|Year : 2016 | Volume
| Issue : 3 | Page : 336-340
A cadaveric study of morphology of portal vein with its clinical importance
Harsimarjit Kaur1, Manjeet Singh2, Abha Sheth Bajaj3
1 Department of Anatomy, Government Medical College, Patiala, Punjab, India
2 Department of Orthopaedics, MMIMSR, Mullana, Ambala, Haryana, India
3 Department of Anatomy, Dr. H. S. J. Institute of Dental Sciences and Hospital, Chandigarh, India
|Date of Web Publication||17-May-2016|
Department of Anatomy, Government Medical College, Patiala, Punjab
Source of Support: None, Conflict of Interest: None
Introduction: The morphological mensurative data of the portal venous system is important, as regards portal hypertension and surgical aspects related to portocaval anatomosis. Aims and Objectives: The study under consideration was under taken to determine the actual percentage incidence of major variations occurring in the disposition of the portal vein (PV) and its tributaries. The basis of major variations has different reasons such as genetic, metabolic, hemodynamic factors depending on the type of variations. Materials and Methods: This study was conducted on 30 adult human cadavers by dissection method. The abdomen was opened by standard cruciform incision, and the region of PV was cleaned and observations were made and recorded. Result: The PV had normal standard pattern in 30% cases and the rest 70% showed variations in one or the other form. The splenic vein was variant in 76.6% cases. The superior mesenteric vein showed variation in 73.3% cases. The mode of termination of the inferior mesenteric vein was variable in 60% of cases. Conclusion: The incidence of variations in the portal venous system can be of prime surgical and radiological importance for portocaval anastomosis and to study hemodynamic flow radiologically.
Keywords: Splenic vein, superior mesenteric vein, variations portal vein
|How to cite this article:|
Kaur H, Singh M, Bajaj AS. A cadaveric study of morphology of portal vein with its clinical importance. Med J DY Patil Univ 2016;9:336-40
| Introduction|| |
The term "portal" has been derived from the Latin word "portare" which means to carry. The portal vein (PV) is one of the primitive veins of the amphioxus and modification of its development in connection with right vitelline vein appears to be the recent adaptation. 
According to Williams et al.  and Gilfillan,  the PV begins at the level of second lumbar vertebra by the convergence of superior mesenteric and splenic veins (SVs) anterior to inferior vena cava, posterior to the neck of pancreas. It enters the liver at the right end of porta hepatis, dividing into right and left stems.
The right branch enters the right hepatic lobe, usually receives the cystic vein. The left branch, longer but of smaller caliber,that divides into branches for caudate, quadrate, and left lobe. The tributaries of the PV are SV, superior mesenteric vein (SMV), left gastric vein, right gastric vein, para-umbilical vein, and cystic veins.
The PV receives the tributaries draining venous blood from the sub diaphragmatic part of esophagus, the stomach, small and large intestines (except the lower part of anal canal), the pancreas and spleen. The blood from this vast area passes through liver (hepatic circulation) before returning to general systemic vein, inferior vena cava. 
With the increase in percutaneous hepatobiliary interventions and complex surgical resections, a thorough understanding of variants in PV anatomy is crucial. In most cases, preprocedure cross sectional imaging is available, and although PV variants are depicted on the images, they are not commonly reported.  The surgical management of portal hypertension is a subject of considerable interest, and much attention has been laid on the importance of the portal venous bed in portal venous obstruction. 
Various veins of the portal system have been joined surgically to the veins of inferior vena caval system in the hope that resultant shunting of blood would reduce the portal tension to an extent sufficient to allow recession of the collateral circulation.  Keeping in view of above said medical and surgical importance of PV anatomy, a need to study its morphology was felt.
| Materials and Methods|| |
The material for the study comprised 30 adult human cadavers of known sex with the male to female ratio being 20:10. The abdominal cavity was opened by a cruciform incision passing through the whole thickness of the anterior abdominal wall. The epiploic foramen was identified, and the structures in the right free margin of lesser omentum were cleaned. The PV at its formation and termination at porta hepatis along with its tributaries was cleaned and observed. The observations related to morphological variations of PV and its tributaries were recorded.
The length and breadth of PV for each case was measured with the help of the graduated metric scale. The designated points for length were as:
Proximal point: Acute angle formed at the junction of the SV with SMV.
Distal point: Either the midpoint of the breadth of the PV as it entered the porta hepatis or the acute angle formed at its right and left branches if it divided before entering the porta hepatis.
The breadth of the PV was measured at the midpoint of the proximal and distal points described above with the help of the divider, over the graduated metric scale.
| Results|| |
Of 30 cadavers studied, the normal standard text book anatomy of the portal venous system was found only in three cases. Maximum number of variations in one or other form were observed in the tributaries of SV (76.66%), followed in order of frequency by SMV (73.33%) and in PV (70%).
Length of the portal vein
In the present study, the average length of PV was found to be 62.9 mm, the range being 38-80 cm.
Breadth of portal vein
The average breadth of PV at its midpoint between its formation and termination was found to be 16.8 mm. The maximum breadth observed was 18 mm in 4 cases (13.33%) and minimum being 8 mm in 2 cases (6.66%). Maximum number of cases was observed in the breadth range of 14-16 mm that is, in (43.33%) cases, out of which 11 (36.66%) cases were having breadth of 15 mm.
Formation of portal vein
In the present study, the PV was formed by the union of splenic and SMVs behind the neck of the pancreas, in front of inferior vena cava in the majority of cases (90%). However, it was found to be formed by the union of splenic, superior mesenteric and inferior mesenteric in 3 (10%) cases. In 18 (60%) cases, the portal was formed at the level of the second lumbar vertebra, while in 12 (40%) cases, it was formed at the level of lower border of the first lumbar vertebra.
