(Radiology. 2000;216:86-92.)
© RSNA, 2000
Vascular and Interventional Radiology |
Detection of Thrombosis in the Portal Venous System: Comparison of Contrast-enhanced MR Angiography with Intraarterial Digital Subtraction Angiography1
Burkhard Kreft, MD,
Holger Strunk, MD,
Sebastian Flacke, MD,
Martin Wolff, MD,
Rudolf Conrad, MD,
Juergen Gieseke, PhD,
Dirk Pauleit, MD,
Rainald Bachmann, MD,
Andreas Hirner, MD and
Hans H. Schild, MD
1 From the Departments of Radiology (B.K., H.S., S.F., R.C., J.G., D.P., R.B., H.H.S.) and Surgery (M.W., A.H.), University of Bonn, Sigmund-Freud-Strasse 25, 53105 Bonn, Germany. Received July 19, 1999; revision requested August 30; revision received October 5; accepted October 26. Address correspondence to B.K. (e-mail: kreft@mailer.meb.uni-bonn.de).
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ABSTRACT
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PURPOSE: To determine whether intraarterial digital subtraction angiography (DSA) can be replaced by contrast material–enhanced magnetic resonance (MR) angiography in the assessment of patency or thrombosis of the portal venous system in patients with portal hypertension.
MATERIALS AND METHODS: Thirty-six patients with portal hypertension underwent contrast-enhanced MR angiography and intraarterial DSA for assessment of the portal venous system. The images were evaluated for vessel patency or thrombosis of the portal, splenic, or superior mesenteric vein.
RESULTS: Of the 101 vessels evaluated, 42 were thrombosed. Overall sensitivity, specificity, and accuracy for the detection of thrombosis were 100%, 98%, and 99%, respectively, for MR angiography and 91%, 100%, and 96%, respectively, for DSA; differences between the imaging methods were not statistically significant. Only in four patients with six vessels (6%) were there discordant findings between MR angiography and DSA.
CONCLUSION: Noninvasive contrast-enhanced MR angiography has the potential to replace intraarterial DSA as the standard method to assess the whole portal venous system.
Index terms: Angiography, comparative studies, 957.1242, 957.12942 • Hypertension, portal, 957.711 • Magnetic resonance (MR), vascular studies, 957.129412, 957.12942 • Portal vein, MR, 957.129412, 957.12942 • Portal vein, thrombosis, 957.751
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INTRODUCTION
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Accurate assessment of the portal venous system in patients with portal hypertension is needed to differentiate the causes of the increased portal blood pressure and to plan adequate therapy (1–3). In patients with variceal bleeding, it is necessary to define whether there are pre-, intra-, or posthepatic causes of the portal hypertension. The prehepatic cause of hypertension is usually portal vein thrombosis, which has to be accurately differentiated form intra- and posthepatic causes of portal hypertension in patients with a patent portal venous system (3).
Usually, Doppler ultrasonography (US) is the first imaging modality used in patients with elevated portal pressure and is accurate in the assessment of the portal venous system (4,5). However, in patients who are potential candidates for surgery, that is, for portosystemic shunt procedures, a more exact diagnostic method that covers the whole portal venous system is required (5). Traditionally, assessment of the portal venous system has been achieved with intraarterial splenoportal and mesentericoportal angiography (3,6).
MR angiography with either time-of-flight or phase-contrast techniques and, recently, MR angiography with gadopentetate dimeglumine have been shown to be very promising noninvasive methods for the assessment of the portal venous system (7–13). Contrast-enhanced MR angiography has also been increasingly used at our institution in patients with portal hypertension for the diagnosis of patency or thrombosis of the portal venous system, for the provision of information additional to that provided with US and intraarterial digital subtraction angiography (DSA) in assessing the portal venous system, and for the detection of varices and splenorenal shunts. At the time of our study, MR angiography had not replaced intraarterial DSA as the preoperative imaging method of choice.
After the implementation of a power-gradient system on our 1.5-T machine in October 1997, we were able to perform contrast-enhanced MR angiography with a high spatial resolution and with coverage of the whole portal venous system within one breath hold of 19 seconds, which yielded substantially better results than the techniques formerly used.
The goal of this study was to determine whether intraarterial DSA can be replaced by the improved contrast-enhanced MR angiography in the assessment of patency or thrombosis of the portal venous system in patients with portal hypertension.
