IMAGING OF GALLBLADDER VARIANTS
H MHALLA (1), S MEZGHANI BOUSSETTA (1)
Department of radiology (1) Hospital of Ben Arous. Tunisia
INTRODUCTION
Routine imaging of the gallbladder demonstrates a wide array of imaging
variants, including anomalies in location, number, and configuration. An
awareness of these normal variants may prevent misdiagnosis and will aid
in evaluation of alternative diagnostic possibilities.
OBJECTIVES
The aim of this study is to describe different radiologic findings of gallbladder
variants and embryological events leading to these variants.
MATERIALS AND METHODS
Retrospective study of five patients.
All of them have consulted in regional hospital of Ben Arous.
Abdominal US exam performed for each of them revealed gallbladder
anomalies.
RESULTS AND DISCUSSION
The mean age was 26 years (8 months- 48 years), clinical symptoms were
right upper quadrant pain (4 cases) for 6 months (2 cases), acute pain (2 cases)
and radiological discovery without clinical symptoms (1 case). 3 patients had
congenital anomalies; mega-urethra (1 case), situs inversus (1cas), congenital
scoliosis (1 case). Gallbladder variants were anomalies in location (2 cases)
retrohepatic and left gallbladder, anomalies of number (2 cases) agenesis and
duplicity and anomalies of configuration (1 case) junctional fold gallbladder.
We can notice different gallbladder variants. Anomalies of number such
as duplicity, accessory, agenesis or triplication, in location such as left
sided, suprahepatic, intrahepatic, retroplaced and mobile gallbladder, and
of configuration such as multiseptate and junctional fold gallbladder.
For a better understanding of these variants, we need to understand the
events occurring at the embryological period.
Embryology
In the fourth week of fetal development, the hepatic diverticulum appears as a
cellular outgrowth of the proximal part of the intestinal tube. The hepatic
diverticulum arises as a sacculation consisting of a cranial portion which
further differentiates into glandular tissue and bile ducts. The main portion of
the hepatic diverticulum elongates to form the common bile and hepatic
ducts. The caudal portion of the hepatic diverticulum becomes the gallbladder
and cystic duct. The gallbladder is a solid epithelial cylinder which is carried
from the duodenum by the elongated common duct.
In the seventh week, a lumen is established within the cystic duct.
Anomalies in Number
Agenesis of the gallbladder is rare, as are duplication anomalies.
Triplication gallbladder is exceptional.
Duplicated Gallbladder
The phenomenon is explained by the duplication of the gallbladder vesicle.
Gallbladder duplication is a rare anomaly. Boyden’s classification of double
gallbladders includes:
(1) bilobed incomplete gallbladder division with one cystic duct
(2) complete gallbladder duplication with separate cystic ducts entering the
common hepatic duct (Figure 1)
(3) complete gallbladder duplication with a common cystic duct entering the
common hepatic duct.
Figure 1: Ultrasonography showing two gallbladders with separate ducts (Type 2 of Boyden’s classification).
Differentiation between the specific types of duplication is usually not possible
with sonography. When stones are present, they may be sequestered in one of
the two lobes. When gallstones can be demonstrated to communicate with all
parts of the gallbladder, a folded gallbladder is more likely than duplication.
A more specific sign of gallbladder duplication may be isolated contraction of
the non-diseased lobe with an absence of contraction of the diseased lobe. This
finding may be useful for differentiating between two gallbladder lobes and
other forms of pericholecystic fluid collection. It may also suggest at least
partial duplication of the cystic duct, since a patent cystic duct must be present
to contract the lobe.
Accessory Gallbladder
Boyden presented two theories explaining accessory gallbladder formation:
- The first suggests that the phenomenon is caused by the primary subdivision
of the embryonic primordium into two parts, and accessory gallbladders
represent an outgrowth of a secondary vesicle from some other portion of the
biliary duct system subsequent to the formation of a definitive gallbladder.
- The second theory supports the idea that bile duct buds occur at the junction
of the hepatic ducts. These duct buds usually regress and disappear. However, if
they persist, gallbladder anomalies such as duplication or triplication may
occur. If the bud originates on one of the hepatic or common ducts, the
accessory gallbladder will contain its own cystic duct. If the bud originates
from the cystic duct, a Y-shaped cystic duct will connect the accessory and the
normal gallbladder to the common duct.
Pseudo duplication gallbladder may simulate a double gallbladder.
Agenesis of gallbladder (Figure 3)
The development of the liver and gallbladder system starts around the third
week of gestation, when the primordial liver, called the hepatic diverticulum, is
formed as an outgrowth of the endodermis of the anterior intestine. As the
diverticulum grows, its connection with the intestine narrows to form the
external hepatic bile duct. A small ventral invagination grows in this narrow
area and gradually forms a vacuole that becomes the gallbladder and cystic
duct. A failure of this invagination results in agenesis of the gallbladder.
Figure 3: A, B: T2 axial slices, C: sequence RARE both showing agenesis of gallbladder which appears as a stump.
Triplication of Gallbladder
Triplication of the gallbladder is a very rare congenital anomaly of the biliary tract.
