Arc of Riolan

Last revised by Leonard Boelen on 1 Sep 2023

The arc of Riolan, refers to an anastomosis between the superior mesenteric artery (SMA) and the inferior mesenteric artery (IMA). However, there is no consensus on which anatomical structure this term precisely refers to. It is also known as the mesenteric meandering artery (of Moskowitz) or central anastomotic mesenteric artery, is an arterioarterial anastomosis between the superior and inferior mesenteric arteries.

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 SMA's middle colic branch with the IMA's left colic branch. It forms a short loop that runs close to the root of the mesentery.

When it is present, the arc of Riolan is an important connection between the SMA and IMA in the setting of arterial occlusion or significant stenosis. In proximal SMA occlusion, the arc of Riolan provides collateral flow from the IMA to the SMA territory and vice versa. Where distal abdominal aortic occlusion occurs, it provides collateral flow from SMA to IMA to the iliac vessels (via the superior rectal artery) and the lower limbs (via the external iliac artery).

Both its actual existence and the general need for terms other than those mentioned in Terminologia Anatomica have been questioned by surgeons 2.

It was named after Jean Riolan (1580-1657), French anatomist, not because he discovered the vessel (there is no evidence that he did), but it was named in his honor in 1743 by the Swiss anatomist Albrecht von Haller (1708-1777) 4,5.

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Cases and figures

  • Case 1: DSA angiogram - Arc of Riolan
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  • Case 2: with abdominal aortic aneurysm
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  • Case 3: arc of Riolan (highlighted)
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  • Case 4: with IMA aneurysm
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