(Radiographics. 1999;19:973-987.)
© RSNA, 1999
Contrast-enhanced Three-dimensional MR Portography1
Akira Okumura, MD,
Yuji Watanabe, MD, PhD,
Masako Dohke, MD,
Takayoshi Ishimori, MD,
Yoshiki Amoh, MD,
Kazushige Oda, MD and
Yoshihiro Dodo, MD, PhD
1 From the Department of Radiology, Kurashiki Central Hospital, Miwa 1-1-1, Kurashiki 710-8602, Japan. Presented as a scientific exhibit at the 1997 RSNA scientific assembly. Received April 16, 1998; revision requested May 22 and received September 14; accepted September 16. Address reprint requests to Y.W.
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Abstract
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Three-dimensional (3D) magnetic resonance (MR) portography with contrast material enhancement is a fast means of evaluating the portal venous system that has some advantages over currently used modalities, such as digital subtraction angiography, helical computed tomography, ultrasonography, and nonenhanced MR angiography with time-of-flight and phase-contrast techniques. With contrast-enhanced 3D MR portography, a first-pass study of the mesenteric vasculature is performed after rapid bolus injection of gadopentetate dimeglumine; a 3D fast field echo sequence is used, which can demonstrate the intrahepatic and extrahepatic portal venous system clearly. Repeated sequences after administration of gadopentetate dimeglumine allow separate demonstration of the splanchnic arteries and portomesenteric veins. The images are reconstructed by means of maximum-intensity projection postprocessing, and a subtraction technique can be used to eliminate arterial enhancement and demonstrate portosystemic shunts. The coronal source images simultaneously demonstrate parenchymal lesions of the liver, pancreas, biliary tract, and spleen. This technique is clinically indicated in portosystemic shunt, portal vein thrombosis, hepatocellular carcinoma, pancreatobiliary tumor, hepatic vein obstruction, differentiation of splanchnic arterial from portal venous disease, and gastrointestinal hemorrhage. Its limitations include allergic reactions to contrast media, inappropriate positioning of the 3D acquisition slab, respiratory motion artifacts, and pseudodissection.
Index Terms: Magnetic resonance (MR), maximum intensity projection, 957.12949 • Magnetic resonance (MR), three-dimensional, 957.12917 • Magnetic resonance (MR), vascular studies, 957.12942 • Portal vein, MR, 957.12942 • Portal vein, stenosis or obstruction, 957.75
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INTRODUCTION
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The portal venous system must be evaluated before one can plan treatment in patients with portal hypertension; portal vein thrombosis; or a tumor of the liver, pancreas, or bile duct. Three-dimensional (3D) magnetic resonance (MR) portography has some advantages over other modalities currently used for this purpose (1–5). These other modalities include arterial portography, percutaneous transhepatic portography, and splenoportography, which are invasive and limited by flow dynamics. Color Doppler ultrasonography (US) is noninvasive and relatively inexpensive and can provide semiquantitative information on portal blood flow (6,7), but it is operator dependent and may be unsuccessful when a suitable acoustic window is not available. Contrast material–enhanced helical computed tomography (CT) can demonstrate the portal venous system in a short time (8), but this technique uses ionizing radiation and requires a large amount of contrast material.
Nonenhanced MR angiography with time-of-flight and phase-contrast techniques is another means of demonstrating the portal venous system (9–13) but is limited by its long data acquisition time, motion and flow artifact, and in-plane saturation. Recent studies have demonstrated that MR angiography with contrast enhancement is suited for evaluation of the portal venous system, and its use overcomes flow artifacts and saturation effects (14). MR portograms reconstructed by means of maximum-intensity projection postprocessing, as well as the coronal source images, provide detailed information about both the portal venous system and parenchymal lesions. Furthermore, the images of various diseases of the portal venous system obtained with this technique resemble conventional x-ray angiograms.
In this article, we present the technique, clinical applications, and limitations of contrast-enhanced 3D MR portography.
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TECHNIQUE
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The principle of contrast-enhanced MR portography is to image a high concentration of contrast material circulating in the portal venous system. To keep the portal venous concentration of gadopentetate dimeglumine as high as possible, a large dose (0.2 mmol/kg) is typically injected intravenously (1–4). We have modified this method by using a rapidly administered bolus of gadopentetate dimeglumine in a standard dose (0.1 mmol/kg). There is no consensus as to the optimal technique for contrast-enhanced MR portography, including pulse sequence, two-dimensional or 3D data acquisition, and timing of contrast material injection; the best combination of techniques remains to be determined.
