Morphometry of the Portal Vein: Ultrasound Anatomy about 1000 Cases

Aim: The aim of this study is to determine from a series of 1000 cases the usual dimensions of the portal vein according to the medical ultrasound. Methodology: We realized a transverse study over 2 years (from January 2015 to December 2017). It concerned an ultrasound exploration of the portal vein. The studied population was healthy voluntary subjects visible without history of abdominal trauma and abdominal operating scar. Results: The average age was 39 years ± 12.16 with extremes of 19 years and 70 years. The decade of 21 - 29 years represented 46.2%. The transverse diameter of the portal vein in its origin varied between 8 and 10 mm in 57.9% of the cases. The average was 9.05 ± 2.82 mm with extremes of 5 and 16 mm. The transverse diameter of the portal vein in its ending varied between 8 and 10 mm in 56.9%. In 29.8% of the cases, the length of the portal vein was between 61 and 70 mm and in 8.8% between 81 and 100 mm. The average length was 58 ± 22.3 mm. Before its penetration in the liver, the portal vein divided into 2 branches in 967 cases (96.7%) and in 3 branches in 33 cases (3.3%). Conclusion: This original study shows the normal dimensions of the portal vein to Malian.


Introduction
The portal vein (PV) or the portal trunk carries blood from the diaphragmatic part of the digestive tract, the spleen and the pancreas. Its origin is situated behind the isthmus of the pancreas by the confluence of the superior mesenteric  [1]. The cystic and the left and right gastric veins are other tributaries of the portal vein [2]. In its route the PV is oblique at the top and forward. It ends by giving at the level of the hepatic hilum, right and left branches which move away by limiting an open very obtuse angle at the top. Branches win the corresponding extremity of the cross-functional furrow then sink into the liver. The PV establishes the later plan of the hepatic pedicle [1]. Therefore, in the surgery of the liver and the biliary ways, the PV constitutes an important anatomical mark, its dimensions are variously estimated by the authors [3] [4]. The average length of the trunk wears according to Rouvière is 100 mm and its diameter 15 mm. Castaing in 1999 found that the length of the PV varies between 80 and 100 and its diameter between 15 and 20 mm [2]. But the conditions and the exact siege of the dimensions are not specified by the authors except for Ongoïba [5].
Outside the ultrasound study realized by Ongoïba in 2003, we did not find other anatomo-ultrasound studies on the PV. To mitigate this deficit of search on the morphometry of the portal vein, we led this study with as objective to determine from a series of 1000 cases the usual dimensions of the PV according to the ultrasound.

Materials and Methods
We realized a transverse study over 2 years (between from January 2015 to De- The test meadow which allowed us to standardize the methodology concerned 10 subjects. Then the study concerned 1000 subjects.

Results
The average age subject was 39 ± 12.16 years with extremes of 19 and 70 years.

Highlighting of the Portal Vein and Its Branches
The frequency of the highlighting of the PV was represented in Table 2.
In 98% of the cases the transverse diameter of the portal vein was highlighted in its origin, while in its ending, the transverse diameter was highlighted in 98.5% of the cases, and at least 2 branches were seen in 100%.

Transverse Diameter of the Portal Vein in Its Origin
The transverse diameter of the PV in its origin varied between 8 and 10 mm in 57.9% of the cases. The average was 9.05 ± 2.82 mm with extremes of 5 and 16 mm ( Figure 1). Figure 2 shows the origin and trajectory of the portal vein.

Transverse Diameter of the Portal Vein in Its Ending
The transverse diameter of the PV in its ending varied between 8 and 10 mm in 56.9%. The average was 9.16 ± 2.58 mm with extremes of 6 and 16 mm ( Figure 3). Figure 4 shows the measurement of the transverse diameter of the vein leading to its termination.

Length of the Portal Vein
In 29.8% of the cases, the length of the portal vein was between 61 and 70 mm and in 8.8% between 81 and 100 mm. The average was 58 ± 22.3 mm ( Figure 5).

Number of Terminal Branches of the Portal Vein
Before its penetration in the liver, the portal vein divided into 2 branches in 967      (Figure 6). Table 3 shows the dimensions of the portal vein before and after 20 years. To the subjects from 11 to 20 years, the average of the transverse diameter of the portal vein in its origin was 8.9 ± 2 mm. This diameter was 9.6 ± 1.9 mm to the subjects of more than 20 years (p = 0.298). The difference was not significant. To the subjects from 11 to 20 years, the transverse diameter of the PV in its ending was 9.6 ± 2 mm (p = 0.567). The difference was not significant. Table 4 shows the dimensions of the PV according to the sex. To the male subjects, the average of the transverse diameter of the PV in its origin was 9.7 ± 1.9

Dimensions of the Portal Vein According to the Sex
mm. This average was 9.3 ± 2 mm to the female subjects (p = 0.411).
To the male subjects, the average transverse diameter of the portal vein in its ending was 9.4 ± 2.2 mm. This average to the female subjects was 9.6 ± 1.7    To the female subjects, this average was 57.7 ± 17.8 mm. The difference was statistically significant (p = 0.001).

Discussion
We measured in the ultrasound the transverse diameter of the PV in its origin and in its ending and its length.
We did not find significant difference between certain dimensions (transverse diameters, original and terminals) of the vein of the subjects of less than 20 years versus the subjects of more than 20 years. We did not either find statistically significant difference between certain dimensions (transverse diameters, original and terminals) of the PV of the male subjects versus the female subjects.
In the classic anatomical descriptions the number of subjects is very limited (1 -10) and in certain cases the studied number of subjects is not specified [2] [6] where from the difficulties of comparison between our results and those of the anatomical literature.
The length of the PV had been measured by various authors during anatomical dissections (Table 5). We found a single ultrasound study concerning the length of the portal vein.
Our results are little different from those of Delorme and Seymour [6]. The average reported by Rouvière is superior to ours. It could give some explanation by the fact that the conditions of measure are different: measure made by dissection and ultrasound measure.
The diameter of the PV is a more important parameter because it is one of important criteria to make the diagnosis of high pressure in the portal system.
According to certain authors, the normal diameter of the PV measured in hepatic hilum, should not exceed 12 in 15 mm [7]. The same authors considered that the caliber of the PV is decreasing in the sense of the flow portal [7]. In our sample, we found that the transverse diameters of the PV in its origin and in the ending were respectively 9.05 ± 2.82 mm and 9.16 ± 2.58 mm.
The decreasing caliber of the PV in the sense of the flow portal evoked by Weinreb [7] was not observed in our study.
In the constitution of the PV, intervene two big venous trunks: the spleno mesenteric trunk and the superior mesenteric vein. The place of convergence of A. Kanté et al. these two veins, that is the origin of the portal vein, can be dilated.
In the modal arrangement, the portal vein divides in two branches which penetrate into the liver. In our study this arrangement was observed in 96.7% of the cases. In 3.3% of the cases, the portal vein had three branches. We can consider this phenomenon an anatomical variation or a premature division of the portal vein.

Conclusion
This original study shows the normal dimensions of the portal vein in Malian. These measures can serve in the diagnosis of the portal hypertension.

Authorization of the Ethics Committee
The Ethics Committee of the Faculty of Medicine and Odontostomatologie gave us its agreement for the realization of this study.
The subjects on which were realized various measures gave their consent for the publication.