(Radiographics. 2002;22:141-159.)
© RSNA, 2002
Congenital and Acquired Anomalies of the Portal Venous System1
Carmen Gallego, MD,
Maria Velasco, MD,
Pilar Marcuello, MD,
Daniel Tejedor, MD,
Lourdes De Campo, MD and
Alfonsa Friera, MD
1 From the Department of Radiology, Hospital Universitario de la Princesa, Madrid, Spain. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received March 16, 2001; revision requested May 16 and received June 25; accepted July 2. Address correspondence to C.G., Department of Radiology, Hospital Universitario 12 de Octubre, Avenida de Andalucia Km 5400, 28041 Madrid, Spain (e-mail: mamengallego@terra.es).
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Abstract
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Knowledge of the normal anatomy, most frequent variants, and congenital and acquired anomalies of the portal venous system is of great importance for liver surgery and interventional procedures such as creation of transjugular intrahepatic portosystemic shunts. Radiologic studies of the portal venous system include color Doppler ultrasonography (US), computed tomography (CT), magnetic resonance imaging, and arterial or direct portography. Among the most common branching variants of the portal vein are trifurcation, right anterior portal branch arising from the left portal vein, and right posterior portal branch arising from the main portal vein. Agenesis of the right or left portal vein is the most frequently reported congenital anomaly. Venous collateral vessels due to portal hypertension and cavernous transformation of the portal vein are best evaluated with cross-sectional imaging. Intrahepatic portosystemic, arterioportal, and arteriosystemic fistulas and associated perfusion anomalies have characteristic features at dual-phase helical CT. Color Doppler US is the single most useful tool for demonstration of aneurysms of the portal venous system and bland or neoplastic portal vein thrombosis. CT is also the best means of evaluating gas in the portal venous system, which is no longer an ominous sign and must be differentiated from aerobilia.
© RSNA, 2002
Index Terms: Aneurysm, portal vein, 957.73 • Portal vein, abnormalities, 957.13 • Portal vein, anatomy, 957.92 • Portal vein, flow dynamics, 957.711, 957.752 • Portal vein, gas, 957.779 • Portal vein, thrombosis, 957.751 • Shunts, arterioportal, 957.759 • Shunts, portosystemic, 957.759
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Recognize the normal anatomy, normal variants, and congenital anomalies of the portal venous system.
- Describe the imaging appearances of portosystemic collateral vessels, intrahepatic arteriovenous and venovenous shunts, and aneurysms of the portal venous system.
- Identify perfusion anomalies associated with changes in portal vein hemodynamics.
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Introduction
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The portal venous system comprises all of the veins draining the abdominal part of the digestive tract, including the lower esophagus but excluding the lower anal canal. The portal vein conveys blood from viscera and ramifies like an artery at the liver, ending at the sinusoids. Tributaries of the portal vein, which make up the portal venous system, are the splenic, superior mesenteric, left gastric, right gastric, paraumbilical, and cystic veins. Radiologic evaluation of anomalies of the portal venous system is usually performed with color Doppler ultrasonography (US), helical computed tomography (CT), and magnetic resonance (MR) imaging. Arterial portography, direct portography, and splenoportography may also be used, but these are invasive techniques that are being supplanted by MR venography.
Helical CT is a useful tool for assessing abnormalities of the portal venous system. Biphasic dynamic contrast material–enhanced helical CT of the liver can accurately demonstrate both macroscopic and perfusion disorders of the portal venous system. Most perfusion alterations are seen during the hepatic arterial phase (HAP), with normal attenuation in the portal venous phase (PVP). For the past 3 years, we have been evaluating the helical CT manifestations of congenital and acquired anomalies of the portal venous system. Our protocol for biphasic helical CT of the abdomen is as follows: We inject a total of 150 mL of iodinated contrast material at a rate of 3–3.5 mL/sec. HAP images are acquired 20–25 seconds after the start of the injection, and PVP images are acquired 25–30 seconds later. Color Doppler US, MR imaging, and MR angiography are also performed in some cases.
Congenital anomalies of the portal venous system comprise total or partial agenesis of the portal vein, abnormal branching of the portal vein, venous malposition (in situs inversus totalis or in midgut malrotation), arteriovenous malformations, and persistence of fetal valves. The etiology of aneurysms of the portal venous system and some intrahepatic portosystemic shunts is still controversial. Acquired anomalies of the portal venous system comprise portosystemic and portoportal collateral vessels; occlusion of the portal vein; intrahepatic arterioportal or arteriosystemic shunts; arteriovenous fistulas; and gas, thrombosis, or stents in the portal venous system.
In this article, we present an overview of normal variants and congenital and acquired anomalies of the portal venous system. Specific topics discussed are branching variants of the portal vein, congenital anomalies of the portal vein, portosystemic collateral vessels, cavernous transformation of the portal vein, intrahepatic vascular shunts, aneurysms of the portal venous system, thrombosis of the portal venous system, and gas in the portal venous system.
