Spatial Anatomical Variation of Segmental Hepatic Vasculature and Bile Duct Assessed by Integrated 3D CT Images for Right Lateral Sector Graft Liver Transplantation

In adult living donor liver transplantation (LDLT), a right lateral sector graft is newly introduced to overcome graft-size disparity of the right lobe graft or left lobe graft1-3). However, it is obvious that the procurement of right lateral sector has technical difficulties. High number of either unrecognized or extemporaneously handled biliary and vascular variants poses high risk both to the donor and the recipient4). Thus, understanding of the anatomical variations of sectoral and segmental bile duct, hepatic artery and portal vein of the donor and recipient are a prerequisite. Diagnostic imaging with multidetector computed tomography (MD-CT) allows accurate and noninvasive preoperative evaluation of the hepatobiliary anatomy5,6). And, threedimensional (3D) representation of anatomic structures is thought to improve understanding of complex spatial interactions7,8). We investigate anatomical variations of the segmental portal vein, artery and bile duct for the right lateral sector, including not only variant of each structures but also 3D relationship, based on the integrated 3D images, for guideline of safe right lateral sector graft transplantation.


Imaging technique
All dynamic CT studies were performed with MD-CT (Asteon multi ver. 1.5 Toshiba, Tokyo or LightSpeed Plus, GE Yokogawa, Tokyo). Patients received 100 ml of iopamidol with an iodine concentration of 370 mg/ml (Iopamiron 370; Nihon Schering, Osaka, Japan) as intravenous contrast for vascular imaging. The contrast medium was injected at a rate of 4 ml/sec. with an automatic power injector. Three or four phase scanning was performed with a single breath-hold helical technique at 3 mm collimation, 3.5 helical pitch and 0.75 second gantry rotation speed. Data from the artery dominant phase and the portal vein dominant phase were used to reconstruct the 3 D images. For biliary imaging, in 38 cases, CT scan was acquired 30 minutes after intravenous infusion of 100ml of biliary contrast agent (Meglumine isotraxate, Biliscopin; Shering, Berlin, germany) at a rate of 0.1ml/sec (DIC-CT). In all 38 cases, DIC-CT and dynamic CT scan were performed on different days because of the possible accelerated adverse effects of the vascular and the biliary cotarst media. Each scan was performed with the same focus of view. In 14 cases having percutaneous transhepatic biliary drainage (PTBD) tube, biliary enhanced CT was performed after administering 3-15 ml of 6 % biliary contrast agent (Biliscopin) through the PTBD tube (PTBD-CT). The adequate volume of contrast agent was determined by the previously performed PTBD cholangiography. MDCT cholangiography was performed by intravenous injection of a biliary contrast agent in 38 cases, and by injection from percutaneous biliary drainage tube in 14.

Image interpretation
Analysis of the image data was performed based on source images and 3D postprocessing images on commercially available workstations (Intage rvse, KGT, Tokyo and VertualPlace, AZE, Osaka). 3D reconstruction of the hepatic vasculature was made using a volume rendering algorithm. The volume rendered images were obtained in projections selected to depict the course of hepatic vasculature best. The resulting 3D images of the hepatic artery, portal vein and the bile duct rendered for each step of the artery dominant phase, portal vein dominant phase and the DIC-CT/PTBD-CT respectively were carefully reviewed and compared with the axial source images to ensure that no important structure was inadvertently deleted from the 3D images. 3D images of the hepatic artery, portal vein and the bile duct (Fig 1-A, Fig 1-B, Fig 1-C) which were adjusted to position each other focusing at the hepatic hilum on 2D axillary, sagital and coronary imaging sequences, were further integrated into a single image (Fig 1-D).

Diagnostic examination
In 52 of the 66 evaluated patients, the MD-CT studies were considered as diagnostic. The study was not diagnostic in the remaining 14 patients because of the poor timing of the contrast and image acquisition. 5 patients had poor arterial phase images, 13 had poor biliary images and 4 had both. Portal imaging was satisfactory in all patients. The advantages of MD-CT are mainly faster capability, improved temporal resolusion, improved spatial resolusion and increased effectiveness of the intravascular contrast agent. Reliability of the 3D MD-CT on the anatomical evaluation has been reported in several articles 5,6,9,10) . However, a problem is that 3D reconstruction imaging does not protect www.intechopen.com

Anatomical variant of portal veins
Ramification pattern of the right portal vein was defined into 5 types according to Nakamura's classification 11) (Figure 2). It is reported that ramification of the portal vein has a few anomalies compared with the bile duct and the artery 6) . Nevertheless, as to the right lateral portal vein (RLP), the single portal vein cases were only 30 cases, 57.7% and others had dual RLPs with (10 cases, 19.2%) or without (12, 23.1%) a common ostia at origin (Fig. 3).

