Abstract          Knowledge of surgical anatomy of liver and its associated variations is prerequisite in liver transplantation surgeries. In the right lobe transplantation, the hepatectomy line passes approximately 1 cm to the right side of the middle hepatic vein as a standard procedure. In surgery after transplantation of liver, venous reconstruction-anastomosis is done. Variations in the drainage pattern of hepatic veins have been reported from time to time. Awareness of associated anatomical variations is important for avoidance of potential surgical complications. We conducted a retrospective multi-slice spiral CT study of hepatic veins, whereby, we studied 100 abdominal CT scans which were reported as normal. We studied the length and the number of branches of hepatic veins and measured the distance of their peripheral-most branch from the nearest hepatic surface. We also studied if any accessory hepatic vein was present. We observed that right hepatic vein was longest (mean length-131.26mm) hepatic vein followed by middle (mean length-122.62mm) and last of all, the left (mean length- 93.15mm) hepatic vein. Most of the right (46%) and middle (45%) hepatic veins were visualized up to third order while most of the left (42%) hepatic veins were having less branches and were visualized up to second order. Most of the right (45) and left (49) hepatic veins were 10-15mm from the hepatic surface while most of the middle hepatic vein wasin the range of 15-20mm. We found Accessory hepatic veins in 18% of cases. Hence it is necessary to evaluate hepatic venous architecture preoperatively in surgeries like liver transplantation and hepatectomy.
Key Words: Accessory hepatic vein, hepatic veins, LDLT, multi-slice spiral CT scan.

INTRODUCTION
Living Donor Liver Transplantation (LDLT) is an important surgical option for the patients of the end stage liver disease as cadaveric livers are less available. Living-donor liver transplantation requires 2 operations: first -a partial hepatectomy performed on the donor; and second - hepatectomy of recipients own liver with orthotropic liver transplantation. In LDLT, plane of cleavage passes parallel to the middle hepatic vein. For that reason, it should be known which important vascular structures are present along the hepatectomy plane. When the veins are clamped without prior knowledge of these variations, ischemic necrosis can occur in the segments drained by these veins and this may lead to graft failure in the recipient.1 Accessory hepatic veins are occasionally present. Ipnjury to these veins during surgery can result in hemorrhage. This may cause acute necrosis of segments supplied by them.2,3,4 In transplantation surgery, it is necessary to know the angio-architecture of the donor and the recipient, which will help in choosing the right therapeutic option and in preventing post-operative complications. Nazil Erbay5 et al.(2002), Hribernik M6 et al. (2003) and others had studied the presence of accessory hepatic veins. Yuya Onodera7 in 2004, studied the distance of peripheral-most venous branch of minor inferior hepatic veins draining the lower portion of liver. However a thorough search and review of literature revealed that none of the past studies studied the length, branch order of the major hepatic veins and measured the distance of their peripheral most branches from the nearest hepatic surface. Present study is multi-slice spiral CT study of venous drainage of liver.
MATERIALS AND METHOD
Study Site: Department of Anatomy and Department of Radio-diagnosis of a tertiary health care center. We conducted a retrospective study of multi-slice spiral CT scans of venous drainage of liver whereby we studied the venous architecture of 100 normal livers after injecting an iodinated contrast material intravenously, over a period of past 18 months. CT scans with poor visualization of the venous architecture and Cases which had been operated for hepatic resection or had undergone any other operative procedure in the region of liver were excluded from the study.
Method
We studied 100 CT scans of liver which were taken on a Philips brilliance 64 slice spiral CT after intravenous administration of 100-120 ml of non-ionic contrast agent Iohexol 350 at a flow rate of 5 ml/s. We used the Terrarecon software, installed in the computer for the measurements. We studied the CT scans in axial, coronal, sagittal and oblique planes. The frames were freezed along the long and short axis of the hepatic veins, for maximum visualization and then the measurements were made. We took an average of 3 readings to minimize the errors, and got them confirmed by a Radiologist. We studied the following parameters
Length of major hepatic veins: We measured the length of the major hepatic veins from the point of their confluence into IVC up to where their diameter reduced to 1mm (fig.1).


Figure 1: The length of Right Hepatic Vein

Distance of peripheral-most venous branch of hepatic vein from the nearest hepatic surface: Peripheral-most venous branch (PMVB) of hepatic vein is the one having diameter of 1mm. We measured the distance of such peripheral-most venous branch (PMVB) of each major hepatic vein from the nearest liver surface. (fig2,3)

Figure 2: Distance of PMVB of RHV from hepatic surface(RHV- Right hepatic vein, PMVB-Peripheral-most venous branch)

Figure 3: The distance of PMVB of MHV from hepatic surface (MHV-Middle hepatic vein, PMVB-Peripheral-most venous branch)

Branch order of hepatic veins: Branch order of a hepatic vein means number of times it branches. We counted the branch order of each major hepatic vein.
Presence or absence of Accessory veins: In addition to right, middle and left hepatic vein, any other vein draining into IVC was considered as accessory hepatic vein. We noted the presence of such hepatic veins.

