AJR 2001; 177:389-394
© American Roentgen Ray Society
Anatomic Variants of the Biliary Tree
MR Cholangiographic Findings and Clinical Applications
Koenraad J. Mortelé1,2 and
Pablo R. Ros3
1
Department of Radiology, University Hospital Ghent, De Pintelaan 185, 9000
Ghent, Belgium.
2
Present address: Department of Radiology, Brigham and Women's Hospital,
Harvard Medical School, 75 Francis St., Boston, MA 02115.
3
Department of Radiology, Brigham and Women's Hospital, Harvard Medical School,
Boston, MA 02115.
Received January 2, 2001;
accepted after revision January 29, 2001.
Address correspondence to K. J.
Mortelé.
Introduction
Radiologists have become increasingly familiar with the Couinaud
nomenclature describing hepatic segmental anatomy, especially as it is
depicted by cross-sectional imaging techniques, such as CT and MR imaging
[1,
2]. However, knowledge of the
cholangiographic appearances of the normal anatomy of the biliary tree, as
well as those of their anatomic variants, is unfortunately restricted to a
minority of—usually—interventional images
[2]. Because MR cholangiography
is becoming the modality of choice for noninvasive evaluation of abnormalities
of the biliary tract and because surgical procedures such as liver resections
and partial liver transplantations are increasing in frequency and complexity,
a more widespread understanding of biliary anatomy and potential variations is
needed.
In this article, we present MR cholangiograms to illustrate normal and
aberrant hepatic biliary segmental anatomy. Additionally, we discuss the
significance of familiarity with the MR cholangiographic biliary segmental
anatomy to clinical practice.
MR Cholangiography: Technique
All MR cholangiograms were obtained with a 1.0-T scanner (Magnetom Expert;
Siemens, Erlangen, Germany). A body phased array coil with four elements,
centered below the xiphoid process, was used for signal reception. All
displayed images were applied with the thick-section rapid acquisition with
relaxation enhancement (RARE) MR cholangiographic "snapshot"
technique. We performed the fatsuppressed RARE technique with a section
thickness of 25-40 mm in a coronal or coronal oblique orientation (relaxation
time, 2.800 msec; effective TE, 1.100 msec; image matrix, 240 x 256;
field of view, 200 x 200 mm; refocusing flip angle, 180°). The
resulting images were displayed as projection images of the biliary tree after
a 7.13-sec acquisition time.
Normal Hepatic Biliary Ductal Anatomy
According to the Couinaud classification, the liver consists of eight
distinct hepatic segments, which have their own portal venous supply and
hepatic venous drainage system
[1,
2]. The anatomically distinct
segment I, or caudate lobe, lies between the fissure for the ligamentum
venosum and the vena cava inferior. The rest of the liver is divided by the
middle hepatic vein into a right and left liver lobes. The right liver lobe
consists of segments V-VIII. The superior segments (VII and VIII) are
separated from the inferior segments (V and VI) by the horizontal portion of
the right portal vein, whereas the anterior segments (V and VIII) are divided
from the posterior segments (VI and VII) by a coronal oblique plane containing
the right hepatic vein. The left liver lobe contains segments II-IV and is
divided into lateral segments (II and III) and a medial segment (IV or
quadrate lobe) by the umbilical fissure and falciform ligament. The left
hepatic vein forms the coronal separation of the lateral segment: segment II
is posterior and superior to the vein, whereas segment III is anterior and
inferior to it.
The individual biliary drainage system is parallel to the portal venous
supply [2] (Figs.
1,2,3A,3B).
The right hepatic duct drains the segments of the right liver lobe (V-VIII)
and has two major branches: the right posterior duct draining the posterior
segments, VI and VII, and the right anterior duct draining the anterior
segments, V and VIII. The right posterior duct has an almost horizontal
course, whereas the right anterior duct tends to have a more vertical course.
The right posterior duct usually runs posterior to the right anterior duct and
fuses it from a left (medial) approach to form the right hepatic duct. The
left hepatic duct is formed by segmental tributaries draining segments II-IV.
