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A novel anatomic variation of the intrahepatic biliary tree in live liver donor surgery: A case report

Highlights • We presented a novel anatomic variation of intrahepatic biliary tree, which had never been reported.• The computerized overlay visualization of MRCP and 3-D CT helped biliary anatomical understanding for operation planning.• Precise preoperative evaluation helped safe living donor surgery and living donor liver transplantation.


Introduction
With the many reports of bile duct anatomic variation, preoperative imaging evaluation of the biliary system is becoming commonplace. Such evaluation-e.g., endoscopic retrograde cholangiography or magnetic resonance cholangiopancreatography (MRCP)-is extremely important to avoid biliary injury during hepatobiliary surgery and postoperative biliary complications.
The present report describes a novel anatomic variation in the biliary tree of a live-liver donor. Precise image analysis helped accomplish successful donor hepatectomy and implantation in the recipient.
This case report has been reported in line with the SCARE 2020 criteria [1]. * Corresponding author.

Presentation of case
A 52-year-old healthy woman, who had no medical history, was admitted to our hospital as a live-liver donor for her husband. She underwent dynamic computed tomography (CT) and MRCP as part of the standard live-liver donor evaluation of the liver and biliary system. Dynamic CT scan showed normal hepatic vascular anatomy of both extrahepatic and intrahepatic tributaries. Based on the estimated liver volume, a right lobe graft was deemed preferable. The bile duct evaluation by MRCP, however, showed a previously unknown variation. That is, the left-side bile ducts joined the right-side bile duct separately. Segment 2 of the bile duct (B2) independently drained into the posterior branch, forming a common channel (B2+posterior), before joining the anterior branch. Finally, after addition of the anterior branch, bile duct segments 3 and 4 (B3+4) drained into the conglomerate B2+posterior+anterior common channel to form the common hepatic duct (Fig. 1A). The computerized overlay visualization of MRCP and three-dimensional CT vascular images helped to clarify this anatomic variation (Fig. 1B).   The donor then successfully donated her right lobe graft, with intraoperative cholangiography confirming the preoperative findings ( Fig. 2A). That is, her right lobe graft had two bile duct orifices: a posterior branch and an anterior branch. Most importantly, the preoperative imaging revealed the anatomic variation, allowing us to avoid surgical missteps that would have injured the donor's remnant bile ducts of B2 and B3+4 into the common hepatic duct (Fig. 2B). The donor was discharged 14 days after her liver donation surgery without complications.

Discussion
The anatomic biliary tree variations were reported to be found in approximately 30%-60% [2,3], and until now, numerous numbers of rare anatomic variations of the biliary tree have been reported [4][5][6][7][8]. Therefore, precise preoperative evaluation of the biliary tree anatomy is extremely important to avoid intraoperative and postoperative complications associated with hepatobiliary surgery, including live-liver donor surgery.
We have searched and found no other reports of the variation pattern seen in our case. Iida et al. [9] reported a somewhat similar variation, although in that report segment B2 joined the anterior branch first, followed by the B2+anterior common channel and finally the posterior branch. Also in that case, B3 separately drained into this B2+anterior+posterior bile duct to form a common hepatic duct. The variation in our case differed from the one they described. In our case, bile ducts in the dorsal part of the liver (B2 and posterior) joined first, followed by bile ducts in the ventral part of the liver (anterior and B3+4), draining into the dorsal common channel.
The computerized overlay visualization of MRCP and threedimensional CT provided a clear anatomic picture that allowed us to devise a precise operative strategy for live-liver donation in terms of the anatomic relation between the vascular and biliary structures.

Conclusion
We presented a hitherto unknown anatomic variation of the biliary tree. Our case showed that precise evaluation helps with surgical planning and performing a safe operation even in the presence of such a challenging bile duct anatomic variation.

Declaration of competing interest
All authors declare no conflict of interest.

Funding
All authors have no funding of research.