INTRODUCTION
Despite advancement in hepatic interventions, potential vascular complications might occur in hepatobilliary surgery due to topographical alteration with structural variability of porta hepatis (PH) or hepatic hilum resulting high degree of morbidity or even death [24]. In order to address the complications posed by variant vasculo-biliary system, detailed knowledge about portal anatomy assumes critical. Variations of biliary tree and hepatic arterial anatomy are reported more frequent than portal venous variants. Careful handling of such circulatory and biliary dynamics of liver is important during live donor liver transplantation. As surgical view is limited to delineate hepatic anatomy, introduction of minimally invasive methods also remains challenging for surgeons. Moreover, presence of aberrant components might be an obstacle during operation if over-looked. Unanticipated anatomical variations may cause increase in graft ischaemia time with associated risk of post-operative graft dysfunction and emphasizes need of additional anastomosis [3, 5, 11, 23].
Unfortunately, magnetic resonance cholangiopancreatography (MRCP) study prior to any surgical intervention often fail to recognise all anomalies with certainty. Sensitivity of MRCP is only 74% in defining bile duct anomaly. Pre-treatment computed tomography failed to identify aberrant left hepatic artery in 31% cases [17, 27]. Therefore, accuracy and reliability of radiological analysis is still depending on anatomical references. Thus, present cadaveric study was attempted to revisit the vascular and biliary components of liver at PH updating the unusual configurations with an effort aimed at morphometry.
MATERIALS AND METHODS
One hundred and ten formalin fixed adult cadaveric livers of unknown age and sex without any pathological lesion were observed. Dissection of PH was done meticulously to observe number and position of portal vein (V), hepatic artery (A) and hepatic ducts (D). Specimens deviated from two divisions of portal vein, hepatic artery and hepatic duct were marked as variant and noted carefully with photographs. Different types of PH were categorised on the basis of morphology (number portal vein associated with number of hepatic artery and hepatic duct). For determination of morphometric data of PH and its exact position on inferior surface, following parameters were measured and mentioned in Figure 1 as follows:
- dimensions of PH:
- transverse diameter (‘a’ — from left to right end of PH),
- antero-posterior diameter (‘b’ — from anterior to posterior end of PH),
- circumference (‘c’ — along the margin of non-peritoneal area with thread and finally thread length was calculated);
- measurements of inferior surface of liver for position of PH:
- distance from left end of inferior surface of liver to left margin of PH — marked as “A”,
- distance from right end of inferior surface of liver to right margin of PH — marked as “B”,
- distance from postero-inferior border of liver to posterior margin of PH — marked as “C”,
- distance from inferior border of liver to anterior margin of PH — marked as “D”.
All measurements were done thrice at the level of portal vein before its division by vernier calliper, measuring scale and thread and average of three measurements were finally taken. Data were summarised by descriptive statistics and results were tabulated. All statistical calculations were performed using software SPSS version 23.
RESULTS
Standard morphology of PH was found in 20%. Rests 80% were variants in terms of numbers of either by portal vein or hepatic artery or hepatic duct or in combinations. Numeral normalcy was highest in hepatic artery followed by portal vein and hepatic duct. In all cases, arrangements of portal structures were ducts-arteries-veins from anterior to posterior. Detailed morphology of portal structures are depicted in Table 1 as follows:
- portal vein (V): conventional two divisions were present in 55.5% specimens. In the rest, vein was either single or three or four in numbers respectively;
- hepatic artery (A): usual presentation of two divisions was in 59.1% livers. In the rest, artery was variable with higher incidence in cases of single followed by three, four, five or six arteries respectively;
- hepatic duct (D): classical arrangement was in 51.8% cases. In the rest, PH represented with either single or with three ducts.
Portal structures, n (%) | Dimensions of porta hepatis [cm] | |||
Vein [V] | One | 41 (37.3) | Transverse diameter | |
Two | 61 (55.5) | Range | 2.0–4.0 | |
Three | 6 (5.5) | Mean ± SD | 2.93 ± 0.51 | |
Four | 2 (1.8) | 95% CI: LL/UL | 2.83/3.03 | |
Artery [A] | One | 21 (19.1) | Antero-posterior diameter | |
Two | 65 (59.1) | Range | 1.2–2.8 | |
Three | 14 (12.7) | Mean ± SD | 1.82 ± 0.38 | |
Four | 6 (5.5) | 95% CI: LL/UL | 1.75/1.89 | |
Five | 2 (1.8) | Circumference | ||
Six | 2 (1.8) | Range | 4.8–11.5 | |
Hepatic duct [D] | One | 51 (46.4) | Mean ± SD | 8.33 ± 1.63 |
Two | 57 (51.8) | 95% CI: LL/UL | 8.02/8.64 | |
Three | 2 (1.8) | |||
Figure 2 represents details about incidences of different morphological types of PH.