Our current MR portography protocol is as follows: MR imaging is performed with a 1.5-T superconducting magnet system (Gyroscan ACS-NT; Philips Medical Systems, Eindhoven, The Netherlands) with a 15-mT/m gradient. The patient is positioned supine on the patient table. A peripheral intravenous line is placed in the subcutaneous veins of the forearm or antecubital fossa with a 19-gauge needle. Three-dimensional fast imaging is performed with a fast field echo technique and a quadrature body coil in the coronal plane. The imaging parameters are as follows: 8.7/2.7 (repetition time msec/echo time msec), 35° flip angle, one signal acquired, partial-echo acquisition, 330–400-mm field of view, and 205 x 256 matrix. The thickness of slabs and sections varies depending on the patient so as to cover the entire portal, splenic, and superior mesenteric veins. The range of thicknesses is as follows: slab thickness, 80–130 mm; section thickness, 4–10 mm; and overlap, 2–5 mm. The imaging time for each sequence is 12–24 seconds, which permits breath-hold imaging. Images are obtained before and after rapid intravenous injection of gadopentetate dimeglumine in a 0.1-mmol/kg bolus. The injection is performed within 5 seconds and is followed by flushing with physiologic saline solution (20 mL). Five imaging sets are consecutively acquired after injection of gadopentetate dimeglumine (Fig 1).
Before imaging, patients are instructed to hold their breath in the same manner five times consecutively with short intervals between the breath holds; they rehearse to help reduce respiratory motion artifact. Patients have an oxygen mask on the nose and mouth and breathe oxygen at the rate of 3 L/min during the examination. Debilitated patients who are unable to hold their breath for 12–24 seconds are instructed to perform shallow breathing during imaging.
Contrast-enhanced 3D MR portograms are created by compressing images of the portal phase (usually the second or third 3D data set acquired after administration of gadopentetate dimeglumine) with maximum-intensity projection. A subtraction technique can be used to eliminate arterial enhancement when such enhancement conceals the portal venous system. The 3D data set obtained immediately after administration of gadopentetate dimeglumine is usually an arterial-dominant phase and is used as a mask for image subtraction. The subtraction is performed with commercially available software. The second or third 3D data set acquired after administration of gadopentetate dimeglumine is subtracted section by section. Contrast-enhanced MR portograms with arterial-phase subtraction are created by compressing subtracted images of the portal phase with maximum-intensity projection.
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CLINICAL APPLICATIONS
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Contrast-enhanced 3D MR portography can demonstrate the intrahepatic and extrahepatic portal venous system as well as hepatic veins. Its advantages over digital subtraction angiography (DSA) include its large field of view, its short imaging time, and its noninvasive nature and low risk of complications, which permit repeated studies. Clinical applications of contrast-enhanced 3D MR portography include portal hypertension (portosystemic shunt, portal vein obstruction, hepatic vein obstruction), hepatic encephalopathy, ascending portal thrombophlebitis, hepatocellular carcinoma and pancreatobiliary tumors, gastrointestinal hemorrhage, and differentiation of splanchnic arterial disease from portal venous disease. In patients with portal hypertension, 3D MR portography can be used to evaluate portosystemic shunt, hepatopetal collateral pathways, and obstruction of the portal or hepatic veins. In planning treatment for hepatic encephalopathy, it is important to identify the causative portosystemic shunt. In suspected cases of ascending portal thrombophlebitis, it is important to assess the severity of portal vein obstruction as well as portal collateral vessels. In patients with hepatocellular carcinoma or pancreatobiliary tumors, one must determine the presence or absence of portal vein invasion when planning treatment. Other applications include detection of the bleeding point in patients with gastrointestinal hemorrhage and differentiation of splanchnic arterial disease from portomesenteric venous disease (1,4).
Portosystemic Shunt
It is important to evaluate portosystemic collateral pathways in patients with hepatic encephalopathy and portal hypertension due to such conditions as liver cirrhosis, chronic hepatitis, Banti disease, and Budd-Chiari syndrome because such patients are at high risk of hepatic coma and massive hemorrhage from esophagogastric varix. In general, portosystemic shunts can be formed anywhere in the abdomen and include esophagogastric varix (Fig 2); paraumbilical vein; and mesenteric-gonadal (Fig 3), mesenteric-retroperitoneal (Fig 4), portophrenic, intrahepatic portosystemic (Fig 5), and splenorenal (Figs 2, 6) shunts (15). Therefore, it is necessary to survey the whole abdomen.
