Intestinal Arterial Thromboembolism

• Non-strangulation infarction.
• There is often a functional obstruction at point of infarction.
• Relatively rare as the bowel has a good anastomosing blood supply.

Thrombosis of cranial mesenteric artery caused by Strongylus vulgaris larvae (Courtesy of Bristol BioMed Image Archive)

Horses

• E.g. Strongylus vulgaris larvae migrating in cranial mesenteric artery in horse
  • Cause arteritis with thickening of wall
    • Due to fibrin and debris deposition and hypersensitivity reaction
  • Leads to vasoconstriction
    • May occlude lumen and encourage thromboemboli.
  • Can cause ischaemic necrosis of a segment of small intestine
  • Is less common now that Strongylus vulgaris infections are declining.
• E.g. equine salmonellosis.

Infarction of the small bowel (Courtesy of Bristol BioMed Image Archive)

Verminous endarteritis

• Caused by larvae of S. vulgaris within the cranial mesenteric artery
• Also called "verminous aneurism" (misnomer as aneurism = dilatation/thinning of blood vessel wall; also, aneurisms are rare)
• Wall of artery grossly thickened (organising thrombi, inflammatory responses)
• Can be detected on rectal palpation
• Many cases asymptomatic
• May get embolism → infarction of areas of intestinal wall → colic or chronic ulceration (note: generally good collateral circulation; therefore colic is not inevitable)
• Aberrant larvae may cause thrombosis in other arteries; e.g. iliac, cerebral, coronary
• Avermectin/milbemycins or fenbendazole are used to control migrating S. vulgaris larvae

Small Animals

• Especially dogs
• Road traffic accidents produce and infact in the gut.
• Renal disease also causes infarction.
  • Particularly nephrotic syndrome.
  • Anticoagulant proteins are lost in the urine, leading to a prothrombic state in the ciruclation.

Pathology

• Similar to that caused by venous congestion.
• See sharply delineated dark areas in bowel that are flaccid with loss of tone.
  • These become necrotic followed later by peritonitis.