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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 4  |  Issue : 3  |  Page : 146-151

Determination of normal portal vein congestive index on 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
3 Department of Family Medicine, Ahmadu Bello University Teaching Hospital, Zaria, Nigeria
4 Department of Radiology, Lagos University Teaching Hospital, Idi-Araba, Lagos, Nigeria

Date of Web Publication8-Dec-2014

Correspondence Address:
Dr. Joshua O Aiyekomogbon
Department of Radiology, Ahmadu Bello University Teaching Hospital, Sika-Zaria, Kaduna
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/2278-9596.146411

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  Abstract 

Background: Portal hypertension is a major abnormality of the portal venous system and it is a commonly encountered clinical condition with multiple causes and several sequelae. The need for an imaging parameter that will aid its early diagnosis cannot be overemphasized, bearing in mind that portal pressure monitoring devices are not available in most tertiary hospitals in Nigeria. This prospective study was aimed at using ultrasound to determine the normal Portal Vein Congestive Index among adults in Zaria, Nigeria.
Patients and Methods: The study was conducted over a period of 6 months spanning 15 th November 2011 to 14 th May 2012 at the Radiology Department of Ahmadu Bello University Teaching Hospital, Zaria. Following an overnight fast by the 186 eligible participants, the portal vein diameter, cross sectional area and flow velocity were obtained using ultrasound Doppler equipment (Mindray diagnostic ultrasound system, Model DC-3, 2010-2012, Nanshan, Shenzen, PR China). B-Mode gray-scale for the assessment of dimensions, and Duplex Doppler Ultrasound Scan techniques for interrogation of the flow pattern and velocity. These parameters were then used to obtain the congestive index of the subjects.
Results: The portal vein hemodynamic parameters were as follows mean (SD): Cross sectional area, 1.097 cm 2 (0.203) (ranged 0.89-1.30); mean flow velocity, 15.44 cm/s (2.628) (ranged 12.80-18.10); and congestive index, 0.0722 cmS (0.0135) (ranged 0.0587-0.0857). All measurements in males were significantly higher than those in females (P < 0.001); and the portal vein congestive index increased significantly with age (P = 0.006).
Conclusion: Reference values of normal congestive index of the portal vein have been established and may be used for the assessment of patients with liver diseases or portal hypertension in this environment.

Keywords: Congestive index, ultrasound scan, portal vein


How to cite this article:
Aiyekomogbon JO, Ibinaiye PO, Tabari AM, Chom ND, Yusuf R, Aiyebelehin AO, Soyebi K, Igashi JB. Determination of normal portal vein congestive index on ultrasound scan among adults in Zaria, Nigeria. Arch Int Surg 2014;4:146-51

How to cite this URL:
Aiyekomogbon JO, Ibinaiye PO, Tabari AM, Chom ND, Yusuf R, Aiyebelehin AO, Soyebi K, Igashi JB. Determination of normal portal vein congestive index on ultrasound scan among adults in Zaria, Nigeria. Arch Int Surg [serial online] 2014 [cited 2024 Mar 28];4:146-51. Available from: https://www.archintsurg.org/text.asp?2014/4/3/146/146411


  Introduction Top


The portal vein 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 much 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 at the level of the L1/L2 disc space. [2],[3] It runs posterior to the common bile duct and the hepatic artery to the porta hepatis, where it divides into right and left branches to supply the right and left lobes of the liver. [2] The portal vein supplies 75-80% of blood to the liver while hepatic artery supplies 20-25%.

Portal hypertension is a major consequence of the abnormalities of the portal venous system and a commonly encountered clinical condition with multiple causes and several sequelae. It is responsible for substantial economic, social, psychologic and mental burdens, and its causes could either be pre-hepatic, hepatic or post-hepatic. [4],[5],[6] The most common cause of portal hypertension is cirrhosis of the liver. [7] Cirrhosis results from scarring of the liver, an injury caused by hepatitis, alcohol abuse, schistosomiasis or other causes of liver damage.

Liver cirrhosis is a common finding in Zaria, and its complications are also frequently seen. [7] The commonest of these complications is portal hypertension. [7],[8] Post chronic hepatitis B viral infection which has a high prevalence rate of 10% has been implicated as the commonest cause of liver cirrhosis and then portal hypertension in Zaria. [7] The need to establish a highly sensitive imaging parameter that will aid early diagnosis of portal hypertension cannot be over emphasized.

