British Journal of Radiology 75 (2002),919-929 © 2002 The British Institute of Radiology
Colour Doppler ultrasound flow patterns in the portal venous system
C Görg, MD,
J Riera-Knorrenschild, MD and
J Dietrich, MD
Department of Internal Medicine, Philipps-University, Baldingerstraße, 35043 Marburg, Germany
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Abstract
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Doppler ultrasound is a well established method for assessment of the portal venous system to detect the direction of portal blood flow. It is helpful for non-invasive diagnosis of intra-abdominal portosystemic shunts, especially in patients with cirrhosis. Less attention has been paid to other influences on portal venous flow, e.g. tricuspid regurgitation, increased hepatic out-flow resistence, respiratory cycle. The aim of this pictorial review is to describe the spectrum of physiological and pathological Doppler ultrasound flow patterns in the portal venous system.
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Introduction
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Several physiological and pathological Doppler ultrasound flow patterns of the portal vein and/or its branches are known (Table 1
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Principal determinants of portal venous pulsatility may include retrograde trans-sinusoidal transmission of atrial pulsation [1], the respiratory cycle [2] and transmission of vena caval, hepatic arterial or splanchnic arterial pulsations [2].
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Physiological flow pattern
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In healthy adults, portal venous flow has been described as being continuous hepatopetal on Doppler ultrasound [3] (Figure 1). Minimal variations caused by respiration and cardiac cycle are evident (Figure 2). Two different scoring systems for quantification of portal venous modulation have been used.
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Figure 2. Doppler ultrasound of the portal vein with minimal pulsatile modulation of the portal flow in a healthy adult.
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Portal vein pulsatility is characterized by the ratio between minimum and peak portal vein velocities [4]. A pulsatility ratio >0.54 was found in over 90% of normal individuals [5]. The venous pulsatility index [(maximum frequency shift-minimum frequency shift)/maximum frequency shift] was 0.48±0.31 (mean±standard deviation) in healthy adults [2].
Recently, even marked pulsatile hepatopetal flow of the portal vein has been described, particularly in thin subjects with a venous pulsatility index of >0.5 (Figure 3), with an inverse correlation to body mass [2]. Decreased pulsatility has been observed when the patient is sitting and during deep inspiration, and in obese subjects [1]. It has been suggested that abdominal pressure is the common factor affecting portal vein pulsatility in these subjects [2].
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Figure 3. Doppler ultrasound of the portal vein with marked pulsatile modulation of the portal flow in a thin, healthy adult.
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Pathological flow patterns
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Different pathological flow patterns of portal venous blood flow exist (Table 1
). A marked pulsatile hepatopetal or hepatofugal flow in the portal vein and/or its branches is seen under pathological conditions, tricuspid regurgitation, increased hepatic outflow resistance, liver diseases.
Pulsatile flow in the portal vein has predominantly been found in patients with severe right heart failure (Figure 4), demonstrating right atrial pressure negatively correlated with portal vein pulsatility ratio [6]. All patients with hepatofugal pulsatile flow were in the New York Heart Association (NYHA) Class III or IV [6]. A pulsatile hepatopetal flow was found more often in patients with NYHA Class I or II [6]. Pathophysiologically tricuspid regurgitation is the predominantly suggested cause for the duplex Doppler ultrasound phenomena of pulsatile portal vein flow [7].
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Figure 4. Colour Doppler ultrasound of the hepatic vein and portal vein in a patient with heart failure, New York Heart Association Calss III and tricuspid regurgitation (left), having a triphasic flow in the hepatic vein (middle) and a marked pulsatile flow of the portal vein (right).
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Additionally, portal vein–hepatic vein fistula [8] and portocaval shunts may cause pulsatile portal flow [9].
Recently it has been assumed that severe pulmonary hypertension is responsible for a second pathophysiological mechanism that may induce hepatopetal or hepatofugal pulsatile portal vein flow, irrespective of degree of tricuspid regurgitation [10, 11]. In cases with constrictive pericarditis (Figure 5) and mediastinal haematoma (Figure 6), pericardial cyst, pericardial effusion (Figure 7) or right atrial tumour (Figure 8), the high right atrial pressure is presumably responsible for a pressure-related hepatic venous out-flow block with subsequent trans-sinusoidal hepatoportal shunting, similar to the mechanical outflow block that causes reversed pulsatile flow in liver cirrhosis (Figure 9) [12]. In patients with chronic hepatitis C, marked pulsatility in the portal vein has been associated with inflammation but not with other parameters of the histological activity index or intrahepatic fat deposition [13].