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Branching Variants of the Portal Vein
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The portal vein results from the confluence of the superior mesenteric and splenic veins posterior to the neck of the pancreas. In its most common branching pattern, it divides at the porta hepatis into right and left portal veins. As it courses cranially, the right portal vein first gives off branches to the caudate lobe and then divides into anterior and posterior branches, which subdivide into superior and inferior segmental branches to supply the right lobe of the liver. The left portal vein first has a horizontal course to the left and then turns medially toward the ligamentum teres (umbilical portion), supplying the lateral segments (seg-ments II and III) of the left lobe. It describes a wide and anteriorly concave curve and ends in the superior and inferior segmental branches of segment IV (Fig 1).
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Figure 1. Normal branching pattern of the portal vein. Coronal (left) and axial (right) diagrams show that the main portal vein (1) divides into the right (2) and left portal veins. The left portal vein first courses horizontally (horizontal portion [3]), then turns anteriorly (umbilical portion [4]) toward the ligamentum teres (6). The Cantlie line corresponds to the median fissure and extends from the gallbladder (7) to the inferior vena cava. It is located to the right of the umbilical ligament and divides the liver into right and left lobes. 5 = branch to segment IV.
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The landmarks that we use to describe the normal anatomy of the portal venous system at the liver are the main and right portal vein, the lateral segment and umbilical portion of the left portal vein, the ligamentum teres, the inferior vena cava, and the fossa for the gallbladder. The Cantlie line is defined as a line passing through the gallbladder toward the inferior vena cava and corresponds to the median fissure. It serves as a boundary between the right and left lobes (Figs 1, 2).
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Figure 2a. Most common anatomy of the portal venous system. (a) Contrast-enhanced CT scan shows the horizontal portion of the left portal vein (arrow), which is large. (b) Contrast-enhanced CT scan shows the umbilical portion of the left portal vein (arrowhead), which extends in a wide, concave, anterior curve toward the umbilical ligament. (c) Contrast-enhanced CT scan shows the gallbladder, which is located to the right of the ligamentum teres (arrow).
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Figure 2b. Most common anatomy of the portal venous system. (a) Contrast-enhanced CT scan shows the horizontal portion of the left portal vein (arrow), which is large. (b) Contrast-enhanced CT scan shows the umbilical portion of the left portal vein (arrowhead), which extends in a wide, concave, anterior curve toward the umbilical ligament. (c) Contrast-enhanced CT scan shows the gallbladder, which is located to the right of the ligamentum teres (arrow).
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Figure 2c. Most common anatomy of the portal venous system. (a) Contrast-enhanced CT scan shows the horizontal portion of the left portal vein (arrow), which is large. (b) Contrast-enhanced CT scan shows the umbilical portion of the left portal vein (arrowhead), which extends in a wide, concave, anterior curve toward the umbilical ligament. (c) Contrast-enhanced CT scan shows the gallbladder, which is located to the right of the ligamentum teres (arrow).
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Variants in the normal branching pattern of the intrahepatic portal vein (Fig 3) have been reported since 1957 and occur in approximately 20% of the population (1–3). The most common patterns include trifurcation of the main portal vein (Fig 4) (7.8%–10.8%), right posterior segmental branch arising from the main portal vein (4.7%–5.8%), and right anterior segmental branch arising from the left portal vein (2.9%–4.3%) (2–4). A spectrum of branching variants of the portal vein associated with malposition of the gallbladder has been described in recent years (5,6). Findings comprise an abnormal course of the horizontal portion of the left portal vein and an abnormal umbilical portion that is located above the gallbladder fossa. The gallbladder is deviated to the left and may lie to the left of or astride the ligamentum teres. The Cantlie line does not serve as a boundary between the right and left lobes in these cases (Figs 5, 6). The theory proposed to explain these findings is abnormal regression of the left umbilical vein with persistence of the right umbilical vein. The persistent right umbilical vein would form a right umbilical portion of the left portal vein. Since a whole spectrum of this variant has been reported (5,6), it has yet to be established whether all anomalous umbilical portions originate from a right umbilical vein.
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Figure 3. Four most common branching patterns of the intrahepatic portal vein. A, Coronal diagram shows the normal branching pattern. B, Coronal diagram shows trifurcation of the main portal vein. The right portal vein is not present, and the main portal vein divides into the right anterior, right posterior, and left portal veins at the same level. C, Coronal diagram shows the right anterior branch arising from the left portal vein. The main portal vein divides into the right posterior and left portal veins, and the right anterior portal vein arises from the left portal vein. D, Coronal diagram shows the right posterior branch arising from the main portal vein. The first branch to split off is the right posterior branch. The main portal vein then continues to the right for a variable distance and bifurcates into the right anterior and left portal veins.
