • The kidneys of pigs and dogs.
    • The spleen of the pig.
    • The intestine of the horse.
    • N.B Infarction of the heart and brain is rare in animals.
Kidney Infarcts
  • Typically appear on the cortex.
  • Appear as a sharply demarcated pale area surrounded by a red line of haemorrhage.
    • A white line of [[Neutrophils - WikiBlood|neutrophils]] forms inside the red line after a few days.
  • The necrotic tissue undergoes liquefactive necrosis.
    • The area is invaded by fibrous tissue.
      • Eventually the lesion ends up as a pale, depressed scar.
Splenic infarcts
  • Appear red in colour due to haemorrhage into the necrotic area.
  • This is an important diagnostic lesion in swine fever.
Intestinal Infarcts
  • Small emboli break off followinf thrombosis and occlude intestinal vessels.
    • Small intestinal infarcts develop.
      • Thought to cause bouts of colic.
  • Strongylus vulgaris may also cause intestinal infacts in the horse.
    • Lodge at the root of the cranial mesenteric artery.
  • Emboli from the venous system may end up in the lung.
  • The lung has an extensive collateral cirulcation, and so little damage is caused.