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Verification of blood flow path reconstruction mechanism in distal sigmoid colon and rectal cancer after high IMA ligation through preoperative and postoperative comparison by manual subtraction CTA

Open AccessPublished:January 11, 2023DOI:https://doi.org/10.1016/j.ejso.2023.01.012

      Abstract

      Introduction

      We aimed to investigate manual subtraction computed tomography angiography (MS-CTA) to further confirm the distribution and classification of LCA (left colic artery) ascending/descending branches, then observe the postoperative blood flow path to illustrate how the above branches evolved to postoperative blood path.

      Material and methods

      89 patients with distal sigmoid and rectal cancer were referred in our observation and underwent MS-CTA between June 2020 and March 2022. We classified the distribution of LCA and confirmed whether there exists AMCA (accessory middle colic artery). Then we planned blood flow path based on the classification of LCA branches before operation. High ligation was applied in regular radical surgery. During operation, we carefully protect the bifurcation of ascending and descending LCA. Then we compared the planned blood flow path with the actual postoperative blood flow path to verify the mechanism we proposed previously.

      Results

      Of 89 patients, 82 cases met our criteria, we summarized 6 distribution pattens of LCA ascending and descending branches. These preoperative pattens are consistent with the inspection during operation. The postoperative blood flow path of 6 pattens is evolved from the above adjacent anastomotic branches and is consistent with the planned blood flow path. We also found 2 cases with IMA stenosis and 1 case with SMA stenosis under pathological condition, and their compensatory blood flow path is in accordance with our theory. The rate of the anastomotic leakage in our study group is relatively low (7.3%).

      Conclusion

      MS-CTA could confirm the distribution of LCA and AMCA, display accurate postoperative blood reconstruction path after IMA high ligation, and it further verified the mechanism we proposed previously, which is the proximal anastomotic branches forming new blood flow path from high-pressure area to the low-pressure area. This mechanism might be helpful for performing accurate laparoscopic sigmoid and rectal cancer surgery.

      Keywords

      Abbreviations:

      MS-CTA (manual subtraction computed tomography angiography), LCA (left colic artery), AMCA (accessory middle colic artery), HL (high ligation), LL (low ligation), IMA (inferior mesenteric artery), IMV (Inferior mesenteric vein), DSA (digital subtraction angiography), CTA (computed tomography angiography), EBW (Extended Brilliance Workspace), SMA (superior mesenteric artery), AL (anastomotic leakage), ALCA (ascending left colic artery)

      1. Introduction

      Colorectal cancer is one of the most common malignant cancer in the world and surgery is the main curative treatment [
      • Dekker E.
      • Tanis P.J.
      • Vleugels J.L.A.
      • Kasi P.M.
      • Wallace M.B.
      Colorectal cancer.
      ].
      The debate between high ligation (HL) and low ligation (LL) of IMA (inferior mesenteric artery) has lasted for decades [

      Miskovic D, Ahmed J, Bissett-Amess R, Gómez Ruiz M, Luca F, Jayne D, et al, Parvaiz A, and European Academy for Robotic Colorectal Surgery (EARCS) 2019 European consensus on the standardization of robotic total mesorectal excision for rectal cancer Colorectal Dis Off J Assoc Coloproctology G B Irel 21 270–6.

