(Radiographics. 1999;19:415-429.)
© RSNA, 1999
Diagnostic Pitfalls of MR Cholangiopancreatography in the Evaluation of the Biliary Tract and Gallbladder
Yuji Watanabe, MD, PhD1,
Masako Dohke, MD1,
Takayoshi Ishimori, MD1,
Yoshiki Amoh, MD1,
Akira Okumura, MD1,
Kazushige Oda, MD1,
Shinji Koike, MD1 and
Yoshihiro Dodo, MD, PhD1
1 Department of Radiology, Kurashiki Central Hospital, Miwa 1-1-1, Kurashiki 710-8602, Japan
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Abstract
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Magnetic resonance (MR) cholangiopancreatography is a noninvasive imaging technique that has proved accurate in the diagnosis of biliary obstruction. However, various diagnostic pitfalls have been reported with MR cholangiopancreatography that were not encountered previously at conventional biliary imaging. These pitfalls may simulate or mask various pathologic conditions of the extrahepatic bile duct or main pancreatic duct and may be caused by a variety of factors. Because of its postprocessing nature, maximum-intensity-projection reconstruction may mask a small gallstone if the stone is surrounded by hyperintense bile and may cause false ductal disconnection or duplication when a breath hold is not performed perfectly. Extraductal factors (eg, metallic surgical clips, intravascular metallic coils, gas in the stomach or duodenum) can cause signal loss in the adjacent part of the extrahepatic bile duct, which may in turn lead to a false-positive diagnosis of ductal narrowing or obstruction. Normal vascular structures including the right hepatic and gastroduodenal arteries can cause pseudo-obstruction of the extrahepatic bile duct by pulsatile compression. Intraductal factors (eg, gas, hemorrhage, debris, iodinated contrast material) reduce the signal intensity of the bile, which may result in pseudo-obstruction, false filling defects, or a nonvisualized gallbladder or bile duct. Knowledge of the existence and high prevalence of these diagnostic pitfalls should help prevent misinterpretation of MR cholangiopancreatograms.
Index Terms: Bile ducts, MR, 76.1214 • Gallbladder, MR, 762.1214 • Magnetic resonance (MR), technology, 76.1214 Pancreatic ducts, MR, 774.1214
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INTRODUCTION
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Magnetic resonance (MR) cholangiopancreatography is a noninvasive imaging technique for the evaluation of patients with suspected pancreatobiliary disease (1–9). MR cholangiopancreatography is based on the principle that static fluids can be imaged with heavily T2-weighted sequences including gradient-echo, turbo spin-echo, and single-shot turbo spin-echo sequences (1–23). The images of pancreatobiliary disease seen at MR cholangiopancreatography resemble those obtained with conventional pancreatobiliary imaging techniques such as drip-infusion cholangiography, endoscopic retrograde cholangiopancreatography, and percutaneous transhepatic cholangiography. With the development of MR cholangiopancreatographic technique, this procedure has proved accurate in the diagnosis of the presence and level of biliary obstruction (1–11). However, various diagnostic pitfalls not encountered previously at conventional biliary imaging have been reported at MR cholangiopancreatography and may simulate or mask various pathologic conditions of the extrahepatic biliary system and main pancreatic duct (14–23). These pitfalls include maximum-intensity-projection (MIP) reconstruction artifact, extraductal causes (eg, metallic surgical clips, intravascular metallic coils, gas in the stomach and duodenum, normal vascular structures), and intraductal causes (eg, gas, hemorrhage, debris, iodinated contrast material).
In this article, we describe and illustrate basic MR cholangiopancreatographic techniques, along with diagnostic pitfalls and suggested troubleshooting procedures.
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TECHNIQUES OF MR CHOLANGIOPANCREATOGRAPHY
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MR cholangiopancreatography is based on the principle that static fluids have long T2 relaxation times. Static fluids (including bile and pancreatic fluids) have high signal intensity on heavily T2-weighted MR images, whereas solid organs such as the liver and pancreas have low signal intensity. To date, a variety of MR cholangiopancreatographic techniques have been developed. Single-shot turbo spin echo is one of the more rapid pulse sequences used to obtain MR cholangiopancreatograms and may well prove optimal (10–14). Technical considerations other than pulse sequences have included two-dimensional versus three-dimensional acquisition, respiratory triggering versus breath-hold scanning, and single-section versus multisection acquisition, both of which are included in our current protocol and are discussed later in the article (4–23). At present, there is no clear consensus as to what constitutes optimal MR cholangiopancreatographic technique, and it remains to be determined which combination of techniques is optimal for visualizing the biliary tree and pancreatic ducts.
