Features of morphometric parameters of vessels in the human portal venous system identified by multislice computed tomography

The aim of this study was to identify the morphometric features of the human portal venous system by means of multislice computed tomography (MSCT). Materials and methods. A contrast X-ray study of the portal vein was carried out in 53 men who were treated in the surgical departments of the Krasnoyarsk Regional Hospital No. 1. The average age of the patients was 54.9 ± 1.7 years (36–71 years). Measurements were performed on 3D models of the vascular bed in the portal venous system (GE Advantage Workstation and Siemens singo.via workstations). Branching patterns, length, diameter, angle of the portal vein formation relative to the midline of the human body, and angles of formation of the vessels forming the portal vein in the frontal plane were evaluated. Results. Variations in the morphometric parameters of the intrahepatic vessels of the portal vein are obvious, although the branching patterns are not diverse and are reduced to one type – the magistral pattern (according to V.N. Shevkunenko). The veins that form the portal vein are represented by three systems, each of which has a stem and tributaries that differ in branching patterns and other morphological characteristics. Conclusion. The findings of the study made it possible to supplement the scientific materials regarding branching patterns and morphological characteristics of the portal vein and its tributaries as well as to use the morphometric characteristics of the superior and inferior mesenteric and splenic veins to resolve the issues of surgical intervention on the abdominal organs.


INTRODUCTION
Variability of the human portal venous system is beyond doubt [1][2][3][4][5]. Features of interposition, branching of veins included in this system, and its stereometric and linear characteristics define the development, course, and methods of surgical intervention for several surgical diseases, which eventually determines the outcome of surgical pathology [6][7][8]. According to leading gastrointestinal surgeons, enhancement of diagnosis of the structural features in the portal venous system will allow to answer many questions about the therapeutic and diagnostic strategy in the preoperative period [9][10][11][12].
Radiographic testing of vessels, organs, and entire systems in various areas of medical practice shows good diagnostic results [13,14]. A study carried out on a stationary X-ray machine in order to identify the features of rectal vessels of the portal venous system proved high information capacity of the method and allowed to find out postmortem characteristics, such as morphometry, spatial location, and vein branching [15][16][17][18].
Variant anatomy of major vessels of the portal venous system has been studied by a number of authors [19][20][21][22]. In 2018, I.V. Gaivoronsky et al. presented the main results characterizing variants of portal vein trunk formation and quantitative measurements of the vein length, diameter, and roots, showing a wide range of morphometric characteristics. The results obtained by multislice computed tomography (MSCT) of the abdominal cavity were defined as markers that allowed for planning an optimal surgical strategy and reducing postoperative complications on the part of the mesenteric and portal vein system in acute extensive portal vein or superior mesenteric vein thrombosis [6].
However, the study results can be applied only to operations on abdominal organs, in which the major vessels of the portal venous system are involved. According to A.V. Kolsanov et al. (2017), for a comprehensive study of the portal venous system of living people, it is eligible and competent to use contrast computed tomography with bolus tracking, which is one of the most precise methods to estimate morphometric features of vascular formations. Such a technique is the best for studying variant angioanatomy with visualization of vessels with a diameter of 1 mm and more, which allows to use this method not only in choosing the surgical strategy to treat portal hypertension, but also in all types of liver and pancreatic resection, liver transplantation etc. [9].
The aim of the study was to identify the morphological features of the human portal venous system.

