DOI:10.2214/AJR.05.0772
AJR 2006; 187:1536-1543
© American Roentgen Ray Society
Congenital Anomalies and Normal Variants of the Pancreaticobiliary Tract and the Pancreas in Adults: Part 1, Biliary Tract
Jinxing Yu1,
Mary Ann Turner1,
Ann S. Fulcher1 and
Robert A. Halvorsen1
1 All authors: Department of Radiology, VCU Health Systems, Virginia
Commonwealth University, 1250 East Marshall St., Richmond, VA 23298.
Received May 5, 2005;
accepted after revision August 31, 2005.
Address correspondence to J. Yu.
Abstract
OBJECTIVE. The purpose of this article is to highlight the imaging
features of congenital anomalies and normal variants of the biliary tract with
contemporary imaging techniques such as MR cholangiopancreatography (MRCP),
MRI, and helical CT.
CONCLUSION. Recognizing findings of congenital anomalies and normal
variants of the biliary tract at MRCP, MRI, and helical CT, and knowledge of
the clinical significance of each entity, are important for establishing a
correct diagnosis and in guiding appropriate clinical management.
Keywords: biliary system • congenital • CT • developmental anomalies • MRI
Introduction
Congenital anomalies and normal variants of the biliary tract may be
clinically significant. For instance, aberrant or accessory biliary ducts may
predispose patients to inadvertent ductal ligation at laparoscopic
cholecystectomy [1] and may
complicate surgeries, such as living donor right lobe liver transplantation
[2]. Recent advances in MRI, MR
cholangiopancreatography (MRCP), and MDCT have improved image quality greatly
and have contributed to the increased recognition of these entities.
Congenital anomalies and normal variants involving the biliary tract include
aberrant or accessory biliary ducts, aberrant cystic duct insertion; bile duct
cysts, alterations of the biliary tract associated with situs anomalies, and
anomalous junction of the common bile duct with the pancreatic duct.
Recognition of these entities as anomalies and normal variants may avoid
diagnostic errors, aid in surgical planning, and prevent inadvertent ductal
injury.
Aberrant Biliary Ducts
Anatomic variations of the biliary tract occur commonly
[3]
(Fig. 1). Normally, the right
and left hepatic ducts converge at the portal hepatis to form the common
hepatic duct. The right hepatic duct has two major branches—an anterior
or ventrocranial branch, and a posterior or dorsocaudal branch. The left
hepatic duct also has two major branches—medial and lateral. A right
dorsocaudal branch draining into the left hepatic duct, also known as a
crossover anomaly, is a common anomaly of the biliary system (Figs.
1C,
2, and
3). This branch drains the
posterior segment of the right lobe of liver and joins the left main, rather
than the right main, hepatic duct. An aberrant or accessory right hepatic
biliary duct emptying into the common hepatic duct or cystic duct (Figs.
1D, 1E,
2, and
4) is also common; it is seen
in 7.4% of patients undergoing cholangiography
[3]. MRCP, mangafodipir
trisodium-enhanced MRCP, CT cholangiography, and ERCP readily detect accessory
and aberrant biliary ducts. Failure to recognize these anatomic variants may
result in inadvertent ductal ligation, biliary leaks, and strictures,
especially at laparoscopic cholecystectomy and living donor right lobe liver
transplantation [1,
2].
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Fig. 1 —Normal and variant biliary ducts. A, Normal biliary
tree. B, Trifurcation of biliary duct (arrow). C, Right
dorsocaudal branch (arrow) draining into left hepatic duct. D,
Aberrant right hepatic duct (arrow) emptying into common hepatic
duct. E, Aberrant right hepatic duct (arrow) draining into
cystic duct.
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Fig. 2 —51-year-old man imaged for liver donor work-up. Coronal
thick-slab MR cholangiopancreatography reveals dorsocaudal branch of right
hepatic duct (arrows) draining into left hepatic duct
(arrowhead). Aberrant right hepatic duct (open arrow) drains
into common hepatic duct. Common bile duct (CBD), cystic duct (curved
arrow), pancreatic duct (P), duodenum (D), and biliary bifurcation (bif)
are noted.
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Fig. 3 —46-year-old woman undergoing surgery for liver donor
transplantation. Intraoperative cholangiogram reveals dorsocaudal branch
(arrows) of right hepatic duct emptying into left hepatic duct.
Common bile duct (CBD), duodenum (D), and biliary bifurcation (bif) are
noted.
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Fig. 4 —57-year-old woman with abdominal pain. Coronal thick-slab MR
cholangiopancreatography shows right aberrant biliary duct (open
arrows) draining into common hepatic duct. Cystic duct remnant is noted
(curved arrow). Common bile duct (CBD), pancreatic duct (P), duodenum
(D), and biliary bifurcation (bif) are noted.
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Aberrant Cystic Duct Insertion: Low Insertion into Distal Common Bile Duct and Insertion into Right Hepatic Duct
Currently, laparoscopic cholecystectomy is performed far more frequently
than open cholecystectomy in the treatment of patients with gallstone disease.