      ,
      • Zeng J.
      • Su G.
      High ligation of the inferior mesenteric artery during sigmoid colon and rectal cancer surgery increases the risk of anastomotic leakage: a meta-analysis.
      ,
      • Yang Y.
      • Wang G.
      • He J.
      • Zhang J.
      • Xi J.
      • Wang F.
      High tie versus low tie of the inferior mesenteric artery in colorectal cancer: a meta-analysis.
      ]. In recent years, several prospective studies and meta-analyses have showed that there was no significant difference in the incidence of anastomotic leakage between HL and LL of IMA [
      • Hajibandeh S.
      • Hajibandeh S.
      • Maw A.
      Meta-analysis and trial sequential analysis of randomized controlled trials comparing high and low ligation of the inferior mesenteric artery in rectal cancer surgery.
      ,
      • Fujii S.
      • Ishibe A.
      • Ota M.
      • Watanabe K.
      • Watanabe J.
      • Kunisaki C.
      • et al.
      Randomized clinical trial of high versus low inferior mesenteric artery ligation during anterior resection for rectal cancer.
      ,
      • Mari G.M.
      • Crippa J.
      • Cocozza E.
      • Berselli M.
      • Livraghi L.
      • Carzaniga P.
      • et al.
      Low ligation of inferior mesenteric artery in laparoscopic anterior resection for rectal cancer reduces genitourinary dysfunction: results from a randomized controlled trial (HIGHLOW trial).
      ]. While HL has some advantages in some aspects, such as simple operation and low anastomotic stoma tension [
      • Mari G.M.
      • Crippa J.
      • Cocozza E.
      • Berselli M.
      • Livraghi L.
      • Carzaniga P.
      • et al.
      Low ligation of inferior mesenteric artery in laparoscopic anterior resection for rectal cancer reduces genitourinary dysfunction: results from a randomized controlled trial (HIGHLOW trial).
      ,
      • Reddy S.H.S.
      • Gupta V.
      • Yadav T.D.
      • Singh G.
      • Sahni D.
      Lengthening of left colon after rectal resection: what all is adequate? A prospective cohort study.
      ,
      • Guo Y.
      • Wang D.
      • He L.
      • Zhang Y.
      • Zhao S.
      • Zhang L.
      • et al.
      Marginal artery stump pressure in left colic artery-preserving rectal cancer surgery: a clinical trial.
      ,
      • Fukuoka A.
      • Sasaki T.
      • Tsukikawa S.
      • Miyajima N.
      • Ostubo T.
      Evaluating distribution of the left branch of the middle colic artery and the left colic artery by CT angiography and colonography to classify blood supply to the splenic flexure.
      ]. The classical anatomical theory about the blood supply of descending sigmoid colon after HL is from the “Riolan's arch” and the marginal arch, but the formation and the cause of the “Riolan's arch” are unknown. In addition, the IMV ligation is at the same plane as the IMA ligation or higher ligation, which may cause injury to the "potential “Riolan's arch”". Overall, due to the limitation of methodology, these questions were not answered very well, thus it is necessary to investigate small vessel imaging for the branching pattern of LCA at splenic flexure and the mechanism of blood flow path reconstruction after HL [
      • Fukuoka A.
      • Sasaki T.
      • Tsukikawa S.
      • Miyajima N.
      • Ostubo T.
      Evaluating distribution of the left branch of the middle colic artery and the left colic artery by CT angiography and colonography to classify blood supply to the splenic flexure.
      ].
      Preoperative imaging of blood vessels is not only informative for choosing the ligation position, but also useful for prevention of intraoperative vascular injury. Some studies have showed preoperative vascular anatomy in sigmoid colon and rectal cancer by using digital subtraction angiography (DSA) or CT angiography (CTA) [
      • Zhang C.
      • Li A.
      • Li F.
      The angiographic anatomy of the inferior mesenteric artery in elder].
      ,
      • Bian L.
      • Wu D.
      • Chen Y.
      • Zhang Z.
      • Ni J.
      • Zhang L.
      • et al.
      Clinical value of multi-slice spiral CT angiography, colon imaging, and image fusion in the preoperative evaluation of laparoscopic complete mesocolic excision for right colon cancer: a prospective randomized trial.
      ]. DSA was considered as the gold standard for evaluating mesenteric blood vessels, DSA examination was applied preoperatively for surgeons to make strategies. However, DSA only gives a two-dimensional image and it is unrealistic to run DSA merely for observing postoperative blood flow. Previous studies about 3D reconstruction imaging of colorectal vessels still have some deficiencies and limitations. The reconstructed 3D CT images only display the arteries alone, and most of them can only display the main vessels and main branches. For veins, small branches, terminal branches and arteries from marginal arch are not visualized or poorly visualized [
      • Murono K.
      • Kawai K.
      • Kazama S.
      • Ishihara S.
      • Yamaguchi H.
      • Sunami E.
      • et al.
      Anatomy of the inferior mesenteric artery evaluated using 3-dimensional CT angiography.
      ,
      • Ke J.
      • Cai J.
      • Wen X.
      • Wu X.
      • He Z.
      • Zou Y.
      • et al.
      Anatomic variations of inferior mesenteric artery and left colic artery evaluated by 3-dimensional CT angiography: insights into rectal cancer surgery - a retrospective observational study.
      ].
      Some surgeons used indocyanine green to manifest the intraoperative angiography to determine the blood supply of anastomotic bowel. However, indocyanine green can only display superficial small blood vessels, but not the “Riolan's arch” [
      • Ishii M.
      • Hamabe A.
      • Okita K.
      • Nishidate T.
      • Okuya K.
      • Usui A.
      • et al.
      Efficacy of indocyanine green fluorescence angiography in preventing anastomotic leakage after laparoscopic colorectal cancer surgery.
      ,
      • Liu D.
      • Liang L.
      • Liu L.
      • Zhu Z.
      Does intraoperative indocyanine green fluorescence angiography decrease the incidence of anastomotic leakage in colorectal surgery? A systematic review and meta-analysis.
      ]. It is hard to illustrate the deep or invisible path of blood vessels, thus it cannot guide surgeons to avoid injuries to the “Riolan's arch”.
      Our previous study [
      • Wang Y.
      • Shu W.
      • Ouyang A.
      • Wang L.
      • Sun Y.
      • Liu G.
      The new concept of physiological “Riolan's arch” and the reconstruction mechanism of pathological Riolan's arch after high ligation of the inferior mesenteric artery by CT angiography-based small vessel imaging.
      ] deduced the mechanism of the blood flow pathway after HL by analogy with the hydrodynamic mechanism. When performing small vessel imaging, we developed manual subtraction CTA (MS-CTA) which is much simpler than the small blood vessel extraction method of GE workstation and it helped surgeons to observe blood flow path in a three-dimensional view.
      In this study, we further proved our "theory" through the preoperative and postoperative clinical observation by MS-CTA and provided a clue for surgeons to plan the ligation level of IMA and a clear landscape of reconstructed postoperative blood flow path.

