since couinaud 's segment viii is the largest segment of the liver and patients with hepatocellular carcinoma ( hcc ) often have impaired liver function , reduced anatomical resection of the ventral part of segment viii ( s8vent ) has been used as an alternative to full anatomical resection of segment viii in its entirety in actual clinical settings .
anatomical resection of s8vent is generally considered a demanding procedure due to its anterosuperior location , its boundaries marked by tributaries of the middle or right veins and their tributaries , and the complete absence of anatomical landmarks on the liver surface , particularly in the cirrhotic liver .
several techniques of anatomical resection have been proposed , including the technique involving puncture of the portal branch as proposed by makuuchi et al .
that technique remains the most precise and practical method for anatomical demarcation on the liver surface .
however , there are no accurate methods to identify the demarcation line inside the liver and divide the liver parenchyma along the intersegmental or intersubsegmental plane , which is not a straight line but rugged and irregular .
the current authors have proposed a method of identifying the intersegmental and intersubsegmental border inside the liver to facilitate more precise anatomical subsegmentectomy .
his liver function was normal , and his indocyanine green retention rate at 15  min was 6.5% .
the tumor was located in the ventral part of segment viii ( s8vent ) ( fig .
according to three - dimensional images ( iqqa - liver , edda technology , princeton , nj , usa ) , one tributary of the middle hepatic vein ( mhv ) , designated v8i , was running between s8vent and the dorsal part of segment viii ( s8dor ) .
another tributary of the mhv , designated v8 - 5i , was running between s8vent and the ventral part of s5 ( s5vent ) ( fig .
volumetric analysis indicated that the volume of the sviii was 297  cm ( 22.1% of the total liver volume ) and that the volume of s8vent was 165  cm ( 12.3% ) .
after laparotomy and thoracotomy along the ninth intercostal space with a j - shaped incision , intraoperative ultrasonography was used to scan the entire liver to determine access to the vascular architecture and the tumor .
thoracophrenolaparotomy facilitated mobilization of the right liver and provided excellent views of the insertion of the hepatic veins into the vena cava .
guided by ultrasound , about 5  ml of indigo carmine dye ( indigocarmine injection 20  mg/5  ml ; daiichi sankyo , tokyo , japan ) was injected into the proximal part of portal branch of s8vent ( p8vent ) after clamping of the hepatic artery .
the border of stained surface of the liver was marked using electrocautery and the tumor was located within the resection line ( fig .
the locations of the aforementioned p8 vent , v8i , and v8 - 5i were then ascertained and marked on the surface ( fig .
flow was intermittently occluded by clamping of the hepatoduodenal ligament , and the parenchyma was dissected using the clamp and crush method . the sequence of liver parenchymal transection is shown in fig .
after the small tributary of v8 - 5i was exposed , it was followed all the way to the main trunk of the mhv .
the portal pedicle of s8vent , which lay near the v8 - 5i , was then ligated and divided .
after anatomical resection of s8vent , v8i and v8 - 5i were clearly exposed in almost their entirety and then preserved .
the main trunk of the mhv between the two tributaries was also exposed ( fig .
the operating time was 240  min and intraoperative blood loss was 50  ml .
drains were inserted in the transected surface of the liver and right subphrenic space , and these drains were removed on day 6 postoperatively .
an intercostal drain was left in the pleural space and removed on day 2 postoperatively .
according to the oncological principle , it is reasonable to radically remove hcc by inclusion of the feeding portal area since the portal vein is the main gate for intrahepatic tumor spread .
meanwhile , the volume to be resected is limited since patients with hcc often have background liver disease . anatomic segmental or subsegmental resection , taking into consideration both preservation , to the maximal extent possible , of liver functional parenchyma and eradication of intrahepatic metastasis , would be a theoretically reasonable procedure .
several studies have demonstrated the superiority of anatomic resection in comparison to non - anatomic resection , showing better disease - free or overall survival . as for this patient ,
the tumor was located in the ventral part of s8vent , so the anatomical subsegmentectomy of s8vent was decided .
however , anatomical segmentectomy , and especially s8vent resection , is technically demanding and two main difficulties exist .
one relates to the demarcation of s8vent on the liver surface and the other relates to the direction of transection along the intersubsegmental planes inside the liver .
several studies have described techniques for demarcation of s8vent on the liver surface . of these ,
the intraoperative ultrasound - guided portal branch puncture technique proposed by makuuchi et al . in the mid-1980s is still the most precise method . in relation to the direction of transection along the intersubsegmental planes inside the liver , sakairi and makuuchi
proposed a method in which the portal pedicle is clasped and dye is injected . with this method , staining of the portal unit persists even after resection is complete , and the margin of the portal unit within the parenchyma is easily followed during transection .
however , if a small branch of the portal vein is injured in an actual clinical setting , the dye spreads to the dividing planes and also stains the counter plane .
moreover , a recent study showed that the subsegmental border visualized between the ventral and dorsal region always coincided with the plane of the v8i according to computer simulations , so the subsegmental plane can reasonably be divided along with v8i by preserving the very small tributaries near the liver surface and following them to determine where they meet as they run into v8i .
the small venous tributaries meet along the way , gradually becoming a larger vessel that eventually joins the main three hepatic veins .
the method is time - consuming but may be the only method to accurately divide the liver parenchyma along the intersegmental or intersubsegmental plane demarcation . in the current case ,
a tributary of the mhv ( v8 - 5i ) was found to be running on the segment border of s8vent and s5vent in three - dimensional images and it was detected and exposed during transection .
the landmark vein of v8 - 5i in the transverse s8s5 intersegmental plane was determined for the first time since it had not been described in the literature . in recent practice , these subsegmental venous tributaries have been exposed as they are in anatomical studies .
anatomical s8vent resection is technically demanding , and previously reported techniques for anatomical resection are not without their drawbacks . proposed here
is a more accurate method of dividing the liver parenchyma along the intersubsegmental and intersegmental demarcation to facilitate more precise anatomical s8vent resection .
written informed consent was obtained from the patient for publication of this case report and accompanying images .
a copy of the written consent is available for review by the editor - in - chief of this journal on request .
xiang , dong , and makuuchi had done the study conception and design and drafted the manuscript .
the acquisition of data was done by xiang , liu , dong , and sano .
 highlightsanatomical resection of s8vent is generally considered a demanding procedure.there are no accurate methods to identify the demarcation line inside the liver by far.we proposed a new method to divide the intersegmental plane by exposing and following the small tributaries of hepatic vein near the liver surface.this method is time - consuming , but it is an effective way to divide the intersegmental plane . 