Evaluation of Numerical and Positional Variations of the Hepatic Veins: A Cadaveric Study.

INTRODUCTION: Hepatic veins are the major linking vessels between systemic and portal circulation. Numerical and positional variation of the hepatic veins can play a significant role during surgical interventions on the liver.
MATERIALS AND METHODS: Gross anatomical study regarding the number and arrangement pattern of hepatic veins was undertaken on 88 adult livers which were stored in 10% formalin after the regular dissection classes. RESULT: Six livers (7%) were found to be drained only by major hepatic veins, whereas 82 out of 88 livers (93%) had accessory (minor) hepatic veins. The total number of persistent hepatic veins ranged from 2 to 10 with the highest prevalence of four hepatic veins (35.2%) followed by 5 (19.3%) and 6 (17%). The presence of three major veins was seen in 45 (51%) livers while 41 (47%) livers had two major hepatic veins. Remaining two livers (2%) showed the presence of four major hepatic veins. In 95% specimens, the minor hepatic veins entered the inferior vena cava below the level of entry of major veins. In 2.5% cases, their entry point was above the major veins and in 2.5% cases, the entry point was below major veins.
CONCLUSION: The data resulting from this study provides a clear idea about the number and drainage pattern of the hepatic veins into the liver. Knowledge of numerical and positional variations of hepatic veins could be useful in normal Doppler ultrasound hepatic vein flow velocities and their variation with respiration in healthy adults as comparable with the similar approach of superior vena cava.

INTRODUCTION

Hepatic veins are the intrahepatic vessels that traverse through the substance of liver. They are usually arranged in two groups; an upper group and a lower group. The upper group or main hepatic veins are usually two in number-right and left hepatic veins (LHVs). The third main hepatic vein is the middle hepatic vein (MHV). These veins drain blood from the liver into inferior vena cava. The MHV serves a useful landmark in radiological and ultrasonographic investigations as it lies usually in the sagittal plane and divides the liver into the right and left physiological (true) lobes.[1]

There are usually three main hepatic veins. However, there may be few accessory or minor hepatic veins which are smaller vessels. Thus, the number of hepatic veins is highly variable. The consequences of dysfunctional hepatic veins are often reflected in diseases and disorders associated with the liver. The severity of which depends on the number of hepatic veins that are affected. When the major hepatic veins are either fully or partially occluded, diminished blood flow from the liver to inferior vena cava is manifested which result in portal hypertension.[2]

Hepatic veins constitute a principal link between portal and systemic circulation. Their numerical and positional variations are therefore desirable to be familiar before performing any medical treatments and surgical procedures involving the liver. In the current study, we have made an attempt to document the numerical and positional variations of hepatic veins. We believe that this data can be useful to clinicians, surgeons, and radiologists who deal with the liver and its associated disorders.

MATERIALS AND METHODS

The present study involved a gross anatomical observation of number and position of hepatic veins at their entry point into the inferior vena cava. A total number of 88 isolated livers were obtained from formalin embalmed adult human cadavers of South Indian origin. Gender wise categorization of the livers was not possible since the livers in the store were obtained from various cadavers dissected in the past 15 years. These cadavers were donated to the institution for medical education and advancement. During dissection classes for medical students, the livers were removed carefully along with the sufficient segment of hepatic part of the inferior vena cava. Total number of major and minor hepatic veins opening into inferior vena cava was noted. The position of the minor hepatic vein in relation to the major hepatic veins at their entry point into the inferior vena cava was also observed and noted. Hepatic veins with lumen size measuring more than 1.5 cm were considered as major hepatic veins while remaining were categorized as minor hepatic veins. Sample photographs of livers with numerical and positional variations of hepatic veins were taken.

RESULTS

In the current study, 82 out of 88 (93%) livers were drained by major and minor hepatic veins while 6 livers (7%) were found to be drained by major hepatic veins only [Graph 1]. Total number of hepatic veins including both major and minor veins ranged from 2 to 10 in number with the predominant incidence of having 4 hepatic veins (35.2%). The next higher number of hepatic veins was attributed to 5 hepatic veins with the incidence of 19.3% followed by 3 hepatic veins with the incidence of 14.7% [Table 1 and Graph 2]. As a rare observation, one liver was found to be drained by two major hepatic veins only without any other accessory or minor hepatic veins [Figure 1].

Graph 1

Overall incidence of major and minor hepatic veins

Table 1

Profile of number of hepatic veins with their percentage of incidence

Total number of hepatic veins	Number of cases (n = 88)	Percentage
2	01	1.1%
3	13	14.7%
4	31	35.2%
5	17	19.3%
6	15	17%
7	07	7.9%
8	02	2.2%
9	01	1.1%
10	01	1.1%

Graph 2

Graphic representation of incidence of hepatic veins

Figure 1

Liver with 2 major (M) hepatic veins

Further, following descriptive profiles about major and minor hepatic veins were observed [Table 2]. Among 13 livers drained by 3 hepatic veins, 5 livers had all 3 major hepatic veins [Figure 2] while remaining 8 livers had 2 major and 1 minor hepatic veins.

