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 Table of Contents  
ORIGINAL ARTICLE
Year : 2015  |  Volume : 2  |  Issue : 1  |  Page : 33-38

Determination of normal portal vein parameters on triplex ultrasound scan among adults in Zaria, Nigeria


1 Department of Radiology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
2 Department of Chemical Pathology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria

Date of Submission27-May-2014
Date of Acceptance22-Oct-2014
Date of Web Publication17-Feb-2015

Correspondence Address:
Philip Oluleke Ibinaiye
Department of Radiology, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2384-5147.150469

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  Abstract 

Background: There are many causes of the portal vein (PV) disease and these include portal hypertension (PHT), PV thrombosis, PV gas and PV stenosis/obstruction. PHT is a common clinical presentation of portal venous disease with multiple causes and several sequelae. There is a need for an imaging parameter that will aid early diagnosis of PHT since portal pressure monitoring devices are not available in most tertiary hospitals in Nigeria. Aims and Objectives: To determine the normal values of PV parameters using triplex ultrasound (US) among adults in Zaria, Nigeria. Settings and Design: This prospective study was conducted over a period of 6 months between November 2011 and May 2012 at the Radiology Department of Ahmadu Bello University Teaching Hospital, Zaria. Materials and Methods: Following an overnight fast, US scan was performed on 186 eligible participants. The diameter, cross-sectional area (CSA) and flow velocity of the PV were obtained. Results: The PV parameters obtained were as follows (mean ± standard deviation): PV diameter, 1.09 ± 0.22 cm (range: 0.87-1.31); CSA, 1.10 ± 0.203 cm 2 (range: 0.89-1.30) and mean flow velocity, 15.44 ± 2.63 cm/s (range: 12.80-18.10). All the measurements in males were significantly higher than those in females (P < 0.001). Conclusion: The normal values of PV parameters have been established in adult subjects in Zaria. These values will serve as a reference to detect abnormalities of dimensions and flow velocities in the PV, thus enabling quantitative evaluation of patients with suspected PV disease.

Keywords: Cross-sectional area, diameter, portal vein, ultrasound, velocity


How to cite this article:
Ibinaiye PO, Aiyekomogbon JO, Tabari MA, Chom ND, Hamidu AU, Yusuf R. Determination of normal portal vein parameters on triplex ultrasound scan among adults in Zaria, Nigeria. Sub-Saharan Afr J Med 2015;2:33-8

How to cite this URL:
Ibinaiye PO, Aiyekomogbon JO, Tabari MA, Chom ND, Hamidu AU, Yusuf R. Determination of normal portal vein parameters on triplex ultrasound scan among adults in Zaria, Nigeria. Sub-Saharan Afr J Med [serial online] 2015 [cited 2022 Aug 13];2:33-8. Available from: https://www.ssajm.org/text.asp?2015/2/1/33/150469


  Introduction Top


The portal vein (PV) is a unique conduit delivering blood from the capillaries in the intestinal wall and spleen to the capillaries in the hepatic sinusoids. [1] It is less prone to anatomical variation than the hepatic artery and is normally formed posterior to the neck of the pancreas, by the union of the superior mesenteric vein (SMV) and the splenic vein (SV) at the level of the L1/L2 disc space. [2],[3] It runs posterior to the bile duct and the hepatic artery at the porta hepatis, where it divides into right and left branches to supply the right and left lobes of the liver. [2] The PV supplies 75-80% of blood flow to the liver while hepatic artery supplies 20-25%.

Portal vein disease is a common clinical presentation of chronic liver disease with multiple causes and several sequelae. Chronic liver disease is responsible for substantial economic, social, psychologic and mental burdens, and its causes could either be prehepatic, hepatic or posthepatic. [4],[5],[6] The most common cause of portal hypertension (PHT) is cirrhosis of the liver. Cirrhosis results from scarring of the liver, an injury caused by hepatitis, alcohol abuse, schistosomiasis or other causes of liver damage. Low flow velocity, reversal of flow, increase diameter and area are seen in PHT; high flow velocity, reduced diameter and area are seen in PV stenosis; while absence flow, increase diameter and area are seen in PV thrombosis. [1]

Liver cirrhosis and its complications are common findings in Zaria. [7] The commonest of these complications is PHT. [7],[8] Postchronic hepatitis B viral infection which has a high prevalence rate of 10% has been implicated as the commonest cause of liver cirrhosis and PHT in Zaria. [7] The need to establish a highly sensitive imaging parameter that will aid early diagnosis of PV disease cannot be over emphasized.