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MATERIALS AND METHODS
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Patients
At the time of the study, MR angiography and intraarterial DSA were both required at our surgery department for preoperative planning, that is, before shunt procedures or before liver transplantation. The retrospective study included 36 consecutive patients in whom extrahepatic portal hypertension was suspected on the basis of clinical information and/or Doppler US findings and who were routinely referred for both contrast-enhanced MR angiography and intraarterial DSA in their diagnostic work-up to assess the portal venous system. Each patient gave informed consent for the MR angiographic and DSA examinations. Both examinations were performed within a mean of 5 days (range, 1–18 days).
The underlying cause of the portal hypertension was as follows: hepatic cirrhosis in 20 patients (alcohol-induced in seven, virus-induced in four, autoimmune hepatitis–induced in two, cryptogenic in seven), history of neonatal umbilical vein sepsis after catheterization in four patients, congenital hepatic fibrosis in one patient, posttraumatic portal vein thrombosis in one patient, veno-occlusive disease of the liver in one patient, protein C deficiency in one patient, polycythemia in two patients, and unknown cause in six patients. Eighteen patients had recurrent episodes of gastroesophageal bleeding in their history.
There were 20 female and 16 male patients, with a mean age of 42 years (range, 13–65 years). Seventeen of these patients underwent a portosystemic shunt operation, five patients underwent liver transplantation, and the remaining 14 patients underwent no surgery.
MR Angiography
MR imaging was performed with a 1.5-T imager (ACS-NT Compact plus; Philips Medical Systems, Best, the Netherlands; 23 mT/m; rise time, 0.2 msec; slew rate, 115) by using the body coil. After the localizer images were obtained, a breath-hold multisection T1-weighted fast-field-echo gradient-echo sequence (220/4.5 [repetition time msec/echo time msec]; flip angle, 100°; field of view, 360 mm; rectangular field of view, 70%; matrix 128 x 256; 24 sections; section thickness, 8.0 mm; gap, 0.8 mm; one signal acquired; imaging time, 42 seconds) and a respiratory-triggered T2-weighted turbo spin-echo sequence (2,800/80; field of view, 360 mm; rectangular field of view, 80%; matrix, 181 x 256; 24 sections; section thickness, 8.0 mm; gap, 0.8 mm; four signals acquired; imaging time, 2 minutes 24 seconds) were performed in the upper part of the abdomen.
Dynamic contrast-enhanced MR angiography was performed by using a three-dimensional T1-weighted fast-field-echo sequence (4.7/1.4; flip angle, 40°; field of view, 480 mm; rectangular field of view, 80%; matrix, 163 x 512; 70 sections; section thickness, 1.8 mm [overlapping]; one signal acquired; imaging time, 19 seconds per breath hold). This sequence was repeated three times, with data acquisition in the hepatic arterial, portal venous, and hepatic venous phases after bolus injection of 40 mL of gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) with a power injector (Spectris MR injector; Medrad Europe, Maastricht, the Netherlands) with a flow rate of 8 mL/sec. The contrast material injection was always followed by an automatic physiologic saline flush (20 mL) to deliver the whole volume of the contrast medium.
When to start the sequence after the contrast material administration was determined by using the bolus-timing method with a 2-mL test bolus of gadopentetate dimeglumine in 26 patients, as previously described (14). In the remaining 10 patients, a real-time bolus-tracking method was used with a T1-weighted fast-field-echo sequence (4.3/1.4; flip angle, 40°; field of view, 530 mm; matrix, 180 x 256; one section; section thickness, 100 mm; one signal acquired). Complex raw data sets continuously acquired after injection of contrast medium were subtracted from a mask raw data set acquired without contrast medium enhancement; this mask was typically chosen to be one of the first three images acquired.
A fast Fourier transformation was applied to generate images with a time resolution of 0.9 second and immediately display them on the screen. With this method, the contrast medium bolus was MR fluoroscopically depicted (seen as in real-time imaging) as it passed the thoracic veins, the heart, and the lungs. Because of a technical time delay of 5 seconds between the bolus-tracking sequence and the start of the MR angiographic sequence, the latter was started when the contrast medium bolus was in the left ventricle. Within these 5 seconds, the patient was instructed to hold his or her breath for the hepatic arterial phase data acquisition. Between the hepatic arterial and portal venous phases, the patient was allowed to breathe once; between the portal venous and venous phases, the patient was allowed to breathe twice.
