The 'meandering mesenteric artery' also known as the arc of Riolan is a collateral artery, first described by Jean Riolan (1580-1657), that directly connects the proximal superior mesenteric artery with the proximal inferior mesenteric artery and may serve as a vital conduit when one or the other of these arteries is occluded. Flow can be forward (IMA stenosis) or retrograde (SMA stenosis), depending on the site of obstruction. Such obstruction results in increased size and tortuosity of this meandering artery, which may be detected by arteriography; the presence of a large arc of Riolan thus suggests occlusion of one of the major mesenteric arteries.