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(Radiographics. 2001;21:23-37.)
© RSNA, 2001

EDUCATION EXHIBIT

Pitfalls in MR Cholangiopancreatographic Interpretation1

Hiroyuki Irie, MD, Hiroshi Honda, MD, Toshiro Kuroiwa, MD, Kengo Yoshimitsu, MD, Hitoshi Aibe, MD, Kenji Shinozaki, MD and Kouji Masuda, MD

1 From the Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. Recipient of a Magna Cum Laude award for a scientific exhibit at the 1999 RSNA scientific assembly. Received March 27, 2000; revision requested May 5 and received May 22; accepted May 26. Address correspondence to H.I. (e-mail: hiirie@dr.hosp.kyushu-u.ac.jp).


   Abstract
Top
 Abstract
LEARNING OBJECTIVES
 Introduction
 Pitfalls in MRCP Interpretation
 Conclusion
 References
 
Magnetic resonance (MR) cholangiopancreatography (MRCP) is widely used in the evaluation of pancreatobiliary disorders. However, numerous related pitfalls may simulate or mask pancreatobiliary disease. Maximum-intensity-projection (MIP) reconstructed images completely obscure small filling defects and may demonstrate respiratory motion artifacts. T2 weighting may vary with different MR imaging sequences and influence MRCP findings. Incomplete imaging may create confusion regarding ductal anatomy or disease. Furthermore, MRCP yields only static images and thus may fail to depict various anomalies. Limited spatial resolution makes differentiation between benign and malignant strictures with MRCP alone extremely difficult. Susceptibility artifacts may be caused by metallic foreign bodies or gastric-duodenal gas. Fluid accumulation may produce a pseudolesion or pseudostricture, although changing the imaging angle or section thickness may be helpful. Pneumobilia may be misinterpreted as bile duct stones, and true stones may be overlooked. Pulsatile vascular compression can cause pseudo-obstruction of the bile duct. Use of both source and MIP reconstructed images obtained from different angles can help avoid cystic duct–related pitfalls. Repeat MRCP or conventional MR imaging can help avoid pitfalls related to the periampullary region. Segmental collapse of the normal main pancreatic duct may be misinterpreted as stenosis, but administration of secretin is helpful. An awareness of these pitfalls and possible solutions is crucial for avoiding misinterpretation of MRCP images.

Index Terms: Bile ducts, MR, 76.1214 • Magnetic resonance (MR), maximum intensity projection, 76.1214, 774.1214 • Pancreatic ducts, MR, 774.1214


   LEARNING OBJECTIVES
Top
 Abstract
 LEARNING OBJECTIVES
Introduction
 Pitfalls in MRCP Interpretation
 Conclusion
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
Pitfalls in MRCP Interpretation
 Conclusion
 References
 
Magnetic resonance (MR) cholangiopancreatography (MRCP) is increasingly being used to evaluate pancreatobiliary disease, providing a noninvasive alternative to endoscopic retrograde cholangiopancreatography (ERCP) (1). Many reports have described its usefulness and diagnostic accuracy in evaluating various pancreatobiliary abnormalities (2–5), and, according to some reports, in many instances MRCP can replace diagnostic ERCP (6,7).

Recently, several investigators have discussed the pitfalls of MRCP interpretation (8–10). In our clinical experience, we too have observed various diagnostic pitfalls of MRCP not previously encountered in conventional pancreatobiliary imaging. These pitfalls or diagnostic errors may have a variety of causes and may simulate or mask various diseases of the pancreatobiliary tract (8–10). An awareness of these pitfalls is crucial if misinterpretation is to be prevented.

In this article, we discuss and illustrate various pitfalls in the MRCP interpretation of pancreatobiliary disease, including limitations of acquisition technique and reconstruction artifacts, limitations of MR imaging pulse sequences, incomplete imaging of the pancreatobiliary tract, static imaging, limited spatial resolution, susceptibility artifacts, normal anatomy simulating disease, pitfalls related to bile duct stones, nonpathologic bile duct narrowing due to pulsatile vascular compression, misinterpretation related to the cystic duct, pitfalls related to the periampullary region, and pseudostenosis of the normal main pancreatic duct. We also suggest strategies for the recognition and avoidance of these pitfalls.