Anatomical variant of biliary system
The pattern of branching of the biliary system in the right lobe is classified into 7, based on tributary from the right lateral sector ( Figure 4). 49 cases have single right lateral duct (RLD), and 3 have dual RLDs. Pattern I is normal anatomy in which RLD and the right  paramedian duct (RPMD) join to form the right hepatic duct which further joins the left hepatic duct to form the common hepatic duct. Pattern II is trifurcation of RL, RPMD and the left hepatic duct. In Pattern III, RLD joins the left hepatic duct. Pattern IV is the joining of RLD to the common hepatic duct. Pattern V, VI and VII are dual RLDs. Pattern V is dual RLD insertion into RPMD independently. In Pattern VI, there are two right hepatic ducts each formed by the joining of separate RPMD and RLD. Pattern VII is multiple RLDs and RPMDs. Incidence of each type in our series were Pattern I: 33 patients, 63.5%, Pattern II: 8, 15.4%, Pattern III: 5, 9.6%, Pattern IV: 3, 5.8%, Pattern V: 1, 1.9%, Pattern VI: 1, 1.9% and Pattern VII: 1, 1.9%. I) normal anatomy: 33 cases, 63.5%, II) trifurcation: 8 cases, 15.4%, III) RLD joins the left hepatic duct: 5 cases, 9.6%, IV) RLD joins the common hepatic duct: 3 cases, 5.8%, V) dual RLDs insert to RPMD independently: 1 case, 1.9%, VI) two right hepatic ducts each is formed by the joining of separate RPMD and RLD: 1 case, 1.9%, VII) multiple RLDs and RPMDs: 1 case, 1.9% *RPMD: right paramedian duct, RLD: right lateral duct, LHD: left hepatic duct

Anatomical variant of arteries
The branching pattern of the right lateral artery (RLA) is demonstrated in Figure 5. The single RLA was observed in 38 patients (73.1%) and dual RLAs in 14 (26.9%). A single RLA arising from the right hepatic artery was seen in 33 patients. RLA was originating from a replaced right hepatic artery from the superior mesenteric artery in 3 patients and from the gastroduodenal artery in one patient. RLA arising from the middle hepatic artery as an accessory artery was seen in another patient (Fig.5-d). Among patients with dual RLAs, in 9, arteries were originating independently from the right hepatic artery (Fig.5-e). In 4 patients, dual arteries were taking off independently from the replaced right hepatic artery from the superior mesenteric artery (Fig.5-f). Combined supply from a right lateral branch of the right hepatic artery and a branch of the gastroduodenal artery was also seen in another patient (Fig5-g).

3D relationship of the artery, bile duct and portal vein for right lateral sector
3 D relationship of the artery and bile duct to the right lateral sector with reference to the portal vein branches were studied. We defined the right lateral bile duct/artery which run dorsally and superiorly to RMPV as a 'north-turning' duct/artery and the bile duct/artery which run ventrally and inferiorly to the right portal vein and RMPV was defined as a 'south-turning' duct/artery 12) (Fig 6). In 49 patients with single RLD, 44 had the 'northturning' duct and 5 had the 'south-turning' duct. In 3 patients with multiple RLDs, one had both of 'south-turning' variety and the other two showed a combination of 'north-turning' and 'south-turning' ducts. Among 38 cases of single RLA, 8 had 'north-turning' artery and 30 had 'south-turning' artery. Out of 14 dual RLAs cases, in 6, a combination of 'northturning' and 'south-turning' arteries were observed. In the remaining 8 cases, all demonstrated 'south turning' arteries. In 27 patients of the single artery-bile duct-portal vein for the right lateral sector, the combination of "south-turning" artery and "north turning" bile duct was the most frequent pattern (22 cases) (Fig. 7). In all of them, the artery was running cranial or ventral to the bile duct and the portal vein at the sectional plane of origin of RLPV. The bile duct was sited cranial to the portal vein in 20 cases and dorsal in 2. The "south-turning" artery -"southturning" bile duct combination was observed in 3 cases and the "north-turning" artery -"south-turning" bile duct combination in two. Among these patients with these two patterns, 4 had the artery sited dorsally or cranially to the bile duct.