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Figures 2, 3. (2) Esophagogastric varix in a 58-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large gastric varix and splenorenal shunt (arrows), but a dilated coronary vein and esophageal varix (arrowheads) are not clearly seen due to superimposition of the aortic enhancement. (b) Contrast-enhanced 3D MR portogram with arterial-phase subtraction reveals not only the esophageal varix but also a large mediastinal varix. Open arrow = portal vein, solid arrow = inferior vena cava. (3) Mesenteric-gonadal shunt in a 68-year-old man with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram reveals a portosystemic collateral pathway from the ileocolic vein (solid arrow) to the right testicular vein (open arrow). Contrast-enhanced CT included only the upper abdomen and thus did not reveal this mesenteric-gonadal shunt. Note the small hepatic hemangioma (arrowhead).
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Figures 2, 3. (2) Esophagogastric varix in a 58-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large gastric varix and splenorenal shunt (arrows), but a dilated coronary vein and esophageal varix (arrowheads) are not clearly seen due to superimposition of the aortic enhancement. (b) Contrast-enhanced 3D MR portogram with arterial-phase subtraction reveals not only the esophageal varix but also a large mediastinal varix. Open arrow = portal vein, solid arrow = inferior vena cava. (3) Mesenteric-gonadal shunt in a 68-year-old man with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram reveals a portosystemic collateral pathway from the ileocolic vein (solid arrow) to the right testicular vein (open arrow). Contrast-enhanced CT included only the upper abdomen and thus did not reveal this mesenteric-gonadal shunt. Note the small hepatic hemangioma (arrowhead).
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Figures 2, 3. (2) Esophagogastric varix in a 58-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large gastric varix and splenorenal shunt (arrows), but a dilated coronary vein and esophageal varix (arrowheads) are not clearly seen due to superimposition of the aortic enhancement. (b) Contrast-enhanced 3D MR portogram with arterial-phase subtraction reveals not only the esophageal varix but also a large mediastinal varix. Open arrow = portal vein, solid arrow = inferior vena cava. (3) Mesenteric-gonadal shunt in a 68-year-old man with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram reveals a portosystemic collateral pathway from the ileocolic vein (solid arrow) to the right testicular vein (open arrow). Contrast-enhanced CT included only the upper abdomen and thus did not reveal this mesenteric-gonadal shunt. Note the small hepatic hemangioma (arrowhead).
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Figures 4, 5. (4) Mesenteric-retroperitoneal shunt in a 56-year-old woman with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram shows a large portosystemic collateral pathway from the inferior mesenteric vein (solid arrow) to the left iliac vein (open arrows). Note that the dilated inferior mesenteric vein connects with the confluence of the splenic and superior mesenteric veins. (5) Intrahepatic portosystemic shunt in a 62-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large intrahepatic portosystemic collateral pathway (solid arrow) from the right portal vein (open arrow) to an accessory hepatic vein. Note that the intrahepatic portal vein branches are small. (b)Axial fat-suppressed T1-weighted MR image (500/18) clearly demonstrates the collateral pathway (arrow).
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Figures 4, 5. (4) Mesenteric-retroperitoneal shunt in a 56-year-old woman with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram shows a large portosystemic collateral pathway from the inferior mesenteric vein (solid arrow) to the left iliac vein (open arrows). Note that the dilated inferior mesenteric vein connects with the confluence of the splenic and superior mesenteric veins. (5) Intrahepatic portosystemic shunt in a 62-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large intrahepatic portosystemic collateral pathway (solid arrow) from the right portal vein (open arrow) to an accessory hepatic vein. Note that the intrahepatic portal vein branches are small. (b) Axial fat-suppressed T1-weighted MR image (500/18) clearly demonstrates the collateral pathway (arrow).
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Figures 4, 5. (4) Mesenteric-retroperitoneal shunt in a 56-year-old woman with liver cirrhosis and hepatic encephalopathy. Contrast-enhanced 3D MR portogram shows a large portosystemic collateral pathway from the inferior mesenteric vein (solid arrow) to the left iliac vein (open arrows). Note that the dilated inferior mesenteric vein connects with the confluence of the splenic and superior mesenteric veins. (5) Intrahepatic portosystemic shunt in a 62-year-old man with alcoholic liver cirrhosis and hepatic encephalopathy. (a) Contrast-enhanced 3D MR portogram shows a large intrahepatic portosystemic collateral pathway (solid arrow) from the right portal vein (open arrow) to an accessory hepatic vein. Note that the intrahepatic portal vein branches are small. (b) Axial fat-suppressed T1-weighted MR image (500/18) clearly demonstrates the collateral pathway (arrow).
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Figure 6a. Gastric varix and splenorenal shunt in a 64-year-old man with liver cirrhosis. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows a dilated coronary vein (straight solid arrow), gastric varix (open arrow), and splenorenal shunt (curved arrow). The vertical white line (arrowhead) is an artifact caused by subtraction of the aortic enhancement. (b) Arterial portogram obtained with celiac arteriography also demonstrates these collateral pathways, which are less conspicuous than on the MR portogram (a). (c) Contrast-enhanced MR portogram obtained after balloon-occluded retrograde transvenous obliteration no longer shows the gastric varix, although the splenorenal shunt is still seen to be patent (arrow).
