Middle colic artery

The middle colic artery (MCA) is a branch of the superior mesenteric artery (SMA) that supplies the transverse colon. It is one of the three major colic branches of the SMA alongside the ileocolic artery and the right colic artery and is among the most constant, being present in approximately 95% of individuals.

Origin and course

The MCA arises from the anterior surface of the SMA, typically near the inferior border of the pancreas. It enters the transverse mesocolon and courses anteriorly toward the transverse colon, where it typically bifurcates into a right branch and a left branch. The right branch anastomoses with the ascending branch of the right colic artery (or directly with the ileocolic artery when the right colic artery is absent), while the left branch anastomoses with the ascending branch of the left colic artery from the inferior mesenteric artery (IMA). These anastomoses contribute to the marginal artery of Drummond, a continuous paracolic arterial arcade along the mesenteric border of the colon.

Anatomical variations

Significant variability exists in MCA anatomy:

• Branching pattern: The right and left branches may arise from a common trunk (most common, ~5760%) or originate separately from the SMA (~3342%).

• Accessory middle colic artery (aMCA): Present in approximately 7-49% of cases, the aMCA arises independently from the SMA and typically courses toward the splenic flexure region. Its trajectory often runs in proximity to the inferior mesenteric vein and the lower pancreatic border.

• Bifurcation position: The MCA bifurcation may occur to the left of, anterior to, or to the right of the superior mesenteric vein (SMV), with the anterior position being most common (~53%).

Collateral circulation

The left branch of the MCA participates in forming the arc of Riolan (inconstant), a direct anastomotic channel between the SMA and IMA territories. This collateral pathway is clinically important in maintaining colonic perfusion when either the SMA or IMA is compromised by atherosclerotic disease or surgical ligation. The splenic flexure represents a watershed area between the SMA and IMA territories, making it particularly vulnerable to ischemia.