Ischemic colitis pathophysiology

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-In-Chief: Hamid Qazi, MD, BSc [2] Cafer Zorkun, M.D., Ph.D. [3]

Pathophysiology

The pathophysiology of ischemic colitis is as follows:

Colonic Blood Supply

• The colon receives blood from both the superior and inferior mesenteric arteries.
• The blood supply from these two major arteries overlap, with abundant collateral circulation.
• There are weak points, or "watershed" areas, at the borders of the territory supplied by each of these arteries.
  • These watershed areas are most vulnerable to ischemia when blood flow decreases, as they have the fewest vascular collaterals.

• The rectum receives blood from both the inferior mesenteric artery and the internal iliac artery
  • The rectum is rarely involved by colonic ischemia due to this dual blood supply.

Development of Ischemia

• Under ordinary conditions, the colon receives between 10% and 35% of the total cardiac output.
• If blood flow to the colon drops by more than about 50%, ischemia will develop.
• The arteries feeding the colon are very sensitive to vasoconstrictors; presumably this is an evolutionary adaptation to shunt blood away from the bowel and to the heart and brain in times of stress. As a result, during periods of low blood pressure, the arteries feeding the colon clamp down vigorously.
• A similar process can result from vasoconstricting drugs such as ergotamine, cocaine, or vasopressors. This vasoconstriction can result in non-occlusive ischemic colitis.

Microscopic Pathology

• A range of pathologic findings are seen in ischemic colitis, corresponding to the spectrum of clinical severity.
  • In its mildest form, mucosal and submucosal hemorrhage and edema are seen, possibly with mild necrosis or ulceration.
  • With more severe ischemia, a pathologic picture resembling inflammatory bowel disease (i.e. chronic ulcerations, crypt abscesses and pseudopolyps) may be seen.
  • In the most severe cases, transmural infarction with resulting perforation may be seen.
  • After recovery, the muscularis propria may be replaced by fibrous tissue, resulting in a stricture.
  • Following restoration of normal blood flow, reperfusion injury may also contribute to the damage to the colon.

Images

By Nephron - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8171438

Micrograph of a colonic pseudomembrane, a finding that may be associated with ischemic colitis. H&E stain.

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