Application for right lateral sector transplantation
Although reconstruction of multiple portal veins and bile ducts has been challenging in LDLT, it is recently reported that multiple branches can be reconstructed safely using technical modifications in the right lobe or left lobe graft transplantation. Kyoto team reported that dual portal branches can be reconstructed safely with or without interposed venous graft 11) . They also described that all the biliary variants were successfully reconstructed with an acceptable complication rate, those are 9.3% bile leaks and 8.5% of a) "south-turning" artery and "north-turning" bile duct; both artery and bile duct run through the cranial side of RLP: 13 cases, 48.1%, artery runs through the ventral side with bile duct running through cranial side: 7 cases, 25.9%, and with bile duct running through the dorsal side: 2 cases, 7.4% b) "south-turning" artery runs through the cranial side with "south-turning" bile duct running through the ventral side: 2 cases (7.4%), and with bile duct running through the dorsal side: 1 case, 3.7% c) "north-turning" artery runs through the cranial with "north-turning" bile duct running through the cranial side: 2 cases, 7.4% *RLA: right lateral artery, RLD: right lateral duct, RLP: right lateral portal vein stenosis, in grafts with multiple biliary orifices. However, the branches of portal vein and bile duct for right lateral sector are smaller and its variants are more complicated. In dual duct cases especially when one duct runs dorsally to RLPV and other ventrally, reconstruction of dual ducts partitioned by the portal vein should be unacceptably difficult. We observed 2 cases with this anomaly. Even in the cases of single RLD, 3 cases had RLD run dorsal side of the RLPV. This anomaly is also difficult to be reconstructed because duct reconstruction should be interfered by the ventrally located RLPV.
This study revealed 14 cases, 26.9%, had dual RLA. The branch or branches for the right lateral sector are thinner and shorter than those of the right lobe graft or left lobe graft. Reconstruction of all dual arteries may be difficult in right lateral sector transplant. How to reconstruct multiple graft arteries remains controversial. Some institution recommended that livers with aberrant arteries should not to be used because these graft require multiple arterial reconstructions with high incidence of postoperative arterial thrombosis [13][14][15] . On the other hand, Ikegami et al. 16) recommended to reconstruct only thickest artery if intraoperative doppler shows pulsatile arterial flow and arterial signal in the corresponding segment of the non-anastomosed arteries. Even though, preoperative precise identification of the arterial variants by imaging and the accurate assessment of the feasibility are essential components of a successful right lateral graft LDLT.

Conclusion
In 9-18% of potential donors, the right lateral sector has volumetric advantage compared to the left lobe 2,3) . However, anomalies of the hepatic vasculature cause further limitation for the feasibility of transplantation. In our study, cases having single portal vein, single artery and single bile duct are only 27 among 52 (Fig.8). Therefore, to increase safe right lateral sector LDLT and to overcome donor shortage, accurate preoperative anatomical evaluation and excellent surgical technique coping with the particular anatomical variants are required. Anatomical understanding based on the 2D images is not sufficient 8) . The understanding of the 3D vascular and biliary anatomy will contribute to a better definition of the anatomical contraindications for transplantation, and to achieve successful right lateral sector LDLT. Computed Tomography (CT), and in particular multi-detector-row computed tomography (MDCT), is a powerful non-invasive imaging tool with a number of advantages over the others non-invasive imaging techniques. CT has evolved into an indispensable imaging method in clinical routine. It was the first method to non-invasively acquire images of the inside of the human body that were not biased by superimposition of distinct anatomical structures. The first generation of CT scanners developed in the 1970s and numerous innovations have improved the utility and application field of the CT, such as the introduction of helical systems that allowed the development of the "volumetric CT" concept. In this book we want to explore the applications of CT from medical imaging to other fields like physics, archeology and computer aided diagnosis. Recently interesting technical, anthropomorphic, forensic and archeological as well as paleontological applications of computed tomography have been developed. These applications further strengthen the method as a generic diagnostic tool for non-destructive material testing and three-dimensional visualization beyond its medical use.