Termination of portal vein
The PV terminated at porta hepatis as a single trunk in 21 (70%) cases, and it divided into right and left branches before termination in 9 (30%) cases [Figure 1].
|Figure 1: Extra hepatic branching of portal vein (Rt.br: Right branch, Lt.br: Left branch, LG: Left gastric vein, SV: Splenic vein, IPD: Inferior pancreatico duodenal, RGE: Right gastroepiploic vein, RC: Right colic vein)|
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The SV was formed near the splenic hilus by the convergence of a no. of trunks (5-1 in no). In one of the cases, one trunk arose independently from the upper pole of spleen and joined the main trunk almost in its middle.
In the present study, many variations in its tributaries have been observed and presented in [Table 1].
From the above table, it is clear that apart from its normal tributaries, the middle colic vein was an additional tributary, found in 3.33% cases [Figure 2].
|Figure 2: Middle colic vein terminating into splenic vein. LG1, LG2: Left gastric veins, IPD: Inferior pancreatico duodenal, RGE: Right gastroepiploic vein, RC: Right colic vein|
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Superior mesenteric vein
Superior mesenteric vein is commenced in the right iliac fossa by the union of veins from terminal ileum and pancreas in the present study. However, a wide range of variation has been observed in its tributaries.
Inferior mesenteric vein
Inferior mesenteric vein was found to drain into SMV in 12 (40%) cases. In 1 (3.33%) cases, there were two right colic veins uniting with each other, joined the right gastroepiploic and inferior pancreaticiduodenal veins were ultimately drained into SMV.
| Discussion|| |
Embryologically, the PV is formed in the 2 nd month of gestation by selective involution of the vitelline veins, which have multiple bridging anastomoses anterior and posterior to the duodenum. Alterations in the pattern of obliteration of these anastomoses can result in several variants.  Several dramatic PV variants have been described, ,, including duplications, congenital absence and absence of PV branching (in which a single PV enters the right liver and courses into the left, giving only segmental branches along its course). These variants can be quite obvious with modern cross sectional imaging. 
According to Michels,  PV measures 8-10 cm from the point of origin to its termination, the width being 8-14 mm. The comparative data of present observations with those of previous workers is shown in [Table 2].
The present observations are in accordance with those reported by Douglass et al.  and Rousselot et al. 
The length of the PV in the right free margin of the lesser omentum is quite enough to be used for the porta systemic shunts, ligation of the PV trunk in liver transplants, etc. There may be extra hepatic portal block occurring due to thrombosis etc., in the length of the PV. 
PV variations constitute a significant proportion of vascular variation in right lobe grafts, and their incidence has been reported as high as 22% in previous publications. , The clinical implications of PV variation include technically challenging operations with complex reconstruction, as well as the rejection of potential donors. 
The comparative statement regarding the breadth of the PV with previous workers is shown in [Table 3].
The range of breadth was complying with that found by previous workers. In one case, there was an extensive fibrosis in the region of the foramen of Winslow leading to the decrease in the breadth of PV.
The observations on the mode of formation of PV have been compared with previous workers in [Table 4].
The present study is in consonance with Thomson,  Gilfillan,  and Rousselot et al. 
The clinical significance of the point of formation of the PV on magnetic resonance (MR) angiography can be put as that, areas of flow exist and are subjected to signal loss while doing MR angiography on the portal system. Signal loss is a fairly common occurrence at the portal confluence, where there is mixing of blood from the SV and SMV which may meet together at nearly right angles. 
The oblique orientation of the PV often makes it difficult to be assessed in the transverse on MR angiogram.  Welch  have used the fact that the PV in the anterior lip of epiploic foramen and inferior vena cava in the posterior lip course parallel to each other at the upper border of pancreas and lower border of liver where they can be used to do side-to-side anastomosis between the two. The abdominal approach offers obvious difficulty for this procedure since the PV normally lies behind the hepatic artery and common bile duct. Hence, this delicate anastomosis must be carried out behind these structures for which thoracoabdominal approach is much easier for proper visualization and handling of the structures. 
In few cases, the SV was found to be completely embedded in the posterior surface of the pancreas. In such cases, it becomes exceedingly difficult to mobilize the SV for the preparation of splenorenal anastomosis and also during operations of carcinoma of head and neck of the pancreas.  In one of the cases, one trunk arose independently from the upper pole of the spleen and joined the main trunk almost in its middle. Such long trunks, instead of SV, can be of use in a splenorenal anastomosis, when these trunks are of sufficient diameter. 
The choice between a direct portacaval anastomosis and a splenorenal shunt or other anastomosis is necessarily a surgical and physiological one, although anatomy found at operation may make it difficult for carrying out the actually planned procedure. This is especially true for an end to side splenorenal anastomosis in which kidney is spared. A pronounced perisplenitis, for instance, may make the isolation and mobilization of SV impossible  and also variations in the point of confluence of SV may make it necessary to use one of its tributaries such as lower splenic, or left gastroepiploic vein in place of SV. 
| Conclusions|| |
The present study was undertaken with the intention of determining the approximate % incidence of major variations in the disposition of the PV and its tributaries. The PV had a normal standard pattern in 30% cases, being variant in remaining 70% in one or other form.
The mean length of PV came out to be 62.9 mm, the range being 38-80 mm. The mean breadth was 16.8 mm with the range being 8-18 mm.
PV divided into right and left branches at the porta hepatis in 9% cases.
Thanks to the divine souls who helped to materialize this manuscript possible.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4]