We perform all MR cholangiopancreatography with a 1.5-T MR imager (Gyroscan ACS-NT; Philips Medical Systems, Best, The Netherlands) with 15-mT/m gradients. A circular surface coil is used to obtain a high signal-to-noise ratio and high spatial resolution. Generally, fat suppression with a frequency-selective presaturation technique with spectral presaturation inversion recovery is used to achieve complete suppression of background signal intensity. However, when a metallic surgical clip is known to be present in the patient's abdomen, fat suppression is not used. In cooperative patients, all MR cholangiopancreatography is performed during breath hold at end expiration. In infants and in debilitated or uncooperative patients, single-section MR cholangiopancreatography is performed at end expiration during quiet breathing and multisection MR cholangiopancreatography is performed with respiratory triggering during quiet breathing.
Single-Section MR Cholangiopancreatography
A single-shot turbo spin-echo sequence, which is a fast, heavily T2-weighted sequence with long echo train lengths, is used for single-section MR cholangiopancreatography. Imaging parameters are as follows: repetition time msec/echo time msec = 8,000/1,300, echo train length = 256, 1 signal acquired, 220-mm field of view, 65-mm-thick coronal sections, and a 256 x 256 matrix. A short acquisition time (2.6 seconds) permits breath-hold scanning. No further postprocessing is necessary. Three images—an anterior image and two anterior-oblique images—are obtained for stereoscopic viewing.
With single-section MR cholangiopancreatography, fluid-containing structures have such high signal intensity that even a single thick section clearly demonstrates the biliary tree and pancreatic ducts. Furthermore, a short imaging time allows almost all patients to perform a breath hold perfectly, thereby reducing respiratory motion artifacts.
Multisection MR Cholangiopancreatography
A single-shot turbo spin-echo sequence is used with half-Fourier acquisition and fat suppression for multisection MR cholangiopancreatography. Multiple contiguous thin sections are obtained in a coronal plane. Imaging parameters are as follows: repetition time msec/echo time msec = 8,000/400, echo train length = 128, 1 signal acquired, 220-mm field of view, 18 contiguous 4-mm-thick sections with 1-mm overlap, and a 205 x 256 matrix. Scan time is 18 seconds, permitting breath-hold image acquisition. The coronal source images obtained with fat suppression is compressed and reconstructed into composite MR cholangiopancreatograms with an MIP algorithm. Oblique images are obtained with frontal to lateral reconstruction at 15° intervals.
Multiple coronal non–fat-suppressed images are obtained with similar parameters and can be used as reference images for the interpretation of MR cholangiopancreatograms. Non–fat-suppressed images are less degraded by susceptibility artifact from gas in the stomach or duodenum than are fat-suppressed images. Moreover, non–fat-suppressed images demonstrate a clear anatomic relationship between the pancreatobiliary duct and solid organs such as the liver and pancreas.
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DIAGNOSTIC PITFALLS OF MR CHOLANGIOPANCREATOGRAPHY
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A variety of diagnostic pitfalls may simulate or mask pathologic conditions at MR cholangiopancreatography. These pitfalls may be caused by MIP reconstruction artifact, susceptibility artifact from gas or metal, pulsatile vascular compression, or material that is hypointense at T2-weighted MR imaging. The three latter causes may be either extraductal or intraductal, depending on the site of causative materials. Extraductal factors include metallic surgical clips, intravascular metallic coils, gas in the stomach or duodenum, and normal vascular structures. Intraductal factors include gas, hemorrhage, debris, and iodinated contrast material. The causes of diagnostic pitfalls, the pathologic conditions being simulated or masked, and various troubleshooting procedures are summarized in the Table.
MIP Reconstruction Artifact
Nonvisualized Gallstone or Polypoid Tumor.—Because of the postprocessing nature of MIP reconstruction, a small gallstone or polypoid lesion may not be visualized at multisection MR cholangiopancreatography when surrounded by hyperintense bile (Fig 1) (15–17). Careful interpretation of the coronal source images can help prevent misdiagnosis. In contrast, single-section MR cholangiopancreatography provides a projection image resembling a fluoroscopic view and enables visualization of a small stone as a filling defect. Transaxial T2-weighted MR imaging may also allow such visualization.
