Ischaemic Colitis
A fall in colonic perfusion below what the mucosa needs, striking hardest at the watershed zones where two arterial territories barely overlap, so the splenic flexure suffers first and the resulting mucosal injury produces the classic pairing of left-sided pain and bloody diarrhoea.
Definition
Ischaemic colitis is inflammation and injury of the colon resulting from a reduction in its blood supply. It is the commonest form of intestinal ischaemia, usually affecting watershed areas of the colon, and is often transient and self-limiting.
First principles
Watershed territories are the weakest link in colonic blood supply
The colon is supplied by the superior and inferior mesenteric arteries, which anastomose via marginal and other collateral vessels, but at certain points, chiefly the splenic flexure (junction of SMA and IMA territories, Griffiths' point) and the rectosigmoid junction (Sudek's point), the collateral supply is at its sparsest. These watershed zones receive blood from the very ends of two separate arterial trees rather than a single robust vessel, so they are the first and most severely affected whenever perfusion pressure falls anywhere in the system.
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