A CT-Based 3D Anatomical Mapping Study of Right Posterior Portal and Hepatic Venous Patterns: Revisiting Liver Segmentation and Its Surgical Implication

Background: Classical Couinaud’s segmentation assumes the dichotomous division of the right posterior portal vein (RPPV) into P6 and P7. However, increasing imaging evidence suggests substantial anatomical variability, limiting the intraoperative identification of segmental borders and providing guidance for subsegmental resection. Methods: We retrospectively analyzed contrast-enhanced five-phase computed tomography (CT)-based three-dimensional reconstructions from 100 consecutive eligible cases (2020–2025). Third-order RPPV branching patterns were classified into three types: bifurcation (PV-type 1), loops (PV-type 2), and others (PV-type 3). We measured the 3D distances from the posterior portal origin to the first major branch point and performed volumetric analysis of territories supplied by individual third-order branches using Ziostation REVORAS. Hepatic vein anatomy was categorized as HV-type 1 (a fissure plane forming an intersegmental vein), HV-type 2 (a landmark vein without plane formation), or HV-type 3 (neither) and compared between portal types. Results: PV-type 1 was observed in 45 cases (45.0%), while PV-type 2 was seen in 53 cases (53.0%); however, two cases (2.0%) showed other patterns. The distance to the first branch point was shorter in PV-type 1 than in PV-type 2 (8.89 ± 7.87 vs. 17.3 ± 8.36 mm; p < 0.001). In PV-type 1, the first caudal branch territory (corresponding to S6) accounted for 43.8% ± 12.6% of the posterior section, whereas the first-branch cone-unit territory in PV-type 2 accounted for 14.9% ± 8.64% (p < 0.001). The HV-type 1/2/3 ratios differed by portal type (PV-type 1: 29/16/0; PV-type 2: 25/14/14; p < 0.001), and 26.4% of PV-type 2 cases lacked any hepatic venous landmarks. Conclusions: PV-type 2 peripheral RPPV branching was observed in 53% of cases. Although conventional Couinaud-based segmentectomy with the Glissonian approach and vein-guided transection was suitable for PV-type 1, cone-unit-based anatomical resection supported by individualized preoperative simulation and intraoperative navigation may prove useful for PV-type 2 anatomy.