Dr. Hartman is a Resident in Radiology and Dr. Barish is an
Assistant Professor of Radiology in the Department of
Radiology, Boston University Medical School, Boston Medical
Center, Boston, MA.
Magnetic resonance cholangiopancreatography (MRCP) is becoming
the primary noninvasive method for imaging the biliary tree and
pancreatic duct. With heavily T2-weighted sequences, fluid-filled
structures appear bright against a dark background. The
gallbladder, biliary tree, and pancreatic duct are displayed in a
similar manner as in invasive methods such as endoscopic retrograde
cholangiopancreatography (ERCP) and percutaneous transhepatic
cholangiography (PTC). The main role of MRCP has been to replace
and eliminate the diagnostic portion of an ERCP or PTC. Frequently,
a diagnostic MRCP can obviate an invasive procedure or suggest the
need for a different invasive procedure from that which was
originally planned. Magnetic resonance cholangiopancreatography
should be considered the test of choice in all patients after a
failed or incomplete ERCP. Magnetic resonance
cholangiopancreatography has been shown to be useful in the
detection of calculi, tumors, strictures, obstructions, and
congenital anomalies. It is also helpful for presurgical planning
and postsurgical follow-up.
Since MRCP images resemble those obtained during direct
cholangiography, they are well accepted by gastroenterologists and
surgeons. Magnetic resonance cholangiopancreatography pulse
sequences are available on nearly all modern MRI scanners, and MRCP
is well tolerated by patients. Since exogenous contrast material is
not needed, patients with contrast allergies, renal failure, or a
history of atopy can be imaged safely. Initial limitations of MRCP,
such as metallic-clip artifacts, respiratory motion, and long
procedure times, have been overcome. However, cardiac pacemakers,
certain aneurysm clips, and other implanted medical devices may
preclude the use of MRCP.
MRCP pulse sequences
Bile and pancreatic fluid are rich in protons, resulting in a T2
relaxation time that is much longer than that of surrounding
tissues. On heavily T2-weighted sequences, fluid within the biliary
tree, gallbladder, and pancreatic duct is bright, while background
tissues are suppressed. Signal from background fat, which is
usually high on fast T2-weighted sequences, can be decreased with
the use of fat-suppression techniques. Magnetic resonance
cholangiopancreatography is usually performed using one of the
hybrid rapid acquisition with relaxation enhancement (RARE)
sequences or their derivatives.
The introduction of single-shot RARE techniques and half-Fourier
acquisition single-shot turbo-spin echo (HASTE) imaging has reduced
imaging times to within a single breath-hold. The trade-off
associated with these more rapid sequences is a loss of spatial
resolution. These breath-hold techniques are best applied in two
forms: a single, thick coronal (or axial) slab and a multislice,
thin coronal sequence.
MRCP versus ERCP
Direct cholangiography methods (ERCP and PTC) offer certain
advantages that cannot be reproduced with MR methods. Both ERCP and
PTC yield images with higher spatial resolution, and both
techniques have therapeutic as well as diagnostic applications.
However, even with the higher spatial resolution of these invasive
methods, visualization of bile duct morphology with MRCP equals or
exceeds that of ERCP
without the associated morbidity or mortality. The risks of ERCP
include pancreatitis, sepsis, hemorrhage, duodenal and bile duct
perforation, and death.
Endoscopic retrograde cholangiopancreatography also causes
pancreatitis in 1.5% to 3.9% of cases, and the mortality rate is 0%
Endoscopic retrograde cholangiopancreatography is also
associated with failure rates as high as 3% to 10%.
These failed examinations may occur because the operator has
limited experience or because of complex ductal anatomy.
Biliary-enteric anastomoses and obstructions can also make ERCP
difficult, if not impossible. After a failed or incomplete ERCP,
MRCP should be considered the diagnostic test of choice. In this
group of patients, MRCP has been shown to have a sensitivity of
97%, a specificity of 100%, and an accuracy of 98% for the
diagnosis of pancreaticobiliary disease.
Forty percent to 70% of patients who undergo ERCP have negative
If MRCP were performed before ERCP, mortality, morbidity, and
healthcare costs could therefore be reduced by limiting ERCP only
to those individuals who would benefit from this more invasive
Biliary calculi are seen as relative areas of decreased signal
surrounded by bright bile (figures 1 and 2). Many studies have
investigated the use of MRCP for the detection of
choledocholithiasis, and excellent results have been reported, with
sensitivities of 85% to 100%, specificities of 90% to 99%, and
accuracies of 89% to 97%.