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Figure 5. Colour Doppler ultrasound in a patient with constrictive pericarditis (arrows) (left). A triphasic flow is seen in the hepatic vein (middle) and pulsatile flow in the portal vein (right). RV, right ventricle.
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Figure 6. Colour Doppler ultrasound of the hepatic vein and portal vein in a patient with mediastinal haematoma. A triphasic flow is seen in the hepatic vein (left) and a pulsatile flow with a reversed component of the portal vein (right).
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Figure 7. Colour Doppler ultrasound in a patient with pericardial effusion (left), and triphasic flow in the liver vein (middle) and pulsatile flow in the portal vein (right).
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Figure 8. Colour Doppler ultrasound in a patient with primary cardial lymphoma with a tumour in the right atrium (left), triphasic flow in the hepatic vein (middle) and pulsatile flow in the portal vein (right).
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Figure 9. Colour Doppler ultrasound of the hepatic vein (LV) and portal vein (VP) in a patient with liver cirrhosis having a monophasic flow in the hepatic vein (left) and a marked pulsatile flow of the portal vein (right).
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A less well understood mechanism for reversed portal flow leads to hepatofugal flow in the portal vein and/or its branches. It is well known that the respiratory cycle modulates portal venous flow via intra-abdominal pressure (Figure 10) [1, 2]. High abdominal pressure during deep inspiration may cause reversal flow in patients with severe right heart failure or liver disease (Figure 11) and may be seen only in peripheral branches of the portal venous system (Figure 12). Under certain circumstances, even in patients with the absence of cardiac and liver disease a short time reversed portal vein flow can be seen during deep inspiration using color Doppler ultrasound (Figure 13).
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Figure 10. Colour Doppler ultrasound of the portal vein (left and middle) in a patient with heart failure, New York Heart Association Calss III, having a marked pulsatile flow with reversed flow during deep inspiration (arrows) (right).
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Figure 11. Doppler ultrasound in a patient with a pericardial effusion (PE) (left) and a pulsatile flow in the portal vein with a short reversed flow during deep inspiration (arrow) (right). RV, right ventricle; LV, left ventricle.
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Figure 12. Colour Doppler ultrasound of the splenic vein (left and middle) in a patient with liver cirrhosis, oesophageal varices and ascites. Arrows indicate flow direction. A marked pulsatile flow was seen in the portal venous system with reversed flow in the hilar splenic vein during deep inspiration (arrow, right).
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Figure 13. Colour Doppler ultrasound of the portal vein (left and middle) in a patient 1 week post-gastrectomy. Arrows indicate flow direction. During normal inspiration (arrow A) a breath dependent reversed flow was seen (right).
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It is generaly accepted that colour Doppler ultrasound enables the detection of the presence and direction of blood flow in the portal venous system. Continuous hepatofugal flow in the portal vein trunk is found with an overall prevalence of 8.3% in patients with liver cirrhosis [14] (Figure 14). Prevalence did not differ in relation to the aetiology of liver cirrhosis. However, reversed flow was found more often in patients classified as Child's B and C cirrhosis than those classified as Child's A cirrhosis [14]. Reversed portal venous blood flow develops when the intrahepatic resistance is greater than the resistance of portosystemic collaterals. It is likely that the increase of intrahepatic resistance owing to structural abnormalities, i.e. hepatic vein sclerosis, Disse space collagenization and hepatocyte enlargement, plays the predominant role in the developement of reversed portal flow [15]. A possible association has been found between abnormal flow direction and the presence of oesophageal varices, ascites and spontaneous portosystemic shunts, with the strongest association being with shunts [16]. Analysis of the direction of flow in the portal vein is therefore strongly warranted in assessing portal hypertension. Various haemodynamic patterns with reversed flow do exist (Figures 15 and 16). The clinical significance of this Doppler phenomenon is still unclear, but it may play a protective role against future risk of bleeding [14].