OBSERVATION AND RESULTS

Length of major hepatic veins

Table 1: The descriptive statistics of the length of Hepatic Veins

(RHV-Right hepatic vein, MHV-Middle hepatic vein, LHV-Left hepatic vein). The right hepatic vein was the longest in 76% cases, maximum length being -190 mm. In maximum number of cases – the mean length of RHV was - 127mm Most of the right (66) and middle (77) hepatic veins were between 100-150mm long, while the left hepatic veins (59) were shorter and below 100 mm.
Distance of peripheral- most venous branch of hepatic veins from the nearest hepatic surface is shown in table no 2
Table 2: Distance of Peripheral-Most Venous Branch (PMVB) of Hepatic veins from the nearest hepatic surface in different groups

We observed that, the distance of PMVB of most of the right (45) and left (49) hepatic veins was 10-15mm from the nearest hepatic surface while most of the middle hepatic veins (30) were little more far (15-20mm) from the hepatic surface.
Branch order of hepatic veins counted is shown in table no 3

Table 3: Branch order of Hepatic Veins

We observed most of the right (46) and middle (45) hepatic veins up tothird order while most of the left hepatic veins (42) were having less branches and were traced up to second order.
Co-relation of the distance of PMVB of hepatic veins from the nearest hepatic surface with their branch order –(PMVB – Peripheral-most venous branch)
When Spearman’s co- relation was applied to the distances of Peripheral-Most Venous Branches of major hepatic veins with their branch order, it showed negative co-relation in all the three major hepatic veins. The co-relation was significant for all the three hepatic veins. Negative co-relation means as branch order of hepatic veins increases the distance of peripheral-most venous branch of hepatic vein from the nearest hepatic surface decreases.

Table 4: Significant negative co-relation between distances of Peripheral-Most Venous Branch of Right Hepatic Vein with branch order

(RHV-Right Hepatic Vein, PMVB- Peripheral-Most Venous Branch)

From the above table, there is negative co-relation between branch order of Right hepatic vein and distance of its peripheral most venous branch from the hepatic surface. As p value is 0.001 which is less than 0.05, the negative co-relation is significant. Likewise we also found significant negative co-relation between the distances of Peripheral-most venous branches of the middle and left hepatic veins with their branch order.
Presence of accessory vein
The transplantation surgeon must know the presence of accessory hepatic vein before surgery. Hence we studied the presence and location of accessory hepatic veins in the present study. We observed accessory veins in only 18% of cases. Among that 4 were Inferior Right Hepatic Veins (IRHV) and remaining were right middle accessory veins.

DISCUSSION
A thorough search and review of literature revealed that none of the past studies studied the length of the major hepatic veins. However, in Live Donor Liver Transplantation (LDLT), for right lobe graft, hepatic resection is carried out in a plane parallel to the middle hepatic vein. So, depending upon the type of graft, the plane of resection varies according to the length and branching pattern of major hepatic veins. Congestion of even a thin branch of major hepatic veins can lead to major post-operative hemorrhage. Therefore information regarding the length and branch order of major hepatic veins is important and can be used by surgeons in different hepatobiliary surgeries especially in liver transplantation.  Keeping in mind this aspect of surgery, we measured the length of the hepatic veins from the point of joining the IVC to the diameter of 1 mm. We found the Right hepatic vein to be longest (mean-131.26±26.45 mm, range-100 to 150 mm) followed by Middle hepatic vein (mean-122.62±20.38 mm, range- 75.5 to 172 mm). The left hepatic vein was shortest (mean-93.15± 18.97mm, range 46 to 130 mm). Yuya Onodera7 in 2004, studied the distance of peripheral-most venous branch of minor inferior hepatic veins draining the lower portion of liver. However studies with distance of peripheral-most venous branch of major hepatic veins have not been found in the literature search. Ours is the only study with the distance of peripheral-most venous branch of major hepatic veins. The importance of the distance of peripheral-most venous branch of hepatic veins lies in reconstruction anastomosis in liver transplantation. Hence this parameter was included in the present study. We found that in70% of cases, PMVB of right hepatic vein was within 15 mm from the nearest hepatic surface. In middle hepatic vein, 82% of cases were within 20 mm while for left hepatic vein 79% were within 15 mm from hepatic surface. While taking the plane of cleavage accidental injury of accessory vein can cause post-operative hemorrhage and graft failure. Hence the knowledge of presence of accessory vein is important and thus included in our study. 18 % of cases showed the presence of accessory hepatic vein. Out of which four were inferior right hepatic veins (IRHV) and the rest were right middle accessory veins.

Table 5: Presence of Accessory hepatic veins in different studies

The findings of the present study are close to the findings of Mohamed R Elkholay10 (2013), Fang CH9 (2012) and Hribernik M6 (2003) who found 20%, 21% and 27% of accessory hepatic veins. Among all accessory veins, four were inferior hepatic vein.

CONCLUSION
In present study, we found variations in the length and the distances of peripheral- most venous branch of different hepatic veins from the nearest hepatic surface. The knowledge of length is important in deciding the plane of cleavage in hepatic resection while the distance of peripheral most branches is very important for hepatic venous reconstruction anastomosis in the transplantation surgery. Branch order of hepatic veins also varies from first order to fifth order. Accessory hepatic veins can be present which can alter the surgical approach. So in liver transplantation, pre-operative evaluation of hepatic venous architecture is necessary to reduce post- operative complications like hemorrhage and to prevent graft failure.

REFERENCES