[Evaluation of inferior mesenteric vessel and ureter by contrast-enhanced abdominal pelvic CT and its clinical influence on laparoscopic rectal surgery].

Objective: To assess the anatomic relationship of inferior mesenteric artery (IMA)/inferior mesenteric vein (IMV) with ureter by contrast-enhanced abdominal pelvic CT, in order to provide guidance for vascular management and ureteral protection in laparoscopic rectal surgery. Methods: A retrospective cohort study was conducted. Image data of contrast-enhanced abdominal pelvic CT at Department of Medical Radiography of Peking University First Hospital in November 2018 were enrolled. Exclusion criteria: (1) previous history of abdominal or pelvic surgery; (2) scoliosis deformities; (3) missing images; (4) minors; (5) inferior mesenteric vascular disease or tumor involvement resulting in suboptimal imaging; (6) poor image quality. Finally, contrast-enhanced abdominal pelvic CT data of 249 cases were collected, including 120 males and 129 females with mean age of (60.1±13.4) years. Multi-planar reconstruction (MPR) and maximum intensity projection (MIP) were used to evaluate the anatomic relationship of IMA/IMV with ureter. IMA root location, IMA length, branch types of IMA, distance between major branches, distance between IMA/IMV and ureter at the level of root of IMA, left colic artery (LCA) root, abdominal aortic bifurcation, and sacral promontory were measured and association between IMA/IMV and ureter site was summarized. Results: The distance from IMA root to the aortic bifurcation and sacral promontory was (42.0±8.5) mm and (101.8±14.0) mm, respectively. The length of IMA was (38.5±10.7) mm. The proportion of IMA roots locating at levels of the 2nd, 3rd, and 4th lumbar vertebra was 3.2% (8/249), 79.5% (198/249), and 17.3% (43/249), respectively. The higher the level of the lumbar vertebra, the longer the IMA [length of IMA originating from the 2nd, 3rd, 4th lumbar vertebra level: (42.4±10.9) mm, (39.5±10.4) mm, (33.0±10.9) mm, respectively; F =7.48, P <0.001]. In 111 cases (44.6%), LCA arose independently from IMA (type 1), and the distance between LCA and the first branch of sigmoid artery (SA) was (15.0±7.4) mm; in 56 cases (22.5%), LCA and SA had a common trunk (type 2), with a length of (11.0±8.5) mm; in 78 cases (31.3%), LCA branched with SA at the same point (type 3); LCA was absent in 4 cases (1.6%)(type 4). The length of IMA in LCA-deficient type 4 was (54.8±18.0) mm, which was longer than (38.2±10.5) mm in LCA-presence type (type 1, type 2 and type 3) and the difference was statistically significant ( t =-3.11, P =0.002). The distance between the ureter and IMA was the longest at the level of IMA root [(35.7±8.1) mm], was the shortest at the level of the aortic bifurcation [(22.4±6.4) mm], and the distance between the ureter and IMA in different planes was significantly different ( F= 185.70, P <0.001). The distance between the ureter and IMV was the longest at the level of the sacral promontory [(21.1±9.0) mm], was the shortest at the level of LCA root [(12.0±5.7) mm], whose difference was also statistically significant ( F =87.66, P< 0.001). Conclusions: CT post-processing techniques including MPR and MIP can efficiently and accurately assess the branch types of IMA and anatomical relationship between IMA/IMV and ureter, and provide insights into laparoscopic rectal surgery for surgeons. IMA/IMV and ureter depart farthest at the level of IMA root. Artery first and plane second strategy in the middle approach of laparoscopic rectal surgery is considerable and feasible.