   Pitfalls in MRCP Interpretation
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Pitfalls in MRCP Interpretation
Conclusion
 References
 
Limitations of Acquisition Technique and Reconstruction Artifacts
MRCP images may be acquired using either single-section projection imaging or sequential multisection imaging with thin sections followed by maximum-intensity-projection (MIP) reconstruction (11). MIP reconstructed images completely obscure small filling defects due to the partial volume effect (12); therefore, evaluation should be based on the source images (Fig 1). Single-section projection MRCP is performed with thick sections, which may also obscure small filling defects, although these defects might be visible as areas of decreased signal intensity.



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  		Figure 1a.   Limited depiction of disease with MIP reconstruction due to the partial volume effect. (a) Source MRCP image shows filling defects within the gallbladder (arrows). (b) MIP reconstructed image does not depict the filling defects.

 


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  		Figure 1b.   Limited depiction of disease with MIP reconstruction due to the partial volume effect. (a) Source MRCP image shows filling defects within the gallbladder (arrows). (b) MIP reconstructed image does not depict the filling defects.

 
Respiratory motion artifact can present another problem in MIP reconstruction when a patient does not perform an adequate breath hold (13). On such occasions, the common bile duct and main pancreatic duct may appear disconnected, stenotic, dilated, or duplicated (Fig 2).



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  		Figure 2a.   Respiratory motion artifact. (a) MIP reconstructed image from a study performed during an incomplete breath hold demonstrates a respiratory motion artifact mimicking a duplicated main pancreatic duct (arrows). (b) MIP reconstructed image from a repeat study reveals a normal-appearing main pancreatic duct. Hepatolithiasis, which was obscured in a, is now clearly seen (arrow).

 


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  		Figure 2b.   Respiratory motion artifact. (a) MIP reconstructed image from a study performed during an incomplete breath hold demonstrates a respiratory motion artifact mimicking a duplicated main pancreatic duct (arrows). (b) MIP reconstructed image from a repeat study reveals a normal-appearing main pancreatic duct. Hepatolithiasis, which was obscured in a, is now clearly seen (arrow).

 
Overestimation of ductal narrowing and pseudostricture results from the nature of MIP reconstruction and from the limited spatial resolution of MRCP (Fig 3) (8).



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  		Figure 3a.   Pseudostenosis caused by MIP reconstruction. (a) MIP reconstructed image shows a "stenosis" in the pancreatic body (arrows). (b) Single-projection MRCP image demonstrates a normal main pancreatic duct.

 


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  		Figure 3b.   Pseudostenosis caused by MIP reconstruction. (a) MIP reconstructed image shows a "stenosis" in the pancreatic body (arrows). (b) Single-projection MRCP image demonstrates a normal main pancreatic duct.

 
Limitations of MR Imaging Pulse Sequences
Recently, single-shot fast spin-echo sequences have become the standard method of MRCP image acquisition. Some variation in the degree of T2 weighting can occur among these sequences and influence MRCP imaging findings. MRCP with a half-Fourier single-shot turbo spin-echo sequence depicts not only static fluid in the pancreatobiliary tree but also slow-flow vascular structures (eg, portal vein, hepatic vein) (14) due to a relatively short echo time (Fig 4). True rapid acquisition with relaxation enhancement (RARE) MRCP, which involves a very long echo time, does not depict blood vessels (Fig 4) (14); consequently, it may not allow visualization of the bile duct when the duct is filled with thick or hemorrhagic bile (Fig 5).



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  		Figure 4a.   Right portal vein mimicking an accessory right hepatic duct. (a) Half-Fourier single-shot turbo spin-echo MRCP image depicts the right portal vein with high signal intensity (arrows), a finding that suggests the presence of an accessory right hepatic duct. (b) On a true RARE MRCP image, the right portal vein is not seen.

 


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  		Figure 4b.   Right portal vein mimicking an accessory right hepatic duct. (a) Half-Fourier single-shot turbo spin-echo MRCP image depicts the right portal vein with high signal intensity (arrows), a finding that suggests the presence of an accessory right hepatic duct. (b) On a true RARE MRCP image, the right portal vein is not seen.