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Figure 6b. Gastric varix and splenorenal shunt in a 64-year-old man with liver cirrhosis. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows a dilated coronary vein (straight solid arrow), gastric varix (open arrow), and splenorenal shunt (curved arrow). The vertical white line (arrowhead) is an artifact caused by subtraction of the aortic enhancement. (b) Arterial portogram obtained with celiac arteriography also demonstrates these collateral pathways, which are less conspicuous than on the MR portogram (a). (c) Contrast-enhanced MR portogram obtained after balloon-occluded retrograde transvenous obliteration no longer shows the gastric varix, although the splenorenal shunt is still seen to be patent (arrow).
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Figure 6c. Gastric varix and splenorenal shunt in a 64-year-old man with liver cirrhosis. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows a dilated coronary vein (straight solid arrow), gastric varix (open arrow), and splenorenal shunt (curved arrow). The vertical white line (arrowhead) is an artifact caused by subtraction of the aortic enhancement. (b) Arterial portogram obtained with celiac arteriography also demonstrates these collateral pathways, which are less conspicuous than on the MR portogram (a). (c) Contrast-enhanced MR portogram obtained after balloon-occluded retrograde transvenous obliteration no longer shows the gastric varix, although the splenorenal shunt is still seen to be patent (arrow).
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Hepatic encephalopathy is caused by a massive portosystemic shunt, which can be easily detected with contrast-enhanced 3D MR portography because it covers the whole abdomen. In contrast, a shunt in the pelvic region may be overlooked with CT because CT studies usually include only the upper abdomen in patients with portal hypertension (Fig 3). In addition, it is difficult to determine the complex anatomy of portosystemic shunts on axial CT scans. Color Doppler US may not demonstrate a porto-systemic shunt because these shunts can develop anywhere in the abdomen (11).
Esophagogastric varix can be clearly demonstrated with contrast-enhanced 3D MR portography, especially when it is performed with arterial-phase subtraction (Figs 2, 6). This technique is also useful for assessing and monitoring the effects of sclerotherapy (Fig 6).
Portal Vein Obstruction
Obstruction of the portal veins can be caused by various conditions, such as portal vein thrombosis, ascending portal thrombophlebitis (Fig 7), pancreatitis, hepatocellular carcinoma, and malignant pancreatobiliary tumors, which result in prehepatic portal hypertension (16). Consequently, portal venous collateral pathways develop in both hepatopetal and hepatofugal directions. Hepatofugal collateral pathways were described earlier. Hepatopetal collateral pathways include the cavernous transformation of the portal vein that develops in main portal vein obstruction (Fig 8); the dilated pancreaticoduodenal venous arcades that develop in superior mesenteric vein obstruction (Fig 9); and the dilated gastroepiploic, short gastric, and coronary veins that develop in splenic vein obstruction (Fig 10) (6).
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Figures 7, 8. (7) Ascending portal thrombophlebitis in a 2-year-old girl with fever, diarrhea, and hepato-splenomegaly. Contrast-enhanced 3D MR portogram (a) and coronal source image (b) show occlusion of the superior mesenteric vein and portal vein with a hepatopetal collateral pathway through the dilated pancreaticoduodenal venous arcade (arrow) and a hepato-fugal collateral pathway forming an esophageal varix (arrowheads). Note the atrophic right lobe of the liver. (8) Cavernous transformation of the portal vein in an asymptomatic 63-year-old woman. Contrast-enhanced 3D MR portogram clearly shows dilated periportal collateral vessels (arrow) from the superior mesenteric vein and splenic vein to the intrahepatic portal vein branches (arrowhead).
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Figures 7, 8. (7) Ascending portal thrombophlebitis in a 2-year-old girl with fever, diarrhea, and hepato-splenomegaly. Contrast-enhanced 3D MR portogram (a) and coronal source image (b) show occlusion of the superior mesenteric vein and portal vein with a hepatopetal collateral pathway through the dilated pancreaticoduodenal venous arcade (arrow) and a hepato-fugal collateral pathway forming an esophageal varix (arrowheads). Note the atrophic right lobe of the liver. (8) Cavernous transformation of the portal vein in an asymptomatic 63-year-old woman. Contrast-enhanced 3D MR portogram clearly shows dilated periportal collateral vessels (arrow) from the superior mesenteric vein and splenic vein to the intrahepatic portal vein branches (arrowhead).