      2. Material and methods

      2.1 Patients

      89 patients with distal sigmoid colon or rectal cancer at the Jinan central hospital were received routine laparoscopic surgery from June 2020 to March 2022. The inclusion criteria as follows: (1) patients with distal sigmoid colon and rectal cancer; (2) cTNM stage was confirmed to be I–III on MRI or CT; (3) Laparoscopic anterior resection (LAR) was performed. The exclusion criteria as follows: (1) The starting time of arterial phase scanning is earlier; (2) The anatomic structure is not clear; (3) No enhanced CT after operation (only 5 cases). The patients were routinely re-examined by the enhanced CT after 6 months’ operation. MS-CTA was performed with 1 mm DICOM data in the arterial phase. Comparison was made between postoperative blood flow path and preoperative planned blood flow path. All cases were operated by the same group of experienced surgeons who majored in colorectal cancer. This study was approved by the Ethics Committee of Jinan Central Hospital. Since this study was fundamental research, information was provided to the participants in place of informed consent, and they were given the right to opt out.

      2.2 Equipment and data processing

      Routine abdominal and pelvic enhancement CT before surgery was performed. 128-slice multidetector-row computed tomography (Siemens Healthcare GmbH CT scanner) scanner generate 1.0 mm image slices that can be re-constructed into 1.0 mm DICOM image data and was uploaded to the PHILIPS workstation. Image processing analysis was performed using a 3D volume rendering (VR) technique with the Extended Brilliance Workspace (EBW) software. Then the 3D imaging program of abdominal blood vessel was applied for further analysis.