 


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  		Figure 5a.   Hemobilia. (a) Half-Fourier single-shot turbo spin-echo MRCP image shows the common bile duct (arrows). (b) True RARE MRCP image does not depict the common bile duct. Hemorrhage through the duodenal papilla was confirmed at duodenal endoscopy.

 


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  		Figure 5b.   Hemobilia. (a) Half-Fourier single-shot turbo spin-echo MRCP image shows the common bile duct (arrows). (b) True RARE MRCP image does not depict the common bile duct. Hemorrhage through the duodenal papilla was confirmed at duodenal endoscopy.

 
Incomplete Imaging of the Pancreatobiliary Tract
It is essential that all portions of the ductal system be visualized at MRCP. Failure to visualize a ductal segment may result in confusion regarding pancreatobiliary duct anatomy or disease (Fig 6) (9).



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  		Figure 6a.   Incomplete imaging of the bile duct. (a) On an MRCP image, the intrahepatic bile ducts of both hepatic lobes appear to be dilated, a finding that raises suspicion for hepatic hilar obstructing tumor. (b) On a T1-weighted MR image (scout view) obtained for sequential multisection MRCP, the right hepatic lobe is not included. Dilated intrahepatic ducts of the left medial segment are seen mimicking dilated intrahepatic ducts of the right hepatic lobe. Horizontal lines indicate the 2-cm section thickness and direction of the source images. The diagnosis was cholan-giocarcinoma in the left hepatic lobe.

 


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  		Figure 6b.   Incomplete imaging of the bile duct. (a) On an MRCP image, the intrahepatic bile ducts of both hepatic lobes appear to be dilated, a finding that raises suspicion for hepatic hilar obstructing tumor. (b) On a T1-weighted MR image (scout view) obtained for sequential multisection MRCP, the right hepatic lobe is not included. Dilated intrahepatic ducts of the left medial segment are seen mimicking dilated intrahepatic ducts of the right hepatic lobe. Horizontal lines indicate the 2-cm section thickness and direction of the source images. The diagnosis was cholan-giocarcinoma in the left hepatic lobe.

 
In some instances, incomplete imaging may lead to mistakenly identifying a vertically oriented main pancreatic duct as the distal common bile duct (Fig 7) (9). It is important to meticulously analyze both the source images and the projection image to visualize and evaluate the anatomy of the entire pancreatobiliary tract.



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  		Figure 7a.   Vertical main pancreatic duct. (a) Source MRCP image shows a pseudostricture (arrow) between the common bile duct and the vertically oriented main pancreatic duct. (b) MIP reconstructed image shows no stricture of the common bile duct and reveals the vertical course of the main pancreatic duct in the pancreatic head.

 


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  		Figure 7b.   Vertical main pancreatic duct. (a) Source MRCP image shows a pseudostricture (arrow) between the common bile duct and the vertically oriented main pancreatic duct. (b) MIP reconstructed image shows no stricture of the common bile duct and reveals the vertical course of the main pancreatic duct in the pancreatic head.

 
Static Imaging
In contrast to ERCP or percutaneous trans-hepatic cholangiography, which allow real-time observation of the ducts and are therefore "dynamic" studies, MRCP yields only static images of the ducts. Consequently, the presence of communication between a cystic lesion and the main pancreatic duct may be difficult to ascertain (Fig 8) (15). An anomalous junction of the pancreatobiliary duct may be missed if the common channel is short (16). In both benign and malignant disease, the biliary tree may be totally collapsed after percutaneous transhepatic biliary drainage has been performed to decompress bile duct obstruction. In such cases, MRCP fails to demonstrate the common bile duct, which otherwise is almost always depicted at MRCP, and the site of obstruction may be mistaken for a more proximal portion of the biliary tree (Fig 9).



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  		Figure 8a.   Mucin-producing pancreatic tumor mimicking a choledochal cyst. (a) MRCP image does not demonstrate communication between the main pancreatic duct and a cystic lesion, which may be misinterpreted as a choledochal cyst. (b) MRCP image obtained in a different patient demonstrates a true choledochal cyst.

