Arc of Riolan:
The arc of Riolan (AOR) is also known as the meandering mesenteric artery or central anastomotic mesenteric artery.
It is an inconstant artery that connects the proximal superior mesenteric artery (SMA) or one of its primary branches to the proximal inferior mesenteric artery (IMA) or one of its primary branches. It is classically described as connecting the middle colic branch of the SMA with the left colic branch of the IMA. It forms a short loop that runs close to the root of the mesentery.
When present, the AOR is an important connection between the SMA and IMA in the setting of arterial occlusion or significant stenosis. It provide collateral circulation.