Sixteen types of PH were configured morphologically by numerical presence of structures in ascending order giving priority to vein, then artery and then duct. Thus, type 1 represented the minimum number of portal vein with minimum number of hepatic artery and duct; whereas type 16 represented maximum number of portal vein with variable number of hepatic arteries and ducts. Type 3 (1V2A2D) was found as highest incidence followed by type 9 (2V2A2D) and type 7 (2V1A1D), respectively. In total 13.6% cases (type 1, 4, 6, 14) all of the three portal structures (vein, artery and ducts) were atypical in number. Maximum number of structures were noted as 9 (2V6A1D) in type 13. Absence of structures was not witnessed by present study.
Morphometry
Table 1 represents details about dimensions.
- Dimensions of PH: Morphometric data as transverse diameter (a) larger than antero-posterior diameter (b) indicated outline of PH was slightly oval in transverse plane.
- Measurements for position of PH: In left–right plane, length of “A” varied from 5.4 to 10.5 cm, with mean ± standard deviation (SD): 7.55 ± 1.36, whereas “B” varied from 5.2 to 11.6 cm, with mean ± SD: 7.35 ± 1.49. In antero-posterior plane, “C” and “D” ranged from 2 cm to 3.7 cm with mean ± SD: 2.76 ± 0.49 and 3.2 cm to 6.7 cm with mean ± SD: 4.87 ± 0.99, respectively.
Schematic representation of morphometric measurements with position PH is shown in Figure 1.
Results of the present study with previous works have been compared in Tables 2 and 3 regarding morphology and morphometry of PH, respectively.
|
Present study [%] |
Sapna et al. [23] [%] |
Gupta et al. [12] [%] |
Neginhal and Kulkarni [20] [%] |
||
|
Vein |
One |
37.3 |
50.8 |
84 |
26 |
|
Two |
55.5 |
44.1 |
12 |
72 |
|
|
Three |
5.5 |
5.1 |
4 |
– |
|
|
Four |
1.8 |
– |
– |
2 |
|
|
Artery |
One |
19.1 |
20.3 |
4 |
8 |
|
Two |
59.1 |
55.9 |
32 |
56 |
|
|
Three |
12.7 |
15.3 |
36 |
26 |
|
|
Four |
5.5 |
8.5 |
25 |
8 |
|
|
Five |
1.8 |
– |
4 |
2 |
|
|
Six |
1.8 |
– |
– |
– |
|
|
Duct |
One |
46.4 |
79.7 |
76 |
100 |
|
Two |
51.8 |
16.9 |
20 |
– |
|
|
Three |
1.8 |
3.4 |
4 |
– |
|
|
Classical portal structures |
20% |
1.7% |
0% |
0% |
|
|
Highest combination of portal structures |
1V2A2D (23.6%) |
1V2A1D (25.4%) |
2A1V1D (32%) |
2V2A1D (36%) |
|
DISCUSSION
Highly variable vascular and biliary structures of the PH can impact clinical outcomes [3, 5, 9, 13]. In present study, arrangements of portal structures were traditional in all livers as previously reported [12, 20, 23], but their number varied. Classical structures were seen in 20% cases in present study which was either missing or in a very low percentage (01.7%) in previous studies [12, 20, 23]. Rather authors [12, 20, 23] reported different “non-traditional” portal anatomy in higher percentages. We also found varied combinations of portal structures as 16 types. Type 3 represented as highest number (23.6% cases) which is in conflict with previous studies. In our study, maximum number of veins was 4, arteries were 6 and ducts were 3, which is discrepant with others by numbers and percentages. Vascular injury along with biliary tract trauma has a mortality of 50–75% for portal vein and 40–80% for hepatic artery. The most difficult part of management encountered in abdominal trauma is associated with PH injuries which have high potential for immediate or late mortality [25]. Thus, knowledge of prevalence of morphological variation is quite often helpful for surgical planning. So, it is imperative that the clinician working on this area must be well versed with the detail of anatomical knowledge and its variations.