Maximum intensity projection (MIP) images were reconstructed from the three-dimensional data set for each breath hold in the hepatic arterial, portal venous, and hepatic venous phases by a radiologist (S.F., R.C.). Nine standard projections with different projection angles were routinely used in all patients. When necessary, additional segmented MIP images were obtained with a dedicated workstation (Easy-Vision 4.0; Philips Medical Systems).
Intraarterial DSA
Intraarterial DSA was performed with selective catheterization of the splenic and superior mesenteric arteries. This was followed by automatic injection of 25–40 mL of a low-osmolality nonionic contrast agent (iopromide [Ultravist 300; Schering]) with a flow rate of 5-10 mL/sec. Images were acquired during the hepatic arterial and portal venous phases at one frame every 1–2 seconds.
Image Analysis
Each set of images was retrospectively reviewed by one radiologist (B.K., H.S.) who did not know the results of the other imaging method. Evaluation included the assessment of vessel patency and of the presence of a thrombosis in the portal, splenic, or superior mesenteric vein. Thrombosis was classified as either partial nonocclusive or complete. The location of the thrombosis was further subdivided as proximal or distal. In addition, the presence of a cavernous transformation of the portal vein was evaluated.
Statistical Analysis
For comparison of the two imaging methods, a standard of reference was defined as follows: The definite diagnosis was made by means of consensus with the combined reading of the contrast-enhanced MR angiograms and DSA images and by means of surgical validation in 22 patients. In the remaining patients (n = 14), who did not undergo surgery, the definite diagnosis was achieved by means of consensus with the combined reading of images obtained with the two methods and by means of results obtained with additional imaging modalities (Doppler US, computed tomography [CT], and CT during arterial portography [CTAP]). Four patients had discrepant findings between MR angiography and intraarterial DSA; confirmation of the definite diagnosis was achieved with surgery in three patients and with Doppler US and CTAP in one patient.
Sensitivity, specificity, positive and negative predictive values, and accuracies for the detection of thrombosis were calculated by using standard methods. A 
2 test was performed to analyze differences in the detectability of thrombosis at MR angiography and DSA (threshold, 2 = 3.21) by using the SPSS software for Windows (SPSS, Chicago, Ill). The Fisher exact test was used to calculate P values. A P value of less than .05 indicated a significant difference.
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RESULTS
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Overall, 101 vessels were evaluated: 36 portal veins, 36 superior mesenteric veins, and 29 splenic veins. In seven patients, the spleen had been surgically removed. Of the 101 vessels evaluated, 95 (94%) had agreement between the two modalities. In six vessels (6%) in four patients, findings were discordant.
There were a total of 42 thrombosed vessels in the portal venous system: 23 portal veins, five splenic veins, and 14 superior mesenteric veins. Complete thrombosis was present in 20 (87%) of the 23 portal veins, four (80%) of the five splenic veins, and nine (64%) of the 14 superior mesenteric veins. Partial nonocclusive thrombosis was apparent in three (13%) of 23 portal veins, one (20%) of five splenic veins, and five (36%) of 14 superior mesenteric veins.
The overall sensitivities for the detection of thrombosis in the portal venous system for MR angiography and DSA were 100% and 91%, respectively, without significant differences between the two imaging methods (2 = 96.9; P < .001) (Table). The sensitivity of MR angiography for the detection of thrombosis of the portal vein, the splenic vein, or the superior mesenteric vein was always 100% (2 = 32.0, 29.0, or 36.0, respectively; P < .001) (Table). In comparison, the sensitivity of DSA for the detection of thrombosis of the portal vein, the splenic vein, or the superior mesenteric vein was 96%, 80%, or 86%, respectively (2 = 32.0, 22.3, and 28.3, respectively; P < .001). Again, there were no significantly different results between the two imaging modalities with regard to each part of the portal venous system (Figs 1, 2).
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Sensitivity, Specificity, Positive and Negative Predictive Values, and Accuracy of Contrast-enhanced MR Angiography and Conventional Intraarterial DSA in the Detection of Thrombosis in the Portal Venous System
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Figure 1a. Images obtained in a 21-year-old woman with a history of recurrent esophageal bleeding who was suspected to have portal vein thrombosis with cavernous transformation on the basis of color Doppler US findings. (a) Selective coronal MIP image from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle) and (b) anteroposterior intraarterial DSA splenoportographic image. Both a and b show a right portal vein thrombosis (solid arrow) with collateral vessels (arrowheads) lateral to the patent main portal vein. The signal intensity differences within the portal venous system in a are caused by less contrast medium concentration in the splenic vein (large open arrow in a) than in the superior mesenteric vein (small open arrow in a) because of pooling of contrast medium within the spleen. The intraluminal flow artifacts were not seen on the late hepatic vein images (not shown) and could therefore be differentiated from a luminal thrombus.
