Lobing and segmentation of the liver The left, right, square and caudal lobes of the liver divided from the surface do not really reflect the structural features of its internal ductal system and thus are not suitable for liver surgery to perform partial hepatectomy Accurate segmentation of the lesion by the CT physician can be of great help to the surgeon. Nowadays, there is no unified international nomenclature for the lobing and segmentation of the liver, but there are 2 methods most commonly used to be not commonly used. 2. The second method of lobar segmentation is based on the distribution of the Gleason system, which divides the liver into left and right halves, which are further divided into 8 segments (Quinard classification): Segment I: caudate lobe. Segment II: equivalent to the upper left outer lobe segment. Segment III: lower segment of the left outer lobe. Segment IV: left inner lobe. Segment V: right anterior lobe inferior segment. Segment VI: right posterior lobe inferior segment. Segment VII: right posterior lobe superior segment. Segment VIII: right anterior lobe superior segment. The segments of the liver are named mainly according to the ductal system within the liver. The portal vein, hepatic artery, and hepatobiliary ducts are companionally wrapped in the same Glisson sheath, so they are called the Glisson system or portal system. The segmentation of the liver made according to the distribution of the portal system is called the portal liver segment. The segmentation of the liver made according to the area of hepatic venous drainage in a finger-like relationship with the portal vein is called the venohepatic segment. Because the intrahepatic bile ducts are accompanied by the intrahepatic portal vein, the nomenclature of the portal liver segments is used in hepatobiliary surgery. couinaud the liver segments according to the portal system are marked clockwise with Roman numerals from Ⅰ Ⅱ Ⅲ Ⅳ Ⅴ Ⅵ Ⅷ, in which the left inner lobe and caudate lobe are no longer segmented. The liver is divided into 8 segments, mainly divided by the hepatic venous system and the portal venous system. The middle hepatic vein divides the liver into two lobes, the right and the left. The right hepatic vein divides the right lobe of the liver into two parts, the right anterior and right posterior. The left hepatic vein divides the left lobe of the liver into the left inner lobe and the left outer lobe. The portal venous system travels within the hepatic segments. Segment I is the caudate lobe, which is shown in CT between the portal and vena cava veins; segment II (against the top) and segment III (against the bottom) constitute the left outer lobe; segment IV is the square lobe, which is also the left inner lobe; segment V (against the bottom) and segment VIII (against the top) constitute the right anterior lobe of the liver; segment VI (against the bottom) and segment VII (against the top) constitute the right posterior lobe of the liver. As for the division of segment II from segment III, segment V from segment VIII, and segment VI from segment VII, the rough method is to use the intrahepatic portal vein branch or the hilar plane as the division mark, and what appears in the above plane is against the top, segment II, segment VII, and segment VIII, and the following level is segment III, segment V, and segment VI. The right hepatic vein is used as the demarcation between segment V and VI, and segment VII and VIII. The hepatic vein is used as the boundary in cross-section on imaging, and the divisions of 2, 3; 5, 8; 6, 7 are approximately the left and right branching planes of the portal vein. The significance of liver segmentation: it can understand the location of the lesion, especially for patients with malignant tumors of the liver, and thus guide the treatment. The segmentation of the liver is closely related to the anatomy of the liver, and once the anatomy of the liver is understood and applied to the analysis of imaging, the segmentation of the liver can be understood skillfully. 2. Segmentation mainly depends on CT. CT: Firstly, the three major veins of the liver are identified: the middle hepatic vein, the left hepatic vein and the right hepatic vein; the portal vein and its bifurcation sites are identified. The portal vein bifurcation can be distinguished from the upper and lower section, that is, liver S5/S8,S6/S7, above the portal vein bifurcation is S8,S7; between the right hepatic vein and the middle hepatic vein is the right anterior lobe, after the right hepatic vein is the right posterior lobe; general rule, from CT, the first to see is S8, then S2,3, the left outer lobe of the liver is bounded by the hepatic fissure, which is easier to identify, the left inner lobe is the area between the hepatic fissure and the middle hepatic vein , the level of the gallbladder downward is S5, the last level is generally the hepatic S6, and the inferior vena cava and portal vein are sandwiched by the caudate lobe, S1.