Table 2 presents comparison of portal structures between present and previous studies.
Knowledge about portal vein variation is important in identifying the location of liver lesion as portal vein along with hepatic veins are used as landmarks in determining segmental anatomy of liver [11]. Transhepatic embolisation of portal vein is gaining acceptance as a method to induce contralateral liver hypertrophy in patients with small future remnant livers [16]. Absence of the right portal vein occurs in 16.5% of patients and is associated with trifurcation of the main vein to right anterior, posterior segmental veins and left portal vein. Absence of left portal vein occurs in 1% of patients. Portal vein trifurcation is a relative contraindication to liver transplantation using living donors as multiple anastomoses needed for right lobe graft transplantation [18]. In another study, incidence of overall variations of portal vein was as high as 27.4%; main portal vein branching variation was 21.5% and right portal vein variation was 3.9% [14]. In 51% of the liver, portal vein did not bifurcate before entering the liver [23]. We also found the same in 37.3% cases. On the other hand, portal vein bifurcation and trifurcation were in 83.3% and 15.2% cases [4]. We too noted three veins in 5.5% liver. Though most abdominal venous variations are asymptomatic, awareness about existence of these variations decreases the complication rates in surgical procedures [5, 9].
While liver transplantation is often the best treatment option for end-stage acute or chronic hepatic disease, vascular complications following transplantation may hamper long-term success with an incidence rate as high as 9% [2, 7]. Furthermore donor selection is influence by arterial anatomy as liver grafts with multiple arteries are usually avoided [18]. Standard hepatic artery persists in 50–75% patients as previously reported [10, 13, 22, 26] but we found in 59.1% cases. Contrarily, variant anatomy has important implications in planning liver resections or placement of hepatic artery infusion catheters or pumps [10, 22, 26]. Multiple arteries (three-five) were reported in varied percentages by previous authors [12, 20, 23]. We also observed multiple arteries (maximum 6) in 21.8% liver.
Risk of bile duct variation is increased by presence of variant portal vein [26]. Normal biliary anatomy is thought to be present in 58% of the population [3, 19]. MRCP study shows an aberrant right hepatic duct in 4.8%, a right posterior hepatic duct in 5.7% and trifurcation of the duct in 0.8% of patients [8]. Kostov and Kobakov [15] found variation of hepatic ducts in 27.8% cases. Other authors reported the absence of right hepatic duct in 26% and absence of left hepatic duct in 2% of cases (Ohkubo et al., 2004 [21]). Single hepatic duct was observed in 100% cases by Neginhal and Kulkarni [20], 79.7% by Sapna et al. [23] and 76% cases by Gupta et al. [12]. However, our study found only 46.4% PH with single duct. Three ducts were seen in 3.4% and 4% by Sapna et al. [23] and Gupta et al. [12], respectively. Our study documented only 1.8% cases with 3 ducts. Accurate knowledge about such accessory hepatic ducts and also their position is important, especially during laparoscopic cholecystectomies, as incidence of bile duct injuries is as twice as high when compared with open cholecystectomies [6].
As majority of interventional procedures are made at the PH, which has a different location on the visceral surface of the liver, meticulous surgical technique and expertise are necessary to approach in a systematic way to obtain complete removal of tumour in peritoneal carcinomatosis. The centripetal approach from right side, left side and from anterior side is recommended to achieve a complete circumferential dissection [1]. Thus, a thorough assessment PH before initiation of dissection is needed. To describe the location of the PH in respect of the borders of the visceral surface we performed detailed morphometric measurements which have not been reported yet. Regarding dimensions of porta (antero-posterior diameter, transverse diameter and circumference), our study is very close to Neginhal and Kulkarni [20] report, but quite different from others [12, 23]. Table 3 presents comparison of morphometry of PH between previous and present study.
CONCLUSIONS
Literature on anatomical knowledge of PH has not proved to be adequate to reduce the incidence of iatrogenic complications. Thus our main focus was to study portal anatomy as it guides surgical decision-making and impacts on outcomes. Variable portal structures were noted in 80% cases in this study. High incidence of variations helped us to come into a conclusion on anatomical classification of 16 types of PH depending on the number of structural pattern which may contribute additional benefit particularly in the field of portal surgery. Present study also found maximum 6 arteries in PH which differ from previous studies. Till now no anatomical morphometric study regarding position of PH has been reported as per our knowledge, which needs to be highlighted to achieve best possible results in surgical techniques in this challenging area of the abdomen.