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Figure 1a. Nonvisualized gallbladder cancer due to MIP postprocessing. (a) Multisection MR cholangiopancreatogram shows only minimal deformity of the gallbladder (arrow). No filling defect is seen. (b) Coronal source image reveals gallbladder cancer as a filling defect with a multinodular surface (arrows). (c) Single-section MR cholangiopancreatogram shows gallbladder cancer as an irregularly shaped filling defect (arrows).
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Figure 1b. Nonvisualized gallbladder cancer due to MIP postprocessing. (a) Multisection MR cholangiopancreatogram shows only minimal deformity of the gallbladder (arrow). No filling defect is seen. (b) Coronal source image reveals gallbladder cancer as a filling defect with a multinodular surface (arrows). (c) Single-section MR cholangiopancreatogram shows gallbladder cancer as an irregularly shaped filling defect (arrows).
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Figure 1c. Nonvisualized gallbladder cancer due to MIP postprocessing. (a) Multisection MR cholangiopancreatogram shows only minimal deformity of the gallbladder (arrow). No filling defect is seen. (b) Coronal source image reveals gallbladder cancer as a filling defect with a multinodular surface (arrows). (c) Single-section MR cholangiopancreatogram shows gallbladder cancer as an irregularly shaped filling defect (arrows).
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Respiratory Motion Artifact.—Multisection MR cholangiopancreatography requires an 18-second breath hold. When a single breath hold is not performed perfectly, misregistration of the common bile duct (CBD) or main pancreatic duct may occur (16,17). In such a setting, multisection MR cholangiopancreatography with use of MIP postprocessing may reveal that the CBD and main pancreatic duct are disconnected, stenotic, dilated, or duplicated (Fig 2). In contrast, single-section MR cholangiopancreatography demonstrates good continuity of the ducts even in an uncooperative patient because the short imaging time (2.6 seconds) allows reduction of respiratory motion artifact. Another troubleshooting method is careful interpretation of coronal source images.
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Figure 2a. Respiratory motion artifact. (a) Multisection MR cholangiopancreatogram shows the biliary tree (solid arrows) and main pancreatic duct (arrowheads) as discontinuous and duplicated. Gallstones (open arrows) in the gallbladder are not well delineated due to MIP reconstruction artifact. (b) Single-section MR cholangiopancreatogram shows the CBD, main pancreatic duct (arrowheads), and multiple gallstones (arrows) more clearly than multisection MR cholangiopancreatography (cf a). Note the pancreatic cysts (*) and dilated right renal pelvis (+).
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Figure 2b. Respiratory motion artifact. (a) Multisection MR cholangiopancreatogram shows the biliary tree (solid arrows) and main pancreatic duct (arrowheads) as discontinuous and duplicated. Gallstones (open arrows) in the gallbladder are not well delineated due to MIP reconstruction artifact. (b) Single-section MR cholangiopancreatogram shows the CBD, main pancreatic duct (arrowheads), and multiple gallstones (arrows) more clearly than multisection MR cholangiopancreatography (cf a). Note the pancreatic cysts (*) and dilated right renal pelvis (+).
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Overestimation of Ductal Narrowing.—The degree of ductal narrowing tends to be overestimated at MR cholangiopancreatography compared with endoscopic retrograde cholangiopancreatography due to underestimation of the ductal caliber (Fig 3). This underestimation results from the nature of MIP reconstruction and the lower spatial resolution of MR cholangiopancreatography (19). It may also result from the fact that MR cholangiopancreatography depicts the biliary tree in a physiologic in vivo state, whereas endoscopic retrograde cholangiopancreatography depicts the biliary tree under pressure from contrast material injection.
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Figure 3a. Overestimation of ductal narrowing. (a) Multisection MR cholangiopancreatogram demonstrates biliary obstruction at the junction of the common hepatic duct (CHD) (solid arrow) and accessory right hepatic duct (open arrow) due to invasion of gallbladder neck cancer. Note the conical deformity of the gallbladder (arrowheads). (b) Endoscopic retrograde cholangiopancreatogram reveals that the CHD (arrow) is severely stenotic but not completely obstructed.
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Figure 3b. Overestimation of ductal narrowing. (a) Multisection MR cholangiopancreatogram demonstrates biliary obstruction at the junction of the common hepatic duct (CHD) (solid arrow) and accessory right hepatic duct (open arrow) due to invasion of gallbladder neck cancer. Note the conical deformity of the gallbladder (arrowheads). (b) Endoscopic retrograde cholangiopancreatogram reveals that the CHD (arrow) is severely stenotic but not completely obstructed.