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Figure 1b. Images obtained in a 21-year-old woman with a history of recurrent esophageal bleeding who was suspected to have portal vein thrombosis with cavernous transformation on the basis of color Doppler US findings. (a) Selective coronal MIP image from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle) and (b) anteroposterior intraarterial DSA splenoportographic image. Both a and b show a right portal vein thrombosis (solid arrow) with collateral vessels (arrowheads) lateral to the patent main portal vein. The signal intensity differences within the portal venous system in a are caused by less contrast medium concentration in the splenic vein (large open arrow in a) than in the superior mesenteric vein (small open arrow in a) because of pooling of contrast medium within the spleen. The intraluminal flow artifacts were not seen on the late hepatic vein images (not shown) and could therefore be differentiated from a luminal thrombus.
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Figure 2a. Images obtained in a 30-year-old man with alcohol-induced hepatic cirrhosis who was suspected to have acute portal vein thrombosis on the basis of color Doppler US findings. (a) Coronal MIP image from the portal venous phase of contrast-enhanced three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) transverse T1-weighted gradient-echo MR image (220/4.5, 100° flip angle) obtained after gadopentetate dimeglumine administration, and (d) anteroposterior intraarterial DSA splenoportographic image. In a and b, the thrombosis (arrow) of the main portal vein is clearly seen; however, the extent of the thrombosis is better appreciated in b because of the signal void. The thrombus (arrow in c) is also clearly seen in c. In a, there is prolonged contrast medium enhancement of the hepatic artery (arrowhead), which was confirmed on the hepatic arterial phase image (not shown). d also shows complete thrombosis of the portal vein and a splenic vein up to a point just proximal to the portal confluence (solid arrow). The inferior mesenteric vein filling is retrograde (small open arrow), and gastroesophageal varices are filled (large open arrow). In comparison with the angiographic images, the MR images show the whole portal venous system better. The portal vein thrombosis was surgically verified during liver transplantation.
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Figure 2b. Images obtained in a 30-year-old man with alcohol-induced hepatic cirrhosis who was suspected to have acute portal vein thrombosis on the basis of color Doppler US findings. (a) Coronal MIP image from the portal venous phase of contrast-enhanced three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) transverse T1-weighted gradient-echo MR image (220/4.5, 100° flip angle) obtained after gadopentetate dimeglumine administration, and (d) anteroposterior intraarterial DSA splenoportographic image. In a and b, the thrombosis (arrow) of the main portal vein is clearly seen; however, the extent of the thrombosis is better appreciated in b because of the signal void. The thrombus (arrow in c) is also clearly seen in c. In a, there is prolonged contrast medium enhancement of the hepatic artery (arrowhead), which was confirmed on the hepatic arterial phase image (not shown). d also shows complete thrombosis of the portal vein and a splenic vein up to a point just proximal to the portal confluence (solid arrow). The inferior mesenteric vein filling is retrograde (small open arrow), and gastroesophageal varices are filled (large open arrow). In comparison with the angiographic images, the MR images show the whole portal venous system better. The portal vein thrombosis was surgically verified during liver transplantation.
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Figure 2c. Images obtained in a 30-year-old man with alcohol-induced hepatic cirrhosis who was suspected to have acute portal vein thrombosis on the basis of color Doppler US findings. (a) Coronal MIP image from the portal venous phase of contrast-enhanced three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) transverse T1-weighted gradient-echo MR image (220/4.5, 100° flip angle) obtained after gadopentetate dimeglumine administration, and (d) anteroposterior intraarterial DSA splenoportographic image. In a and b, the thrombosis (arrow) of the main portal vein is clearly seen; however, the extent of the thrombosis is better appreciated in b because of the signal void. The thrombus (arrow in c) is also clearly seen in c. In a, there is prolonged contrast medium enhancement of the hepatic artery (arrowhead), which was confirmed on the hepatic arterial phase image (not shown). d also shows complete thrombosis of the portal vein and a splenic vein up to a point just proximal to the portal confluence (solid arrow). The inferior mesenteric vein filling is retrograde (small open arrow), and gastroesophageal varices are filled (large open arrow). In comparison with the angiographic images, the MR images show the whole portal venous system better. The portal vein thrombosis was surgically verified during liver transplantation.
