Quantitative Anatomical Study Of Variant Right Hepatic Veins Based On Three-dimensional Visualization Technique

Background and objectives In addition to the right hepatic vein(RHV)in the right hepatic venous system,variant right hepatic veins(VRHVs)that drain the right liver directly into the inferior vena cava(IVC)can be frequently noted.Large variant right hepatic veins,with diameter≥5 mm,have important clinical significance in in liver disease progression,liver transplantation and hepatectomy.The objectives of this study include:1.To evaluate the right hepatic venous system containing variant right hepatic veins with diameter≥5 mm by using three-dimensional(3D)visualization technique and to propose the classification of variant right hepatic venous system.2.To measure the length of retrohepatic inferior vena cava(RHIVC)and the diameters of right hepatic vein,middle hepatic vein(MHV)and variant right hepatic veins,and then quantitatively analyze the correlation.3.To measure the drainage area volume of the right hepatic vein,the middle hepatic vein and the variant right hepatic vein,and analyze the correlation between the vein diameters and the corresponding hepatic vein drainage area volume.4.To further analyze the venous drainage system of the right liver’s segments when the variant right hepatic veins exits,to provide reference for the clinical practice of liver hepatobiliary surgery.Methods The imaging data of 650 patients who underwent contrast-enhanced CT scans of the upper abdomen in Zhujiang Hospital of Southern Medical University were retrospectively analyzed.The CT date of patients with large variant right hepatic veins were selected for 3D reconstruction of liver and intrahepatic vascular models.According to the position of the variant right hepatic veins in the retrohepatic inferior vena cava,there were three main types of variant right hepatic venous system:Type Ⅰ,the RHV and the inferior right hepatic vein(IRHV);Type Ⅱ,the RHV,IRHV and the middle right hepatic vein(MRHV);Type Ⅲ,RHV,IRHV and the superior right hepatic vein(SRHV).According to the number of IRHVs,each type could be further divided into different subtypes:subtype a,1 IRHV;subtype b,2 IRHVs;subtype c,3 IRHVs and so on.Liver segmentation was performed according to the Couinaud anatomical classification of liver segments.Based on blood flow topology,liver venous drainage area analysis was performed.Using the distance measurement tool on the 3D visualization software,the length of the retrohepatic inferior vena cava as well as the diameters of the right hepatic vein,the middle hepatic vein and the variant right hepatic veins were measured.The total liver volume as well as each drainage area volume of the right hepatic vein,the middle hepatic vein and the variant right hepatic veins were measured using the volume measurement tool.The venous drainage system of the right liver’s segments was observed.The drainage of the right hepatic venous system with anatomical variation was also analyzed.Results Among 650 patients,CT data of 110 patients with large variant right hepatic veins were selected for 3D reconstruction,and the incidence of large variant right hepatic veins was 16.93%(110/650).The age of the selected patients was 51.82 ±14.01 years,and the male to female ratio was 49/61.According to the analysis of variant right hepatic venous system,110 cases of right hepatic venous system configuration were divided into seven types(three main types and seven subtypes).Type Ⅰ was further divided into three subtypes:Type Ⅰa(59/110,53.64%),in addition to RHV,1 IRHV was present;Type Ⅰb(31/110,28.18%),in addition to RHV,2 IRHVs were present;Type Ⅰc(1/110,0.91%),in addition to RHV,3 IRHVs were present.Type Ⅱ was further divided into two subtypes:Type Ⅱa(11/110,10.00%),in addition to RHV,1 MRHV and 1 IRHV were present;Type Ⅱb(3/110,2.73%),in addition to RHV,1 MRHV and 2 IRHVs were present.Type Ⅲ was further divided into two subtypes:Type Ⅲa(4/110,3.64%),in addition to RHV,1 SRHV and 1 IRHV were present;Type Ⅲb(1/110,0.91%),in addition to RHV,1 SRHV and 2 IRHV were present.The length of retrohepatic inferior vena cava was positively correlated with the diameters of right hepatic vein and variant right hepatic vein.The diameter of the right hepatic vein was negatively correlated with the diameter of the variant right hepatic vein.The the number of variant right hepatic veins and their sum of diameters was positively correlated.Diameter of right hepatic vein was positively correlated with its drainage area volume(rs=0.489,P<0.001),but negatively correlated with variant right hepatic vein drainage area volume(rs=-0.460,P<0.001).With the increase of the number of variant right hepatic veins,the drainage area volume of the right hepatic vein and its proportio of the whole liver significantly decreased(P<0.001).Although part of the middle hepatic vein was involved,the right hepatic vein and the variant right hepatic veins were the main draining veins in the right posterior section of the liver.Different numbers of the large variant right hepatic veins affect the drainage of RHV,MHV,and VRHV on the right liver,which should be used as an evaluation point for clinical decision making such as liver resection and liver transplantation.Conclusions In this study,the right hepatic venous system was divided into seven types by using 3D visualization technique according to the opening position and number of variant right hepatic veins.The diameter and drainage area volume of the right hepatic vein system could be clearly displayed on the 3D model and quantitatively analyzed.The drainage system of each segment of the right liver was also described in this study.In conclusion,in the clinical practice of liver resection,liver transplantation,etc.,which needs to understand the anatomical characteristics of the hepatic vein,the evaluation of the right hepatic vein system according to the classification of this study can make a more appropriate clinical decision.