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Figures 7, 8. (7) Ascending portal thrombophlebitis in a 2-year-old girl with fever, diarrhea, and hepato-splenomegaly. Contrast-enhanced 3D MR portogram (a) and coronal source image (b) show occlusion of the superior mesenteric vein and portal vein with a hepatopetal collateral pathway through the dilated pancreaticoduodenal venous arcade (arrow) and a hepato-fugal collateral pathway forming an esophageal varix (arrowheads). Note the atrophic right lobe of the liver. (8) Cavernous transformation of the portal vein in an asymptomatic 63-year-old woman. Contrast-enhanced 3D MR portogram clearly shows dilated periportal collateral vessels (arrow) from the superior mesenteric vein and splenic vein to the intrahepatic portal vein branches (arrowhead).
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Figures 9, 10. (9) Portal vein obstruction caused by surgery for cancer of the pancreatic tail in an asymptomatic 66-year-old man. Contrast-enhanced 3D MR portogram with arterial-phase subtraction clearly shows obstruction of the superior mesenteric vein (solid arrow) and hepatopetal collateral pathways through the pancreaticoduodenal veins (open arrow). The aorta is not subtracted completely, and the left renal vein and inferior vena cava are superimposed on the portal vein and the collateral pathways. (10) Splenic vein obstruction after endoscopic sclerotherapy in a 61-year-old woman with alcoholic liver cirrhosis. Endoscopic sclerotherapy was performed to treat massive hemorrhage from a ruptured gastric varix. (a) Contrast-enhanced 3D MR portogram does not reveal the splenic vein. Note the filling defect at the confluence of the splenic and superior mesenteric veins (straight solid arrow). A gastric varix (open arrow), splenorenal shunt (arrowhead), and dilated left ovarian vein (curved arrow) are also seen. (b) Arterial portogram obtained with celiac arteriography reveals splenic vein obstruction with a dilated gastroepiploic vein as a hepatopetal collateral pathway. The gastric varix and splenorenal shunt are still patent, and the dilated left ovarian vein is seen emptying toward the pelvis. Iodized oil is seen in the splenic vein and gastric varix.
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Figures 9, 10. (9) Portal vein obstruction caused by surgery for cancer of the pancreatic tail in an asymptomatic 66-year-old man. Contrast-enhanced 3D MR portogram with arterial-phase subtraction clearly shows obstruction of the superior mesenteric vein (solid arrow) and hepatopetal collateral pathways through the pancreaticoduodenal veins (open arrow). The aorta is not subtracted completely, and the left renal vein and inferior vena cava are superimposed on the portal vein and the collateral pathways. (10) Splenic vein obstruction after endoscopic sclerotherapy in a 61-year-old woman with alcoholic liver cirrhosis. Endoscopic sclerotherapy was performed to treat massive hemorrhage from a ruptured gastric varix. (a) Contrast-enhanced 3D MR portogram does not reveal the splenic vein. Note the filling defect at the confluence of the splenic and superior mesenteric veins (straight solid arrow). A gastric varix (open arrow), splenorenal shunt (arrowhead), and dilated left ovarian vein (curved arrow) are also seen. (b) Arterial portogram obtained with celiac arteriography reveals splenic vein obstruction with a dilated gastroepiploic vein as a hepatopetal collateral pathway. The gastric varix and splenorenal shunt are still patent, and the dilated left ovarian vein is seen emptying toward the pelvis. Iodized oil is seen in the splenic vein and gastric varix.
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Figures 9, 10. (9) Portal vein obstruction caused by surgery for cancer of the pancreatic tail in an asymptomatic 66-year-old man. Contrast-enhanced 3D MR portogram with arterial-phase subtraction clearly shows obstruction of the superior mesenteric vein (solid arrow) and hepatopetal collateral pathways through the pancreaticoduodenal veins (open arrow). The aorta is not subtracted completely, and the left renal vein and inferior vena cava are superimposed on the portal vein and the collateral pathways. (10) Splenic vein obstruction after endoscopic sclerotherapy in a 61-year-old woman with alcoholic liver cirrhosis. Endoscopic sclerotherapy was performed to treat massive hemorrhage from a ruptured gastric varix. (a) Contrast-enhanced 3D MR portogram does not reveal the splenic vein. Note the filling defect at the confluence of the splenic and superior mesenteric veins (straight solid arrow). A gastric varix (open arrow), splenorenal shunt (arrowhead), and dilated left ovarian vein (curved arrow) are also seen. (b) Arterial portogram obtained with celiac arteriography reveals splenic vein obstruction with a dilated gastroepiploic vein as a hepatopetal collateral pathway. The gastric varix and splenorenal shunt are still patent, and the dilated left ovarian vein is seen emptying toward the pelvis. Iodized oil is seen in the splenic vein and gastric varix.