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Figure 2d. Images obtained in a 30-year-old man with alcohol-induced hepatic cirrhosis who was suspected to have acute portal vein thrombosis on the basis of color Doppler US findings. (a) Coronal MIP image from the portal venous phase of contrast-enhanced three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) transverse T1-weighted gradient-echo MR image (220/4.5, 100° flip angle) obtained after gadopentetate dimeglumine administration, and (d) anteroposterior intraarterial DSA splenoportographic image. In a and b, the thrombosis (arrow) of the main portal vein is clearly seen; however, the extent of the thrombosis is better appreciated in b because of the signal void. The thrombus (arrow in c) is also clearly seen in c. In a, there is prolonged contrast medium enhancement of the hepatic artery (arrowhead), which was confirmed on the hepatic arterial phase image (not shown). d also shows complete thrombosis of the portal vein and a splenic vein up to a point just proximal to the portal confluence (solid arrow). The inferior mesenteric vein filling is retrograde (small open arrow), and gastroesophageal varices are filled (large open arrow). In comparison with the angiographic images, the MR images show the whole portal venous system better. The portal vein thrombosis was surgically verified during liver transplantation.
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Discrepancies with regard to the sensitivity (correct diagnosis of thrombosis) existed between MR angiography and DSA in three patients. In these patients, five vessels were partially occluded by thrombus (two portal veins, one splenic vein, and two superior mesenteric veins), which was correctly diagnosed with MR angiography. Four of these partially thrombosed vessels were not seen on intraarterial DSA images, and one partially thrombosed portal vein was diagnosed as complete thrombosis with DSA (Fig 3). The partial thrombosis was confirmed with CTAP in all of these cases.
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Figure 3a. Images obtained in a 49-year-old man with hepatitis C-induced liver cirrhosis who was suspected to have complete thrombosis of the portal vein on the basis of color Doppler US findings. (a) Coronal MIP image and (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) anteroposterior intraarterial DSA splenoportographic image, and (d) anteroposterior intraarterial DSA mesentericoportographic image. a and b correctly show partial thrombosis of the portal (1), splenic (2), and superior mesenteric (3) veins (arrows in a); however, partial nonocclusive thrombus of the proximal portal vein (arrow in b) is best appreciated in b. In c and d, complete thrombosis of the portal vein is diagnosed, because the remainder of the perfused lumen of the portal vein (arrow in c) is thought to be a collateral vessel. Note in d that there is retrograde flow in the inferior mesenteric vein (large arrow) and reversed flow from the superior mesenteric to the splenic (small arrow) vein, which cannot be seen in a and b; however, partial thrombosis of the splenic and superior mesenteric veins are better visualized in a and b.
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Figure 3b. Images obtained in a 49-year-old man with hepatitis C-induced liver cirrhosis who was suspected to have complete thrombosis of the portal vein on the basis of color Doppler US findings. (a) Coronal MIP image and (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) anteroposterior intraarterial DSA splenoportographic image, and (d) anteroposterior intraarterial DSA mesentericoportographic image. a and b correctly show partial thrombosis of the portal (1), splenic (2), and superior mesenteric (3) veins (arrows in a); however, partial nonocclusive thrombus of the proximal portal vein (arrow in b) is best appreciated in b. In c and d, complete thrombosis of the portal vein is diagnosed, because the remainder of the perfused lumen of the portal vein (arrow in c) is thought to be a collateral vessel. Note in d that there is retrograde flow in the inferior mesenteric vein (large arrow) and reversed flow from the superior mesenteric to the splenic (small arrow) vein, which cannot be seen in a and b; however, partial thrombosis of the splenic and superior mesenteric veins are better visualized in a and b.