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Figure 5. Portal vein anomaly associated with malposition of the gallbladder. Coronal (left) and axial (right) diagrams show that the first branch to split off is the right posterior portal vein. The main portal vein (1) then courses superiorly, giving off the right anterior portal vein and a small, ascending umbilical portion of the left portal vein (4). The gallbladder (7) is located astride the umbilical ligament and does not serve as a boundary between the right and left lobes. 2 = right portal vein, 3 = horizontal portion of the left portal vein, 5 = branch to segment IV, 6 = ligamentum teres.
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Figure 6a. Portal vein anomaly associated with malposition of the gallbladder. (a) Contrast-enhanced CT scan shows a small, ascending umbilical portion of the left portal vein (arrowhead). (b) Contrast-enhanced CT scan shows the umbilical ligament (arrow). The horizontal portion of the left portal vein is not seen. (c) Contrast-enhanced CT scan shows a neoplastic gallbladder (arrows), which is below the umbilical ligament. The Cantlie line is deviated to the left.
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Figure 6b. Portal vein anomaly associated with malposition of the gallbladder. (a) Contrast-enhanced CT scan shows a small, ascending umbilical portion of the left portal vein (arrowhead). (b) Contrast-enhanced CT scan shows the umbilical ligament (arrow). The horizontal portion of the left portal vein is not seen. (c) Contrast-enhanced CT scan shows a neoplastic gallbladder (arrows), which is below the umbilical ligament. The Cantlie line is deviated to the left.
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Figure 6c. Portal vein anomaly associated with malposition of the gallbladder. (a) Contrast-enhanced CT scan shows a small, ascending umbilical portion of the left portal vein (arrowhead). (b) Contrast-enhanced CT scan shows the umbilical ligament (arrow). The horizontal portion of the left portal vein is not seen. (c) Contrast-enhanced CT scan shows a neoplastic gallbladder (arrows), which is below the umbilical ligament. The Cantlie line is deviated to the left.
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Knowledge of these variants is important because ligation of the left portal vein during liver resection or split liver transplantation in some of these cases may lead to necrosis of more than 80% of the liver (5,6).
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Congenital Anomalies of the Portal Vein
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Congenital anomalies of the main portal vein include prepancreatic portal vein, which is frequently associated with situs inversus and other congenital malformations (7); double portal vein; congenital agenesis of the portal vein (8); and congenital agenesis of the major branches of the portal vein. Knowledge of these variants is important for surgical planning and for creation of transjugular intrahepatic portosystemic shunts.
Congenital agenesis of the major branches of the portal vein is the most frequently reported congenital anomaly and should be differentiated from acquired atrophy of the hepatic lobes (9–14). Congenital agenesis is thought to be secondary to failure of the right and left portal veins to develop (10) or thrombosis of the affected lobe or segment during embryologic growth (14). In congenital agenesis of the right hepatic lobe, the right portal vein, right hepatic duct, and right hepatic vein are not identified (9,10). A retrohepatic gallbladder, posterolateral interposition of the right colic flexure, and superior migration of the right kidney are shared features of both congenital agenesis and severe atrophy of the right lobe (Fig 7). Agenesis of the left hepatic lobe is indicated by absence of hepatic parenchyma to the left of the gallbladder fossa and absence of a recognizable ligamentum teres and left portal vein (11). The presence of a rudimentary left portal vein favors the diagnosis of atrophy of the left lobe (Fig 8). Common features of both agenesis and atrophy of the left lobe are a superior location of the gallbladder just beneath the diaphragm, an abnormal U-shaped configuration of the stomach, and an abnormally high duodenal bulb on images from an upper gastrointestinal series (12,13).
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Figure 7a. Atrophy of the right hepatic lobe in a patient with choledocholithiasis. (a) Contrast-enhanced CT scan shows a posteriorly located gallbladder. Agenesis can be ruled out because of the presence of intrahepatic dilated branches of the right hepatic duct (arrow) and a severely atrophied right portal vein (arrowhead). (b) Contrast-enhanced CT scan shows marked hypertrophy of the left hepatic lobe and caudate lobe in association with posterolateral interposition of the hepatic flexure and upward deviation of the right kidney. Arrow = choledocholith.
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Figure 7b. Atrophy of the right hepatic lobe in a patient with choledocholithiasis. (a) Contrast-enhanced CT scan shows a posteriorly located gallbladder. Agenesis can be ruled out because of the presence of intrahepatic dilated branches of the right hepatic duct (arrow) and a severely atrophied right portal vein (arrowhead). (b) Contrast-enhanced CT scan shows marked hypertrophy of the left hepatic lobe and caudate lobe in association with posterolateral interposition of the hepatic flexure and upward deviation of the right kidney. Arrow = choledocholith.
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Figure 8a. Atrophy of the left hepatic lobe. (a) Contrast-enhanced CT scan obtained during the PVP shows a rudimentary left portal vein (arrow) at the medial surface of the liver. There is severe atrophy of the left hepatic lobe (arrowhead). (b) Contrast-enhanced CT scan obtained at the level of the porta hepatis shows absence of the left lobe and left portal vein.