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Figure 14. (a) Colour Doppler ultrasound of the portal venous system in a patient with alcoholic fatty liver cirrhosis and continuous hepatofugal flow in the portal vein (the arrows indicate flow direction). (b) The same patient had hepatofugal flow in the mesenteric vein (left) and regular hepatopetal flow in the splenic vein (right). Arrows indicate flow direction.
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Figure 15. Four different haemodynamic flow patterns of continuous flow in the portal vein, the splenic vein and the mesenteric vein (Gaiani S, et al. 1991 [14]). (a) Isolated reversed flow in the mesenteric vein. (b) Isolated reversed flow in the splenic vein. (c) Reversed flow in the portal vein and the splenic vein. (d) Reversed flow in the portal vein and the mesenteric vein.
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Figure 16. (a) Colour Doppler ultrasound of the portal venous system in a patient with liver cirrhosis and continuous hepatofugal flow in the portal vein (left) and hepatopetal flow in the mesenteric vein (VMS) (right). Arrows indicate flow direction. (b) The same patient had reversed flow in the splenic vein (left). The splenic vein (VL) drained into a large perirenal collateral. Arrows indicate flow direction.
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Additionally, continuous reversed portal flow has been described in iatrogenic portosystemic shunts (Figure 17), Budd–Chiari syndrome [17] (Figure 18), cavernous transformation of the main portal vein (Figure 19) and veno-occlusive liver disease after bone marrow transplantation [18].
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Figure 17. Colour Doppler ultrasound of the portal vein in a patient with liver cirrhosis and a transjugular intrahepatic portosystemic shunt (TIPS) (left). In the umbilical segment of the portal vein a reversed flow was seen (right). Arrows indicate flow direction.
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Figure 18. Colour Doppler ultrasound of the portal vein in a patient with breast cancer, diffuse metastative disease of the liver and occlusion of the hepa-tic veins (Budd-Chiari syndrome) (arrows left). In the portal vein a reversed flow was seen (middle, right). Arrows indicate flow direction. VC, vena cava.
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Figure 19. Colour Doppler ultrasound in a patient with cavernous transformation of the portal vein (left) having reversed flow in the splenic vein (middle) and a large perisplenic collateral (right). Arrows indicate flow direction. P, pancreas; Co, confluens.
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Continuous hepatofugal flow in branches of the portal vein is a specific sign for portal hypertension [16]. Portosystemic collateral blood vessels develop from pre-existing small portal vessels and may lead to portosystemic shunting [14]. Depending on collateral size and amount of blood drainage from the portal venous system, hepatofugal portal venous flow may be found in the portal venous trunk, sections of the portal venous systems or only in small portal venous branches, e.g. left gastric vein (Figure 20, Figure 21) [19].
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Figure 20. Colour Doppler ultrasound in a patient with liver cirrhosis and portal hypertension and reversed flow in the left gastric vein (VCV). VP, portal vein.
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Figure 21. Colour Doppler ultrasound of the spleen in a patient with liver cirrhosis. Trans-splenic vessels were seen (middle) with a hepatofugal venous flow (right). Arrows indicate flow direction.
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A stagnant or venous "0" flow may occur in cirrhotic patients. Very slow velocities (less than 2 cm s-1) cannot be detected because the Doppler signal is lower than the threshold of the equipment receiver [6] (Figure 22). Additional respiratory modulation can be observed (Figure 23). There is some evidence that ultrasound contrast enhancement is useful for assessment of blood flow direction with regard to the discrimination on stagnant or venous "0" flow [20].
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Figure 22. Colour Doppler ultrasound of the portal vein in a patient with fatty liver cirrhosis and a "0" flow in the portal vein (VP).
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Figure 23. Colour Doppler ultrasound in a patient with alcoholic fatty liver cirrhosis with a hepatopetal flow during expiration (left) an a venous "0" flow in the portal vein during inspiration (right).
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Conclusion
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Color Doppler ultrasound of the portal vein and its branches shows a wide spectrum of different flow patterns.
In patients with liver cirrhosis, assessment of the direction of portal flow is helpful for diagnosis of portal hypertension. Various other conditions, such as cardial and respiratory cycles, may influence portal venous flow.
Received for publication November 29, 2001.
Revision received April 2, 2002.
Accepted for publication May 9, 2002.
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Abstract
Introduction