Ultrasound (US) is a valuable tool for diagnosing abnormalities of the portal venous system, and with real-time gray-scale and Doppler US, evaluation of the PV has become relatively simple and reliable. [9] This takes into account PV dilatation, decreased flow velocity and flow reversal which are the physiological changes associated with PHT, therefore, the sensitivity of these parameters in the diagnosis of PHT is relatively high. [10],[11],[12],[13]

In a study conducted by Moriyasu et al., [10] the sensitivity of using the cross-sectional area (CSA) of PV for detection of patients with both cirrhosis and idiopathic PHT was higher (65%) than the sensitivity (63%) using blood flow velocity. US, a cheap, readily available, nonionizing and noninvasive imaging modality allows for accurate evaluation of the PV. There is a need for a local ultrasonographic reference value of normal PV indices in our environment as most values in the literature are from the Caucasian population.


  Materials and methods Top


This prospective study was carried out over a 6-month period between November 2011 and May 2012 at the Radiology Department of Ahmadu Bello University Teaching Hospital (ABUTH), Zaria, Kaduna state, North-West Nigeria. The hospital serves a population of about 40 million people, spread across the entire north-west as well as, parts of north-east and north-central regions. It also serves parts of Niger, Cameroun and Chad republics.

A total of 186 subjects out of the 200 recruited subjects was found eligible for the study. A consent form indicating willingness to participate in the study was signed by each participant.

Subjects were recruited from volunteer hospital staff and medical students, patients on routine medical check-up from the general out-patient/family medicine department of the institution.

Excluded from the study were those with known hepatobiliary diseases, cardiac diseases, PHT and splenomegaly, previous history of cholecystectomy or cardiac operation, abnormal liver function test (LFT) findings, pregnancy irrespective of gestational age and any abnormality on the abdominal US. The presence of bowel gas in the upper abdomen of some subjects resulted in obscuration of the PV, making it particularly difficult or impossible to measure the PV parameters. Such participants were excluded from the study. There was difficulty in assessing PV in some obese patients, and such patients were also excluded from the study.

The age, sex, height and weight of each participant was taken. Body mass index (BMI) was derived for each participant from recorded height and weight using the formula: Weight/height 2 (kg/m 2 ). [14]

The last menstrual period of female participants was documented and this, in conjunction with pelvic US scan was used to exclude pregnancy.

Prospective participants were interviewed and examined to exclude history of liver or cardiac disease, PHT, previous cholecystectomy or cardiac surgery.

Blood samples of the subjects were taken for LFT assessment. Those with abnormal LFT results were excluded.

Data collected were recorded in the data collection form.

Ultrasound technique

Ultrasound of the upper abdomen was carried out using a Mindray diagnostic US system (Model DC - 3, 2010-2012, Nanshan, Shenzhen, PR China), with Doppler facilities. Gray-scale US was used for the assessment of dimensions of the PV, and duplex Doppler US (pulsed wave and color flow) for flow pattern and velocity in the PV. A curvilinear transducer with a frequency range of 2.5-6.0 MHz was used for both gray-scale and Doppler US. This range of frequencies was required to suit different body habitus of the subjects.

All subjects were scanned in the morning after an overnight fast. [15] Following application of coupling gel to the area of interest, the subjects were scanned during quiet respiration in the supine position or left lateral decubitus position. Panoramic assessment of the liver, spleen and peritoneal cavity was done to rule out any abnormality.

The PV is visible on US as it courses towards the liver posterior to the common bile duct and hepatic artery. Its wall appears hyperechoic on gray scale US scan. Pulsed and color flow Doppler help in identification of the vessel. On color Doppler, PV shows smooth fill in of color at low gain while, in the hepatic artery, gain needs to be increased slightly to fill in vessel lumen with color. Also on pulsed Doppler, PV shows continuous low-velocity waveform with respiratory variation while hepatic artery shows a low resistance waveform with systolic and diastolic components.