Detection of anatomic variants that may increase the risk of bile duct injury
during cholecystectomy has become more relevant with the advent of the
laparoscopic approach [1]. MRCP
has proven to be accurate in the diagnosis of anatomic variants of the biliary
tree. Low insertion of the cystic duct into distal common bile duct
(Fig. 5) occurs in 9% of all
individuals. Cystic duct insertion into the right hepatic duct
(Fig. 6) is a rare variant of
the cystic duct. Failure to recognize these variants may lead to
misidentification of the common bile duct (CBD) or right hepatic duct (RHD)
for the cystic duct, and may result in inadvertent ligation or severance of a
portion of CBD or RHD.
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Fig. 5 —44-year-old woman with chronic pancreatitis. Coronal
thick-slab MR cholangiopancreatography shows cystic duct (arrows)
with low insertion (arrowhead) into distal common bile duct (cbd).
Gallbladder (GB) is noted.
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Fig. 6 —40-year-old woman with bile leak after cholecystectomy. ERCP
image shows cystic duct remnant (arrows) insertion into aberrant
right hepatic duct (open arrows). Biliary bifurcation (bif) and
common bile duct (CBD) are noted.
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Bile Duct Cysts
A bile duct cyst is a relatively rare congenital cystic dilation of the
biliary tree that most commonly involves the extrahepatic bile duct. According
to the Todani system, there are five types of bile duct cysts (Figs.
7A,
7B,
7C,
7D,
7E, and
7F).
Type 1: Choledochal Cyst
Type 1 bile duct cysts account for 80% to 90% of all bile duct cysts and
are characterized by fusiform dilation of the extrahepatic bile duct
(Fig. 7A). It is theorized that
choledochal cysts form as the result of reflux of pancreatic secretions into
the bile duct via an anomalous junction of the common bile and pancreatic
ducts. The classic triad of jaundice, abdominal pain, and mass is not commonly
seen in adult patients. Because the cyst should be resected completely to
prevent associated complications, such as ascending cholangitis,
cystolithiasis, and malignant transformation
[4], accurate determination of
the length of the extrahepatic bile duct involved by the cyst is crucial in
surgical planning. MRCP is an effective imaging technique for diagnosis and
preoperative evaluation of bile duct cysts
[5] (Figs.
8A and
8B). On initial imaging,
obstructive biliary dilation should be excluded. In contrast to obstruction
that results in dilation of the intra- and extrahepatic bile ducts, type 1
bile duct cysts show dilation of the extrahepatic bile duct with little, if
any, dilation involving intrahepatic ducts. The caliber of the duct located
above and below the cyst is usually normal.
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Fig. 8A —50-year-old woman with jaundice. Coronal thick-slab MR
cholangiopancreatography shows large type 1 bile duct cyst of extrahepatic
bile duct (arrows). Right and left hepatic ducts are slightly
distended (open arrows). Gallbladder (GB) and duodenum (D) are
noted.
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Fig. 8B —50-year-old woman with jaundice. Percutaneous transhepatic
cholangiogram of same patient shows large type 1 bile duct cyst of
extrahepatic bile duct containing contrast material (arrows).
Slightly distended left and right hepatic ducts are noted (open
arrows). Percutaneous needle (Perc), gallbladder (GB), and duodenum (D)
are noted.
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Type 2: Diverticulum
Type 2 bile duct cysts account for 3% of all bile duct cysts and represent
a true diverticulum. At imaging, type 2 bile duct cysts are seen as saccular
outpouchings arising from the supraduodenal extrahepatic bile duct or the
intrahepatic bile ducts (Fig.
7B).
Type 3: Choledochocele
Choledochoceles account for 5% of all bile duct cysts and represent
protrusion of a focally dilated, intramural segment of the distal common bile
duct into the duodenum (Fig.
7C). Although choledochoceles may manifest in adults with episodic
abdominal pain, jaundice, nausea, and vomiting, many are detected incidentally
in patients without symptoms referable to the biliary tract. MRCP and direct
cholangiography reveal a bulbous dilation of the intramural portion of the
bile duct bulging into the duodenum (Figs.
9A,
9B, and
9C). Choledochoceles may be
successfully managed with endoscopic sphincterotomy, surgical excision, or
both, in symptomatic patients.
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Fig. 9A —30-year-old man with periampullary mass seen on CT performed
at another institution. Coronal oblique, thin-slab MR cholangiopancreatography
(MRCP) image reveals oval-shaped high-signal-intensity contour
(arrows) of distal common bile duct (CBD) protruding into duodenum
(D), which represents choledochocele. Pancreatic duct (P) is noted.
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Fig. 9B —30-year-old man with periampullary mass seen on CT performed
at another institution. Axial T2-weighted image shows fluid-filled structure
(arrows) protruding into duodenum (D). Pancreas (P) is noted.
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Fig. 9C —30-year-old man with periampullary mass seen on CT performed
at another institution. ERCP image shows contrast-filled and oval-shaped
structure (arrows) of distal common bile duct (CBD) protruding into
duodenum (D), which represents choledochocele seen at MRCP and MR.