 


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  		Figure 8b.   Mucin-producing pancreatic tumor mimicking a choledochal cyst. (a) MRCP image does not demonstrate communication between the main pancreatic duct and a cystic lesion, which may be misinterpreted as a choledochal cyst. (b) MRCP image obtained in a different patient demonstrates a true choledochal cyst.

 


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  		Figure 9.   Collapsed biliary tree after percutaneous transhepatic biliary drainage. MRCP image reveals a stricture of the main pancreatic duct at the pancreatic head (arrow) and a diffusely dilated pancreatic duct upstream. The common bile duct cannot be identified, which suggests that the entire duct has been affected by the disease process. At surgery, the intrapancreatic common bile duct was found to be invaded by pancreatic cancer; however, the extrapancreatic common bile duct was intact.

 
Limited Spatial Resolution
The low spatial resolution of MRCP is not in itself a pitfall but should be kept in mind, and evaluation of ductal stricture based on MRCP findings alone should be avoided because differentiation between benign and malignant strictures becomes difficult if not impossible (Fig 10). This shortcoming is mainly related to poor visualization of the branch ducts and difficulty in evaluating the stenotic portion of the main pancreatic duct (1). MRCP with a half-Fourier single-shot turbo spin-echo sequence has a maximum resolution of 1 mm (1); however, this is not considered to be sufficient for pediatric patients (17), and evaluation of these patients (especially infants) with MRCP remains a diagnostic problem (Fig 11).



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  		Figure 10a.   MRCP images demonstrate a benign stricture (chronic pancreatitis) (a) and a malignant stricture (pancreatic head cancer) (b). Differentiation between the two entities is almost impossible.

 


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  		Figure 10b.   MRCP images demonstrate a benign stricture (chronic pancreatitis) (a) and a malignant stricture (pancreatic head cancer) (b). Differentiation between the two entities is almost impossible.

 


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  		Figure 11.   Choledochal cyst in a 4-year-old girl. MRCP image shows a dilated common bile duct (arrows) without intrahepatic bile duct dilatation, a finding that clearly indicates the presence of a choledochal cyst. However, the main pancreatic duct cannot be seen, and the presence of an anom-alous junction of the pancreatobiliary duct, which is important for treatment, is indeterminate.

 
Susceptibility Artifacts
Metallic foreign bodies such as surgical clips or endovascular coils produce adjacent signal loss and may cause pseudo-obstruction (Fig 12) (2), although MRCP is not as prone to this susceptibility artifact as other MR imaging sequences. However, surgical clips for laparoscopic cholecystectomy are usually made of titanium, which is nonmagnetic and does not cause signal loss. Gas in the stomach and duodenum may produce a susceptibility artifact, which may be more prominent at fat-suppressed MRCP (10).



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  		Figure 12a.   Susceptibility artifact. (a) MRCP image shows decreased signal intensity in the right hepatic lobe (arrows), a finding that may be interpreted as a right hepatic duct stricture. (b) CT scan demonstrates a metallic coil in the right hepatic lobe. (c) T1-weighted MR image demonstrates markedly decreased signal intensity caused by this metallic clip.

 


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  		Figure 12b.   Susceptibility artifact. (a) MRCP image shows decreased signal intensity in the right hepatic lobe (arrows), a finding that may be interpreted as a right hepatic duct stricture. (b) CT scan demonstrates a metallic coil in the right hepatic lobe. (c) T1-weighted MR image demonstrates markedly decreased signal intensity caused by this metallic clip.

 


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  		Figure 12c.   Susceptibility artifact. (a) MRCP image shows decreased signal intensity in the right hepatic lobe (arrows), a finding that may be interpreted as a right hepatic duct stricture. (b) CT scan demonstrates a metallic coil in the right hepatic lobe. (c) T1-weighted MR image demonstrates markedly decreased signal intensity caused by this metallic clip.

 
Normal Anatomy Simulating Disease
Fluid within the stomach or duodenum may produce a pseudolesion in the pancreatobiliary tract because of the proximity of these anatomic structures. Fluid located between gastric folds may be incorrectly perceived as fluid within an ectatic irregular pancreatic duct. If the duodenal bulb contains fluid and air, it may be mistaken for a gallstone (Fig 13). The duodenal diverticulum may mimic a pancreatic cystic mass. In addition, a hepatic cystic lesion and fluid within the urinary tract may produce a pseudolesion of the pancreas (Fig 14). Overlapping intestinal fluid may obscure the pancreatobiliary tract or produce a pseudostricture. Performing MRCP from a different angle or with a different section thickness may resolve this problem (Fig 15). Alternatively, a negative oral contrast agent such as high-concentrate ferric ammonium citrate may be used (18).