The common hepatic duct is formed by fusion of the right hepatic duct, which
is usually short, and the left hepatic duct. The bile duct draining the
caudate lobe usually joins the origin of the left or right hepatic duct
[3]. The cystic duct
classically joins the common hepatic duct below the confluence of the right
and left hepatic ducts. This normal biliary anatomy is thought to be present
in 58% of the population
[3].
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Fig. 1. —Normal biliary anatomy. Drawing shows normal hepatic biliary
segmental anatomy, as described by Couinaud
[1], and normal fusion of
cystic duct with common hepatic duct. Note normal confluence of right
posterior duct (small arrowheads) and right anterior duct (large
arrowheads) to form right hepatic duct (arrow).
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Fig. 2. —Normal hepatic ductal anatomy in 27-year-old healthy female
volunteer. Projective MR cholangiogram shows normal fusion of draining duct of
segment I (arrowhead) with left hepatic duct. Note normal confluence
(arrow) of right posterior duct and right anterior duct.
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Fig. 3A. —Normal hepatic ductal anatomy in 47-year-old man with biliary
obstruction due to chronic pancreatitis. Projective coronal MR cholangiogram
shows tributaries of common hepatic duct in their most common configuration:
left hepatic duct (long arrow) and right posterior duct (short
arrow) fusing with right anterior duct (small arrowhead) to form
right hepatic duct (large arrowhead).
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Fig. 3B. —Normal hepatic ductal anatomy in 47-year-old man with biliary
obstruction due to chronic pancreatitis. Projective coronal oblique MR
cholangiogram better shows normal confluence of right posterior duct
(small arrowheads) and right anterior duct (large
arrowheads) to form right hepatic duct (arrow).
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Common Anatomic Variants of the Biliary Tree
The most common anatomic variants in the branching of the biliary tree
described involve the right posterior duct and its fusion with the right
anterior or left hepatic duct
[2,
3]. As mentioned earlier, the
right posterior duct normally passes posteriorly to the right anterior duct
and joins it from the left to form the right hepatic duct, which then forms a
junction with the left hepatic duct to form the common hepatic duct. Drainage
of the right posterior duct into the left hepatic duct before its confluence
with the right anterior duct is the most common anatomic variant of the
biliary system and reported to occur in 13-19% of the population
[2,
3] (Figs.
4 and
5).
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Fig. 4. —Common biliary variant in 45-year-old woman with symptoms of
extrahepatic cholestasis. Projective MR cholangiogram shows, besides lithiasis
in common hepatic duct (black arrow), drainage of right posterior
duct (white arrow) into left hepatic duct (large arrowhead)
before joining right anterior duct (small arrowhead).
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Fig. 5. —Common biliary variant in 63-year-old woman with
choledocholithiasis. Projective MR cholangiogram illustrates, besides
choledocholithiasis (black arrow), the most common biliary anomaly
consisting of emptying of right posterior duct (white arrow) into
left hepatic duct (arrowhead).
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In approximately 12% of the healthy population, the right posterior duct
will not pass the right anterior duct posteriorly, but will empty into the
right aspect of the right anterior duct
[2]
(Fig. 6).
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Fig. 6. —Common biliary variant in 57-year-old asymptomatic woman with
increased serum amylasemia. Projective MR cholangiogram shows reversal of
normal left-right relationship of right posterior duct and right anterior duct
with lateral (right) emptying of right posterior duct (arrow) into
right anterior duct (small arrowhead). Note presence of normal
variant (large arrowhead) of pancreatic ductal system (pancreas
divisum).
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Another common variant (11%) of the main hepatic biliary branching is the
so-called triple confluence, which is an anomaly characterized by simultaneous
emptying of the right posterior duct, right anterior duct, and left hepatic
duct into the common hepatic duct
[3]. In patients with this
variant, the right hepatic duct is virtually nonexistent
(Fig. 7).
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Fig. 7. —Common biliary variant in 34-year-old woman with recurrent
cholestasis after cholecystectomy. Projective MR cholangiogram shows triple
confluence of right anterior duct (small arrowhead), right posterior
duct (arrow), and left hepatic duct (large arrowhead).
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Generally, there are three common variants in the cystic ductal anatomy
[3,
4]: a low cystic duct
insertion, characterized by a fusion of the cystic duct with the distal third
of the extrahepatic bile duct (9%) (Fig.