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Figure 3c. Images obtained in a 49-year-old man with hepatitis C-induced liver cirrhosis who was suspected to have complete thrombosis of the portal vein on the basis of color Doppler US findings. (a) Coronal MIP image and (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) anteroposterior intraarterial DSA splenoportographic image, and (d) anteroposterior intraarterial DSA mesentericoportographic image. a and b correctly show partial thrombosis of the portal (1), splenic (2), and superior mesenteric (3) veins (arrows in a); however, partial nonocclusive thrombus of the proximal portal vein (arrow in b) is best appreciated in b. In c and d, complete thrombosis of the portal vein is diagnosed, because the remainder of the perfused lumen of the portal vein (arrow in c) is thought to be a collateral vessel. Note in d that there is retrograde flow in the inferior mesenteric vein (large arrow) and reversed flow from the superior mesenteric to the splenic (small arrow) vein, which cannot be seen in a and b; however, partial thrombosis of the splenic and superior mesenteric veins are better visualized in a and b.
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Figure 3d. Images obtained in a 49-year-old man with hepatitis C-induced liver cirrhosis who was suspected to have complete thrombosis of the portal vein on the basis of color Doppler US findings. (a) Coronal MIP image and (b) coronal single section from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (c) anteroposterior intraarterial DSA splenoportographic image, and (d) anteroposterior intraarterial DSA mesentericoportographic image. a and b correctly show partial thrombosis of the portal (1), splenic (2), and superior mesenteric (3) veins (arrows in a); however, partial nonocclusive thrombus of the proximal portal vein (arrow in b) is best appreciated in b. In c and d, complete thrombosis of the portal vein is diagnosed, because the remainder of the perfused lumen of the portal vein (arrow in c) is thought to be a collateral vessel. Note in d that there is retrograde flow in the inferior mesenteric vein (large arrow) and reversed flow from the superior mesenteric to the splenic (small arrow) vein, which cannot be seen in a and b; however, partial thrombosis of the splenic and superior mesenteric veins are better visualized in a and b.
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There was 100% (17 of 17 cases) agreement between MR angiography and intraarterial DSA in the detection of cavernous transformation of the portal vein.
The overall specificities for exclusion of thrombosis (correct diagnosis of vessel patency) in the portal venous system were 98% for MR angiography and 100% for angiography (Table). Similar results were obtained for assessment of portal, splenic, or superior mesenteric vein patency, with a specificity of 92%, 100%, or 100%, respectively, for MR angiography and a specificity of 100%, 100%, or 100%, respectively, for DSA—again, without significant differences (Table). In one patient, there were discrepant findings with regard to correct assessment of vessel patency between MR angiography and intraarterial DSA. MR angiography showed a false-positive partial thrombosis of the portal vein, whereas DSA correctly did not show any evidence of thrombosis, which was confirmed with CT and Doppler US (Fig 4). This false-positive MR angiographic finding was caused by a susceptibility artifact adjacent to the portal vein, which led to substantial signal intensity loss within the vessel. This artifact was not appreciated at the first MR angiographic reading (Fig 4).
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Figure 4a. Images obtained in a 59-year-old woman with a history of duodenal variceal bleeding. (a) Coronal MIP image from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) transverse respiratory-triggered T2-weighted turbo spin-echo MR image (2,800/80), and (c) anteroposterior intraarterial DSA splenoportographic image. In a, and on the single-section images (not shown), there is an area of decreased signal intensity (arrow) in the midportion of the portal vein, which was falsely thought to represent partial nonocclusive thrombus. In b, the diagnosis was further supported by a rim of increased signal intensity (arrow) in the ventral part of the portal vein. However, color Doppler US and intraarterial DSA (c) did show a normal main portal vein (solid arrow in c) and splenic vein (open arrow in c) and no evidence of partial portal vein thrombosis. The decreased-signal-intensity area within the portal vein in a was probably caused by a susceptibility artifact from adjacent bowel gas, whereas the rim of increased signal intensity in b was most probably caused by slow-flowing blood. Note the duodenal varices (arrowhead in a), which were seen only with contrast-enhanced MR angiography.
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Figure 4b. Images obtained in a 59-year-old woman with a history of duodenal variceal bleeding. (a) Coronal MIP image from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) transverse respiratory-triggered T2-weighted turbo spin-echo MR image (2,800/80), and (c) anteroposterior intraarterial DSA splenoportographic image. In a, and on the single-section images (not shown), there is an area of decreased signal intensity (arrow) in the midportion of the portal vein, which was falsely thought to represent partial nonocclusive thrombus. In b, the diagnosis was further supported by a rim of increased signal intensity (arrow) in the ventral part of the portal vein. However, color Doppler US and intraarterial DSA (c) did show a normal main portal vein (solid arrow in c) and splenic vein (open arrow in c) and no evidence of partial portal vein thrombosis. The decreased-signal-intensity area within the portal vein in a was probably caused by a susceptibility artifact from adjacent bowel gas, whereas the rim of increased signal intensity in b was most probably caused by slow-flowing blood. Note the duodenal varices (arrowhead in a), which were seen only with contrast-enhanced MR angiography.