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  		Figure 13a.   Air bubbles mimicking gallstones. (a) Findings on an MRCP image raise suspicion for stones in the neck of the gallbladder (arrow). (b) Axial T2-weighted MR image reveals that the suspected stones are air bubbles within the duodenal bulb (arrow). Stricture and dilatation of the main pancreatic duct owing to chronic pancreatitis are also seen.

 


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  		Figure 13b.   Air bubbles mimicking gallstones. (a) Findings on an MRCP image raise suspicion for stones in the neck of the gallbladder (arrow). (b) Axial T2-weighted MR image reveals that the suspected stones are air bubbles within the duodenal bulb (arrow). Stricture and dilatation of the main pancreatic duct owing to chronic pancreatitis are also seen.

 


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  		Figure 14.   Pseudolesion of the pancreas. MRCP image shows the proximal ureter mimicking the dilated branch duct of the pancreatic head (large arrows). Small arrows indicate a mucin-producing tumor of the pancreas.

 


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  		Figure 15a.   Overlapping gastric fluid. (a) Coronal thick-section (5 cm) MRCP image shows the stomach distended by fluid. This finding may be related to a previous pancreatoduodenectomy and obscures the main pancreatic duct in the pancreatic tail. (b) MRCP image obtained with thinner (2-cm) sections along the pancreatic longitudinal direction clearly demonstrates a dilated main pancreatic duct.

 


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  		Figure 15b.   Overlapping gastric fluid. (a) Coronal thick-section (5 cm) MRCP image shows the stomach distended by fluid. This finding may be related to a previous pancreatoduodenectomy and obscures the main pancreatic duct in the pancreatic tail. (b) MRCP image obtained with thinner (2-cm) sections along the pancreatic longitudinal direction clearly demonstrates a dilated main pancreatic duct.

 
Pitfalls Related to Bile Duct Stones
Pneumobilia may be misinterpreted as bile duct stones, although it is easily recognized at axial MRCP or T2-weighted MR imaging (7). Air bubbles float ventrally to the bile, producing air-fluid levels (Fig 16).



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  		Figure 16a.   Pneumobilia. (a) MRCP image shows defects within the common bile duct (arrows), findings that raise suspicion for common bile duct stones. (b) Axial MRCP image demonstrates a defect floating ventrally to the bile (arrow), a finding that indicates the defect to be pneumobilia.

 


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  		Figure 16b.   Pneumobilia. (a) MRCP image shows defects within the common bile duct (arrows), findings that raise suspicion for common bile duct stones. (b) Axial MRCP image demonstrates a defect floating ventrally to the bile (arrow), a finding that indicates the defect to be pneumobilia.

 
Tiny stones as small as 2 mm can be detected at MRCP (2); on the other hand, even large or impacted stones can be difficult to detect at MRCP because high-signal-intensity bile is rarely noted around the low-signal-intensity stones (Fig 17) (8). MRCP performed from different angles (eg, axial imaging) may be useful in this setting.



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  		Figure 17a.   Bile duct stones. (a) MIP reconstructed image demonstrates a dilated common bile duct with abrupt occlusion distally (arrow). (b) Source MRCP image reveals two large bile duct stones (arrows) that were not visualized on the MIP reconstructed image.

 


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  		Figure 17b.   Bile duct stones. (a) MIP reconstructed image demonstrates a dilated common bile duct with abrupt occlusion distally (arrow). (b) Source MRCP image reveals two large bile duct stones (arrows) that were not visualized on the MIP reconstructed image.

 
Occasionally, a signal void is seen in the nondependent central portion of the bile duct and may be misinterpreted as stones (Fig 18), although a signal void in this location is unlikely to represent this finding. The signal void tends to appear in dilated ducts and at the point of insertion of a large cystic duct, where swirling flow can occur, and is considered to be flow artifact (7). Flow-sensitive MR imaging (eg, time-of-flight MR angiography) may show flow within the bile duct and help confirm this central type of signal void to be a flow artifact (Fig 18).



