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Annular portal vein variation

The portal vein (PV) is formed from the convergence of the superior mesenteric and splenic veins. Distally, it divides into right and left branches; the right branch of PV further divides into anterior and posterior divisions. Variations in the anatomy of the PV are detected by imaging and surgery, guiding both radiological and surgical procedures. Here, we present a case of an annular PV variation. A 48-year-old man presented with a half-year history of recurrent jaundice. Contrast-enhanced computed tomography (CT) suggested hilar cholangiocarcinoma. CT revealed an annular PV variation. The PV ramified into right anterior and right posterior branches that formed a circle (Fig. 1). The left PV originated from this circle and the hepatic artery of S7 passed through the circle. Right hepatectomy was performed, which confirmed this variation (Fig. 2). Variations of the PV are uncommon but some of them are incidentally detected. Variations in the anatomy of the PV have an embryological basis and the PV is normally formed during Weeks 4–10 of embryonic development. The two common variations are trifurcation of the PV, which divides into right anterior, right posterior and left branches, and early branching of the right posterior PV from the main PV. This case presents a less common variation of the right anterior and right posterior branches forming a circle with the left PV (Fig. 3). It may be another kind of early branching of the right posterior PV from the main PV. The normal form and function of the liver confirm that this variation does not adversely affect liver development or patient’s health. Blood flows within the circle created by an annular PV via the right anterior, right posterior and left branches of PV. As the hepatic artery passes through the ring-like annular PV variation, it is easily found and hardly ever injured. However, awareness of potential PV variations is important in planning liver surgery, where an