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The right and left colonic adhesion to the posterior parietal peritoneum is the result of the fusion of the lateral sides of the colonic mesentery after final embryonic gut rotation. This fusion plane is recreated in mobilizing right and left colon The sigmoid length and cecal fixation are variable from individual to individual.
Normal but variable collateral communications exist between visceral territories in the pancreatoduodenal arcades and the marginal artery (of Drummond). If one visceral vessel is compromised, for example the IMA by an abdominal aneurysm, the left colon may survive on collateral circulation. When slow occlusion of the SMA or IMA occurs, small communications within the proximal mesentery may hypertrophy forming a large meandering mesenteric artery (arc of Riolan).