Ultrasound is a valuable tool for diagnosing abnormalities of the portal venous system, and with the development of real-time gray-scale ultrasonography and Doppler interrogation, evaluation of the portal venous system has become relatively simple and reliable. [9] The ratio of portal vein's cross sectional area to portal blood flow velocity is termed congestive index (CI). This takes into account portal vein dilatation and decreased flow velocity, which are the two physiological changes associated with portal hypertension, and it is therefore the most sensitive and specific ultrasonographic parameter used in establishing the diagnosis of portal hypertension. [10],[11],[12],[13] The sensitivity of congestive index (CI) for detection of patients with both cirrhosis and idiopathic portal hypertension was 67% when the normal range was set at mean ± 2 SD. [10] The sensitivity of the CI in the diagnosis of portal hypertension is therefore relatively high.

Ultrasound, a cheap, readily available, non-ionizing and non-invasive imaging modality allows accurate diagnosis of portal vein diseases, the commonest of which is portal hypertension. There is need for local ultrasonographic reference values of normal portal vein indices, especially the much more sensitive congestive index, in our environment as most values in the literatures are basically those of the Caucasians. This study was therefore aimed at determining the normal Portal Vein Congestive Index among adults in Zaria, Nigeria using ultrasound, which could stand as a reference value in this environment.


  Patients and Methods Top


This prospective study was carried out over a 6-month period spanning 15 th November 2011 to 14 th May 2012 at the Radiology Department of Ahmadu Bello University Teaching Hospital (ABUTH), Zaria, Nigeria. A total of one hundred and 86 subjects out of the 200 recruited individuals were finally found eligible for the study.

The criteria for inclusion included: normal consenting hospital staff and medical students, and eligible patients on routine medical check-up from the Family Medicine department of the institution.

Thorough clinical evaluation to rule-out hepatobiliary diseases, gray scale ultrasound scan to exclude liver diseases and ascites, and liver function tests (LFTs) were used to ascertain normalcy and eligibility of the subjects. Those excluded from the study were individuals with hepatobiliary diseases, cardiac diseases, portal hypertension and splenomegaly, previous history of cholecystectomy or cardiac operation, abnormal LFT findings, pregnancy and un-fasted patients.

The study was carried out with Ultrasound Doppler equipment (Mindray diagnostic ultrasound system, Model DC-3, 2010-2012, Nanshan, Shenzen, PR China). B-Mode gray-scale for the assessment of dimensions, and Duplex Doppler Ultrasound Scan techniques for interrogation of the flow pattern and velocity. A curvilinear transducer with a frequency range of 2.5-6.0 MHz was used for both gray-scale and Doppler ultrasound scan. This range of frequencies was required as the subjects scanned were of different body habitus.

Having ascertained eligibility of the subjects, the procedure was explained to them and informed consent obtained. Age and sex of the participants were documented. Also, height and weight of each participant were taken in order to calculate the Body Mass Index (BMI) using the formula: Weight/height 2 (Kg/m 2 ). [14] The last menstrual period (LMP) of the female participants was documented and this coupled with pelvic ultrasound scan were used to exclude pregnancy. The research participants were clinically evaluated to ensure that none of them had history of liver or cardiac diseases, portal hypertension, or have had cholecystectomy or cardiac operation.

The subjects were scanned in the morning after an overnight fast. [15] Following application of ultrasound gel to the area of interest to serve as acoustic coupling agent, the subjects were scanned during quiet respiration in supine position. Panoramic assessment of the liver, spleen and peritoneal cavity was done to further ascertained normalcy of the subjects. The portal cross sectional area and mean flow velocity were measured at a point just distal to the union of the splenic and superior mesenteric veins in right oblique position [Figure 1] and [Figure 2] as suggested by Anakwue et al. [16] These parameters were used to determine the portal vein congestive index of the subjects.
Figure 1: A transverse scan at the epigastrium via a subcostal approach demonstrating the normal cross sectional area of the portal vein (PV) = 1.21 cm2. GB = Gallbladder, PV = Portal vein

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Figure 2: A Duplex Doppler ultrasound scan at the level of the epigastrium of the same patient as in Figure 1 via a subcostal approach demonstrating the measurement of normal mean velocity of the portal vein (14.0 cm/s) and characteristic forward (centripetal) monophasic
venous flow with minimal respiratory variation.