      2.3 Manual subtraction CTA protocol

      Firstly, track the axial of blood vessels to delineate the targeted vessels and draw a draft sketch based on the targeted area. Secondly, the automatic bone removal program was applied, then the soft tissue background of the anterior and posterior abdominal walls was removed with the manual subtraction (Freehand exclude-sculpt anything from the active view) function (Fig. 1A–B). The small intestinal vascular branches and small intestinal soft tissue were gradually removed from the coronal angle (Fig. 1C–D), and attention should be paid to the AMCA and LCA ascending branches to keep the marginal arch complete at splenic flexure. In the end, the images of IMV and descending colon were preserved completely, thus it highlights that we can display the ascending and descending branches of LCA till the marginal arch.
      Fig. 1
      Fig. 1Procedure of manual Subtraction CTA. A: Freehand exclude-sculpt anything from the active view, two blue lines circles the area what will be excluded. B: The view after freehand exclude-sculpt function. C–D: The view after removal of the small intestinal vascular branches and small intestinal soft tissue. The red arrow shows the trunk of AMCA and LCA.

      2.4 Means of laparoscopic surgery

      We applied the IMA high ligation routinely in regular radical surgery. The LCA from the IMA directed to the splenic flexure usually flows to the cephalic side in a small arch reverse direction paralleled with the IMV. This type of LCA is often divided into ascending branch (splenic flexural branch) and descending branch (descending colonic branch) at the level of the IMA originated from abdominal aorta. Attention should be paid to protect the bifurcation of ascending and descending branches of LCA when IMV is dissected.

      2.5 Postoperative MS-CTA

      Six months after the operation, the abdominal and pelvic enhanced CT examination was routinely performed. Then the DICOM data of the arterial phase were analyzed by MS-CTA to have complete postoperative blood flow path images and compared with the blood flow path planned before the operation.

      3. Results

      3.1 Patient characteristics

      Between June 2020 and March 2022, 89 patients with distal sigmoid and rectal cancer treated at the Jinan central hospital, of 82 patients met our criteria in this study. The baseline characteristics of these patients are shown in Table 1.
      Table 1Patient characteristics.
      Clinical characteristicsvalues
      male57
      female25
      Age, median (range)61 (39–81)
      BMI, mean ± SD23.25 ± 3.7

      3.2 Six pattens of blood flow and AMCA based on the preoperative observation

      According to the routine preoperative CT, we classified six pattens of blood flow of LCA (Fig. 2). This classification provided a guide for the subsequent personalized treatment of blood vessels. The blood flow pathway for each patten is described as bellows: In patten Ia, the LCA ascending branch went upward to the splenic flexure of the transverse colon and the high-horizontal branch reached the splenic flexure of descending colon at the inferior margin of pancreas, while the LCA descending branch went to the descending colon at inferior pole of kidney. Ib LCA had no descending branch. In patten IIa, the LCA ascending branch reached at the splenic flexure of the descending colon and descending branch same as Ia. No descending branch in IIb. In patten III, the LCA ascending branch went to the descending colon at the inferior pole of kidney. In patten IV, LCA went directly to the descending colon. AMCA (accessory middle colic artery) is a branch artery originating directly from the SMA (superior mesenteric artery) and more proximally than the first jejunal artery and supplied the splenic flexure [
      • Fukuoka A.
      • Sasaki T.
      • Tsukikawa S.
      • Miyajima N.
      • Ostubo T.
      Evaluating distribution of the left branch of the middle colic artery and the left colic artery by CT angiography and colonography to classify blood supply to the splenic flexure.
      ]. The percentage of each pattern is as bellowing:Ia = 19.5%(16/82); Ib = 11% (9/82); Ⅱa = 25.6% (21/82); Ⅱb = 13.4% (11/82); Ⅲ = 18.3%(15/82); Ⅳ = 12.2% (10/82). Among the 82 patients, there were 24 patients (29.3%) with AMCA.
      Fig. 2
      Fig. 2Six pattens of blood flow based on the preoperative observation Type Ia, the LCA ascending branch went upward to the splenic flexure of the transverse colon and the high-horizontal branch reached the splenic flexure of descending colon at the inferior margin of pancreas, while the LCA descending branch went to the descending colon at inferior pole of kidney. Type IIa, the LCA ascending branch reached at the splenic flexure of the descending colon and descending branch same as Ia. Type Ib, the LCA ascending branch went to the direction as type Ia, but without descending branch. Type IIb, the LCA ascending branch went to the direction as type IIa, but without descending branch. Type III, the LCA ascending branch went to the descending colon at the inferior pole of kidney. Type IV, LCA went directly to the descending colon. IMV: inferior mesenteric vein; LCA: left colic artery; AMCA: accessory middle colic artery.