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Extraductal Factors
Metallic Foreign Material.—Metallic foreign material such as surgical clips and intravascular metallic coils produce adjacent signal loss (18,19). When surgical clips are located close to the biliary tree, signal void artifacts may cover a proximal segment of the biliary tree and cause pseudo-obstruction on MR cholangiopancreatograms (Figs 4, 5). Careful inspection of coronal source images and transaxial T2-weighted images may reveal that signal void foci are eccentric and are not located in the extrahepatic bile duct. Results of plain radiography or CT can easily confirm the presence and position of surgical clips. To minimize signal loss caused by metallic foreign material, frequency-selective fat suppression techniques such as spectral inversion recovery should not be used for MR cholangiopancreatography (Fig 6).
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Figure 4a. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 4b. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 4c. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 5a. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 5b. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 5c. Figures 4, 5. (4) Pseudostenosis due to signal loss caused by a surgical clip used in cholecystectomy. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow). The appearance of the stenosis resembles that of a bile duct tumor. No dilatation of the upstream biliary tree is seen. (b) Drip-infusion cholangiogram reveals three surgical clips (arrowheads) near the normal CHD. (c) Drip-infusion cholangiographic computed tomographic (CT) scan also shows no stenosis of the CHD (arrow) close to the surgical clip (arrowhead). (5) Pseudo-obstruction due to signal void caused by a surgical clip used in gastrectomy. (a) Multisection MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Although the obstruction resembles a bile duct tumor or stone, no dilatation of the upstream bile duct is seen. (b) Transaxial fat-suppressed T2-weighted MR image reveals a large, round signal void (arrowheads) close to the gallbladder. (c) Drip-infusion cholangiographic CT scan reveals a metallic surgical clip (open arrows) at the duodenal bulbs, corresponding to the center of the signal void on the transaxial T2-weighted image (cf b). Note the high attenuation of the CBD (solid arrow) and intrahepatic bile duct.
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Figure 6a. Pseudo-obstruction caused by a surgical clip used in gastrectomy. (a) Single-section fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow) and main pancreatic duct (arrowhead) due to signal loss caused by a surgical clip. A pancreatic cyst is also seen (*). (b) Single-section non–fat-suppressed MR cholangiopancreatogram reveals a normal-appearing CBD. No obstruction is seen. (c) Contrast material–enhanced CT scan demonstrates a metallic surgical clip (white arrow) at the duodenal bulbs, close to the CBD (black arrow).
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Figure 6b. Pseudo-obstruction caused by a surgical clip used in gastrectomy. (a) Single-section fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow) and main pancreatic duct (arrowhead) due to signal loss caused by a surgical clip. A pancreatic cyst is also seen (*). (b) Single-section non–fat-suppressed MR cholangiopancreatogram reveals a normal-appearing CBD. No obstruction is seen. (c) Contrast material–enhanced CT scan demonstrates a metallic surgical clip (white arrow) at the duodenal bulbs, close to the CBD (black arrow).
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Figure 6c. Pseudo-obstruction caused by a surgical clip used in gastrectomy. (a) Single-section fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow) and main pancreatic duct (arrowhead) due to signal loss caused by a surgical clip. A pancreatic cyst is also seen (*). (b) Single-section non–fat-suppressed MR cholangiopancreatogram reveals a normal-appearing CBD. No obstruction is seen. (c) Contrast material–enhanced CT scan demonstrates a metallic surgical clip (white arrow) at the duodenal bulbs, close to the CBD (black arrow).
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Gas in the Stomach and Duodenum.—Gas in the gastrointestinal tract creates a signal void larger than the gas pocket itself due to susceptibility artifact. When the signal void artifact covers a segment of the extrahepatic bile duct, pseudo-obstruction can occur (19). The middle and lower CBD are the most common sites of pseudo-obstruction, which is caused by susceptibility artifact from gas in the gastric antrum, duodenal bulb, and parapapillary diverticulum (Figs 7, 8). Careful inspection of coronal source images and transaxial T1- and T2-weighted MR images may reveal that signal void foci are eccentric. CT or barium examination of the duodenum is also useful in confirming the presence of a duodenal diverticulum and of gas within the diverticulum. Non–fat-suppressed coronal or transaxial heavily T2-weighted MR imaging may help distinguish pseudo-obstruction from true stenosis by minimizing susceptibility artifact.