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  		Figure 18a.   Flow artifact. (a) MRCP image shows a defect in the central portion of the common bile duct (arrow). No such defect was seen at ERCP. (b) Time-of-flight MR angiogram demonstrates high signal intensity within the common bile duct (arrow), a finding that represents ductal flow.

 


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  		Figure 18b.   Flow artifact. (a) MRCP image shows a defect in the central portion of the common bile duct (arrow). No such defect was seen at ERCP. (b) Time-of-flight MR angiogram demonstrates high signal intensity within the common bile duct (arrow), a finding that represents ductal flow.

 
Nonpathologic Bile Duct Narrowing Due to Pulsatile Vascular Compression
Pulsatile vascular compression can cause pseudo-obstruction of the bile duct, which may be in a physiologic state (19). The hepatic arteries and gastroduodenal artery are closely related anatomically to the bile duct. The most common site of nonpathologic narrowing is the common hepatic duct (Fig 19), followed by the left hepatic duct and the midportion of the common bile duct (Fig 20) (10). The right hepatic artery may compress the common hepatic duct or left hepatic duct at the posterior aspect, whereas the gastroduodenal artery may compress the mid-portion of the common bile duct at the right anterolateral aspect. ERCP images may less frequently depict nonpathologic narrowing caused by arterial impression because contrast material is injected into the biliary tree with positive pressure (19). Source images obtained at MRCP, T2-weighted MR imaging, or MR angiography are useful in identifying the causative artery.



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  		Figure 19a.   Common hepatic duct narrowing caused by the right hepatic artery. (a) MIP reconstructed image shows narrowing of the common hepatic duct (arrow). (b) Source MRCP image reveals a flow void traversing the common hepatic duct (arrows), a finding that represents the right hepatic artery.

 


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  		Figure 19b.   Common hepatic duct narrowing caused by the right hepatic artery. (a) MIP reconstructed image shows narrowing of the common hepatic duct (arrow). (b) Source MRCP image reveals a flow void traversing the common hepatic duct (arrows), a finding that represents the right hepatic artery.

 


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  		Figure 20a.   Common bile duct narrowing caused by the gastroduodenal artery. (a) MRCP image shows eccentric narrowing of the midportion of the common bile duct (arrow). (b) Axial T2-weighted MR image reveals the close anatomic relation between the common bile duct (black arrow) and the gastroduodenal artery (white arrow).

 


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  		Figure 20b.   Common bile duct narrowing caused by the gastroduodenal artery. (a) MRCP image shows eccentric narrowing of the midportion of the common bile duct (arrow). (b) Axial T2-weighted MR image reveals the close anatomic relation between the common bile duct (black arrow) and the gastroduodenal artery (white arrow).

 
Misinterpretation Related to the Cystic Duct
En face visualization of cystic duct insertion into the bile duct may suggest an intraductal filling defect such as stones (Fig 21). Performing MRCP from different angles makes it possible to follow the cystic duct and to generate an approximate image of the apparent filling defect (9).



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  		Figure 21a.   Pseudodefect at the site of cystic duct insertion. (a) MIP reconstructed image shows a signal void in the common bile duct (arrow). (b) Source MRCP image reveals that the site of cystic duct insertion (arrow) corresponds to the signal void on the reconstructed image.

 


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  		Figure 21b.   Pseudodefect at the site of cystic duct insertion. (a) MIP reconstructed image shows a signal void in the common bile duct (arrow). (b) Source MRCP image reveals that the site of cystic duct insertion (arrow) corresponds to the signal void on the reconstructed image.

 
When the cystic duct runs parallel to the common hepatic duct for some distance, the two structures together may be mistaken for a dilated common bile duct (Fig 22). This pitfall is most likely to occur on an MIP reconstructed image. Therefore, the source images should be evaluated carefully (8).



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  		Figure 22a.   Pseudodilatation of the common bile duct. (a) MIP reconstructed image shows the cystic duct and the common hepatic duct running parallel (arrows), a finding that may be mistaken for a dilated common bile duct. (b) Source MRCP image reveals the anatomic relation of the cystic duct (arrows) and the common hepatic duct.

