Watershed areas in the colon:
(1) cecum and proximal ascending colon
(2) splenic flexure
(3) rectosigmoid junction
Cecum and proximal ascending colon
(1) The terminal ileum, cecum and proximal ascending colon are supplied by the ileocolic artery (which arises from the superior mesenteric artery).
(2) 50% of people may have a poorly developed marginal artery of Drummond.
Splenic flexure:
(1) Branches of the middle colic artery (from the superior mesenteric artery) supply the transverse colon, while branches of the left colic artery (from the inferior mesenteric artery) supply the descending colon.
(2) Griffith's point = portion of the splenic flexure that may be devoid of vasa recta.
(3) 5% of the population have an absent or diminished marginal artery of Drummond.
Rectosigmoid junction:
(1) Sudeck's "critical point" = area distal to the origin of the last sigmoid arterial branch arising from the inferior mesenteric artery.
(2) The last sigmoid arterial branch may have an anastomosis with a branch of the superior rectal artery. If there is no anastomosis then the risk of ischemic injury at Sudeck's point increases.