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Depending on the vessel orientation and the subject's body habitus, the portal vein was accessed either through a subcostal approach pointing the transducer postero-caphalad, or a right intercostal approach pointing the transducer medially. When visualization of the portal vein was optimal, the waveforms were obtained by using an angle of inclination equal or less than 60 o . The mean portal venous velocity was determined electronically with the software package of the ultrasound machine and the cross sectional area was obtained using ellipse mode of the ultrasound system. All measurements were made twice by the same observer, and the average calculated to enhance accuracy of the results and reduce intra-observer variability. [16]

The congestive index of the portal vein was then calculated using this formula:

Congestive index (CI) = Cross sectional area (CSA)/Mean blood flow velocity.

Ethical considerations

Approval to carry out the study was obtained from the ethical and research committee of Ahmadu Bello University Teaching Hospital. The data collected from the participants was kept with utmost confidentiality and patients had the choice to deny consent or opt out of the study at any stage.

Data analysis

The results were reported as mean (SD). Collected data were analyzed using Statistical Package for Social Science (SPSS) version 16. 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 evaluate the correlation between numeric variables. All tests of significance were two-tailed, and P values less than 0.05 were considered statistically significant.


  Results Top


The age and sex distribution of the subjects is shown in [Table 1]. 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 whereas 96 (51.6%) were females, with a male: Female ratio of 1:1.07.
Table 1: Frequency distribution of the subjects by sex and age groups

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The mean values of the portal vein cross sectional area, mean velocity and congestive index of the entire research participants are shown in [Table 2]. The cross sectional area ranged between 0.894-1.30 cm 2 , with a mean value of 1.097 cm 2 (0.203). The mean flow velocity was 15.44 cm/s (2.63), ranged between 12.8-18.1 cm/s. The congestive index of the portal vein ranged from 0.0587-0.0857 cmS, with a mean value of 0.0722 cmS (0.0135).
Table 2: The means and standard deviations of portal vein haemodynamic parameters

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The mean values and standard deviations of the portal venous hemodynamic parameters by sex are shown in [Table 3]. The male subjects had significantly higher mean values of portal vein cross sectional area and congestive index than the female subjects (P < 0.001). The mean flow velocity was also higher in males than females but the sex difference was not statistically significant.
Table 3: The means and standard deviations of portal vein haemodynamic parameters by sex

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There was a positive relationship between congestive index of the portal vein and age groups of the research participants [Table 4]. A linear increase in the congestive index was noted from second to fourth decade. In the fifth decade however, the congestive index was found to be marginally lower than the value obtained for those between 30 and 39 years. An increase was however observed for those above 50 years of age. The difference was statistically significant (P = 0.006). [Figure 3] shows the graphical relationship between congestive index and age-groups. [Table 5] shows the correlation of congestive index with age and BMI. There was a positive correlation between congestive index and age (P = 0.002, r = 0.233). No correlation was however noted between congestive index and BMI.
Table 4: The portal vein congestive index by age group (ANOVA)

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Table 5: Correlation of congestive index with age and body mass index (BMI)

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Figure 3: Graphical representation of the relationship between congestive index and age group

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  Discussion Top


Over the years, studies have shown strong correlation between portal venous ultrasonic findings and clinical portal hypertension. [12],[13] Although, other organ changes involving the spleen, liver, hepatic arteries and splanchnic vessels are also required in making a diagnosis of portal hypertension, portal venous changes are the most reliable. [12]

The mean value of the cross sectional area of the portal vein in this study was 1.10 cm 2 (0.20). Previous studies did not show any significant variations of portal vein cross sectional areas among ethnic groups. [17] This explains why the mean value obtained in the present study is similar to the value obtained by Moriyasu et al., [10] in their study where mean cross sectional area of the portal vein of 0.99 cm 2 (0.28) was noted. Also, the findings of Brown et al., [18] revealed a supine cross sectional area of 1.13 cm 2 (0.27) among normal Caucasians which is in consonance with the outcome of the present study.

The value of the mean flow velocity in the index study was 15.44 cm/s (2.63). This is similar to the findings of Moriyasu et al., [10] where they had 15.3 cm/s (4.0) as the mean value of the mean flow velocity of the portal vein (P = 0.8007). The similarities also show that racial factors do not have significant influence on this parameter. However, the findings of Brown et al., [18] contrast this as they found a mean value of 12.32 cm/s ± 5.90 (P = 0.001). Rokni Yazdi and Soutouden [19] findings on the mean value of the mean flow velocity of the portal vein were also significantly higher than the values obtained in the current study (P < 0.0001). They studied 37 healthy adults and found a mean velocity of 27.32 cm/s. The differences observed may be due to differences in the technique and equipment used. The sample size and age of the subjects could also contribute to the variations. RokniYazdi and Soutouden [19] used 37 healthy adults, whose ages ranged between 20-40 years, and also their participants were investigated during Ramadan fasting period. The possibility of long term fasting affecting hemodynamics of the portal vein should be considered as one of the reasons for the marked disparity in the mean velocity found by these researchers and the present study.