The PV parameters (diameter, CSA and mean flow velocity) were measured at a point which was midway between the confluence of the splenic and SMV and bifurcation of the PV during quiet inspiration by the same sonologist [Figure 1], [Figure 2], [Figure 3] as described by Anakwue et al. [16]
Figure 1: A transverse scan at the epigastrium via a subcostal approach demonstrating the normal diameter of the portal vein (PV) = 1.10 cm. PV = Portal vein, IVC = Inferior vena cava, AO = Abdominal aorta, GB = Gall bladder

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Figure 2: A transverse scan at the epigastrium via a subcostal approach demonstrating the normal cross-sectional area of the portal vein (PV) = 1.21 cm2. PV = Portal vein, IVC = Inferior vena cava, AO = Abdominal aorta, GB = Gall bladder

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Figure 3:

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Depending on the vessel orientation and the subject's body habitus, the PV was accessed either through a subcostal approach with the transducer directed posterio-caphalad or through the right intercostal approach with the transducer directed medially. When visualization of the PV was optimal, the spectral waveforms were obtained using a Doppler angle of inclination equal or less than 60΀ and the sample volume size was 2/3 of vessel diameter.

The mean PV flow velocity was determined electronically from the US machine when the transducer was oriented along the longitudinal axis of the main PV using a paramedian or slightly oblique plane.

The formula for mean flow velocity = 0.57 Χ V max /Cosθ. [10]

Where V max = maximum velocity, θ = Doppler angle of inclination (60΀) and 0.57 = correction factor of parabolic flow.

The CSA was obtained using the ellipsoid method while the anterio-posterior diameter was taken with electronic calipers placed on the echogenic walls of the vein from a transverse scan.

All measurements were taken twice by the same observer, and the average calculated to enhance accuracy of the results and reduce intra-observer variability. [16]

Ethical considerations

Approval to carry out the study was obtained from the Ethical and Research Committee of ABUTH.

Data analysis

The data were analyzed using Statistical Package for Social Science version 16. The results are presented as mean ± standard deviation.

Independent sample t-test was used to evaluate the sex differences in the values while ANOVA was used to evaluate the differences between age groups. Pearson correlation was used to determine the correlation between numeric variables. All tests of significance were two-tailed, and P < 0.05 was considered statistically significant.


  Results Top


The age range of the participants was 18-64 years, with a mean of 35.89 ± 11.25 years. Ninety (48.4%) of these were males while 96 (51.6%) were females, with a male: Female ratio of 1:1.07.

Majority of the subjects were between the third and fifth decades of life with the highest number of respondents being in the third decade (34.4%). The least group were those <20 years (2 nd decade), which accounted for 1.6%. The frequency distribution of the subjects by sex and age groups is shown in [Table 1].
Table 1: Frequency distribution of the subjects by sex and age groups

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[Table 2] summarizes the mean and range of PV parameters measured. The mean values of the PV diameter, CSA and mean velocity of the subjects were 1.09 ± 0.12 cm, 1.10 ± 0.20 cm 2 and 15.44 ± 2.63 cm/s respectively.
Table 2: PV parameters measured by US

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The mean values and SDs of the portal venous parameters by sex are shown in [Table 3]. The male subjects had significantly higher mean values of PV diameter and CSA than the female subjects (P < 0.001). The mean flow velocity was also higher in males than females, but this sex difference was not statistically significant P = 0.46.
Table 3: The means and SDs of PV parameters by sex

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The mean values of the PV parameters by age groups are shown in [Table 4]. A linear increase in all the parameters with age is noted up to fourth decade, P = 0.04 and 0.006 for diameter and CSA respectively. This trend was however not maintained among subjects above 40 years of age. The increase with age was however not significant for the mean flow velocity with P = 0.842 [Table 4].
Table 4: The means and SDs of PV parameters by age group

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  Discussion Top


In the present study, the mean PV diameter in Nigerian adults in Zaria was 1.09 ± 0.12 cm. This finding is similar to that of Anakwue et al.[16] in south-east Nigeria. They studied 200 apparently healthy adult Nigerians aged 20-79 years and found the mean PV diameter to be 1.15 ± 0.15 cm. The similarity between their results and this study may be due to the fact that both studies were carried out among Nigerians but of different ethnicity. Thus, ethnic variations seem not to have significant influence on PV parameters. [17]

The findings of Tasu et al.[18] in France on PV diameter are also similar to the findings of this study. They studied 30 healthy adults and documented a mean PV diameter of 1.10 ± 0.26 cm. Cosar et al.[19] also found a mean PV diameter of 1.17 ± 0.3 cm among 30 healthy adults in Turkey, which is similar to the findings of this study. These findings further support the fact that race and ethnicity have no influence on PV parameters. [17]

On the other hand, Yazdi and Sotouden [20] reported that the mean PV diameter was 9.6 ± 1.9 mm among 37 healthy Iranian volunteers, which is lower than the mean diameter (10.9 ± 2.2 mm) obtained in the current study. Difference in sample size and technique of measurement may have accounted for this. [21]

The mean value of the CSA of the PV in this study was 1.10 ± 0.20 cm 2 . Previous studies did not also show any significant variations in the CSA of the PV among ethnic groups. [17] This may explain why the mean value obtained in the present study is similar to the value (0.99 ± 0.28 cm 2 ) obtained by Moriyasu et al.[10] in their study of 88 normal Japanese subjects. This is also in agreement with the findings of Brown et al.[22] who recorded CSA of 1.13 ± 0.27 cm 2 among normal caucasians.