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Figure 4c. Images obtained in a 59-year-old woman with a history of duodenal variceal bleeding. (a) Coronal MIP image from the portal venous phase of contrast-enhanced dynamic three-dimensional T1-weighted fast-field-echo MR angiography (4.7/1.4, 40° flip angle), (b) transverse respiratory-triggered T2-weighted turbo spin-echo MR image (2,800/80), and (c) anteroposterior intraarterial DSA splenoportographic image. In a, and on the single-section images (not shown), there is an area of decreased signal intensity (arrow) in the midportion of the portal vein, which was falsely thought to represent partial nonocclusive thrombus. In b, the diagnosis was further supported by a rim of increased signal intensity (arrow) in the ventral part of the portal vein. However, color Doppler US and intraarterial DSA (c) did show a normal main portal vein (solid arrow in c) and splenic vein (open arrow in c) and no evidence of partial portal vein thrombosis. The decreased-signal-intensity area within the portal vein in a was probably caused by a susceptibility artifact from adjacent bowel gas, whereas the rim of increased signal intensity in b was most probably caused by slow-flowing blood. Note the duodenal varices (arrowhead in a), which were seen only with contrast-enhanced MR angiography.
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The overall accuracies were 99% for MR angiography and 96% for intraarterial DSA (Table).
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DISCUSSION
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Precise and reliable assessment of the portal venous system in patients with hepatic cirrhosis and portal hypertension is essential before liver transplantation, nonsurgical transjugular shunting, or surgical portosystemic shunting (3). Especially in patients with portal hypertension and a history of gastroesophageal bleeding, it is mandatory to determine whether the portal venous system is patent or the portal vein or its main branches has thrombosis (1). Noninvasive evaluation can be achieved with color Doppler US, which depicts the portal vein and provides additional information about the velocity and the flow direction. However, Doppler US is observer dependent and is sometimes hampered by inadequate delineation of the whole portal venous system (3–5,15). In patients who are potential candidates for surgery, that is, for portosystemic shunt procedures, a more exact diagnostic method that covers the whole portal venous system is required (3,13).
Recently, the value of MR angiography as another noninvasive procedure for the assessment of the portal venous system has been increasingly recognized. Time-of-flight or phase-contrast techniques have been shown to be promising for the assessment of the portal venous system (1,4,10). Disadvantages in the abdomen include motion artifacts due to breathing with the two techniques, long acquisition times with phase-contrast and respiratory-triggered time-of-flight techniques, inflow of unsaturated spins with the time-of-flight techniques, and incomplete coverage of the whole portal venous system with breath-hold time-of-flight techniques (1). However, good results were obtained with both techniques with regard to the assessment of the portal vein in previous studies.
Finn et al (10) reported a sensitivity and specificity of 100% (three of three) and 96% (26 of 27), respectively, for identifying portal vein occlusion in 30 patients before liver transplantation by using a time-of-flight technique, with surgical confirmation. However, in their study, there were only three patients with portal vein thrombosis. In the study by Hughes et al (11), there was 99% agreement between two-dimensional time-of-flight MR angiography of the portal venous system and other imaging modalities. Silverman et al (16) reported on the combined use of two-dimensional time-of-flight and phase-contrast techniques for MR angiography of the portal vein, with 100% sensitivity and specificity in depicting portal vein patency in the portion of the portal vein important at liver transplantation in 92 patients. In their study, the sensitivity of MR angiography in the detection of thrombosis of the proximal confluence of the portal vein and the main portal vein (10 patients with thrombosis) was also 100%.
Recently, the use of gadolinium-enhanced MR angiography for the depiction of the portal venous system has been advocated (6,17,18). Rodgers et al (6) compared dynamic contrast-enhanced breath-hold two-dimensional fast low-angle shot MR angiography with intraarterial DSA in 18 patients for the evaluation not only of the portal vein but also of the splenic and superior mesenteric veins. Among the 84 vessels evaluated with both modalities, there was agreement in 76 vessels (90%). Because of their results, the authors concluded that contrast-enhanced MR angiography can replace intraarterial DSA in the preoperative evaluation of portal vein patency in most patients (6). With regard to their study, it is notable that two splenic veins were excluded from the field of view because of limited coverage of the portal venous system with 11 5-mm-thick sections with a 10% gap, which resulted in coverage of only 6 cm of the portal venous system in the coronal plane.