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Figure 8b. Atrophy of the left hepatic lobe. (a) Contrast-enhanced CT scan obtained during the PVP shows a rudimentary left portal vein (arrow) at the medial surface of the liver. There is severe atrophy of the left hepatic lobe (arrowhead). (b) Contrast-enhanced CT scan obtained at the level of the porta hepatis shows absence of the left lobe and left portal vein.
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Portosystemic Collateral Vessels
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The most common cause of portosystemic collateral vessels is portal hypertension. Other causes of portosystemic collateral vessels are splenic or splenomesenteric venous stenosis and obstruction due to neoplasms, pancreatitis, or surgery.
Contrast-enhanced thin-section helical CT is probably the best modality for demonstrating portosystemic collateral vessels in patients with chronic liver disease (15,16). MR imaging may be as accurate but is more expensive and less accessible; in addition, some of the rarest pathways (eg, pleuropericardial or thoracic wall varices) can be missed. Familiarity with the most common flow artifacts is mandatory for correct interpretation of MR angiograms of the portal venous system (17,18).
More than 20 pathways have been described, with the most common being gastroesophageal, paraumbilical, splenorenal, and inferior mesenteric collateral vessels. Pleuropericardial-peritoneal, pancreaticoduodenal, splenoazygos, and mesocaval collateral vessels are unusual pathways for decompression of the portal vein.
Coronary, Esophageal, Paraesophageal, and Gastric Collateral Vessels
Coronary collateral veins at the lesser omentum are the most frequently depicted varices at cross-sectional imaging (in approximately 80% of patients with portal hypertension) (15). They are usually accompanied by esophageal and paraesophageal varices and less commonly by retrogastric varices.
Esophageal varices are of major clinical importance because they are a frequent source of gastrointestinal bleeding (15,16). They are embedded in the wall of the esophagus and are sometimes difficult to see at cross-sectional imaging (Fig 9) because of the lack of adipose tissue surrounding them. Endoscopy is more sensitive than CT to the presence of esophageal varices.
Paraesophageal collateral vessels (Fig 10) are located outside the walls of the esophagus and thus cannot be seen with endoscopy (15). They are so bulky that they may simulate a posterior mediastinal mass at chest radiography. Contrast-enhanced CT is more sensitive to paraesophageal varices than to esophageal varices.
Gastric varices are located at the posterosuperior aspect of the gastric fundus and may simulate a gastric neoplasm on nonenhanced CT scans. Most gastric varices drain into the esophageal or paraesophageal veins, but occasionally they drain into the left renal vein (15,16). When a gastrorenal shunt develops, the chances of hepatic encephalopathy increase.
Paraumbilical Collateral Vessels
Paraumbilical collateral vessels are next in frequency; their extent was usually underestimated with conventional angiography alone until the advent of cross-sectional imaging (15,18). Numerous paraumbilical vessels can arise from the left portal vein in patients with cirrhosis. Patent paraumbilical vessels are a good predictor of portal hypertension (Fig 11). They are an acceptable means of decompression of the portal venous system because they are not associated with gastrointestinal bleeding (15). The most common pattern of drainage of paraumbilical veins is through the epigastric veins into the external iliac veins (19). Paraumbilical veins can also connect with subcutaneous vessels of the anterior abdominal wall, creating the caput medusae: a varicose dilatation of subcutaneous veins around the umbilicus (15,16).
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Figure 11. Paraumbilical vessels in a patient with portal hypertension. Contrast-enhanced CT scan shows three paraumbilical vessels (arrows). Aneurysmal dilatation of one such vessel (arrowhead) is also seen.
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Splenorenal Collateral Vessels
Collateral vessels from the splenic hilum to the left renal vein are fairly common. They are desirable spontaneous shunts in portal hypertension because they are not associated with gastrointestinal bleeding (16). However, enlarged shunts are significantly associated with hepatic encephalopathy. A common feature depicted at cross-sectional imaging is an enlarged left renal vein and dilatation of the inferior vena cava at the level of the left renal vein in the presence of a splenorenal shunt.
Mesenteric Collateral Vessels
Inferior mesenteric collateral vessels are less frequent than the collateral vessels mentioned earlier but are of great importance because of their association with rectal bleeding. The portal venous system (superior hemorrhoidal vein) and the systemic venous circulation (middle and inferior hemorrhoidal veins) connect via the hemorrhoidal plexus (15). If one is not aware of a patient’s portal hypertension, mesenteric collateral vessels can be mistaken for a rectal mass protruding into the rectal lumen on nonenhanced CT scans (16) (Fig 12).
Mesocaval shunts are portosystemic collateral vessels between the inferior mesenteric vein and inferior vena cava that are established through lumbar and retroperitoneal veins (15–18). These collateral vessels are not associated with an increased risk of rectal bleeding.
Mesentericorenal collateral vessels between the superior mesenteric vein and the right and left renal veins are the least frequent mesenteric shunts (15).