Table 2

Detailed profile of major and minor hepatic veins

Total number of hepatic veins	Number of livers	Details on major /minor hepatic veins
2	01	Both are major veins
3	13	All 3 major (in 5 livers)
		2 major & 1 minor (in 8 livers)
4	31	2 major & 2 minor (in 19 livers)
		3major & 1 minor (in 12 livers)
5	17	2 major & 3 minor (in 5 livers)
		3major & 2 minor (in 12 livers)
6	15	3 major & 3 minor (in 10 livers)
		4major & 2 minor (in 1 liver)
		2major & 4 minor (in 4 livers)
7	07	4 major & 3 minor (in 1 liver)
		3major & 4 minor (in 5 livers)
		2major & 5 minor (in 1 liver)
8	02	2 major & 6 minor (in 1 liver)
		3 major & 5 minor (in 1 liver)
9	01	2 major & 7 minor (in 1 liver)
10	01	2 major & 8 minor (in 1 liver)

Figure 2

Liver with 3 major (M) hepatic veins

Of 31 livers with the presence of 4 hepatic veins, 19 livers were with 2 major, and 2 minor sets of hepatic veins [Figure 3]; remaining 12 livers had 3 major and 1 minor hepatic veins.

Figure 3

Liver with 4 hepatic veins (2 major [M] and 2 minor [m])

In the cases of 5 hepatic veins, out of 17 livers, 5 livers showed 2 major and 3 minor hepatic veins [Figure 4] and 12 livers had 3 major and 2 minor hepatic veins.

Figure 4

Liver with 5 hepatic veins (2 major [M] and 3 minor [m])

Among 15 livers with 6 hepatic veins, 10 livers had 3 major and 3 minor hepatic veins, while 4 livers had 2 major and 4 minor hepatic veins. Only one liver had 4 major and 2 minor hepatic veins [Figure 5].

Figure 5

Liver with 6 hepatic veins (4 major [M] and 2 minor [m])

Out of total 7 livers with 7 hepatic veins, 5 livers had 3 major and 4 minor hepatic veins, 1 each liver had combination of 4 major and 3 minor [Figure 6], and 2 major had and 5 minor hepatic veins. In a case of 2 livers with 8 hepatic veins, one each had a combination of 2 major with 6 minor hepatic veins [Figure 7] and 3 major with 5 minor hepatic veins.

Figure 6

Liver with 7 hepatic veins (4 major [M] and 3 minor [m])

Figure 7

Liver with 8 hepatic veins (2 major [M] and 6 minor [m])

One each liver had total number of 9 hepatic veins with 2 major and 7 minor [Figure 8] and 10 hepatic veins with the set of 2 major and 8 minor veins [Figure 9].

Figure 8

Liver with 9 hepatic veins (2 major [M] and 7 minor [m])

Figure 9

Liver with 10 hepatic veins (2 major [M] and 8 minor [m])

In a separate comprehensive profile on the presence of number of main hepatic veins, we observed prevailing incidence of the prevalence of 45 livers (51%) consisted of 3 main hepatic veins. The presence of 2 main hepatic veins was observed in 41 livers (47%) and 4 main hepatic veins in 2 livers (2%) [Table 3 and Graph 3].

Table 3

Profile of incidence of major hepatic veins

Number of major hepatic veins	Number of livers (n = 88)	Percentage of incidence
2	41	47%
3	45	51%
4	02	2%

Graph 3

Graphic representation of incidence pattern of major hepatic veins

Among the 82 livers with the persistence of minor hepatic veins, the entry point of the minor hepatic veins into the liver was positioned below major hepatic veins in 78 (95%) livers, while in two cases (2.5%) with 2 minor hepatic veins, one was found to be lying in between the major veins and another below them. In remaining 2 cases (2.5%) with 2 minor hepatic veins one was situated above and another below the major hepatic veins.