Positive- and negative-predictive values have ranged from 77% to
93% and 94% to 100%, respectively.
Successful detection of stones as small as 2 mm has also been
reported with MRCP.
In fact, the detection of choledocholithiasis with MRCP is superior
to that of other noninvasive techniques, such as ultrasound and
computed tomography (CT), which have sensitivities of 20% to 65%
and 45% to 85%, respectively.
The accuracy of MRCP in diagnosing hepatolithiasis is 96%.
Intrahepatic bile duct calculi may be seen as well-defined filling
defects or as cast-like areas of low signal that conform to the
wall of the duct (figure 3).
Other abnormalities in the biliary tract that can be hypointense
on MR (resembling calculi) include blood clots, tumors, air, metal
clips, and parasites. However, calculi tend to have more angled
edges than soft-tissue tumors, a finding that helps to
differentiate these lesions.
Pneumobilia after a biliary-enteric anastomosis or sphincterotomy
can be recognized by examining axial images, preventing an
erroneous diagnosis of choledocholithiasis.
Intraductal air should also rise to the nondependent portion of the
duct, whereas stones should remain dependent.
Low-signal surgical clips appear as eccentric foci of low signal on
raw data images, indicating an extraductal source of these
Ascariasis is characterized by a "bull's-eye" appearance of the
common bile duct.
Maximum-intensity projection (MIP) reconstructions can mask a
small stone in the bile ducts if the stone is surrounded by
hyperintense bile. When the breath-hold is not optimal, MIP images
may also be characterized by ductal disconnections or duplications.
For these reasons, source images should be reviewed
Although it is well accepted that MRCP is an accurate test for
the diagnosis of choledocholithiasis and hepatolithiasis, there is
no consensus regarding its routine use. Since MRCP has a
high-negative predictive value for common bile duct stones, it can
be used to exclude stones in patients with suspected
choledocholithiasis. However, only 30% to 52% of patients thought
to be at high risk for common bile duct stones are actually found
to have stones.
In the future, MRCP could therefore be used to screen high-risk
patients for common duct stones in order to determine whether a
therapeutic ERCP is indicated. In this way, the more invasive
procedure could be avoided in patients without
With MRCP, ducts are seen in their passive state because
contrast material does not need to be injected forcefully to
opacify them. Thus, images reflect the diameter of strictures more
closely than they do with invasive cholangiography (figure 4).
Magnetic resonance cholangiopancreatography has been reported to
have a sensitivity of 100% and a specificity of 98% for the
diagnosis of strictures.
However, reduced spatial resolution and the inability to evaluate
lack of distensibility during MRCP limits visualization of subtle
strictures. Cholecystokinin may also have a role for evaluating the
distensibility of the biliary tree at MRCP.
Extraductal metallic surgical clips, intravascular metallic
coils, or gas in the stomach or duodenum may cause signal loss in
the adjacent extrahepatic bile ducts. This may lead to a
false-positive diagnosis of ductal narrowing. Also,
MIP-reconstructed images can overestimate the length of strictures.
This pitfall can be avoided by evaluating source images and the
amount of bile duct dilatation proximal to an apparent stricture.
Cholestasis is most commonly caused by choledocholithiasis or
neoplasia (pancreatic carcinoma, ampullary carcinoma, and
cholangiocarcinoma). Studies have shown that MRCP has a sensitivity
and specificity >90% for the detection of biliary obstruction.
Magnetic resonance cholangiopancreatography imaging does not depend
on antegrade or retrograde flow of contrast material, so areas
proximal and distal to an obstruction can be visualized.
Obstruction at the ampulla of Vater
Both benign and malignant disease can cause an obstruction at
the ampulla of Vater with dilatation of the common bile duct and
pancreatic duct. Causes include ampullary carcinoma, inflammatory
stenosis, sphincter of Oddi dysfunction, and impacted stones.