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Figure 7a. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Figure 7b. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Figure 7c. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Figure 8a. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Figure 8b. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Figure 8c. Figures 7, 8. (7) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal bulb. (a) Multisection fat-suppressed MR cholangiopancreatogram shows false obstruction of the middle CBD (arrow). Note the signal void resulting from gas in the duodenal bulb (arrowheads). (b) Multisection non–fat-suppressed MR cholangiopancreatogram reveals no false obstruction of the middle CBD. Note that the signal void resulting from gas in the duodenal bulb (arrowhead) appears much smaller than at multisection fat-suppressed MR cholangiopancreatography (cf a). (c) Intraoperative cholangiogram obtained during cholecystectomy reveals a normal CBD. (8) Pseudo-obstruction due to susceptibility artifact from gas in the duodenal diverticulum. (a) Multisection MR cholangiopancreatogram shows false obstruction of the lower CBD resembling a gallstone or ampullary tumor (arrow). Note the slight dilatation of the main pancreatic duct. (b) Endoscopic retrograde cholangiopancreatogram reveals a large duodenal diverticulum (arrow) and anomalous union of the CBD and main pancreatic duct (arrowhead). No obstruction of the lower CBD is seen. (c) Contrast-enhanced CT scan shows gas forming an air-fluid level in the duodenal diverticulum (arrow).
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Pulsatile Vascular Compression.—Pulsatile vascular compression can cause pseudo-obstruction of the extrahepatic bile duct at MR cholangiopancreatography, although such pseudo-obstruction may be in a physiologic state (20). Anatomically, the hepatic arteries and gastroduodenal artery are closely related to the extrahepatic bile duct (Fig 9). The most common site of pseudo-obstruction is the CHD, followed by the left hepatic duct and the middle CBD (Figs 10–12). The causative vessels include the right hepatic, proper hepatic, gastroduodenal, and cystic arteries. The right hepatic artery compresses the common hepatic or left hepatic duct at the posterior aspect, whereas the gastroduodenal artery compresses the middle CBD at the right anterolateral aspect. The extent of false obstruction of the extrahepatic bile duct may depend on the diameter of the causative artery. Troubleshooting methods include dynamic helical CT or contrast-enhanced three-dimensional MR angiography to identify the causative artery (20). However, a more convenient method is careful interpretation of the coronal non–fat-suppressed source image, which can reveal that pseudo-obstruction of the extrahepatic bile duct is caused by the vascular structure passing through the surrounding fat tissue.
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Figure 9. Anatomic relationship between the extrahepatic bile duct and splanchnic arteries. Illustration shows the gastroduodenal artery coursing immediately anterior to the CBD. Note that the cystic, right hepatic, and gastroduodenal arteries abut the extrahepatic bile duct. (Adapted and reprinted, with permission, from reference 21.)
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Figure 10a. Pseudo-obstruction due to pulsatile compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false obstruction of the CHD resembling bile duct cancer or a biliary stone (arrow). No dilatation of the upstream biliary tree is seen. (b) Coronal source image for contrast-enhanced three-dimensional MR angiography reveals a dilated right hepatic artery (solid arrowheads) traversing the CHD (arrows) posteriorly. Note that the right hepatic artery is dilated to supply a hepatocellular carcinoma (open arrowheads).
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Figure 10b. Pseudo-obstruction due to pulsatile compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false obstruction of the CHD resembling bile duct cancer or a biliary stone (arrow). No dilatation of the upstream biliary tree is seen. (b) Coronal source image for contrast-enhanced three-dimensional MR angiography reveals a dilated right hepatic artery (solid arrowheads) traversing the CHD (arrows) posteriorly. Note that the right hepatic artery is dilated to supply a hepatocellular carcinoma (open arrowheads).
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Figure 12a. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow) with no dilatation of the upstream biliary tree. A small stone appears as a filling defect in the lower CBD (arrowhead). (b) Coronal non–fat-suppressed, heavily T2-weighted MR image shows a tubular structure traversing the CHD posteriorly (arrows). A small stone is seen in the lower CBD (arrowhead). (c) Contrast-enhanced CT scan shows the right hepatic artery (arrow) crossing the posterior aspect of the CHD (arrowhead). (d) Endoscopic retrograde cholangiopancreatogram shows no stenosis of the CHD.