8); a medial cystic duct insertion, in which the cystic duct
drains into the left side of the common hepatic duct (10-17%)
(Fig. 8); and a parallel course
of the cystic duct and common hepatic duct, judged to be present when the
cystic duct follows a closely adherent course, parallel to the common hepatic
duct over at least a 2-cm segment (1.5-25%)
(Fig. 9).
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Fig. 9. —Common biliary variant in 33-year-old woman with cholestasis.
Projective MR cholangiogram shows parallel course of cystic duct and common
hepatic duct (arrows). In addition, note drainage of right posterior
duct (arrowhead) into left hepatic duct.
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Uncommon Anatomic Variants of the Biliary Tree
Several less common and usually more complicated anatomic variations of the
bile ducts have been described and consist of both aberrant and accessory bile
ducts. In a clinical context, familiarity with these two different entities is
important because an aberrant bile duct is the only bile duct draining a
particular hepatic segment, whereas an accessory one is an additional bile
duct draining the same area of the liver
[5]. In addition, several
uncommon variations in cystic duct insertion have been reported previously in
the literature [4,
5].
The direct drainage of the right posterior duct into the common hepatic
duct, right- or left-sided, is a variant also known as the aberrant hepatic
duct and is present in approximately 5% and less than 1% of the population,
respectively [2,
3] (Figs.
10 and
11).
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Fig. 10. —Uncommon biliary variant in 54-year-old man with chronic
pancreatitis. Projective MR cholangiogram shows aberrant drainage of right
posterior duct (arrow) into common hepatic duct (small
arrowhead). Note pancreas divisum with ductal changes involving dorsal
dominant duct (large arrowheads).
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Fig. 11. —Uncommon biliary variant in 45-year-old man evaluated for
pancreatitis. Projective coronal MR cholangiogram shows drainage of right
posterior duct (arrow) into common hepatic duct from left side
(arrowhead).
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Accessory hepatic ducts are observed in approximately 2% of patients and
may originate from and run their course along both the left or right ductal
system [3]. They may present as
a solitary finding or in conjunction with aberrant bile ducts (Figs.
12 and
13).
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Fig. 12. —Uncommon biliary variant in 78-year-old woman with recurrent
choledocholithiasis after cholecystectomy. Projective MR cholangiogram shows,
besides choledocholithiasis (black arrows), aberrant drainage of
right posterior duct (white arrow) into left hepatic duct (large
arrowhead). In addition, note drainage of accessory right anterior duct
(small arrowheads) into right posterior duct.
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Fig. 13. —Uncommon biliary variant in 29-year-old woman with
cholelithiasis. Projective MR cholangiogram shows, besides choledocholithiasis
(black arrow), trifurcation of left hepatic duct, right posterior
duct, and right anterior duct, and presence of accessory left hepatic duct
(white arrows) draining into right anterior duct
(arrowhead).
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Other exceedingly rare variations in bile duct branching can be seen and
may range from unique solitary findings to extensively complicated anatomy
(Figs. 14 and
15).
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Fig. 14. —Uncommon biliary variant in 44-year-old man evaluated for
recurrent choledocholithiasis after cholecystectomy. Projective MR
cholangiogram shows aberrant drainage of right posterior duct (arrow)
into inferior aspect of left hepatic duct (arrowhead).
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Fig. 15. —Uncommon biliary variant in 30-year-old woman. Projective MR
cholangiogram shows drainage of accessory left hepatic duct (arrow)
into right anterior duct (large arrowhead) and drainage of right
posterior duct (small arrowhead) into accessory left hepatic
duct.
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Cystic duct insertion occasionally may have an unusual presentation.
Reported uncommon anatomic variations include a high fusion of the cystic duct
with the common hepatic duct (Fig.
16), aberrant fusion of the cystic duct with the right or left
hepatic duct, and similarly, drainage of an aberrant or accessory right
posterior duct into the cystic duct
[4,
5].
Clinical Applications
Evaluation Before Hepatic Surgery
Familiarity with segmental hepatic biliary anatomy is essential for both
staging and localization of intrahepatic liver neoplasms or bile duct tumors
(cholangiocarcinoma). Because therapeutic approach and outcome of, for
example, Klatskin's tumors directly correlate with the biliary extent of the
disease (according to the Bismuth classification
[6]), MR cholangiography allows
a noninvasive determination of the stage of the disease
[7] (Figs.