Semelka et al
studied ampullary carcinoma and found that MRCP was helpful in
determining both the degree of obstruction and the luminal margins
of the tumor. Magnetic resonance cholangiopancreatography also
aided in determining the degree of decompression after biliary
Early cholangiocarcinoma can be a subtle disease. Classic MRCP
findings of cholangiocarcinoma include an abrupt site of biliary
obstruction with marked dilatation proximally (figure 5). In some
cases, it may be difficult to distinguish duct wall thickening
caused by pyogenic cholangitis from that caused by
Cholangiocarcinoma usually arises from the extrahepatic bile ducts,
but may also arise from the intrahepatic ducts.
When intrahepatic, cholangiocarcinoma occurs as a focal or
Magnetic resonance cholangiopancreatography is superior to CT for
defining the proximal extent of biliary tract tumors.
Hepatocellular carcinoma rarely manifests by intrahepatic bile
duct obstruction, but this tumor should be considered in the
differential diagnosis of cholangiocarcinoma if there is an
intrabiliary tumor with an associated hepatic mass.
Malignant obstructions should be evaluated with a complete,
conventional upper abdomen study with T1- and T2-weighted images.
MR provides an "all-in-one" approach for evaluating malignant
obstructions. The sensitivity, specificity, and accuracy of MRCP
for differentiating benign and malignant lesions can be increased
by 17% to 20% when T1-and T2-weighted images are obtained.
The origin, size, and site (hilar, intrahepatic, and subhilar) of
the tumor, definition of tumor margins, and stage of disease can be
depicted without need for other imaging modalities such as CT or
ERCP. Lymphadenopathy, infiltration by hepatic metastases,
mesenteric vascular involvement, distant metastases, and occlusion
of segmental and subsegmental bile duct branches can also be
In some cases, MRCP is sufficient for planning appropriate
therapeutic interventions. It can be used to determine if surgical
revision, endoscopic or percutaneous biliary drainage, or balloon
dilation of a stenotic segment with stent placement is the optimal
therapy. Grading of hilar cholangiocarcinoma by MRCP may also
prevent patients from undergoing an unnecessary ERCP when
endoscopic drainage is not the optimal treatment (segmentally
Laparoscopic cholecystectomy has largely replaced open
cholecystectomy in patients with gallstones. Identification of
aberrant ducts is important, as these ducts can be severed or
ligated if they are mistaken for the cystic duct. Aberrant ducts
tend to enter directly into the cystic duct or just distal to the
confluence of the right and left hepatic ducts.
The most common biliary tract anomaly is an aberrant right hepatic
which may drain into the common hepatic duct, common bile duct, or
Magnetic resonance cholangiopancreatography has a sensitivity of
71%, a specificity of 100%, and an accuracy of 98% for the
detection of aberrant right hepatic ducts.
Although MRCP is well suited for detecting both aberrant ducts and
choledocholithiasis, the routine use of MRCP prior to laparoscopic
cholecystectomy cannot be justified because of the high cost and
low true-positive rate of this technique for the detection of
Biliary cystic disease (choledochal cysts and
Choledochal cysts are cystic dilatations of the biliary tree.
Magnetic resonance cholangiopancreatography can accurately
determine the presence and type of choledochal cyst, the length of
the involved extrahepatic duct, and anomalous unions of the
pancreatic and bile ducts.
Choledochal cysts are best treated by surgical excision and
biliary-enteric anastomosis. Determination of the length of the
involved extrahepatic bile duct by MRCP is crucial for surgical
Evaluation after surgery
Surgical alterations of the gastrointestinal tract after
biliary-enteric anastomoses can make ERCP difficult or impossible.
Magnetic resonance cholangiopancreatography should be considered a
first-line diagnostic method in these patients because it is
capable of providing information about the biliary tree, which
cannot be obtained by invasive procedures.
Anastomotic strictures are usually caused by postoperative
scarring and, less often, by ischemia.
Magnetic resonance cholangiopancreatography can evaluate
anastomotic sites and create a complete "roadmap" of the bile
Magnetic resonance cholangiopancreatography can evaluate the
biliary tract proximal and distal to a duct lacerated at
cholecystectomy. Endoscopic retrograde cholangiopancreatography may
result in incomplete visualization of the biliary tree, showing
only a cut-off sign of the distal bile duct, so that PTC is
required to visualize the proximal biliary system. Information
about anatomy proximal to the transection is important for
determining the strategy for reconstructive surgery. This
information can be provided by MRCP, reducing the need for PTC.