The value of the mean flow velocity of the PV in this study was 15.44 ± 2.63 cm/s. This is similar to the findings of Moriyasu et al., [10] with 15.3 ± 4.0 cm/s. However, the findings of Brown et al.[22] was lower than these as they found a mean value of 12.32 ± 5.90 cm/s (P = 0.001) in 45 healthy British adults. Yazdi and Sotouden [20] recorded significantly higher mean PV flow velocities of 27.3 cm/s in 37 healthy Iranian adults. The differences observed may be due to differences in the measurement technique. Yazdi and Sotouden took the measurements of PV parameters at the crossing point of PV with inferior vena cava, and they did not use the correction factor of 0.57 for parabolic flow in calculating the mean flow velocity. The current study however, adopted the more accurate, reproducible and universally accepted techniques of obtaining PV measurements at a point which is midway between the confluence of the splenic and SMV and bifurcation of the PV during quiet inspiration. [10] We also used the correction factor of 0.57 for parabolic flow in calculating the mean flow velocity. The sample size could also contribute to the variations while Yazdi and Sotouden [20] studied 37 healthy adults in Iran; the current study sample size was 186 healthy Nigerian. Yazdi and Sotouden [20] carried out their study during Ramadan fast and the possibility that long-term fasting may affect the mean flow velocity should be considered in comparing their findings to the current study.

The PV parameters obtained in this study were higher in males than females. The sex differences were statistically significant except for the mean flow velocity. Similarly, Moriyasu et al.[10] studied 88 normal subjects and noted significant differences in CSA and diameter of the PV between males and females (P < 0.001). No significant difference was also noted in the mean flow velocity among gender groups in their study. They however noted that sex differences ceased to exist when the portal flow was expressed either per body weight or per body surface area. Also in the study carried out in Iran by Yazdi and Sotouden [20] significantly higher portal venous parameters were observed among male subjects (P = 0.0001 for diameter and P = 0.014 for mean flow velocity). [10] On the contrary, Chuo et al.[17] did not find any significant difference in the portal venous variables by sex. This may be due to differences in techniques and equipments used for the study. They used two different US machines for their study and Jee et al.[21] had observed that Doppler indices of the portal and SV showed significant inter-equipment variability even when the same technique of measurement is used.

The present study also revealed that all parameters correlated well with age signifying that increase in age leads to a corresponding increase in the values of PV parameters. The highest values were seen in the highest age group (≥50 years) and the lowest values in the youngest group (18-19 years). The age differences were statistically significant except for the velocity. This agrees with the findings of Anakwue et al.[16] in their study of 200 apparently normal Nigerian adults. They reported that the mean diameter of the PV increased with age. They however did not measure CSA in their study, but it could be inferred that as the diameter correlates with age, the CSA should also demonstrate a similar relationship.

On the contrary Chuo et al.[17] did not find any significant differences in parameters of PV among age groups. The disparity noted between these observations and that of the present study may be attributed to differences in techniques and the sample size of the research participants. As noted before, Chuo et al. used two different types of US machine and also studied only 48 adults.

The PV parameters (diameter, CSA and mean flow velocity) did not show any correlation with the height, weight and BMI. This is similar to the findings among Caucasians. [10]

Limitation

The presence of gas in the upper abdomen of some subjects obscured the PV. This made it particularly difficult or impossible to measure the PV parameters. Such participants were excluded from the study. There was difficulty in assessing PV in some obese patients, and such subjects were also excluded from the study.


  Conclusion and recommendations Top


The normal reference values of the parameters of the PV namely, diameter, CSA and mean flow velocity, have been established in our environment. This may help the gastroenterologist, radiologist and other clinicians practicing in this environment to quantitatively evaluate patients with suspected diseases of the PV. A similar study in other parts of the country is recommended. This will help in establishing a normative data for Nigerians. A study that will correlate duplex ultrasonographic findings with direct portal pressure measurements among healthy adults and those with PHT is also recommended.

 
  References Top

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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]


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