The inferior mesenteric artery (IMA) (Figs. 57.1 and 57.2) is the final ventral unpaired branch of the abdominal aorta, originating at the L3 vertebra. It is relatively short, irrigating a large area from the splenic flexure of the colon to the mid-rectum. Due to this extensive coverage, its branches fan out like a short string over a long bowel segment (Skandalakis et al. 2004). The IMA initially gives rise to the left colic artery, which splits into superior and inferior divisions, followed by two or three sigmoid arteries, and continues as the superior (ano)rectal artery. Although traditionally described as following a standard pattern, this is observed in only between 15–16% and 30–40% of cases (Michels et al. 1965; Nelson et al. 1988; Goligher 1949; Basmajian et al. 1955).