Magnetic resonance cholangiopancreatography has a lower spatial
resolution than conventional cholangiography, limiting depiction of
strictures. However, in the case of liver transplantation patients,
this does not represent a significant limitation because the
lesions have a benign origin.
These strictures can be classified either as anastomotic or
nonanastomotic. Nonanastomotic strictures usually involve the
hepatic duct bifurcation, peripheral ducts, or both, and occur in
approximately 8% of patients. Nonanastomotic strictures are
important because they may indicate rejection. Magnetic resonance
cholangiopancreatography enables early visualization of
intrahepatic duct dilatation, which can occur as a result of
Clinicians can therefore be alerted, and action can be taken to
prevent sepsis and graft failure.
Endoscopic biliary drainage tubes
Magnetic resonance cholangiopancreatography can be used to
assess endoscopic biliary drainage (EBD) tubes when malfunction,
dislocation, or migration is suspected. Traditional methods for the
assessment of EBD tubes include ultrasound, biochemical data, and
abdominal radiography. The results of these tests are usually
confirmed with ERCP. Endoscopic biliary drainage tubes do not
generate MR signals. However, bile contained within the lumen
generates high signal. As a result, EBD tubes are usually seen as
paired low-signal lines with a high-signal line between them.
If the bile becomes viscous or if debris accumulates, the
high-signal intensity of bile in the tube may disappear (figure 6).
Magnetic resonance cholangiopancreatography is also useful for
assessing the location and patency of EBD tubes.
Magnetic resonance applications in the pediatric population are
expanding. Magnetic resonance cholangiopancreatography rarely
requires anesthesia; ERCP and PTC cannot be performed on children
However, conscious sedation is required when MRCP is performed on
young or uncooperative patients. Respiratory-triggered MRCP enables
evaluation of major and minor bile ducts, even in uncooperative,
Images can be produced in which the common bile duct and hepatic
ducts are clearly seen in infants as young as 3 days old.
Biliary atresia can cause jaundice in infants. When this anomaly
occurs, MRCP demonstrates nonvisualization of the common bile duct
or common hepatic duct.
Magnetic resonance cholangiopancreatography may also reveal a
triangular-shaped area of high-signal intensity within the porta
hepatis caused by cystic dilation of the bile duct proximally.
Unnecessary exploratory laparotomy in infants with cholestatic
jaundice can also be avoided with MRCP.
Biliary manifestations of cystic fibrosis include
cholelithiasis, narrowing or dilatation of the intrahepatic and
extrahepatic bile ducts, and microgallbladder. These findings can
all be demonstrated with MRCP. Magnetic resonance
cholangiopancreatography is also useful for assessing the presence
and severity of biliary complications in patients with cystic
fibrosis without need for more invasive procedures.
Evaluation of the pancreas
Magnetic resonance cholangiopancreatography has been slower to
develop as a diagnostic tool for the pancreas because of the
smaller caliber of the pancreatic duct. Advances in breath-hold
imaging, surface coils, and the use of pharmacologic agents has
allowed MR pancreatography to become a useful means for evaluating
pancreatic ductal anatomy and function. The use of breath-hold
imaging with surface coils reduces blurring artifacts and improves
visibility. Visualization of the pancreatic duct is further
improved following the administration of secretin. This hormone
causes an increase in pancreatic exocrine function, resulting in a
transient increase in pancreatic ductal diameter, pancreatic fluid
secretion, and pancreatic enhancement. Because of this increase in
pancreatic ductal diameter, the accuracy of MRCP for the detection
of strictures of the pancreatic duct is improved.
Pancreas divisum is the most common anatomic variant of the
pancreas, occurring when the dorsal duct (duct of Wirsung) and
ventral duct (duct of Santorini) fail to fuse. These two ducts
normally fuse during the second month of gestation. When this
process does not occur, the dorsal duct drains most of the
pancreas, including the superior-anterior head, body, and tail,
whereas the ventral duct drains the posterior-inferior head and
uncinate process. The dorsal duct enters the major papilla and the
ventral duct the minor papilla.