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Figure 12b. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow) with no dilatation of the upstream biliary tree. A small stone appears as a filling defect in the lower CBD (arrowhead). (b) Coronal non–fat-suppressed, heavily T2-weighted MR image shows a tubular structure traversing the CHD posteriorly (arrows). A small stone is seen in the lower CBD (arrowhead). (c) Contrast-enhanced CT scan shows the right hepatic artery (arrow) crossing the posterior aspect of the CHD (arrowhead). (d) Endoscopic retrograde cholangiopancreatogram shows no stenosis of the CHD.
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Figure 12c. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow) with no dilatation of the upstream biliary tree. A small stone appears as a filling defect in the lower CBD (arrowhead). (b) Coronal non–fat-suppressed, heavily T2-weighted MR image shows a tubular structure traversing the CHD posteriorly (arrows). A small stone is seen in the lower CBD (arrowhead). (c) Contrast-enhanced CT scan shows the right hepatic artery (arrow) crossing the posterior aspect of the CHD (arrowhead). (d) Endoscopic retrograde cholangiopancreatogram shows no stenosis of the CHD.
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Figure 12d. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false stenosis of the CHD (arrow) with no dilatation of the upstream biliary tree. A small stone appears as a filling defect in the lower CBD (arrowhead). (b) Coronal non–fat-suppressed, heavily T2-weighted MR image shows a tubular structure traversing the CHD posteriorly (arrows). A small stone is seen in the lower CBD (arrowhead). (c) Contrast-enhanced CT scan shows the right hepatic artery (arrow) crossing the posterior aspect of the CHD (arrowhead). (d) Endoscopic retrograde cholangiopancreatogram shows no stenosis of the CHD.
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Intraductal Factors
Pneumobilia, Hemobilia, and Debris.—Materials that decrease the signal intensity of the bile (eg, gas [Figs 13, 14], hemorrhage, debris [Fig 15]) may mimic gallstones and cause nonvisualization of the gallbladder or extrahepatic bile duct (14,19,20,22–24). Air bubbles in the biliary tree are not difficult to identify at transaxial T2-weighted MR imaging. Air bubbles float ventrally to the bile, producing air-fluid levels. Hemobilia and debris cause filling defects and are very difficult to differentiate from true gallstones at MR imaging or endoscopic retrograde cholangiopancreatography (22–25). Transaxial T1-weighted MR imaging may help distinguish air bubbles from gallstones by demonstrating hemorrhage or debris as areas of hyperintensity.
Iodinated Contrast Material.—Dense iodinated contrast material injected into the biliary tree for endoscopic retrograde cholangiopancreatography and percutaneous transhepatic cholangiography has low signal intensity on heavily T2-weighted MR images. When MR cholangiopancreatography is performed immediately after endoscopic retrograde cholangiopancreatography and percutaneous transhepatic cholangiography, the extrahepatic bile duct and the gallbladder may not be visualized, in which case no information about the biliary tract can be gathered (Fig 16). Therefore, MR cholangiopancreatography should not be performed immediately after endoscopic retrograde cholangiopancreatography or percutaneous transhepatic cholangiography, except when the latter two procedures end in technical failure.
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Figure 16a. Nonvisualized gallbladder due to iodinated contrast material. (a) Multisection MR cholangiopancreatogram performed immediately after endoscopic retrograde cholangiopancreatography demonstrates neither the gallbladder nor the CBD. Note the areas of hyperintensity surrounding the biliary tree and pancreas (solid arrowheads), suggestive of peripancreatic edema and exudate due to acute pancreatitis caused by endoscopic retrograde cholangiopancreatography. Note also the minimal dilatation of the main pancreatic duct (open arrowheads). (b) Transaxial fat-suppressed T2-weighted MR image shows a thin layer of hyperintense bile (arrows) floating on hypointense fluid (*) in the gallbladder. Note that the pancreatic parenchyma is hyperintense relative to the hepatic parenchyma. Peripancreatic exudate is seen as areas of hyperintensity surrounding the pancreas (arrowheads). (c) Transaxial fat-suppressed T1-weighted MR image reveals a hyperintense gallbladder (*) and CBD (arrow) due to the presence of iodinated contrast material. (d) Unenhanced CT scan reveals hyperattenuating iodinated contrast material in the gallbladder (*) and CBD (arrow).
