Description of the Vascular Anatomy of Livers with Absence of the Portal Bifurcation.

BACKGROUND: The absence of the portal bifurcation (APB) is a rare anatomic variation, in which the horizontal part of the left portal vein (PV) is missing. The aim of this study was to identify the vascular architecture in livers with APB. METHODS: Computed tomography data for 17,651 patients were reviewed; five patients (0.03%) were found to present with APB. The liver volume and anatomy of APB patients were compared with those of 30 patients with normal livers. RESULTS: All the APB patients exhibited an independent posterior branch of the PV. The intrahepatic left PV (LPV) ran through either the ventral (n = 2, 40%) or dorsal side (n = 3, 60%) of the middle hepatic vein. The frequency of medial branches diverging from the LPV was higher in patients with APB than in normal patients (p < 0.001). The left hepatic duct (LHD) ran through the inside of the left lobe along the left PV in 40% of the patients with APB, whereas in the remaining 60% of the patients with APB, the LHD ran on the outside of the liver separately from the left PV and joined the right hepatic duct. The liver volume of the left lateral section was significantly smaller (p = 0.014), and the posterior section was significantly larger (p = 0.014) in patients with APB than in patients with normal livers. CONCLUSION: The unique anatomical characteristics and the positional relation of the vessels should be considered preoperatively in patients with APB.