      3.3 Comparison of planned blood flow path and actual postoperative blood reconstruction path

      Here, we showed 6 representatives of pre-/post-operative MS-CTA (Fig. 3). We found an important blood flow path at the inner side of the marginal arch compared with the preoperative CTA. In the I and II LCA preoperative pattens, the red arrows point to the ascending branch of LCA and the descending branch at the inferior pole of kidney. In the III and IV LCA preoperative pattens, the red arrows point to the trunk of AMCA and the lower LCA. All green arrows refer to marginal arch. In the Ia and IIa LCA postoperative patterns, the red arrows point to an important blood flow path at the inner side of marginal arch evolved from the LCA ascending and descending branches. In the Ib and IIb LCA postoperative patterns, the red arrows point to the preserved and thicker LCA trunk, and the green arrows point to the blood flow path compensated by the marginal arch. In the Ⅲ and Ⅳ LCA postoperative patterns, the red arrows point to the source of new blood flow path evolved from AMCA, and the green arrows point to the compensatory path of the marginal arch of the descending sigmoid colon.
      Fig. 3
      Fig. 3Comparison of blood pathway between preoperative LCA and postoperative LCA by MS-CTA In all images, pre represents pre-operative, post represents post-operative. All red arrows point to the trunk of AMCA and the lower LCA. All green arrows refer to marginal arch. The detailed blood flow path is explained in 3.2.

      3.4 Blood reconstruction of pathological cases

      Among the 89 patients, 3 pathological “Riolan's arch” cases were recognized, 2 cases with IMA stenosis (Fig. 4 A and B) and 1 case (Fig. 4C)with SMA stenosis, and their compensatory blood flow path is in accordance with our theory. In the case of IMA stenosis, high ligation is performed directly, but attention was paid to protect the compensatory pathway. In patients with SMA stenosis, the LCA with compensatory enlargement (compensated SMA) was retained during surgery. The red and green arrows refer to the same blood path as 3.3 motioned.
      Fig. 4
      Fig. 4IMA, SMA stenosis and compensatory blood flow path of 3 pathological cases All red arrows point to the left branch of MCA and the lower LCA. All green arrows refer to marginal arch. All yellow arrows point to the stenosis at the root of the IMA or SMA. A and B are two cases with IMA stenosis, C is the case with SMA stenosis.