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Figure 16b. Nonvisualized gallbladder due to iodinated contrast material. (a) Multisection MR cholangiopancreatogram performed immediately after endoscopic retrograde cholangiopancreatography demonstrates neither the gallbladder nor the CBD. Note the areas of hyperintensity surrounding the biliary tree and pancreas (solid arrowheads), suggestive of peripancreatic edema and exudate due to acute pancreatitis caused by endoscopic retrograde cholangiopancreatography. Note also the minimal dilatation of the main pancreatic duct (open arrowheads). (b) Transaxial fat-suppressed T2-weighted MR image shows a thin layer of hyperintense bile (arrows) floating on hypointense fluid (*) in the gallbladder. Note that the pancreatic parenchyma is hyperintense relative to the hepatic parenchyma. Peripancreatic exudate is seen as areas of hyperintensity surrounding the pancreas (arrowheads). (c) Transaxial fat-suppressed T1-weighted MR image reveals a hyperintense gallbladder (*) and CBD (arrow) due to the presence of iodinated contrast material. (d) Unenhanced CT scan reveals hyperattenuating iodinated contrast material in the gallbladder (*) and CBD (arrow).
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Figure 16c. Nonvisualized gallbladder due to iodinated contrast material. (a) Multisection MR cholangiopancreatogram performed immediately after endoscopic retrograde cholangiopancreatography demonstrates neither the gallbladder nor the CBD. Note the areas of hyperintensity surrounding the biliary tree and pancreas (solid arrowheads), suggestive of peripancreatic edema and exudate due to acute pancreatitis caused by endoscopic retrograde cholangiopancreatography. Note also the minimal dilatation of the main pancreatic duct (open arrowheads). (b) Transaxial fat-suppressed T2-weighted MR image shows a thin layer of hyperintense bile (arrows) floating on hypointense fluid (*) in the gallbladder. Note that the pancreatic parenchyma is hyperintense relative to the hepatic parenchyma. Peripancreatic exudate is seen as areas of hyperintensity surrounding the pancreas (arrowheads). (c) Transaxial fat-suppressed T1-weighted MR image reveals a hyperintense gallbladder (*) and CBD (arrow) due to the presence of iodinated contrast material. (d) Unenhanced CT scan reveals hyperattenuating iodinated contrast material in the gallbladder (*) and CBD (arrow).
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Figure 16d. Nonvisualized gallbladder due to iodinated contrast material. (a) Multisection MR cholangiopancreatogram performed immediately after endoscopic retrograde cholangiopancreatography demonstrates neither the gallbladder nor the CBD. Note the areas of hyperintensity surrounding the biliary tree and pancreas (solid arrowheads), suggestive of peripancreatic edema and exudate due to acute pancreatitis caused by endoscopic retrograde cholangiopancreatography. Note also the minimal dilatation of the main pancreatic duct (open arrowheads). (b) Transaxial fat-suppressed T2-weighted MR image shows a thin layer of hyperintense bile (arrows) floating on hypointense fluid (*) in the gallbladder. Note that the pancreatic parenchyma is hyperintense relative to the hepatic parenchyma. Peripancreatic exudate is seen as areas of hyperintensity surrounding the pancreas (arrowheads). (c) Transaxial fat-suppressed T1-weighted MR image reveals a hyperintense gallbladder (*) and CBD (arrow) due to the presence of iodinated contrast material. (d) Unenhanced CT scan reveals hyperattenuating iodinated contrast material in the gallbladder (*) and CBD (arrow).
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CONCLUSIONS
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Several diagnostic pitfalls are associated with MR cholangiopancreatography. MIP reconstruction artifact may cause nonvisualized gallstone, pseudo-obstruction, false duplication, and dilatation. Factors such as metal, gas, pulsatile vascular compression, hemorrhage, and iodinated contrast material may cause pseudo-obstruction or pseudodefect. Knowledge of the existence and high prevalence of these diagnostic pitfalls should help prevent misinterpretation of MR cholangiopancreatograms.
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Figure 11a. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false obstruction of the CHD (arrow). (b, c) Coronal non–fat-suppressed, heavily T2-weighted MR images (b obtained anterior to c) show a tubular structure traversing the CHD posteriorly (arrowheads). The tubular structure proved to be the right hepatic artery at double-phase helical CT (not shown).
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Figure 11b. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false obstruction of the CHD (arrow). (b, c) Coronal non–fat-suppressed, heavily T2-weighted MR images (b obtained anterior to c) show a tubular structure traversing the CHD posteriorly (arrowheads). The tubular structure proved to be the right hepatic artery at double-phase helical CT (not shown).
