Figure 1 Diagrams of the variation of biliary anatomy as described by Couinaud11.
Figure 2 The typical pattern for hepatic ductal anatomy (type A). The right posterior duct (small arrow) fuses with the right anterior duct (large arrow) to form the right hepatic duct, and the common hepatic duct (curved arrow) is formed by fusion of the right hepatic duct and left hepatic duct (arrowhead).
Figure 3 Trifurcation (type B): emptying of the right posterior duct (large arrow), right anterior duct (small arrow), and left hepatic duct (arrowhead) into the common hepatic duct (curved arrow).
Figure 4 Type C1. The right anterior duct (thick arrow) drains into the common hepatic duct (curved arrow). A liver cyst (arrow head) is noted.
Figure 5 Type C2. Ectopic drainage right of the posterior duct (arrowhead) into the common bile duct (curved arrow). Small arrow= right anterior duct, large arrow= left hepatic duct.
Figure 6 Type D1. Ectopic drainage of the right posterior duct (arrowhead) into the left hepatic duct system (thick arrow). Small arrow= right anterior duct, curved arrow= common hepatic duct.
Figure 7 Type D2. Ectopic drainage of the right anterior duct (small arrow) into the left hepatic duct system (arrowhead). Thick arrow= right posterior duct, curved arrow = common bile duct.
Figure 8 Type E2. Absence of hepatic duct confluence
Figure 9 The accessory right posterior duct draining into right hepatic duct (other).
Discussion
Understanding of anatomical variation is critical during surgical procedures, especially when it comes to anatomic areas with high rates of variation, such as the hepatobiliary system.6,8
One study conducted by Choi et al.9 which consisted of 300 consecutive donors for liver transplantation who underwent intraoperative cholangiography, found that 63% of cases displayed typical intrahepatic bile duct anatomy. Atypical intrahepatic duct anatomy types were as follows: triple confluence in 10% (n=29), anomalous drainage of the RPD in to the LHD in 11 % (n=34), and anomalous drainage of the RPD into the CHD in 6% (n= 19) of cases.
A study conducted by Thungsuppawattanakit et al.2 in Thailand, which included 163 cases, found typical intrahepatic bile duct anatomy in 65 % of cases (n=106). Variations from this conventional pattern were seen in the remaining 57 patients, whith trifurcation in 17.2 %( n=28), anomalous drainage of the RPD into the CHD in 5.5% (n=9), and drainage of the RPD into the LHD in 9.2%(n=15).
In this study, we use the Couinaud classification system to classify the variations of biliary anatomy because of its greater applicability and simplicity compared to other classification systems. Deka et al.10 who compared six classification systems, found the system used by Ohkubo et al.13and the Couinaud classification to be the most applicable. The percentages of cases in which these classification systems were not applicable were 3.1% for the system used by Ohkubo et al. and 3.3% for the Couinaud system.
In our study, typical intrahepatic duct anatomy (type A) was found in 74.4 % of subjects, a higher prevalence than those found in other studies.
Couinaud classification B or trifurcation, the second most predominate type, was found in 8.8 % of subjects. This finding is consistent with those of other studies.2,9
In Couinaud type C the right sectoral ducts, or more commonly the anterior sectoral duct, may enter the common hepatic duct distal to the confluence. If this is not recognized it can be very dangerous, and is a common cause of injury during laparoscopic cholecystectomy.11 In this study, type C was found in 3.4 % (C1=0.3% and C2=3.1%) of cases.
In Couinaud type D, the right posterior sectoral duct (and rarely the right anterior sectoral duct), may cross to enter the intrahepatic duct portion of the left hepatic duct. Failure to recognize this prior to right or left hepatectomy can lead to significant post-operative problems, as ligation of these ducts will produce biliary cirrhosis of the segment corresponding to the ducts ligated.2 In this study, type D was observed in 7.5% (D1= 6.2% and D2=1.3 %) of cases.
Accessory hepatic ducts are observed in approximately 2% of patients. These may originate from and run along both the left and right ductal systems. They may present as solitary findings or in conjunction with aberrant bile ducts.3 In this study, we found accessory hepatic ducts in 5.4% of patients, which was higher than in the other studies. Although accessory ducts are a minor aspect of variation, they should not be overlooked in cases of liver transplantation or hepatic resection. Identification of accessory ducts is important if serious complications such as biloma or bile duct leakage are to be avoided. Because electrocautery may seal an accessory duct temporarily, even with careful inspection of the cut margin of the liver, an awareness of possible variation in an accessory duct is important.2
The Kappa agreement of MRCP readings was 0.431, which is considered to represent moderate agreement according to Landis and Koch12. In this study, the biggest discrepancies were found between type A (typical) and type B. This low Kappa may result from the low resolution and the volume average of MRCP, which may interfere the MRCP readings.
Our study was limited in that it was likely to have suffered from selection bias, as only patients suspected of having biliary disease were indicated for MRCP in the first place. In addition, there was no confirmation of biliary configuration from either cholangiography or surgery.
Conclusion
The typical intrahepatic duct, which is the simplest configuration in cases of hepatobiliary surgery,1,9 was the most commonly found anatomical type in our population. However, the use of non-invasive MRCP for evaluation of biliary disease and pre-operative planning is crucial.
References
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