VARIATIONS IN VENOUS AND SEGMENTAL ANATOMY OF THE LIVER - 2-DIMENSIONAL AND 3-DIMENSIONAL MR-IMAGING IN HEALTHY-VOLUNTEERS

OBJECTIVE. The purpose of this study was to use two- and three-dimensi onal analysis of thin-slice MR imaging data to study the anatomic vari ations in the segmental anatomy of the liver. It is important to recog nize these anatomic variations in order to ensure accurate localizatio n of hepatic lesions and preoperative delineation of resection planes. SUBJECTS AND METHODS. T1-weighted MR images of contiguous 4-mm sectio ns were obtained in 10 healthy subjects. We measured the orientations of external and internal hepatic landmarks that indicated segmental bo undaries and created three-dimensional renderings of hepatic veins, in trahepatic portal branches, liver surface, and gallbladder. RESULTS. V ariations in the portal branching pattern were seen in eight of 10 sub jects. Most variations occurred in the right hemiliver and consisted o f the absence of a right portal trunk or the presence of accessory por tal branches. The division between right anterior and right posterior segments was inclined posteriorly (average, 31.2 degrees) relative to the right hepatic vein. The landmarks indicating the position of the u mbilical fissure showed marked variability. Only two of 10 subjects ha d three hepatic veins, with the left and middle veins sharing a common trunk. In the remaining eight subjects, nine accessory veins were pre sent: three left, one middle, and five right. CONCLUSION. Planes of re section in liver surgery are largely determined by the precise positio n of tumor relative to the individual segmental anatomy. Consequently, localization of liver lesions and preoperative delineation of resecti on planes requires consideration of the significant anatomic variation s in the segmental anatomy of the liver. These anatomic variations can be depicted on two- and three-dimensional displays of T1-weighted MR images of contiguous 4-mm sections.