Anatomical Variations of Portal Vein Branches in Subsegment IVb: A 3D Reconstruction-Based Classification to Inform Radical Resection for Gallbladder Cancer.

INTRODUCTION

Subsegment IVb (S4b) is a common site of direct invasion in gallbladder cancer, and its complete resection is critical to achieve negative surgical margins. However, the portal venous anatomy of S4b is highly complex and exhibits significant interindividual variation, which the conventional Couinaud classification fails to adequately delineate. This study utilized three-dimensional visualization to systematically characterize the anatomical features and branching patterns of the portal veins supplying S4b, with the goal of establishing a practical anatomical classification to inform preoperative planning for radical gallbladder cancer surgery.

METHODS

This retrospective analysis utilized thin-slice computed tomography data from 115 patients who underwent abdominal contrast-enhanced computed tomography for a spectrum of clinical indications (e.g., evaluation of focal liver lesions, trauma assessment, or other abdominal pathologies). Three-dimensional reconstruction of the portal venous system was performed using dedicated visualization software. We focused on analyzing the origin, number, course, and common trunk patterns of the internal branches of the left portal vein supplying S4b.

RESULTS

S4b was supplied by 1 to 6 portal vein branches, with 2 to 6 branches observed in 87.1% of cases. The overwhelming majority (>90%) of these branches originated from the umbilical portion of the left portal vein. Based on the common trunks supplying both S4a and S4b, the vascular anatomy was classified into four types: type A (no common trunk, 23.4%), type B (one common trunk 53%), type C (two common trunks 20%), and type D (more than two common trunks or a branch derived from the right portal vein 3.4%). Overall, 73% of patients exhibited 1-2 common trunks. The diameter of these common trunks correlated with their number, and their trajectories consistently coursed toward the S4a segment.

CONCLUSIONS

The proposed four-type classification systematizes the broad spectrum of S4b portal venous anatomy. This framework facilitates a preoperatively planned, targeted resection in radical gallbladder cancer surgery, which is instrumental in optimizing procedural safety and oncologic outcomes.