Other Collateral Pathways
Rare collateral pathways have been reported, including pleuropericardial-peritoneal (Fig 13), splenoazygos, intrahepatic, and from the coronary or splenic veins to the inferior pulmonary vein or to diaphragmatic veins.
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Figure 13a. Pleuropericardial-peritoneal collateral vessel. (a) Contrast-enhanced CT scan shows an enhancing serpentine venous structure (arrowhead) that courses toward the anterior thoracic wall. (b) Contrast-enhanced CT scan shows that the venous structure (arrowhead) arises from the left portal vein.
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Figure 13b. Pleuropericardial-peritoneal collateral vessel. (a) Contrast-enhanced CT scan shows an enhancing serpentine venous structure (arrowhead) that courses toward the anterior thoracic wall. (b) Contrast-enhanced CT scan shows that the venous structure (arrowhead) arises from the left portal vein.
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Portoportal and portosystemic collateral vessels also develop if there is occlusion of the splenic vein. If obstruction occurs near the splenic hilum, collateral vessels develop at the gastric fundus and the greater and lesser omentum, resulting in gastric fundal varices and an enlarged vein of Barkow (omental vein). When splenic vein occlusion is near the splenomesenteric confluence, mesocaval (via the inferior mesenteric vein), hemorrhoidal, splenorenal, or splenoretroperitoneal collateral vessels are the usual portosystemic pathways of decompression (18,19).
In occlusion of the superior mesenteric vein, mesenteric varices and mesentericorenal collateral vessels develop (16,19).
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Cavernous Transformation of the Portal Vein
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Cavernous transformation of the portal vein consists of formation of venous channels within and around a previously stenosed or occluded portal vein that act as portoportal collateral vessels. Two other etiopathogenic theories have been proposed but have not been demonstrated to date: (a) congenital agenesis of the portal vein leading to development of periportal collateral vessels and (b) a hemangioma of the portal vein (20). Conversely to what was initially thought, cavernous transformation of the portal vein can occur as soon as 6–20 days after the thrombotic event, even if partial recanalization of the thrombus develops (20). Dilated biliary branches (cystic and pericholecystic veins) and gastric branches (left and right gastric veins) of the portal vein and the partially recanalized thrombus compose the cavernous transformation of the portal vein (20,21). The development of these vessels supports the theory that cavernous transformation of the portal vein is a portoportal collateral pathway that substitutes for a thrombosed portal vein. The veins are usually insufficient to bypass the entire splenomesenteric inflow, and signs of portal hypertension frequently coexist (20,22).
On contrast-enhanced CT scans, a characteristic beaded appearance (mass of veins) at the porta hepatis is the most frequent finding (Fig 14). Intrahepatic extension of the cavernous transformation (20) and involvement of intrahepatic branches with a normal-appearing main portal vein have also been described (22). Inhomogeneous, peripheral, patchy areas of high attenuation can be seen during the HAP. This pattern of perfusion is frequently seen and occurs because the central regions of the liver are better supplied by the cavernous portal vein than are the peripheral regions; therefore, a peripheral increase in arterial inflow develops (23,24).
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Figure 14a. Cavernous transformation of the portal vein. (a) Contrast-enhanced CT scan obtained during the late HAP shows a beaded appearance (a mass of veins) at the porta hepatis. Because flow through the cavernous portal vein is not sufficient to supply the liver, peripheral areas of increased uptake are seen (arrow), which reflect peripheral increased arterial inflow. (b) Contrast-enhanced coronal MR angiogram obtained in a patient with splenomegaly shows a cavernous portal vein and multiple collateral vessels. (Fig 14b courtesy of Carlos Marín, MD, Hospital San Rafael, Madrid, Spain.)
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Figure 14b. Cavernous transformation of the portal vein. (a) Contrast-enhanced CT scan obtained during the late HAP shows a beaded appearance (a mass of veins) at the porta hepatis. Because flow through the cavernous portal vein is not sufficient to supply the liver, peripheral areas of increased uptake are seen (arrow), which reflect peripheral increased arterial inflow. (b) Contrast-enhanced coronal MR angiogram obtained in a patient with splenomegaly shows a cavernous portal vein and multiple collateral vessels. (Fig 14b courtesy of Carlos Marín, MD, Hospital San Rafael, Madrid, Spain.)
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At Doppler US, hepatopetal flow is observed, but this flow lacks the characteristic respiratory undulation of normal portal vein flow (20). Prominent arterial inflow is also seen, reflecting the diminished flow in the intrahepatic portal veins.
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Intrahepatic Vascular Shunts
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Intrahepatic vascular connections between the hepatic artery, the portal vein, and the hepatic veins are rare. The most frequently reported abnormal communications are the small arterioportal shunts that occur in cirrhotic livers. Most of them are so minute that they are below the threshold of visualization with cross-sectional imaging. Large intrahepatic communications can occur between the portal and hepatic veins (portosystemic shunts), the hepatic artery and portal vein (arterioportal shunts), and the hepatic artery and hepatic veins (arteriosystemic shunts) (25).
