The blood supply to the sigmoid colon and upper rectum is traditionally related to a "critical point" beyond which ligation will cause necrosis. Most surgeons doubt this theory, but experimental proof is lacking. The arteries to the sigmoid colon and rectum have been reinvestigated with special reference to this question in fresh human autopsy material.
Sudeck,1 in 1907, established a "critical point" in the superior hemorrhoidal artery after observing gangrene of the upper rectum in two patients whose superior hemorrhoidal arteries had been ligated just distal to the last sigmoid branch of the inferior mesenteric artery during perineal resection of the rectum. He later found by injection experiments that the vessels of the rectum became filled with injecting material from the inferior mesenteric artery only by traversing a marginal artery above the origin of the last sigmoid branch. If the ligature was placed below the origin of
McGOWAN JR. Collateral Circulation in the Sigmoid Colon. AMA Arch Surg. 1955;71(4):531-537. doi:10.1001/archsurg.1955.01270160057007