MATERIALS AND METHODS
A contrast X-ray study was carried out on 53 men who were treated in the surgical departments of the Krasnoyarsk Regional Hospital No. 1. The inclusion criterion: patients with surgical diseases of the abdominal organs without circulatory disorders. The average age of the patients was 54.9 ± 1.7 years (36-71 years). All patients signed an informed consent to participate in the study. The study was approved by the local Ethics Committee at V.F. Voino-Yasenetsky The measurements were performed on 3D reconstructions of the vascular bed of the portal venous system (GE Advantage Workstation and Siemens singo.via working stations) on the basis of MSCT scans of the abdominal cavity using bolus contrasting with Ultravist-370 (Bayer Pharma AG, Germany). The volume of the used contrast medium was 100 ml, the injection rate was 4 ml per second, and the average radiation exposure was 11.3 mSv.
The contrast X-Ray study is applicable to the study of variants of portal venous system formation and their morphometric patterns, as well as branching patterns at different levels of structural organization using classifications by the T. Nakamura (type Aclassical anatomy, type B -portal trifurcation, type С -intra-; type D -extrahepatic branching of the anterior branch, and type Е -absence of the anterior branch) and V.N. Shevkunenko (magistral, mixed, and distributed patterns) [9,23,24].
The length, diameter, and angle of the portal vein formation relative to the midline of the human body as well as angles of formation of the vessels forming the portal vein in the frontal plane were estimated. The measurements were performed by building a central axis of the vessel with further measuring of its linear parameters [25].
Statistical processing was carried out using the SPSS Statistics 17.0 software package. The normality distribution was assessed using the Shapiro -Wilk test. Characteristics of variational series for quantitative features with nonparametric distribution and data with parametric distribution due to their small number were presented using measures of the central tendency (mean (M), median (Me), mode (Mo)) and measures of variance (standard deviation, range, interquartile range [Q 25 ; Q 75 ]). When comparing two independent samples of nonparametric data, the nonparametric Mann -Whitney U-test was used.

RESULTS AND DISCUSSION
3D models of CT scans of the portal venous system among all the examined men were characterized by constant presence of the portal vein, its right branch (with the anterior and posterior branches) and left branch (with the transverse and umbilical portion), as well as splenic, superior and inferior mesenteric veins, and more superior veins, forming the main tributaries. According to X-ray, the portal vein was a cylinder with the diameter of 14.5 [13.0; 14.5] mm, and the diameter at the place of its formation was similar to the diameter of its origin. The length ranged from 58 to 71 mm and the average length was about 63 mm. The portal vein was formed at the angle of 68 [46; 72]º relative to the midline of the human body, which proves the previously published data on the frequency of the angle (Fig. 1) [6]. The inferior mesenteric vein system contains fewer veins entering its bed compared with the superior mesenteric vein vasculature. The magistral branching pattern of the inferior mesenteric vein is found in 23% of cases, while in 77% of cases this vein is characterized by the mixed pattern (Fig. 3) [23]. In case of the mixed branching pattern, the inferior mesenteric vein enters the superior mesenteric vein between the right colic and jejunal veins. In most cases, the inferior mesenteric vein of the magistral branching pattern enters the splenic vein (Fig. 1) or is an independent tributary of the portal vein. Its diameter is significantly smaller than that of the superior mesenteric vein and reaches 4.5 [2.0; 6.5] mm. Although length values vary depending on the branching characteristics, they do not significantly differ from the values of this parameter for the superior mesenteric vein. The angle of formation, as in the case of inflow into the superior or splenic vein, ranges from 135 to 151º. Linear parameters and formation angles of the inferior mesenteric vein tributaries do not have statistically significant differences ( Table 2).  Unlike the superior and inferior mesenteric vein systems, the splenic vein always has the magistral branching pattern (Fig. 4). The splenic vein has medium diameter (7.5 [5.5; 8.5]  Radiographic testing of the portal venous system using MSCT with bolus tracking has shown high information capacity, which had been previously demonstrated by A.V. Kolsanov et al. [9].

Morphometric parameters of the portal vein roots found by X-ray, Me
Estimating the length, diameter, and formation angles of the portal vein and its tributaries, we came to the conclusion that modern diagnostic imaging techniques with the use of contrast agents should be used to study the portal venous system at various levels of its structural organization.

CONCLUSION
The current study provides quantitative landmarks for the major venous structures in the portal venous system. The research results made it possible to supplement scientific materials regarding the branching patterns and morphological parameters of the portal vein and its branches. The obtained data reflecting morphometric characteristics of the superior and inferior mesenteric veins as well as splenic vein prove variability of veins included in the v. portae system and a wide range of its structural anatomy and can be used to resolve the issues of surgical intervention on the abdominal organs. Variations typical of each venous system should be taken into account when choosing the strategy of managing patients with portal hypertension or at the preoperative stage.