We have been regarded as a dogma of liver anatomy that has gone couinaud's segmental structure for more than half a century. With the recent development of cancer screening system and radiologic images, the early detection rate of hepatoma has increased, and monosegmentectomy is actively being performed. However, I think many liver surgeons would have had experiences where anatomical resection was not easy due to the anatomical variation of the third order branches of portal pedicle when performing monosegmentectomy, especially in the right liver. In addition, the debate of whether anatomical resection can actually improve the prognosis in the hepatoma patients continues. Some surgeons think that they have often experienced difficulties to do anatomical resection due to anatomical variation, so only surgery more than sectionectomy is considered anatomical resection, while other surgeons are performing moderately compromising surgery to conclude that there is no prognostic difference between anatomical resection and non-anatomical resection. Majno P explained that the segmental anatomy of the liver has complexity in 3D image analysis, which can hardly be understood by a simple Couinaud’s anatomy and suggested “1-2-20 concept”. It is based on their observation of the intrahepatic vasculature such that the hepatic inflow or portal vein gives three 1st order branches; left, right anterior and right posterior; and further divides into random 2nd order branches, 9 to 44 in number (mean=20) rather than eight segmental branches, as conventional Couinaud’s model describes. In analogy to Couinaud’s 8 segment scheme, each segment must be supplied by single segmental Glissonean pedicles, but in real life, branching pattern is quite irregular and random. To facilitate communication among doctors, Glisson pedicle of the liver starts with one in the interrogating part, and two 1st order branches arise from it; right and left. The second order branches correspond to right anterior and posterior to the right lobe, and segment 2 branch and umbilical portion beyond Arantius duct to the left lobe. This architecture is constant in most cases, and the structure that form the boundaries or each territories are three hepatic veins. Therefore, “1-2-4-20” law is a more precise description. In other words, it’s the 3rd order branches that are randomly arisen. Randomness in the context describes that there might be variation in number of branches in the left lobe and “sliding of origin” pattern variation along with variation of number of branches in the right lobe of the liver. Under the background of this understanding, I would like to discuss Majno’s three levels of complexity of intrahepatic vasculature. He reclaimed the actual portal vasculature is more complex than Couinaud’s 8 segment structure and suggested three levels of complexity. First level is identical to Couinaud’s 8 segment scheme serves as a common language between clinicians. This level views hepatic vasculature is composed of three hepatic veins and four 2nd order branches of portal pedicles. Second level is not a simplified or theoretical stage of anatomy, but rather is an anatomical level based on the actual branching pattern of Glissonean pedicles that allows surgeons to identify vascular structure by 3D image in modern liver surgery. By this understanding, tailored territorial liver resections have become possible. However, an approach independent of the Couinaud anatomy is required for this level of complexity. Finally, the third level of complexity of liver anatomy (academic level) is a step for anatomists based on the diversity and randomness of portal pedicle branching which allows us to understand the complexity of the vascular tree and segmental anatomy free from Couinaud’s dogma; 1-2-20 or 1-2-4-20 concept sums up the complexity. Under the preoperative 3D image and the acceptance of the concept of three level of complexity, I would like to discuss the tailored approach of monosegmentectomy for segment 8 HCC. There are three techniques in systematic segmentectomy 8 for HCC located in Couinaud segment 8. The first approach is the US-guided dye injection technique, proposed by Professor Makuuchi. The second technique is Takasaki’s cone unit resections through the dorsocranial opening of the main portal fissure. And the third approach is a technique through the anterior opening of main portal fissure. As the anterior liver is thin, the hepatotomy requires a little efforts. It is followed by confirmation, ligation and division of the G8 pedicle(s), and the surface of the S8 is discolored. Thereafter, we remove the stained liver. Since 2016, we have used preoperative 3D image (Synapse 3D, Fuji film), and have confirmed the patterns of intrahepatic anatomical variations of portal venous branches. And we could select the tailored technique in systematic segmentectomy 8 getting the high success rate of anatomical resection. We got the 3D images using Synapse 3D (Fuji film) in 96 LDLT donor liver. There were four types in anatomical variation of right anterior portal branches: Type A(Cranio-caudal type:49 cases, 46.2%), Type B(Ventral-dorsal type: 14 cases, 13.2%), Type C(Radial type: 37 cases, 34.9%) and Type D(Slidden branch type between RAS and RPS: 6 cases, 5.7%). We can do anatomical segmentectomy 8 in only Type A (46%) using conventional technique. Today, I would like to show experiences of tailored surgical approaches (to apply complementally one of the three approaches) according to their patterns in HCC located in segment 8.