The SMA runs along the superior mesenteric vein posterior to the pancreas. It courses in a convex line to the left side. The classic description of SMA shows the presence of four branches originating from the right margin, namely the inferior pancreaticoduodenal artery, which originates as the first branch of SMA, gives off an anterior and a posterior branch, which subsequently anastomose with the anterior and posterior branches, respectively, of the superior pancreaticoduodenal artery. Together, they supply the head of the pancreas and the lower part of the descending, transverse, and ascending portions of the duodenum. The middle colic artery, which gives off two branches, consists of a right branch supplying 2/3 of the right part of the transverse colon. It forms an anastomosis with the ascending branch of the right colic artery and nourishes the ascending part of the colon. The left branch of the middle colic artery supplies 1/3 of the left part of the transverse colon [14]. Together with the ascending branch of the left colic artery, it forms the Riolan arch (also known as the meandering mesenteric artery)[15]. It can serve as a vital conduit when one or more of these other arteries are occluded, the dilation of which is common in patients with isolated mesenteric artery dissection (ISMAD). The prevalence and diameter of the Riolan arch were significantly increased in the ISMAD group compared with the control group (83.16% vs. 35.79%, P < 0.001; 2.63 ± 0.56 mm vs. 2.12 ± 0.39 mm, P < 0.001) [16].
The peripheral arterial arch on the right side of the colon, which also forms the main collateral network between SMA and IMA, is called the artery of Drummond (also known as the marginal artery), which vascularizes the transverse and descending colon and makes an important contribution to the collateral circulation of the left colic structures [15]. The right colic artery, which divides into an ascending branch that joins the ascending right branch of the middle colic artery and together supplies the ascending portion of the colon. It also gives off a descending branch of the right colic artery, which anastomoses with the colic branch of the ileocolic artery [17]. The ileocolic artery supplying the ascending colon, appendix, cecum, and ileum. It is traditionally described as the terminal branch; however, in our study, it served as the terminal branch [3]. From the left margin: the jejunal and ileal arteries forming anastomotic arcades. From these arcades, small straight arteries called vasa recta supply the intestinal wall [3].
The former classification of SMA distinguishes five morphological types based on the presence of certain branches:
Type I, classic (53.33% of cases). Type II, defined by the absence of the inferior pancreaticoduodenal artery (26.67% of cases). Type III characterized by the absence of the right collicular artery (3.33% of cases). Type IV characterized by the presence of a common truncus for the inferior panreaticoduoneal artery and the middle collicular artery (3.33% of cases). Type V, characterized by an abnormal hepatic artery and the absence of the inferior pancreaticoduodenal artery (13.33% of cases) [4].
Based on our results, we found the following distribution of SMA morphological types in the previously presented classification: type 1–74.0%, type 2–13.5%, type 3–5.8%, type 4 and type 5 2.9% each. In 1.0% of cases, the anatomy of SMA corresponded to more than one classification (absence of the right colic artery and absence of the inferior pancreaticoduodenal artery). The above classification allows characterization of most anatomic variants of SMA in a simple and rapid manner. However, it omits the following variants that may be relevant and were detected in our study: an additional common hepatic artery independent of the presence of the inferior pancreaticoduodenal artery (18.3%), a common trunk of the pancreaticoduodenal artery and the jejunal artery (27.9%), a common trunk for the middle and right colic arteries (7.7%), colic branches from the common hepatic artery (1.0%), additional branches to the liver, with normal common hepatic morphology (1.0%), and the inferior pancreaticoduodenal artery branches from the common hepatic artery originating from SMA (1.9%) [18].
In our study, we described three clinical types of SMA.
Type 0 – Fig. 2A - normal risk of thrombosis and additional iatrogenic bleeding, characterized by a common trunk for one large and one small vessel, a common trunk for two large vessels, or the absence of one large vessel in the presence of an additional artery supplying the affected area.
Type 1 – Fig. 2B - high risk of thrombosis and low risk of additional iatrogenic bleeding, characterized by the presence of common trunks for large branches of the SMA or the absence of a large vessel originating from the SMA in the presence of additional arteries supplying the same region.
Type 2 – Fig. 2C - low risk of thrombosis and high risk of additional iatrogenic bleeding, characterized by the presence of all major vessels of the SMA, the presence of additional arteries and arterial anastomoses.
The use of a letter-based code facilitates communication between radiologists and surgeons and allows information to be communicated in a simplified and systematic manner. Emphasis on the functionality of the scale allows its direct application in daily clinical practice and ultimately leads to increased intraoperative patient safety. It is recommended that only the types associated with abnormalities (types 1 and 2) be indicated with a letter code assigned to the region and that type 0 not be indicated to allow clear communication.
Significant differences between postmortem and normal low dose CT should be mentioned. In postmortem CT, higher doses of radiation and hydrophobic paraffin-based contrast agent is used, as opposed to the hydrophilic iodine contrast agent used in low-dose radiation CT patients. These features provide more detailed anatomical images compared to steady-state visualization methods.
Limitations
There are several important limitations that should be noted with this study. First, this study was performed at a single center and involved the analysis of retrospective computed tomography scans. The study involved only individuals belonging to a specific ethnic group (Caucasians). In addition, the male population was overrepresented in the study (70.2%). In addition, we did not analyze the population with confirmed mesenteric thromboembolism or iatrogenic intraoperative bleeding.