      3.5 Cases consistent with classical marginal arch and central “Riolan's arch”

      There were no additional blood vessels observed through the postoperative MS-CTA other than the preoperatively confirmed blood vessel branches. The first case was almost completely compensated by the marginal arch (Fig. 5 A and B). The second case was in accordance with the classic central "Riolan's arch", but the blood flow path compensated by the communicating branch between AMCA and LCA (Fig. 5C and D). The red and green arrows refer to the same blood path as 3.3 motioned.
      Fig. 5
      Fig. 5Cases consistent with classical marginal arch and central Riolan's arch All red arrows point to the trunk of AMCA and the lower LCA. All green arrows refer to marginal arch. A and B are from the same patient and consistent with marginal arch. A: pre-operative MS-CTA; B: post-operative MS-CTA. C and D are from the same another patient. C: pre-operative MS-CTA; D: post-operative MS-CTA and consistent with central Riolan's arch.

      3.6 Postoperative anastomotic leakage

      We observed 7 cases with anastomotic leakage (AL) grade A and grade B, no AL grade C [
      • Rahbari N.N.
      • Weitz J.
      • Hohenberger W.
      • Heald R.J.
      • Moran B.
      • Ulrich A.
      • et al.
      Definition and grading of anastomotic leakage following anterior resection of the rectum: a proposal by the International Study Group of Rectal Cancer.
      ] was observed. The rate of the anastomotic leakage in our study group is relatively low (7.3%).