Portosystemic Shunts
Direct communication between a portal vein and a hepatic vein is uncommon. Several appearances of intrahepatic portosystemic shunts have been described (26). The most frequently reported intrahepatic portosystemic shunt occurs between the right portal vein and the inferior vena cava. It is considered a type of portosystemic collateral vessel because it usually occurs in the clinical setting of portal hypertension and is frequently associated with hepatic encephalopathy (25–27). The least common intrahepatic portosystemic shunt is a communication between a portal vein branch and a hepatic vein through an aneurysm (Fig 15). Multiple diffuse communications between peripheral portal and hepatic veins and a single communication between a portal vein branch and a hepatic vein in one hepatic segment are other appearances of intrahepatic portosystemic shunts (26).
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Figure 15a. Spontaneous intrahepatic portosystemic shunt. (a) Longitudinal color Doppler US image shows an abnormal communication between the left portal vein (VPI) and the middle hepatic veins (VHM). (b) Transverse duplex Doppler US image shows that the left portal vein has an abnormal spectral pattern. The undulating, triphasic waveform resembles that of the middle hepatic vein. (c) Transverse duplex Doppler US image shows that the right portal vein has a normal spectral pattern. (d) Longitudinal duplex Doppler US image shows the spectral pattern of the middle hepatic vein. (e) Oblique coronal two-dimensional contrast-enhanced CT scan obtained with multiplanar reconstruction shows the communication, which occurs through an aneurysmal dilatation of a branch of the left portal vein.
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Figure 15b. Spontaneous intrahepatic portosystemic shunt. (a) Longitudinal color Doppler US image shows an abnormal communication between the left portal vein (VPI) and the middle hepatic veins (VHM). (b) Transverse duplex Doppler US image shows that the left portal vein has an abnormal spectral pattern. The undulating, triphasic waveform resembles that of the middle hepatic vein. (c) Transverse duplex Doppler US image shows that the right portal vein has a normal spectral pattern. (d) Longitudinal duplex Doppler US image shows the spectral pattern of the middle hepatic vein. (e) Oblique coronal two-dimensional contrast-enhanced CT scan obtained with multiplanar reconstruction shows the communication, which occurs through an aneurysmal dilatation of a branch of the left portal vein.
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Figure 15c. Spontaneous intrahepatic portosystemic shunt. (a) Longitudinal color Doppler US image shows an abnormal communication between the left portal vein (VPI) and the middle hepatic veins (VHM). (b) Transverse duplex Doppler US image shows that the left portal vein has an abnormal spectral pattern. The undulating, triphasic waveform resembles that of the middle hepatic vein. (c) Transverse duplex Doppler US image shows that the right portal vein has a normal spectral pattern. (d) Longitudinal duplex Doppler US image shows the spectral pattern of the middle hepatic vein. (e) Oblique coronal two-dimensional contrast-enhanced CT scan obtained with multiplanar reconstruction shows the communication, which occurs through an aneurysmal dilatation of a branch of the left portal vein.
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Figure 15d. Spontaneous intrahepatic portosystemic shunt. (a) Longitudinal color Doppler US image shows an abnormal communication between the left portal vein (VPI) and the middle hepatic veins (VHM). (b) Transverse duplex Doppler US image shows that the left portal vein has an abnormal spectral pattern. The undulating, triphasic waveform resembles that of the middle hepatic vein. (c) Transverse duplex Doppler US image shows that the right portal vein has a normal spectral pattern. (d) Longitudinal duplex Doppler US image shows the spectral pattern of the middle hepatic vein. (e) Oblique coronal two-dimensional contrast-enhanced CT scan obtained with multiplanar reconstruction shows the communication, which occurs through an aneurysmal dilatation of a branch of the left portal vein.
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Figure 15e. Spontaneous intrahepatic portosystemic shunt. (a) Longitudinal color Doppler US image shows an abnormal communication between the left portal vein (VPI) and the middle hepatic veins (VHM). (b) Transverse duplex Doppler US image shows that the left portal vein has an abnormal spectral pattern. The undulating, triphasic waveform resembles that of the middle hepatic vein. (c) Transverse duplex Doppler US image shows that the right portal vein has a normal spectral pattern. (d) Longitudinal duplex Doppler US image shows the spectral pattern of the middle hepatic vein. (e) Oblique coronal two-dimensional contrast-enhanced CT scan obtained with multiplanar reconstruction shows the communication, which occurs through an aneurysmal dilatation of a branch of the left portal vein.
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Both congenital and acquired causes have been postulated for intrahepatic portosystemic shunts, but their origin is still controversial. Persistence of an omphalomesenteric venous system with the right horn of the sinus venosus and rupture of a congenital aneurysm of the portal vein into a hepatic vein are congenital conditions that have been proposed to explain intrahepatic portosystemic shunts. Acquired conditions that would explain intrahepatic portosystemic shunts are development of intrahepatic portosystemic collateral vessels in cirrhotic patients and trauma (25,27).