Pancreas divisum has important implications for ERCP, as
cannulation of the major papilla opacifies only the dorsal duct,
resulting in incomplete visualization of pancreatic ductal
structures. Lack of opacification of ductal structures in the body
or tail of the pancreas at ERCP also may erroneously suggest
occlusion of the main pancreatic duct, leading to an incorrect
diagnosis of pancreatic carcinoma. In contrast, MRCP is excellent
for diagnosing pancreas divisum because this technique can show the
ventral and dorsal ducts simultaneously without need for
cannulation of the major and minor papillae.
Chronic pancreatitis occurs after repeated bouts of acute
pancreatitis, resulting in parenchymal atrophy and fibrosis.
Side-branch ectasia is the most specific and prominent feature of
chronic pancreatitis. The main pancreatic duct is also dilated,
usually with areas of focal narrowing, producing a beaded
appearance. The biliary tract may also become dilated as a result
of fibrosis in the head of the pancreas. In severe pancreatitis,
the normal tapering of the pancreatic duct in the tail of the
pancreas is also lost.
Magnetic resonance cholangiopancreatography may be performed not
only to support a clinical diagnosis of chronic pancreatitis but
also to guide therapeutic planning, detect concurrent biliary
abnormalities, and visualize complications of the disease. In
patients with chronic pancreatitis, moderate and advanced disease
is identified readily. However, early disease may not be detected,
as changes may be present only in small side branches, which are
below the resolution of MR. Therapeutic planning is affected by the
location of strictures, ductal diameter, the presence of stones,
and the presence and location of pseudocysts.
Pancreatic pseudocysts occur as a complication of acute or
chronic pancreatitis. These pseudocysts are encapsulated
collections of pancreatic fluid caused by microperforation of the
pancreatic duct. The surgical definition of a pseudocyst requires
the lesion to be present for at least 6 weeks. Evaluation of cystic
lesions of the pancreas, such as pseudocysts, with ERCP is limited
to lesions that communicate with the main pancreatic duct. However,
<50% of pseudocysts communicate with the pancreatic duct and
fill with contrast material. As a result, <50% of pseudocysts
are detected at ERCP. In contrast, MRCP can visualize pseudocysts
in the absence of communication with ductal structures, so this
technique can detect virtually 100% of pseudocysts and other cystic
lesions of the pancreas, including cystic neoplasms.
Neoplasms of the pancreas
Magnetic resonance cholangiopancreatography can be used to
detect neoplasms of the pancreas and to determine staging, surgical
resectability, and tumor recurrence. Neoplasms of the pancreas
include exocrine and endocrine tumors. Exocrine tumors include
adenocarcinomas, cystic neoplasms (serous microcystic adenomas and
mucinous cystic neoplasms), and rare entities, such as acinar cell
carcinomas, pleomorphic carcinomas, and epithelial neoplasms.
Adenocarcinoma represents 95% of all pancreatic carcinomas. The
prognosis is poor, with mean 1-year survival rates <10%.
Clinical signs of pancreatic carcinoma include jaundice, weight
loss, and Courvoisier's sign (an enlarged nontender gallbladder
caused by tumor obstructing the outflow of bile from the
gallbladder). Dilatation of both the pancreatic and bile ducts
should strongly suggest a malignant tumor in the head of the
pancreas. Once the diagnosis of pancreatic adenocarcinoma has been
made, evaluation of the status of the ductal structures is not
usually necessary. Magnetic resonance cholangiopancreatography
alone contributes little to the management of these patients, but
conventional MR imaging provides important information for
therapeutic planning, including tumor staging and detection of
vascular encasement or other metastatic disease.
Cystic neoplasms are uncommon, representing only 5% to 15% of
all cystic pancreatic masses. Cystic neoplasms can easily be
evaluated with MRCP because of their high fluid content. Serous
microcystic adenomas are benign lesions, typically occurring in
patients older than 60 years of age. The tumors occur in a
relatively equal distribution throughout the pancreas. Serous
microcystic adenomas may appear as solid or cystic lesions. If the
tumor is cystic, more than 6 cysts are usually seen, and the cysts
are usually >2 cm in diameter. Approximately 40% of these tumors
have calcifications, which are usually amorphous and may resemble
starbursts. The soft-tissue component of serous microcystic
adenomas exhibits hypervascular enhancement with intravenous
administration of contrast material. Aspirated contents of the
cysts are glycogen-positive. Roughly 15% of serous microcystic
adenomas contain a central scar.
