Study on the portal ramification pattern of the right anterior sector of the liver and a unique medial branch (PV8c) of the right anterior portal vein

Aim: The concept of Couinaud segmentation is widely used in clinical practice. However, there were no definite anatomical landmarks between segments V and VIII. Therefore, segmentation of the right anterior sector is still controversial. We aimed to investigate the portal segmentation of the right anterior sector using 3D image analysis, and to reveal the existence of the medial branch (PV8c), a unique, characteristic branch of the right anterior portal vein. Methods: The ramification form and pattern of the tertiary portal branch of the right anterior portal vein were retrospectively analyzed, and the frequency of PV8c was evaluated in 261 patients between January 2016 and June 2020. Results: The ramification pattern of tertiary portal branches of the right anterior portal vein was classified into four types: craniocaudal, 28.0% of patients; ventrodorsal, 21.8%; trifurcation, 39.5%; and quadfurcation, 5.7%, and each type was further subdivided into six patterns by focusing especially on the caudal branches. The ramification pattern in the remaining 5.0% of the livers did not belong to the above-mentioned four types. The PV8c branch was identified in 140 of 261 livers (53.6%); the mean proportion of the feeding area of PV8c in the whole liver volume was 3.4%. Conclusion: Since the ramification pattern of tertiary portal branches of the right anterior portal vein does not necessarily show a single pattern, it is important to confirm the portal vein branching in each case during hepatectomy. This is the first study of the details of PV8c by 3D computed tomography.