 


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  		Figure 22b.   Pseudodilatation of the common bile duct. (a) MIP reconstructed image shows the cystic duct and the common hepatic duct running parallel (arrows), a finding that may be mistaken for a dilated common bile duct. (b) Source MRCP image reveals the anatomic relation of the cystic duct (arrows) and the common hepatic duct.

 
Pitfalls Related to the Periampullary Region
The intramural segment of the bile duct tapers and contains little fluid; thus, an impacted stone near the ampulla is difficult to detect because it has no surrounding fluid (8). Axial imaging may be helpful in this situation.

The duodenal papilla can sometimes have a bulging appearance at MRCP and may be misinterpreted as an impacted stone (Fig 23). Conventional MR imaging should be performed to clarify the precise local anatomy.



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  		Figure 23.   Prominent duodenal papilla. MRCP image shows a slightly dilated biliary duct, with the masslike structure protruding into the duodenum (arrow). This finding may raise suspicion for an impacted stone or papillary tumor. In this case, however, duodenal endoscopy revealed a prominent normal duodenal papilla.

 
Contraction of the choledochal sphincter may be misinterpreted as an impacted stone or stricture in the distal bile duct (Fig 24). When this defect is seen at direct cholangiography, it is known as the pseudocalculus sign (20). Unlike with an impacted stone, only the superior margin of the defect is outlined by the high-signal-intensity bile. A more important difference is that the presence of the defect is transient. When a filling defect or stricture is suspected in the periampullary region, repeat MRCP should be performed.



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  		Figure 24a.   Pseudocalculus sign. (a) MRCP image obtained during contraction of the choledochal sphincter shows constriction of the distal common bile duct (arrow), a finding that may be misinterpreted as a stricture or impacted stone. (b) On an MRCP image obtained during relaxation of the choledochal sphincter, the distal common bile duct has a normal configuration (arrow).

 


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  		Figure 24b.   Pseudocalculus sign. (a) MRCP image obtained during contraction of the choledochal sphincter shows constriction of the distal common bile duct (arrow), a finding that may be misinterpreted as a stricture or impacted stone. (b) On an MRCP image obtained during relaxation of the choledochal sphincter, the distal common bile duct has a normal configuration (arrow).

 
Pseudostenosis of the Normal Main Pancreatic Duct
In fasting patients, secretion of pancreatic juice is decreased and the normal main pancreatic duct may be collapsed segmentally. This finding may be misinterpreted as stenosis, although no dilatation of the proximal main pancreatic duct is identified in such cases (Fig 25). The administration of secretin is helpful in this setting. Because secretin increases the secretion of an alkaline pancreatic juice via the main pancreatic duct, it can improve delineation of this structure (21).



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  		Figure 25a.   Normal main pancreatic duct with a collapsed segment. (a) MRCP image shows a normal main pancreatic duct with a collapsed segment (arrows), a finding that may be misinterpreted as stenosis. (b) MRCP image obtained after the administration of secretin shows an increase in the secretion of pancreatic juice, which distends the main pancreatic duct and improves its visualization.

 


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  		Figure 25b.   Normal main pancreatic duct with a collapsed segment. (a) MRCP image shows a normal main pancreatic duct with a collapsed segment (arrows), a finding that may be misinterpreted as stenosis. (b) MRCP image obtained after the administration of secretin shows an increase in the secretion of pancreatic juice, which distends the main pancreatic duct and improves its visualization.

 

   Conclusion
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Pitfalls in MRCP Interpretation
 Conclusion
References
 
Several diagnostic pitfalls are associated with the use of MRCP. Familiarity with the findings that typically lead to misdiagnosis and with the causes of these diagnostic pitfalls may help prevent misinterpretation of MRCP images.


   Footnotes
 
Abbreviations: ERCP = endoscopic retrograde cholangiopancreatography, MIP = maximum-intensity-projection, MRCP = MR cholangiopancreatography, RARE = rapid acquisition with relaxation enhancement


   References
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Pitfalls in MRCP Interpretation
 Conclusion
 References
 

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