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Type 4: Multiple Communicating Intraand Extrahepatic Duct Cysts
Type 4 biliary cysts represent the second most common type of bile duct
cysts (10%) and are subdivided into subtypes A and B (Figs.
7D and
7E). Type 4A is characterized
by fusiform dilation of the entire extrahepatic bile duct with extension of
dilation of the intrahepatic bile ducts (Figs.
10A and
10B). Type 4B cysts are
extremely rare and are seen as multiple cystic dilations involving only the
extrahepatic bile duct.
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Fig. 10A —54-year-old man with abdominal mass and pain. Sonogram shows
aneurysmal dilation of extrahepatic bile duct (arrows). Dotted line
between arrows represents measurement line of sonogram.
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Fig. 10B —54-year-old man with abdominal mass and pain. Coronal
oblique, thin-slab MR cholangiopancreatography shows marked dilation of
extrahepatic bile duct (solid arrows) and left main intrahepatic duct
(open arrow).
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Type 5: Caroli's Disease
Caroli's disease is a rare form of congenital biliary cystic disease
manifested by cystic dilations of intrahepatic bile ducts that may diffusely
involve the right and left hepatic ducts
[6]. There is an association
with benign renal tubular ectasia and other forms of renal cystic disease.
ERCP and MRCP are used to establish the diagnosis. The primary
cholangiographic feature of Caroli's disease is cystic dilation of the
intrahepatic bile ducts seen in conjunction with a normal extrahepatic bile
duct (Figs. 11A and
11B). This finding can also
occur in association with intrahepatic bile duct strictures, stones, abscess,
and manifestations of cirrhosis.
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Fig. 11A —70-year-old woman with jaundice. Coronal oblique, thin-slab
MR cholangiopancreatography shows multiple cystic dilations of intrahepatic
bile ducts (arrows) consistent with Caroli's disease. Common bile
duct (CBD), duodenum (D), and pancreatic duct (P) are noted.
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Fig. 11B —70-year-old woman with jaundice. Coronal T2-weighted image
shows multiple fluid-containing foci (arrowheads) in papillae of
kidneys, indicating renal tubular ectasia (medullary sponge kidney). Saccular
dilations of intrahepatic bile ducts (arrows) are noted.
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Biliary Abnormalities Associated with Situs Anomalies
In situs inversus, the bile ducts are reversed— right to
left—as are the other abdominal organs ("mirror image")
[7] (Figs.
12A and
12B). In situs ambiguous with
polysplenia, the stomach and multiple small spleens usually lie in the right
upper quadrant of the abdomen, and the gallbladder and the liver lie close to
midline (Fig. 13). It is
important to be aware of these entities because situs anomalies may create a
confusing clinical and imaging picture, especially in the setting of diseases
such as acute cholecystitis
[7].
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Fig. 12A —65-year-old man with hepatitis B. Coronal thick-slab MR
cholangiopancreatography shows situs inversus with gallbladder (GB), common
bile duct (CBD), and second portion of duodenum (D) in left upper quadrant,
and pancreatic duct (P) coursing toward right. High signal intensity focus in
right upper quadrant (S) represents fluid in stomach.
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Fig. 12B —65-year-old man with hepatitis B. Axial CT shows gallbladder
(GB) and liver (L) located in left upper abdomen, and stomach (S) and spleen
(Sp) in right upper abdomen. Splenic vein (v) is noted.
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Fig. 13 —42-year-old woman with polysplenia syndrome. Axial CT scan
shows two spleens (Sp) to right of midline. Gallbladder (GB) is near midline
and stomach (S) is on right. Pancreas is foreshortened (P).
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Fig. 14A —49-year-old woman with pancreatitis. Coronal oblique,
thin-slab MR cholangiopancreatography shows 2.4-cm-long common channel
(double arrows) distal to union of distal common bile duct (CBD) and
pancreatic duct (P). Major papilla (open arrow) and duodenum (D) are
noted. Mid common bile duct is focally dilated, which is consistent with type
1 bile duct cyst (Cyst).
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Fig. 14B —49-year-old woman with pancreatitis. Schematic of A. The
double arrows represent long common channel from orifice of papilla (open
arrow) to union of distal common bile duct (CBD) and pancreatic duct (P).
Mid common bile duct is focally dilated, which is consistent with type 1 bile
duct cyst (Cyst). Duodenum is noted (D).
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Anomalous Junction of the Biliary Ductal System with Pancreatic Duct
Anomalous junction of the pancreaticobiliary ductal system is usually
defined as a union of the distal common bile duct and the pancreatic duct
proximal to the duodenum whose length is greater than 1.5 cm
[8]. Anomalous junction of the
pancreaticobiliary ductal system has been reported in association with
cholangiocarcinoma, gallbladder carcinoma, choledocholithiasis, and chronic
pancreatitis. In this entity, pancreatic secretions can reflux into the common
bile duct and can result in the development of a bile duct cyst (type l)
[4,
5] (Figs.
14A and
14B).
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Abstract
Introduction