DISCUSSION

Precise understanding of hepatic vein morphology and their pattern of termination into inferior vena cava is imperative for the safe and successful liver surgery involving surgical resection of the liver, liver transplantation as well as in hepatic trauma.[3] These approaches require special attention on hepatic veins draining the liver segment. Maintaining sufficient hepatic venous drainage even after liver surgery is also essential to prevent postoperative complications resulting from the venous obstruction that frequently involves delayed hemorrhage, deranged liver function, and also bile leakage.[4] An adequate maintenance of hepatic venous drainage is also important as there is no adequate venovenous shunt between hepatic venous systems.[5] Therefore, it has been postulated that the severity of the symptoms and clinical presentations of liver-related complications often will have a direct correlation with the extent of the involvement of hepatic veins.[6]

Fersia and Dawson in the study on evaluation of variant hepatic veins observed the persistence of hepatic veins ranging from 4 to 15 in number. Among this, about 22.2% each of occurrence was attributed to 7 and 8 hepatic veins which were followed by 11.1% each for having 4 and 6 hepatic veins. This observation was comparatively very high compared to the present study except for livers with four hepatic veins. Nevertheless, in the same study, classical three main hepatic veins were observed in 50% of liver specimens while in remaining 50% of livers had only two main (right and left) hepatic veins.[2] This prevalence is almost in agreement to our study, as we noted an incidence of 3 hepatic veins in 51% of livers and that of 2 veins in 47% of livers. Remaining 2% of livers had 4 main veins.

Orguc et al., in the study on variant hepatic venous system reported the prevalence of 47% livers with accessory right inferior hepatic vein among the living liver donor candidates. Among which, 13% were multiple in number. Authors suggested that presence of accessory hepatic veins may not be contradictory for liver donation, but prior knowledge of such numerical variations helps in altering the surgical management.[7]

In the past, studies have been conducted on the drainage pattern of major hepatic veins. Chi-Hua et al. have reported the formation of a common trunk by MHV and LHV in 61% of cases, whereas remaining 39% cases had independent venous drainage of all three major hepatic veins. In the same study, 39% cases had remarkably smaller right hepatic vein (RHV) that was compensated by other veins such as a right inferior hepatic vein, an accessory RHV and/or MHV.[8]

Another similar study by magnetic resonance imaging technique reported the presence of 3 hepatic veins in only 20% of individuals with the existence of common trunk for LHV and MHV. Whereas 80% of subjects had nine accessory hepatic veins.[9] In the present study, the majority of livers had accessory/minor hepatic veins.

It has been stated that the partial occlusion of hepatic veins can be symptomless and might not often lead to severe clinical manifestations either due to portal venous backflow or spontaneous intrahepatic venovenous shunt mechanism.[610] However, complete or near complete occlusion of hepatic veins may be fatal as it could lead to variety of pathological conditions of liver such as veno-occlusive disease, Budd-Chiari syndrome, and congestive hepatomegaly.[11] Parenchymatous dissection during hepatectomy and segmental resection of the liver done in malignant cases require the ligation of main hepatic veins ensuring the maintenance of segmental venous drainage.[12]

Accessory hepatic veins are the smaller vessels of the liver, which ensure the effective venous drainage of the liver. At times, there may be variant accessory hepatic veins such as accessory RHVs, significant accessory hepatic veins, accessory suprahepatic veins, and large accessory hepaticveins.[13]

Marcos et al.,[14] have reported the presence of minor hepatic veins in 40% of livers; whereas about 5% of incidence of large accessory hepatic veins belonging to the inferior group has been reported by Taranikanti et al.,[13] However, in the present study as many as 93% of livers had the presence of accessory or minor hepatic veins irrespective of their number in total.

Much importance is also given to the pattern of openings of the hepatic veins in the management of hepatic trauma associated with hepatic vein avulsion and also in resection of the diseased part of the liver.[3] In this regard, Camargo et al. in 1996 came up with the classification criteria for the hepatic venous openings and according to them, the vena caval openings for the superior group of hepatic veins considered as large openings with the diameter of 1.5-2 cm, whereas for the accessory hepatic veins of the lower group will have medium opening with the diameter of 0.5-1.0 cm.[15] In the present study, among 82 livers with minor hepatic veins, 78 (95%) livers showed the position of minor veins inferior to major hepatic veins representing the inferior group of veins. Two livers (2.5%) with two minor veins, one was present in between two major veins and another one was below them. In two livers (2.5%), one each minor vein was situated above and below the major hepatic veins.

Study on pulsed wave Doppler ultrasound recordings of blood flow velocity in the superior vena cava and hepatic veins of the normal adults by Christopher et al. reported the hepatic vein tracings in the forward flow characteristics is similar to those from superior vena cava but with larger A wave and atrial V wave flow reversals.[16]

An adequate knowledge on the variable disposition of minor hepatic veins is utmost important before ligating the vessels during surgical procedures of the liver. Thorough inspection to ensure any minor hepatic veins sandwiching between the major hepatic veins is warranted to avoid iatrogenic injury which could result when they are left unnoticed.

CONCLUSION

Various anomalies in the pattern of venous drainage of the liver have been identified using imaging techniques. However, cadaveric studies on these veins are lacking. Prior knowledge of the presence of a variable number of hepatic veins and the variable position of minor hepatic veins in relation to major veins is of immense practical importance to the clinician and surgeon in an altered surgical management of the liver. It could also be useful in normal Doppler ultrasound hepatic vein flow velocity measures.

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Conflicts of interest

There are no conflicts of interest.