      4. Discussion

      The ligation level of IMA in colon cancer has been controversial for over 100 years. In the past, the medical radiologist, the surgeon, and the interventional radiologist were relatively independent, and there is no research using DSA method to merely investigate the blood flow. What's more, the “Riolan's arch” discovered by interventional radiologist had no evidence of its evolution. The other technique by indocyanine green fluorescence imaging is with limited application in image displaying since it cannot show larger deep lying blood veins [
      • Peltrini R.
      • Podda M.
      • Castiglioni S.
      • Nuzzo M.M.D.
      • D'Ambra M.
      • Lionetti R.
      • et al.
      Intraoperative use of indocyanine green fluorescence imaging in rectal cancer surgery: the state of the art.
      ].
      Here, we developed a technique named manual subtraction CTA (MS-CTA), which can display both SMA and IMA at same time in one image. Our method “MS-CTA” imaging of MCA and LCA terminal branches has reached the level of DSA imaging (see attachment). What's more, MS-CTA could simultaneously display MCA (AMCA in some cases) and LCA, which intuitively shows the distribution pattern of the MCA and LCA in splenic flexure. By DSA, SMA and IMA are captured separately, and the network between them in the splenic flexure cannot be viewed [
      • Yada H.
      • Sawai K.
      • Taniguchi H.
      • Hoshima M.
      • Katoh M.
      • Takahashi T.
      Analysis of vascular anatomy and lymph node metastases warrants radical segmental bowel resection for colon cancer.
      ]. MS-CTA could clearly reveal the network of colonic branches of SMA and IMA. This network functions as multiple adjacent watersheds [
      • Liu R.
      • Wang Y.
      • Zhang X.-P.
      Revisiting human liver anatomy: dynamic watershed theory.
      ].
      Abundant branches on marginal arterial arch could divert the blood flow, therefore, the velocity and volume of blood flow gradually slow down, achieving dynamic balance at the anastomosis point [
      • Min J.K.
      • Leipsic J.
      • Pencina M.J.
      • Berman D.S.
      • Koo B.-K.
      • van Mieghem C.
      • et al.
      Diagnostic accuracy of fractional flow reserve from anatomic CT angiography.
      ]. As shown in Fig. 3, blood flow through the peripheral branch(marginal arch)of adjacent watersheds goes in opposite directions. when the trunk of one parallel watershed is occluded, the adjacent branches will supply blood flow to the affected side. An increased reverse blood flow in LCA ascending branch and the sigmoid colon artery ascending branch were observed in our study, and a new efficient blood flow path(siphon pipe) was formed by the compensation of shortcut anastomotic branches. This formation mechanism follows the principles of fluid mechanics [
      • Wang W.
      • Mao B.
      • Wang H.
      • Geng X.
      • Zhao X.
      • Zhang H.
      • et al.
      Hemodynamic analysis of sequential graft from right coronary system to left coronary system.
      ,
      • Zhao X.
      • Liu Y.
      • Xie J.
      • Zhao Z.
      • Qiao A.
      Surgical decision of coronary artery bypass grafting for normal left anterior descending artery (lad) and lad with stenosis: sequential graft or not.
      ] which differs with the classical theory of equal blood flow in the marginal arch.
      At the direct-view level, our observation differs with what the classical marginal arch model has showed, it further shows that the shape of transverse colon, the ascending colon and the descending colon are like beach lounger in a 3D view. If the right branch of MCA, the AMCA, and the ascending branch of LCA are considered (they are all at the inferior margin of pancreas), the entire colon marginal arch can be divided into the transverse colon marginal arch, the ascending colon marginal arch and descending colon marginal arch. It indicated that the origin of descending sigmoid colon marginal arch after high IMA ligation is not certainly from the left branch of MCA, but also from a closer accessory MCA, or from the “Riolan's arch” evolved by the ascending and descending branches of Ia, IIa LCA (Fig. 2), which connects the MCA left branch and the marginal arch of distal descending colon and sigmoid colon. This pathway acts like a siphon to ensure blood flow to the marginal arch of the descending sigmoid colon with higher efficiency.
      Compared with previous studies, on one hand, our findings are consistent with the phenomenon summarized in previous studies [
      • Lange J.F.
      • Komen N.
      • Akkerman G.
      • Nout E.
      • Horstmanshoff H.
      • Schlesinger F.
      • et al.
      Riolan's arch: confusing, misnomer, and obsolete. A literature survey of the connection(s) between the superior and inferior mesenteric arteries.
      ] (the connection of the IMA with ALCA is at the level of the left transverse colon), but we found a deeper mechanism: LCA (Ia, Ib, IIa, IIb) marginal arch of the splenic flexure is the terminal branch of the ALCA ascending branch. The above marginal arches extend to the right and form a watershed area with the left branch (marginal arch) extending from the MCA. When the IMA is ligated at a high level, the anastomotic point of the marginal arch at the watershed area compensates and expands to form a thicker marginal arch (see Fig. 3), with reverse flow in the ascending branch of the LCA.
      On the other hand, the reported mechanism of central communications between the SMA and IMA is the tiny intermesenteric arteries at the level of the duodenojejunal flexure, running along the cranial part of the IMV [
      • Lange J.F.
      • Komen N.
      • Akkerman G.
      • Nout E.
      • Horstmanshoff H.
      • Schlesinger F.
      • et al.
      Riolan's arch: confusing, misnomer, and obsolete. A literature survey of the connection(s) between the superior and inferior mesenteric arteries.
      ]. We observed that the communication bridge is AMCA and it extends to be the marginal arch at the transverse colon splenic flexure. When the IMA is ligated at a high position, the anastomosis at the marginal arch of AMCA and LCA (Ⅲ, Ⅳ) form a new blood flow path in the descending sigmoid colon, then the trunk of the AMCA becomes the source of the new blood flow path, thereby preventing the insufficient compensation of the marginal arch anastomosis. This process follows the principle of fluid mechanics, and the blood flow is supplied from the high-pressure area to the low-pressure area through new collaterals.
      The MS-CTA presents an intuitive display of blood flow, the postoperative reconstruction blood flow presented by MS-CTA is consistent with the preoperative planned blood flow path. Thus, MS-CTA contains strong potential application value which can guide surgeons to plan the level of IMA ligation preoperatively during low sigmoid colon and rectal cancer surgery. Overall, this study provides an important dynamic anatomical theoretical basis for the dispute over the IMA ligation level in colorectal cancer and low-sigmoid colorectal cancer.

      Declaration of competing interest

      The authors declare no conflicts of interest.

      Acknowledgements

      The present study did not have any financial support as it is based on routine operation.

      Appendix A. Supplementary data

      The following are the Supplementary data to this article.

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