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Portal Vein Thrombosis.—Portal vein thrombosis often occurs in liver cirrhosis, ascending portal thrombophlebitis (Fig 7), pancreatitis, and other conditions and after sclerotherapy of a gastroesophageal varix (Fig 10) (16). It is important to assess portal venous patency in these diseases. Contrast-enhanced 3D MR portography provides detailed information not only about the location and length of portal vein obstruction but also about portal collateral pathways. In potential candidates for liver transplantation, it is necessary to evaluate portal venous patency (17). Color Doppler US may not allow portal venous patency to be established (18), but contrast-enhanced 3D MR portography provides accurate information.
Hepatocellular Carcinoma.—In patients with hepatocellular carcinoma, tumor thrombus in the portal vein substantially affects therapy and outcome. Contrast-enhanced 3D MR portograms and the coronal source images can demonstrate an enhanced hepatic tumor in the arterial-dominant phase as well as filling defects and obstruction of intra- or extrahepatic portal veins (Fig 11). It may be difficult to differentiate a tumor thrombus from a conventional thrombus when the tumor thrombus is poorly enhanced.
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Figure 11a. Tumor thrombus of the right portal vein in a 59-year-old man with hepatocellular carcinoma. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows occlusion of the right portal vein (solid arrow) by a tumor thrombus. Note the splenorenal shunt (open arrow). (b) Coronal source image reveals an enhanced hepatocellular carcinoma (arrows) with a tumor thrombus in the right portal vein. (c) Arterial portogram obtained with superior mesenteric arteriography shows the occlusion of the right portal vein (arrow).
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Figure 11b. Tumor thrombus of the right portal vein in a 59-year-old man with hepatocellular carcinoma. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows occlusion of the right portal vein (solid arrow) by a tumor thrombus. Note the splenorenal shunt (open arrow). (b) Coronal source image reveals an enhanced hepatocellular carcinoma (arrows) with a tumor thrombus in the right portal vein. (c) Arterial portogram obtained with superior mesenteric arteriography shows the occlusion of the right portal vein (arrow).
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Figure 11c. Tumor thrombus of the right portal vein in a 59-year-old man with hepatocellular carcinoma. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction shows occlusion of the right portal vein (solid arrow) by a tumor thrombus. Note the splenorenal shunt (open arrow). (b) Coronal source image reveals an enhanced hepatocellular carcinoma (arrows) with a tumor thrombus in the right portal vein. (c) Arterial portogram obtained with superior mesenteric arteriography shows the occlusion of the right portal vein (arrow).
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Pancreatobiliary Tumors.—In patients with pancreatobiliary tumors, it is important to eval-uate portal vein invasion before surgery. CT and DSA have been used for this purpose. Contrast-enhanced 3D MR portography is also an accurate way to diagnose portal vein invasion (19,20) (Figs 12, 13).
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Figure 12a. Resectable bile duct cancer in a 58-year-old woman. (a) Contrast-enhanced 3D MR portogram shows that the portal vein is not encased by the tumor at all, a finding that was confirmed at surgery. The bile duct cancer appears as enhanced parallel lines (arrow). (b) Coronal source image reveals enhanced bile duct cancer of the lower common bile duct with a dilated upstream biliary tree (arrows).
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Figure 12b. Resectable bile duct cancer in a 58-year-old woman. (a) Contrast-enhanced 3D MR portogram shows that the portal vein is not encased by the tumor at all, a finding that was confirmed at surgery. The bile duct cancer appears as enhanced parallel lines (arrow). (b) Coronal source image reveals enhanced bile duct cancer of the lower common bile duct with a dilated upstream biliary tree (arrows).
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Figure 13a. Unresectable malignant islet cell tumor of the pancreatic head in a 57-year-old man. (a) Contrast-enhanced 3D MR portogram shows obstruction of the superior mesenteric vein (arrow). (b) Coronal source image reveals that the poorly enhanced pancreatic head tumor encases the superior mesenteric vein and invades the duodenum (curved arrows). Note the dilated biliary tree (open arrow) and agenesis of the pancreatic tail.
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Figure 13b. Unresectable malignant islet cell tumor of the pancreatic head in a 57-year-old man. (a) Contrast-enhanced 3D MR portogram shows obstruction of the superior mesenteric vein (arrow). (b) Coronal source image reveals that the poorly enhanced pancreatic head tumor encases the superior mesenteric vein and invades the duodenum (curved arrows). Note the dilated biliary tree (open arrow) and agenesis of the pancreatic tail.