Mucinous cystic neoplasms include macrocystic adenomas and
adenocarcinomas. These lesions should be considered malignant
because the adenomas often evolve into adenocarcinomas. In contrast
to serous microcystic adenomas, mucinous cystic neoplasms typically
occur in patients younger than 60 years of age. The ratio of women
to men having these neoplasms is 6:1. Almost all of these lesions
are located in the body or tail of the pancreas. Fewer than 6 cysts
are usually seen, and the cysts are usually >2 cm in diameter
(figure 7). Twenty percent have calcifications, which typically
occur along the rim of the cysts. In contrast to serous microcystic
adenomas, these tumors are hypovascular, although the wall of the
cysts enhances after administration of intravenous contrast
Aspiration of the cysts yields mucin. The mucin is secreted into
the pancreatic duct. At ERCP, this mucin may obstruct the flow of
contrast material through the duct, limiting evaluation. Because of
this limitation, MRCP is potentially more accurate than is ERCP in
depicting mucinous cystadenomas and cystadenocarcinomas. A tumor
that may represent a subset of mucinous cystic tumors is a
duct-ectatic mucinous tumor. In this disease, a papillary tumor is
present in the main pancreatic duct or a side branch of the
pancreatic duct. In the benign form, the papillary tumor consists
of hyperplastic epithelium; whereas in the malignant form, the
tumor is composed of atypical hyperplastic epithelium with areas of
adenocarcinoma. Magnetic resonance cholangiopancreatography can be
used to detect excrescent nodules and septa in these tumors. The
septa consist of a layer of connective tissue with pancreatic duct
epithelium. The correlation of MRCP findings with histopathology is
Duct-ectatic mucinous tumors extrude copious amounts of mucin. As
with mucinous cystic neoplasms, duct-ectatic mucinous tumors may be
better evaluated with MRCP than with ERCP, as mucin obstructs the
flow of contrast material through the pancreatic ducts.
Irie et al
evaluated the ability of MRCP to differentiate benign and malignant
intraductal mucin-producing tumors of the pancreas with MRCP. When
a malignant mucinous lesion is located in the main pancreatic duct,
the duct is diffusely dilated and has a diameter >1.5 cm. With
benign lesions involving the main pancreatic duct, however, the
duct is segmentally dilated. When a malignant mucinous lesion is
located in a branch duct, the main pancreatic duct is usually
mildly dilated. With benign lesions involving a branch duct,
however, the main pancreatic duct is not dilated.
Other neoplasms of the pancreas include endocrine tumors
(insulinomas, gastrinomas, and nonfunctioning islet cell tumors),
lymphoma, metastases, and connective tissue tumors. The ability of
MRCP to depict these neoplasms has not yet been evaluated. However,
MRCP has an overall sensitivity of 84% and specificity of 97% for
diagnosing pancreatic carcinoma, whereas the corresponding
sensitivity and specificity for ERCP are 70% and 94%, respectively.
Limitations of MRCP
Inferior spatial resolution and inability to perform therapeutic
procedures are the major limitations of MRCP when compared with
invasive methods (ERCP and PTC). Artifacts occasionally may cause
confusion when interpreting MRCP images. Pulsatile compression by
normal vascular structures, including the right hepatic and
gastroduodenal artery, can cause pseudo-obstruction of the
extrahepatic bile ducts.
The right hepatic artery passes posterior to the proximal common
hepatic duct, sometimes causing a smooth, short narrowing in the
duct. Arterial pseudo-obstruction artifact can be differentiated
from true biliary obstruction by lack of dilatation upstream to the
stenosis and by visualization of the flow void of the vessel
crossing the duct at the level of the obstruction.
A flow-sensitive sequence, axial T2-weighted sequence, or MR
angiography may also be helpful for identifying these vascular
Portions of the biliary tree can be obscured on MIP images by
overlapping ducts, bowel, and other structures containing fluid.
This is rarely a problem with the source data images, as these
images show small amounts of bile that are cancelled out on MIP
Magnetic resonance cholangiopancreatography is becoming the
primary method for evaluating patients with a variety of biliary
and pancreatic diseases. The absence of ionizing radiation and
safety of this technique make MRCP an excellent diagnostic tool.
With the increased use of MRCP, invasive techniques such as ERCP
and PTC can be reserved for patients who require therapeutic