Helical CT scans obtained during the PVP show a communication between a portal vein branch and the hepatic vein, as well as early and asymmetric enhancement of the hepatic vein. Color Doppler US is the single most useful tool for diagnosis of intrahepatic portosystemic shunts, but in most cases helical CT is performed to confirm the diagnosis. Because resistance is diminished in the portal vein, flow in the involved branch can assume the wavy, triphasic flow pattern of the hepatic veins (Fig 15).
Arterioportal Shunts
Arterioportal shunts may be congenital (vascular malformations in Rendu-Osler disease) or acquired (trauma, iatrogenic causes, cirrhosis) and consist of a communication between the hepatic artery and the portal venous system. They are minute or large intrahepatic arterioportal shunts.
Minute arterioportal shunts in cirrhosis are well documented and are not necessarily related to hepatocarcinoma (Fig 16). They appear as small, wedge-shaped, peripheral or subcapsular areas of increased attenuation with early portal venous filling on HAP CT scans or hepatic arteriograms (25) and demonstrate normal attenuation during the PVP. Occasionally, small, nontumorous arterioportal shunts appear as a nodular, irregularly outlined contour and inhomogeneously increased uptake during the HAP. In this clinical setting, the arterioportal shunt may not be distinguished from a small hepatocarcinoma, and exclusion of a tumor-related arterioportal shunt requires serial examinations (28).
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Figure 16a. Minute arterioportal fistula in a patient with liver cirrhosis. (a) Contrast-enhanced CT scan obtained during the HAP shows a peripheral, wedge-shaped, transient area of high attenuation (arrow). A direct communication between the hepatic artery and the portal vein is not seen. (b) Corresponding contrast-enhanced CT scan obtained during the PVP shows normal attenuation of the hepatic parenchyma. Two-year follow-up revealed no changes in size or morphology.
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Figure 16b. Minute arterioportal fistula in a patient with liver cirrhosis. (a) Contrast-enhanced CT scan obtained during the HAP shows a peripheral, wedge-shaped, transient area of high attenuation (arrow). A direct communication between the hepatic artery and the portal vein is not seen. (b) Corresponding contrast-enhanced CT scan obtained during the PVP shows normal attenuation of the hepatic parenchyma. Two-year follow-up revealed no changes in size or morphology.
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Congenital arteriovenous malformations, liver biopsy (Fig 17), trauma, or liver neoplasms (Fig 18) may lead to large arterioportal fistulas. Not frequently, these fistulas themselves cause portal hypertension and high-output heart failure (29,30). In such cases, portal hypertension may develop rapidly (in weeks to months) due to the increased flow and pressure in the portal venous system. Subsequently, hepatoportal sclerosis and fibrosis of the portal radicles develop, which further contribute to the portal hypertension (30). Helical CT performed during the HAP shows early and marked enhancement of the main portal vein, segmental branches, or major tributaries with an attenuation approaching that of the aorta and early enhancement of the portal vein with nonenhancement of the splenic and mesenteric veins.
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Figure 17a. Postbiopsy arterioportal fistula. (a) Contrast-enhanced CT scan obtained during the HAP shows contrast material in the aorta (arrowhead) and the peripheral segmental branches of the right anterior portal vein (black arrow). The main portal vein and lobar branches are not enhanced. A wedge-shaped, hyperattenuating region of hepatic parenchyma (white arrows) surrounds the fistula. This finding is related to an increase in arterial inflow in the area around the fistula. (b) Axial maximum intensity projection image obtained during the HAP shows the same findings. The aorta, the hepatic artery (arrowhead), and the sublobar branches of the right portal vein (arrow) are markedly enhanced.
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Figure 17b. Postbiopsy arterioportal fistula. (a) Contrast-enhanced CT scan obtained during the HAP shows contrast material in the aorta (arrowhead) and the peripheral segmental branches of the right anterior portal vein (black arrow). The main portal vein and lobar branches are not enhanced. A wedge-shaped, hyperattenuating region of hepatic parenchyma (white arrows) surrounds the fistula. This finding is related to an increase in arterial inflow in the area around the fistula. (b) Axial maximum intensity projection image obtained during the HAP shows the same findings. The aorta, the hepatic artery (arrowhead), and the sublobar branches of the right portal vein (arrow) are markedly enhanced.
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Figure 18a. Neoplastic arterioportal fistula in a patient with multicentric hepatocellular carcinoma. (a) Contrast-enhanced CT scan obtained during the HAP shows tumor (*) invading the left portal vein (arrow) and a tumoral thrombus within the vein. (b) Contrast-enhanced CT scan obtained during the HAP shows that an arterioportal fistula has developed due to invasion by the tumor (*). There is increased uptake of contrast material in the portal vein. Ill-defined areas of increased attenuation are seen (arrowheads), which are related to increased inflow in the peripheral portal vein branches due to the shunt itself. (c) Axial maximum intensity projection image shows equal and simultaneous enhancement of the aorta, hepatic artery, and portal vein. The thrombus in the left portal vein is evident.