The congestive index of the portal vein was 0.0722 cmS (0.0135) in the present study. This is similar to a study carried out in Japan by Moriyasu et al., [10] where a mean CI among 85 normal research participants was 0.070 cmS (0.029) (P = 0.5052). Also, Haag et al., [20] in a study in Germany, correlated duplex ultrasonographic findings with portal venous pressure among 375 patients with clinically diagnosed portal hypertension, and a matched cohort of 100 patients without portal hypertension. The mean value of congestive index among the normal group was 0.07 cmS (0.015), which is also similar to the findings in the present study (P = 1). The congestive index among the 375 patients with clinically diagnosed portal hypertension was significantly higher, in multiples of 3 above the normal findings. Trans-jugular catheterization of the portal vein for direct portal pressure monitoring was also done for these patients, and congestive index was found to correlate positively, though weak, with the portal pressure or porto-systemic pressure gradient (P < 0.05, r = 0.18). Despite the weak correlation between duplex Doppler ultrasonographic findings and portal venous pressures, they found a high sensitivity and specificity for duplex ultrasonographic variables, most especially CI in diagnosing portal hypertension. The weak correlation was assumed to be due to development of collaterals, which influences the duplex ultrasonography variables to a much greater extent than does the portal pressure. [20]

The hemodynamic parameters (cross sectional area, flow velocity and CI) obtained in the present study were higher in males than females. The sex differences were statistically significant for the entire variables except mean flow velocity (P < 0.001 for cross sectional area and congestive index, while P = 0.455 for the differences in velocity that existed among male and female subjects). Moriyasu et al., [10] studied 88 normal subjects and found out that there were significant differences between genders (P < 0.001) in portal vein cross sectional area and portal flow volume. 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 a study carried out in Iran by Rokni-Yazdi and Sotouden [19] where 37 healthy volunteers were investigated for normal Doppler parameters of portal vein and hepatic artery, significantly higher portal venous hemodynamic parameters were observed among male participants (P = 0.0001 for cross sectional area and P = 0.014 for mean flow velocity).

On the contrary, Chuo et al., [17] did not find any significant difference in the portal venous hemodynamic variables among gender groups. This may be due to differences in techniques and equipments used for the study. They used Hawks 2101 and ATL 500 ultrasound machines for their study; Jee et al., [21] observation on Doppler indices in portal and splenic veins showed significant inter-equipment variability. Using two different ultrasound equipments for their study was inappropriate. This must have affected the outcome of their study and may therefore be responsible for the discordance observed in the outcome of their study and the current study.

The present study also revealed that hemodynamic parameters, particularly CI correlated well with age signifying that increase in age leads to a corresponding increase in portal venous congestive index. The highest of the mean values of the congestive index occurred in the highest age-group, ≥50 years and the lowest mean value was noted among the youngest group, 18-19 year age-group. The differences that existed among age groups in the mean values of the hemodynamic parameters, except velocity, were statistically significant with a P value of 0.006 for both congestive index and portal vein cross sectional area. On the contrary Chuo et al., [17] did not find any significant differences in the parameters of portal vein 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.

The congestive index of the portal vein did not show any correlation with the body mass index, but correlated positively with age (P value 0.002, r 0.233). This is similar to the findings among Caucasians. [10]

Limitation

The presence of gas in the upper abdomen of some research participants resulted in obscuration of the portal vein, making it particularly difficult or impossible to measure the cross sectional area and diameter of the vein. Doppler interrogation was also difficult in such circumstances. Such participants were excluded from the study.


  Conclusion Top


Reference values of normal congestive index and hemodynamic parameters of the portal vein have been established and may be used for the assessment of patients with liver diseases or portal hypertension in this environment. The cross sectional area ranged between 0.894 and 1.30 cm 2 , with a mean value of 1.097 cm 2 (0.203), while the mean flow velocity was 15.44cm/s (2.63), ranging between 12.8-18.1 cm/s and the congestive index ranged from 0.0587 to 0.0857 cmS, with a mean value of 0.0722 cmS (0.0135).

A similar study in other geopolitical zones of the country is recommended. This will help in establishing a normative data for Nigerians. Also a study that will correlate duplex ultrasonographic findings with direct portal pressure measurements among healthy adults and those with portal hypertension 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], [Table 5]



 

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