Configuration of hepatic veins in the right surgical lobe of the human liver with special reference to their complementary territorial relationships: morphometric analysis of controlled specimens with clearly defined portal segmentation.

The configurations of hepatic veins, particularly the complementary territorial relationships between the veins, in the right surgical lobes of 156 human livers, the segments of which were identified clearly according to the portal ramification, were studied. In order to assess the functional roles of the vessels, we compared the diameter values of the vessels in the upper region of the lobe under the assumption that this parameter corresponds very closely to the actual blood flow volume through the vessel. The right hepatic vein (RHV) sometimes (17%) developed poorly and drained neither segment V (S5) nor VI (S6); instead, the inferomedial part of the S6 was often (26%) drained by the middle hepatic vein (MHV). However, most thick short hepatic veins (SHVs) did not drain S6 specifically instead of a poorly-developed RHV, but usually drained both S6 and segment VII (S7), irrespective of the configurations of other veins. Sometimes (8%), the RHV, rather than the MHV, drained a large part of S5. Overall, in the lower region of the lobe, the RHV, SHV and MHV showed complementary venous drainage relationships. Furthermore, the RHV usually (75%) ran not between S5 and S6 but through S6, corresponding to its usual territory, and could not be regarded as the intersectorial landmark in the lower region. Although various names have been given to the thick venous tributaries in the upper region of the right lobe, we systematically classified these tributaries into 5 types of "right superior radicles" (RSR), according to their topographical relationships with the right superior portal branches (P7 and P8), RHV, MHV, SHVs and their tributaries. When just thick RSRs were considered, the 5 types (anterior, posterior, lateral, medial and intersegmental) were observed in 90%, 88%, 89%, 38% and 34%, respectively. Notably, all but the intersegmntal RSRs almost always corresponded to a specific segmental territory (S7 or segment VIII (S8) and had specific terminals (at the RHV or MHV), suggesting that these 4 RSRs were proper segmental or intrasegmental veins, whereas, the 5th type showed a different configuration, i.e., an intersegmental vein that drained both S7 and S8, ran along and above the RHV and merged with it. Our morphometric examination of the upper region revealed that the sizes of P7 and P8 increased or decreased simultaneously, and suggested that the RSRs played limited roles in venous return. Rather than the RSRs, the SHVs appeared to drain the overflow in excess of the venous return capacity of the RSRs. Despite their limitations and possible complementary relationships with some veins, however, all the superior veins tended to developed evenly well or poorly. Overall, the venous return did not seem to converge into a single particular vein, but was carried away by multiple superior veins: the RHV, MHV, SHVs, and 5 RSRs.