Three-dimensional gadolinium-en-hanced MR angiography with the applied technique in our study overcomes many of the problems of the former MR angiographic techniques in the evaluation of the portal venous system. Because of the T1 shortening of the blood, rapid three-dimensional volume imaging can cover the entire portal venous system easily with high temporal and spatial resolution. Previous limitations due to necessary breath holds of 30 seconds or more and a limited coverage of the portal venous system were overcome by using high gradient strengths with a very short repetition time and echo time, 4.7/1.4, which allowed the acquisition of 70 sections with a section thickness of 1.8 mm. As a result, coverage of 12.6 cm of the upper part of the abdomen in the coronal plane allowed the visualization of the entire portal venous system, including the portal, splenic, superior mesenteric, and inferior mesenteric veins and typical sites of portosystemic collateral vessels. Furthermore, arterial and venous phase angiograms could be obtained within one study because of the short imaging duration.
Because during the time of this study intraarterial splenoportal and mesentericoportal DSA were still required for preoperative planning by our surgery department, contrast-enhanced MR angiography could be compared with DSA in 36 patients. The comparison of the two modalities showed that DSA can be replaced by contrast-enhanced MR angiography in the assessment of patency or thrombosis of the portal venous system in patients with portal hypertension; there were no significant differences in the assessment of the portal venous system between the two imaging modalities.
Among the 101 vessels evaluated with the two modalities, there was aggreement in 94% and discrepant findings in only six vessels in four patients. There were a total of 42 thromboses in the portal venous system (portal vein, 23; splenic vein, five; superior mesenteric vein, 14). The overall sensitivity, specificity, and accuracy for the detection of thrombosis were 100%, 98%, and 99%, respectively, for MR angiography and 91%, 100%, and 96%, respectively, for angiography. Although MR angiography showed higher sensitivity and accuracy compared with DSA, these differences were not statistically significant with regard to the detection of thrombosis or in the assessment of vessel patency in any part of the portal venous system.
However, due to a higher contrast resolution, MR angiography seems to be even better suited for assessment of the portal venous system in patients with portal hypertension and blood flow diversion into multiple portosystemic collateral vessels, because opacification of the portal vein might be inadequate at DSA portography (3). Another advantage of contrast-enhanced three-dimensional MR angiography in this study is the complete depiction of the portal venous system, including all important collateral pathways and the inferior mesenteric vein, which can also be used in surgical shunt procedures. On the other hand, an advantage of angiography is the higher temporal resolution, the provision of dynamic information, and visualization of the flow direction, which cannot be appreciated with MR angiography.
One limitation of our study is the lack of a surgically confirmed diagnosis in 14 patients. However, in the four patients with discordant findings of MR angiography and intraarterial DSA, the definite diagnosis was made with surgical evaluation in three cases and with other imaging modalities (CTAP and Doppler US) in one case. Another limitation might be the retrospective design of the study.
In summary, our results show that there is no significant difference between contrast-enhanced MR angiography and intraarterial DSA in the detection of thrombosis or the assessment of vessel patency in the portal venous system in patients with portal hypertension. Although more experience with MR angiography should be gained for evaluation of the portal venous system, our study findings indicate that intraarterial DSA might be effectively replaced by noninvasive contrast-enhanced MR angiography as the imaging method of choice for complete evaluation of the portal venous system.
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FOOTNOTES
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J.G. is an employee of Philips Medical Systems, Hamburg, Germany, which manufactured the imaging equipment used in this study.
Abbreviations: CTAP = CT during arterial portography,
DSA = digital subtraction angiography,
MIP = maximum intensity projection
Author contributions: Guarantor of integrity of entire study, B.K.; study concepts, B.K.; study design, B.K., H.S., S.F.; definition of intellectual content, B.K.; literature research, B.K., S.F.; clinical studies, H.S., S.F., M.W. ; data acquisition, H.S., S.F., R.C., D.P., R.B.; data analysis, H.S., B.K., M.W.; statistical analysis, B.K., S.F.; manuscript preparation and editing, B.K.; manuscript review, J.G., A.H., H.H.S.
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