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Page 2 of 8 Ban et al. Hepatoma Res 2021;7:13 I http://dx.doi.org/10.20517/2394-5079.2020.104

controversy about the oncological significance of anatomical hepatectomy, most surgeons would agree
that minimizing vessel dissection on the intersegmental plane makes it easy to perform liver resection. In
contrast with the concept of parenchyma-sparing hepatectomy, some reports suggest that hepatectomy that
[2,3]
does not result in an ischemic area has a better prognosis .
To make an anatomically reasonable dissection, landmarks that serve as indicators of dissection must be
used. One is the root of the responsible Glisson branch and the other is the regional boundary of the liver
surface. In actuality, the boundaries of the dominant region are not a straight line at the liver surface and
are not a flat plane relative to the parenchyma. The traditional method of staining the portal vein is by
its direct puncture to mark the dissection line on the liver surface, and more recently the usefulness of
intraoperative visualization of the dominant region by indocyanine green (ICG) for liver dissection has
[4,5]
been reported . These are techniques that are not limited to laparoscopic surgery but are also common in
open surgery. However, in LLR, intraoperative ultrasonography-guided puncture of the portal vein branch
is technically demanding, and indigo staining is impractical. However, visualization with ICG is extremely
[6]
useful and likely expected to become one of the main techniques in LLR in the future .

Although boundaries are marked on the liver surface as indicators for dissection, landmark structures
in the liver parenchyma during liver dissection are also needed. The hepatic veins, another important
landmark, have traditionally been exposed during hepatic dissection as structures that divide the segment.
Controlling hemorrhage from the hepatic veins and exposing them is an important step in liver resection.
We describe the role of the hepatic vein in LLR on the basis of previous reports and our own experience.

ROLE OF HEPATIC VEINS
Technique for exposing hepatic veins during LLR
There are several benefits of laparoscopic surgery in liver resection. The most notable is the control of
venous bleeding due to pneumoperitoneum. If well controlled by the equilibrium of hepatic venous and
pneumoperitoneum pressures, no bleeding occurs if the pore is small . Lower central venous pressure
[7]
is necessary to lower the hepatic venous pressure. Low intraoperative fluid levels, low airway pressure,
an elevated head position, and other controls on respiration and circulation are essential for minimizing
venous bleeding in LLR. This seems to be the main reason for the results of previous large retrospective
studies and randomized controlled trials that showed less blood loss in LLR compared with open liver
[8,9]
resection . To perform a safe and effective transection following hepatic veins, the collaboration with the
anesthesiologist is of paramount importance.

One of the technical difficulties of LLR is achieving accurate 3-D spatial orientation. It is easy to become
disoriented during the procedure, particularly during partial resection. For example, in the case of a partial
resection of segment 8, the dorsal margin of the tumor may not be sufficient as the resection proceeds.
Observation by ultrasonography during surgery is also essential. If there is a vein on the back side that
serves as a landmark for the resection line, the target hepatic vein can be included on the resection side
once it is exposed, thereby ensuring that the partial resection is performed without missing the resection
line [Figure 1].

It is unquestionably easier to expose the vein during laparoscopic surgery, but this requires basic techniques
to avoid bleeding from the vein. As the vein is dissected from the periphery to the center, the angle of the
small venous branch that confluences to the larger vein causes it to split and injure the branch. To avoid
[10]
this, it is important to dissect from the center to the periphery. Honda et al. introduced a technique that
divides venous injuries into two types: spit injuries, which are peripheral to central injuries, and pulled-
up injuries, which are central to peripheral injuries and are easier to control. The key to this method is
to move the Cavitron ultrasonic surgical aspirator (CUSA) from the root to the peripheral side so that