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We have used contrast-enhanced 3D MR portography and DSA to assess the portal venous system and determine surgical resectability in 20 patients with pancreatobiliary tumors (pancreatic cancer in 13, bile duct cancer in two, carcinoma of the papilla of Vater in two, gallbladder cancer in two, and duodenal tumor in one). These patients were being considered as candidates for surgical resection. Of the 20 patients, 16 underwent surgical exploration (Table), whereas four did not because their tumors were deemed unresectable at CT, DSA, and contrast-enhanced 3D MR portography. Twelve tumors were surgically resected. Results of contrast-enhanced 3D MR portography and DSA agreed in 14 of 16 patients (88%). Contrast-enhanced 3D MR portography allowed identification of 11 of 12 resectable tumors and three of four unresectable tumors with one false-negative and one false-positive reading. DSA allowed identification of all 12 resectable tumors and two of four unresectable tumors with two false-negative readings. The accuracy of contrast-enhanced 3D MR portography was therefore the same as that of DSA.
Hepatic Vein Obstruction
Budd-Chiari syndrome is a rare disorder characterized by hepatic outflow occlusion and caused by various conditions including congenital or idiopathic obstruction, hepatic vein thrombosis due to hypercoagulative state, hepatic veno-occlusive disease after liver transplantation, and hepatic tumors (21). The major symptoms include ascites, hepatomegaly, and abdominal pain. It has been classified into three types according to the location of the occlusion (13,22). Type 1 is defined as occlusion of the inferior vena cava with or without hepatic vein occlusion; type 2, occlusion of major hepatic veins; and type 3, obstruction of the small centrilobular venules (hepatic veno-occlusive disease). From the clinical point of view, Budd-Chiari syndrome should be classified according to whether it can be treated with anticoagulants, surgery, or interventional procedures. In planning treatment, it is important to determine the location and length of hepatic outflow obstruction (21), and contrast-enhanced 3D MR portography is an accurate means of doing this. No hepatic veins can be visualized in hepatic veno-occlusive disease, whereas narrowing of the intrahepatic portal vein may be seen with a delayed circulation time (Fig 14).
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Figure 14a. Hepatic veno-occlusive disease due to anti-phospholipid antibody syndrome in a 39-year-old man with massive ascites and hepatic dysfunction. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction does not reveal the right hepatic lobe, although the right portal vein is seen to be patent (arrow). (b) Coronal source image demonstrates obstruction of the right and middle hepatic veins with no parenchymal enhancement of the right hepatic lobe. The left hepatic vein is well visualized (arrow).
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Figure 14b. Hepatic veno-occlusive disease due to anti-phospholipid antibody syndrome in a 39-year-old man with massive ascites and hepatic dysfunction. (a) Contrast-enhanced 3D MR portogram with arterial-phase subtraction does not reveal the right hepatic lobe, although the right portal vein is seen to be patent (arrow). (b) Coronal source image demonstrates obstruction of the right and middle hepatic veins with no parenchymal enhancement of the right hepatic lobe. The left hepatic vein is well visualized (arrow).
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Splanchnic Arterial Diseases
Contrast-enhanced 3D MR portography has a high enough temporal resolution to enable separate imaging of the arterial and portal phases, which makes it possible to diagnose mesenteric arterial diseases that mimic portal venous diseases. It is important to differentiate mycotic aneurysm of the mesenteric arteries (Fig 15) from portal vein aneurysm because of the high risk of rupture associated with the former. Splanchnic arterial collateral pathways caused by obstruction of major arteries (eg, splenic, superior mesenteric, and hepatic arteries) can also be differentiated from varix of the portal venous system and arteriovenous malformation (Fig 16).
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Figure 15a. Mycotic aneurysm of the superior mesenteric artery in a 62-year-old asymptomatic man. Arterial-phase (a) and portal-phase (b) contrast-enhanced 3D MR portograms clearly show a mycotic aneurysm of the superior mesenteric artery (arrow in a) displacing the superior mesenteric vein (arrow in b).
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Figure 15b. Mycotic aneurysm of the superior mesenteric artery in a 62-year-old asymptomatic man. Arterial-phase (a) and portal-phase (b) contrast-enhanced 3D MR portograms clearly show a mycotic aneurysm of the superior mesenteric artery (arrow in a) displacing the superior mesenteric vein (arrow in b).
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Figure 16a. Splenic artery occlusion and collateral arterial pathways in a 60-year-old man with liver cirrhosis and hematemesis. Contrast-enhanced CT showed dilated vessels in the pancreatic tail. (a) Arterial-phase contrast-enhanced 3D MR portogram shows many small arterial collateral pathways in the left upper quadrant (arrows). There is no early portal venous enhancement, and the splenic artery is not seen. (b) Contrast-enhanced 3D MR portogram shows an enlarged spleen and dilated splenic vein. No portosystemic shunt is seen. (c) Celiac arteriogram shows occlusion of the splenic artery with collateral vessels.
