Variations in venous and segmental anatomy of the liver: two- and three-dimensional MR imaging in healthy volunteers.

OBJECTIVE: The purpose of this study was to use two- and three-dimensional analysis of thin-slice MR imaging data to study the anatomic variations in the segmental anatomy of the liver. It is important to recognize these anatomic variations in order to ensure accurate localization of hepatic lesions and preoperative delineation of resection planes. SUBJECTS AND METHODS: T1-weighted MR images of contiguous 4-mm sections were obtained in 10 healthy subjects. We measured the orientations of external and internal hepatic landmarks that indicated segmental boundaries and created three-dimensional renderings of hepatic veins, intrahepatic portal branches, liver surface, and gallbladder.
RESULTS: Variations in the portal branching pattern were seen in eight of 10 subjects. Most variations occurred in the right hemiliver and consisted of the absence of a right portal trunk or the presence of accessory portal 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 umbilical fissure showed marked variability. Only two of 10 subjects had three hepatic veins, with the left and middle veins sharing a common trunk. In the remaining eight subjects, nine accessory veins were present: three left, one middle, and five right.
CONCLUSION: Planes of resection in liver surgery are largely determined by the precise position of tumor relative to the individual segmental anatomy. Consequently, localization of liver lesions and preoperative delineation of resection planes requires consideration of the significant anatomic variations 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.