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Figure 18b. Neoplastic arterioportal fistula in a patient with multicentric hepatocellular carcinoma. (a) Contrast-enhanced CT scan obtained during the HAP shows tumor (*) invading the left portal vein (arrow) and a tumoral thrombus within the vein. (b) Contrast-enhanced CT scan obtained during the HAP shows that an arterioportal fistula has developed due to invasion by the tumor (*). There is increased uptake of contrast material in the portal vein. Ill-defined areas of increased attenuation are seen (arrowheads), which are related to increased inflow in the peripheral portal vein branches due to the shunt itself. (c) Axial maximum intensity projection image shows equal and simultaneous enhancement of the aorta, hepatic artery, and portal vein. The thrombus in the left portal vein is evident.
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Figure 18c. Neoplastic arterioportal fistula in a patient with multicentric hepatocellular carcinoma. (a) Contrast-enhanced CT scan obtained during the HAP shows tumor (*) invading the left portal vein (arrow) and a tumoral thrombus within the vein. (b) Contrast-enhanced CT scan obtained during the HAP shows that an arterioportal fistula has developed due to invasion by the tumor (*). There is increased uptake of contrast material in the portal vein. Ill-defined areas of increased attenuation are seen (arrowheads), which are related to increased inflow in the peripheral portal vein branches due to the shunt itself. (c) Axial maximum intensity projection image shows equal and simultaneous enhancement of the aorta, hepatic artery, and portal vein. The thrombus in the left portal vein is evident.
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Two types of perfusion anomalies have been reported in large arterioportal shunts (23,24, 31,32): (a) A nonspecific, homogeneous, regional increase in arterial inflow has been reported in the presence of diminished portal vein inflow (in cases of neoplastic thrombosis and arterioportal fistula). This anomaly is not related to the shuntitself and is seen in other clinical settings. It appears as an ipsilateral increase in the attenuation of the hepatic parenchyma during the HAP. (b) An increase in portal vein inflow due to the shunt itself has also been reported. This anomaly appears as a contralateral increase in the attenuation of the hepatic parenchyma with prolonged enhancement of the portal vein during the HAP and PVP.
Reduction and loss of the geographic enhancement of the splenic parenchyma during the HAP has also been reported in association with large arterioportal shunts. This finding has been attributed to diminished splenic artery inflow (31).
At color Doppler US, hepatic artery to portal vein shunts manifest as pulsatility of the portal vein flow.
Arteriosystemic Shunts
The rarest form of an intrahepatic shunt is a communication between the hepatic artery (or other systemic arteries) and the hepatic veins. Such shunts have been reported in congenital arteriovenous malformations of the liver like hereditary hemorrhagic telangiectasia (Rendu-Osler disease), hepatocarcinoma, and large hemangiomas (25,33). Contrast-enhanced CT performed during the HAP shows increased asymmetric and early enhancement of a hepatic vein. Significant changes in the Doppler US waveform of the hepatic vein are seen only in severe cases of congenital arteriovenous malformation (33).
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Aneurysms of the Portal Venous System
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Most aneurysms of the venous system occur in the popliteal, jugular, or saphenous veins, with the rarest being those affecting the femoral, caval, forearm, or portal veins (34). Aneurysms of the portal vein were once thought to be extremely rare but nowadays are well documented and not unusual. They still represent only 3% of all aneurysms of the venous system (35).
Although aneurysms of the portal venous system may be present in patients with liver disease, an overwhelming majority of patients do not have portal hypertension or chronic liver disease. Therefore, portal hypertension could be contributory but is not essential to the development of portal venous system aneurysms (36). Both congenital and acquired causes have been proposed. Reasons to favor a congenital origin are the in utero diagnosis of a portal vein aneurysm (37), evidence of portal venous system aneurysms in patients with histologically proved normal livers (34), and the frequent stability of the aneurysms at follow-up (34–36). Incomplete regression of the distal right vitelline vein leading to a diverticulum that would ultimately develop into an aneurysm in the proximal superior mesenteric vein could explain aneurysms in that location. An inherent weakness of the vessel wall is another theory proposed to support a congenital origin. Theories about an acquired origin are based on the significant presence of aneurysms in patients who have portal hypertension, have had necrotizing pancreatitis, or have undergone abdominal trauma or surgery (35,36,38).
The most common locations are the splenomesenteric venous confluence (Fig 19), main portal vein, and intrahepatic portal vein branches at bifurcation sites; the rarest locations are the splenic, mesenteric, and umbilical veins (Fig 11) (36). Since there are variations in the diameters of both normal and cirrhotic portal veins, an aneurysm of the portal venous system is considered to be present if the vessel diameter is significantly larger at that point than in the remainder of the vessel, especially if the morphology is saccular or fusiform (36). Bilobulated (38) and synchronous (39,40) portal vein aneurysms have also been reported.
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Abstract
LEARNING OBJECTIVES
