Evaluating the hilar bifurcation territory in the human liver caudate lobe to obtain critical information for delimiting reliable margins during caudate lobe surgery: anatomic study of livers with and without the external caudate notch.

The hilar bifurcation (HB), a wedged portion between the left and right portal vein origins, often issues the caudate branch. However, the HB territory in the caudate lobe has not been well recognized during liver surgery. In 50% of 48 human livers (25 usual livers and 23 with the external caudate notch), the HB gave off thick portal branches (> 1 mm) to supply the caudate lobe. Using minute dissections, we identified four cross-sectional configurations of three subdivisions of the caudate lobe (i.e., left, right, and HB portal territories). The HB territory was consistently located in the paracaval portion, although it sometimes (29.2%: type A) extended slightly or deeply into Spiegel's lobe. This leftward HB territorial extension was seen more frequently in livers with the notch (43.6%) than in those without it ("usual" livers) (16.0%). Moreover, in livers with the notch the caudate lobe (usually its right portal territory) tended to extend upward and rightward to attach or surround the terminal portion of the right hepatic vein. Our results suggested that in many cases subdivisions of the caudate lobe cannot be divided simply into right and left portions. The HB branch or territory should be examined to determine the real principal border as well as the subdivisional configuration of the caudate lobe. Combined evaluation of the HB branch(es) and external notch could provide critical information for anatomically sophisticated caudate lobe surgery.