Áreas de Watershed

The colon's blood supply changes hands twice: the superior mesenteric artery supplies up to the proximal two-thirds of the transverse colon, the inferior mesenteric artery takes over to the upper rectum, and the internal iliac artery supplies the lower rectum. The junctions between these territories — Griffith point at the splenic flexure and Sudeck point at the rectosigmoid — depend on narrow anastomotic connections including the marginal artery of Drummond and the arc of Riolan, which are variably developed and sometimes absent. When cardiac output falls or the inferior mesenteric artery is ligated during aortic surgery, these zones infarct first, producing ischaemic colitis with crampy pain, urgency, and bloody diarrhoea and, on CT, thickened colonic wall with thumbprinting. Importantly the rectum is usually spared because of its dual internal iliac supply, which is a helpful discriminator from inflammatory bowel disease. Ischaemic colitis is typically non-occlusive and low-flow, in contrast to acute mesenteric ischaemia of the small bowel, which is embolic and presents with pain out of proportion to examination findings.