17 and
18).
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Fig. 17. —67-year-old woman with Klatskin's neoplasm. Projective MR
cholangiogram shows invasion of common hepatic duct, left hepatic duct, and
right hepatic duct, with sparing of confluence of right anterior duct
(arrow) and right posterior duct (arrowhead): Bismuth type
II cholangiocarcinoma.
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Fig. 18. —44-year-old woman with Klatskin's neoplasm. Projective MR
cholangiogram shows hilar cholangiocarcinoma invading common hepatic duct,
left hepatic duct, and right hepatic duct beyond the bifurcation of right
anterior duct (arrow) and right posterior duct (arrowhead):
Bismuth type IIIA cholangiocarcinoma.
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Furthermore, evaluation of the biliary anatomy is essential before hepatic
lobectomy or segmentectomy. Inaccurate determination of existing biliary
anatomic variations may potentiate ligature or section of these aberrant
ducts, leading to major complications. For example, when performing a left
hepatectomy in a living related transplant donor, it is crucial to recognize
aberrant drainage of the right posterior duct or right anterior duct into the
left hepatic duct, because ligation of these ducts will produce biliary
cirrhosis of segments VI and VII, or segments V and VIII, respectively
[3] (Fig.
19A,19B).
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Fig. 19A. —39-year-old woman who had prior resection of left hepatic
lobe because of metastatic colon cancer. Axial gadolinium-enhanced T1-weighted
MR image shows dilatation of bile ducts in posterior segments of right hepatic
lobe (arrowhead). A 1.5-cm mass, compatible with liver metastasis
(arrows), is present centrally in liver near surgical plane.
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Fig. 19B. —39-year-old woman who had prior resection of left hepatic
lobe because of metastatic colon cancer. Projective MR cholangiogram shows,
except for focal caliber alteration due to metastasis (small
arrowhead), normal aspect of right anterior duct (arrows) with
drainage into right hepatic duct. Dilatation of right posterior duct
(large arrowhead) is not caused by presence of metastasis, but by
aberrant drainage of right posterior duct into left hepatic duct because of
ligation of left hepatic duct during prior surgery.
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Evaluation Before Complex Interventional Biliary Procedures
Noninvasive evaluation of the biliary tree has a high relevance before
percutaneous or endoscopic interventions, not only in assessing the extent of
the disease but also, and more importantly, in determining the most
appropriate approach. For example, it is important to be aware of significant
variations in biliary anatomy to avoid inappropriate or incomplete drainage of
the obstructed bile ducts
[2].
Evaluation Before Cholecystectomy
Although the overall incidence of bile duct injury after laparoscopic
cholecystectomy is usually less than 1%, anatomic factors, including the
presence of anomalies of the hepatic ducts and cystic duct, constitute one of
the major causes of bile duct injuries
[6].
Additionally, some anatomic variations may necessitate altering surgical
technique. For example, in patients with drainage of the cystic duct into the
left side of the common hepatic duct, it is considered dangerous to dissect
the cystic duct up to the left side of the common hepatic duct and, in
general, it is preferable to leave a long cystic duct remnant
[6]
(Fig. 20). Presence of an
aberrant right posterior duct draining into the common hepatic duct or into
the cystic duct, a high fusion of the cystic duct into the common hepatic
duct, and drainage of the cystic duct into the right hepatic duct all may
disorient the surgeon, causing him or her to inadvertently ligate or section
the aberrant ducts.
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Fig. 20. —47-year-old man after cholecystectomy. Projective MR
cholangiogram shows long cystic duct remnant (arrowheads), which was
indicated in patient because of medial insertion of cystic duct. In addition,
note web (arrow) in distal common bile duct.
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Conclusion
Both intra- and extrahepatic biliary anatomy is complex with the existence
of many common and uncommon anatomic variations. The current trend of using MR
cholangiography as the modality of choice in the evaluation of biliary
diseases and the increasing complexity of hepatic surgical procedures and
biliary interventions, however, necessitate a more widespread and appropriate
knowledge of these anatomic variations.
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Introduction
MR Cholangiography: Technique