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Figure 16b. Splenic artery occlusion and collateral arterial pathways in a 60-year-old man with liver cirrhosis and hematemesis. Contrast-enhanced CT showed dilated vessels in the pancreatic tail. (a) Arterial-phase contrast-enhanced 3D MR portogram shows many small arterial collateral pathways in the left upper quadrant (arrows). There is no early portal venous enhancement, and the splenic artery is not seen. (b) Contrast-enhanced 3D MR portogram shows an enlarged spleen and dilated splenic vein. No portosystemic shunt is seen. (c) Celiac arteriogram shows occlusion of the splenic artery with collateral vessels.
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Figure 16c. Splenic artery occlusion and collateral arterial pathways in a 60-year-old man with liver cirrhosis and hematemesis. Contrast-enhanced CT showed dilated vessels in the pancreatic tail. (a) Arterial-phase contrast-enhanced 3D MR portogram shows many small arterial collateral pathways in the left upper quadrant (arrows). There is no early portal venous enhancement, and the splenic artery is not seen. (b) Contrast-enhanced 3D MR portogram shows an enlarged spleen and dilated splenic vein. No portosystemic shunt is seen. (c) Celiac arteriogram shows occlusion of the splenic artery with collateral vessels.
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In patients with gastrointestinal hemorrhage, it is important to survey the whole abdomen in search of an anomalous vascular lesion as a possible bleeding source. Contrast-enhanced 3D MR portography can reveal mesenteric arteriovenous malformations including angiodysplasia by demonstrating a nidus, a venous lake, and dilated mesenteric veins (Fig 17).
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Figure 17a. Ileal angiodysplasia in an 84-year-old woman with massive gastrointestinal hemorrhage. (a) Coronal source image reveals the bleeding point as a hypervascular lesion (solid arrow) with dilated ileal veins (open arrow) in the right lower quadrant. (b) Superior mesenteric arteriogram also reveals angiodysplasia of the terminal ileum (arrow).
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Figure 17b. Ileal angiodysplasia in an 84-year-old woman with massive gastrointestinal hemorrhage. (a) Coronal source image reveals the bleeding point as a hypervascular lesion (solid arrow) with dilated ileal veins (open arrow) in the right lower quadrant. (b) Superior mesenteric arteriogram also reveals angiodysplasia of the terminal ileum (arrow).
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LIMITATIONS
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General contraindications to MR imaging also apply to contrast-enhanced 3D MR portography, which has several other limitations. First, there is a risk of allergic reactions to contrast media, although the incidence is low. Second, this technique is unable to demonstrate the flow direction of the portal venous system, unlike phase-contrast or time-of-flight MR angiography (23,24). Third, important portosystemic collateral vessels may be overlooked when they are too anterior or posterior to the imaging slab or when the slab is positioned inappropriately. Fourth, if the interval between injection of gadopentetate dimeglumine and the start of imaging is too prolonged, the arteries and portal vein may not be differentiated. Fifth, artifacts from respiratory motion and peristaltic bowel movement degrade image quality, especially in debilitated patients who are unable to hold their breath for 12–24 seconds. Sixth, when subtraction techniques are used, respiratory misregis-tration also degrades image quality.
Diagnostic pitfalls include a thin, longitudinal black line that resembles the intimal flap of dissection, although this appearance is not frequently encountered in the portal vein (Fig 18). It may result from flow artifact or partial-echo acquisition artifact.
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Figure 18. Pseudodissection of the portal venous system in a 69-year-old man with liver cirrhosis. Contrast-enhanced 3D MR portogram demonstrates a long, dark stripe that resembles dissection in the middle of the superior mesenteric vein (solid arrows). An esophageal varix is also seen (open arrow).
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CONCLUSIONS
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Contrast-enhanced 3D MR portography provides detailed information about the portal venous system as well as parenchymal lesions in the form of a first-pass study of the mesenteric vasculature after rapid bolus injection of contrast material. This technique is helpful in evaluating the anatomy of the portal venous system and its pathologic conditions, such as portosystemic shunt, portal vein thrombosis, portal vein invasion by hepatic and pancreatobiliary tumors, portal vein aneurysm, and hepatic vein obstruction. Its limitations include allergic reactions to contrast media, inappropriate positioning of the 3D acquisition slab, respiratory motion artifacts, and pseudodissection.
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Acknowledgments
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We thank Hiroko Suyama and Naoko Hirakawa for preparing the manuscript and figures, and we thank the radiologic technologists of the MR division for providing technical support.
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Footnotes
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Abbreviations: DSA = digital subtraction angiography
3D = three-dimensional
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Abstract
INTRODUCTION