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Figure 11c. Pseudo-obstruction due to compression by the right hepatic artery. (a) Multisection MR cholangiopancreatogram shows false obstruction of the CHD (arrow). (b, c) Coronal non–fat-suppressed, heavily T2-weighted MR images (b obtained anterior to c) show a tubular structure traversing the CHD posteriorly (arrowheads). The tubular structure proved to be the right hepatic artery at double-phase helical CT (not shown).
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Figure 13a. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows multiple filling defects (arrows) simulating stones in the dilated CBD. Note the bifurcation anomaly of the main pancreatic duct (arrowhead). (b) Coronal source image also shows multiple filling defects in the CBD (arrows). (c) Transaxial fat-suppressed T2-weighted MR image shows air bubbles (arrows) floating ventrally to the bile and producing air-fluid levels in the CBD and gallbladder.
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Figure 13b. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows multiple filling defects (arrows) simulating stones in the dilated CBD. Note the bifurcation anomaly of the main pancreatic duct (arrowhead). (b) Coronal source image also shows multiple filling defects in the CBD (arrows). (c) Transaxial fat-suppressed T2-weighted MR image shows air bubbles (arrows) floating ventrally to the bile and producing air-fluid levels in the CBD and gallbladder.
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Figure 13c. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows multiple filling defects (arrows) simulating stones in the dilated CBD. Note the bifurcation anomaly of the main pancreatic duct (arrowhead). (b) Coronal source image also shows multiple filling defects in the CBD (arrows). (c) Transaxial fat-suppressed T2-weighted MR image shows air bubbles (arrows) floating ventrally to the bile and producing air-fluid levels in the CBD and gallbladder.
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Figure 14a. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows filling defects in the dilated lower CBD (arrow) and CHD (arrowhead) resembling CBD stones. (b, c) Transaxial heavily T2-weighted MR images demonstrate the filling defects more clearly. The filling defect in the CHD represents gas floating ventrally to the bile (arrowhead in b), whereas that in the lower CBD is a real stone that is sinking and surrounded by hyperintense bile (arrow in c). (d, e) Unenhanced CT scans reveal pneumobilia of the CHD (arrowhead in d) and a soft-tissue-density stone in the lower CBD (arrow in e).
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Figure 14b. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows filling defects in the dilated lower CBD (arrow) and CHD (arrowhead) resembling CBD stones. (b, c) Transaxial heavily T2-weighted MR images demonstrate the filling defects more clearly. The filling defect in the CHD represents gas floating ventrally to the bile (arrowhead in b), whereas that in the lower CBD is a real stone that is sinking and surrounded by hyperintense bile (arrow in c). (d, e) Unenhanced CT scans reveal pneumobilia of the CHD (arrowhead in d) and a soft-tissue-density stone in the lower CBD (arrow in e).
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Figure 14c. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows filling defects in the dilated lower CBD (arrow) and CHD (arrowhead) resembling CBD stones. (b, c) Transaxial heavily T2-weighted MR images demonstrate the filling defects more clearly. The filling defect in the CHD represents gas floating ventrally to the bile (arrowhead in b), whereas that in the lower CBD is a real stone that is sinking and surrounded by hyperintense bile (arrow in c). (d, e) Unenhanced CT scans reveal pneumobilia of the CHD (arrowhead in d) and a soft-tissue-density stone in the lower CBD (arrow in e).
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Figure 14d. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows filling defects in the dilated lower CBD (arrow) and CHD (arrowhead) resembling CBD stones. (b, c) Transaxial heavily T2-weighted MR images demonstrate the filling defects more clearly. The filling defect in the CHD represents gas floating ventrally to the bile (arrowhead in b), whereas that in the lower CBD is a real stone that is sinking and surrounded by hyperintense bile (arrow in c). (d, e) Unenhanced CT scans reveal pneumobilia of the CHD (arrowhead in d) and a soft-tissue-density stone in the lower CBD (arrow in e).
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Figure 14e. Pneumobilia simulating CBD stones. (a) Multisection MR cholangiopancreatogram shows filling defects in the dilated lower CBD (arrow) and CHD (arrowhead) resembling CBD stones. (b, c) Transaxial heavily T2-weighted MR images demonstrate the filling defects more clearly. The filling defect in the CHD represents gas floating ventrally to the bile (arrowhead in b), whereas that in the lower CBD is a real stone that is sinking and surrounded by hyperintense bile (arrow in c). (d, e) Unenhanced CT scans reveal pneumobilia of the CHD (arrowhead in d) and a soft-tissue-density stone in the lower CBD (arr | |
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Abstract
INTRODUCTION