Gallbladder multiplications are not likely to be discovered unless associated with
cholelithiasis, sludge, cholecystitis and carcinoma. Multiple gallbladders are thought to
be caused by the failure of rudimentary bile ducts to regress during embryological
development. Three distinct types are described:
-The first type is characterized by the presence of multiple gallbladders that drain into
the common bile duct via separate cystic ducts.
- The second type is characterized by the presence of two gallbladders with a common
cystic duct entering the common duct, and a third gallbladder with an independent
cystic duct.
-The third type is characterized by the presence of three gallbladders that share a single
cystic duct.
Anomalies in location
Normally, the gallbladder is adjacent to the undersurface of the liver, in
the plane of the interlobar fissure, with the gallbladder neck maintaining
a constant relationship to the porta hepatis. The gallbladder is routinely
found in the right upper quadrant, but may be seen in any part of the
abdomen. While anomalies of positions are rare, the most common of
these are the left sided, intrahepatic, transverse, and retroplaced
(retrohepatic or retroperitoneal).
A left-sided gallbladder location is seen in situs inversus (Figure. 4).
A gallbladder in the left upper quadrant without situs inversus is even rarer.
There are several explanations for that:
-The first is that, the normal gallbladder bud may migrate to the left lobe instead
of the right, and lie on the left side of the ligamentum teres. In this situation, the
portal vein, biliary tree and hepatic artery should be in the normal location and
classified as an ectopic gallbladder.
- The second suggests that, the gallbladder may develop directly from the left
hepatic duct, and is accompanied by a failure in the development of the normal
structure on the right side.
-Third, the left umbilical vein disappears and the right one partly remains.
-The fourth explanation is that, the gallbladder is on the left side of the
ligamentum teres simply because the latter deviated to the right .
The left-sided gallbladder may occur either as a single anomaly or in a malrotation
of the intestine
Figure 4: CT injected axial slices showing ectopic gallblader with gallstone associated with situs inversus
Intrahepatic gallbladders
Have a subcapsular location along the anterior inferior right lobe of the
liver. This poses a problem for scintigraphy, as an intrahepatic
gallbladder can cause a focal defect. When a solitary defect is present in
a technetium liver scan, the differential diagnosis includes neoplasm,
abscess, hematoma, lymphoma, and an aberrant gallbladder.
Sonography can be helpful in these cases.
Suprahepatic gallbladder
The suprahepatic gallbladder is a rare type of gallbladder ectopia, with only
approximately eight cases reported. Most of these patients have either
associated hypoplasia of the right hepatic lobe or a right-sided diaphragmatic
eventration. A suprahepatic gallbladder has been reported with hepatomegaly
due to macronodular cirrhosis. Rarely, the suprahepatic gallbladder may be
intrathoracic, and be associated either with a right-sided diaphragmatic
eventration or a traumatic right-sided diaphragmatic hernia. It may be located
either anteriorly or posteriorly over the dome of the right hepatic lobe. As with
many other ectopic gallbladder locations, it usually has a mesentery that
allows it to float freely in the peritoneal cavity. The cystic duct and vascular
supply of the gallbladder in a suprahepatic location insert normally.
The retroplaced gallbladder (retrohepatic) (Figure. 5)
Is rare and can be either congenital or acquired.
Gallbladder rotation and/or displacement can be caused by hepatic lobe
abnormalities (aplasia, hypoplasia, and hypertrophy) and by abnormal
mobility of the gallbladder itself. From an imaging standpoint, it is
important to realize that when the gallbladder is not visualized in its
normal location, the possibility of an ectopic location must be considered.
Figure 5: A: ultrasonography, B: CT, C: schematic representation, showing retrohepatic location of gallbladder.
A mobile Gallbladder
May have different causes. One type of anomaly may be related to the
congenital deformity. Between the fourth and the seventh week of
embryological development, the pars cystica forms from the hepatic
diverticulum. Abnormal migration with an absence of a gallbladder
mesentery creates a “free floating gallbladder”. Another anomaly occurs
with generalized visceroptosis. The mesentery of the gallbladder and
cystic duct relax and elongate, thus creating a mobile situation.
These anomalies leading to “floating gallbladder” can be responsible for
complications such as torsion or volvolus .
Anomalies in Form
Junctional fold gallbladder
Several variations in the radiologic appearance of gallbladder shape have
been described. The so-called junctional fold is folding of the gallbladder,
usually of the posterior wall, but can occur anteriorly as well. Such
junctional folds occur frequently, and are easily shown by sonography as
well as by other imaging techniques. Careful analysis usually excludes
adjacent disease. The Phrygian cap is a typical. It takes its name from the
ancient Greek headgear, descriptive of this asymptomatic folding of the
gallbladder fundus. This variant is readily identified with sonography and
CT.
Septa of the gallbladder can be either partial or complete. These can lead to
stasis and stone formation.
Multiseptate gallbladder (Figure 6)
Is a rare anomaly, having a multichambered lumen with multiple septa,
creating a honeycombed appearance. Differential possibilities on sonography
include desquamated gallbladder mucosa, and possibly polypoid
cholesterolosis.
The coexistence of biliary symptoms with multiseptate gallbladder has been
well established, and most patients have biliary pain suggestive of cholecystitis
Gallbladders containing one to three septa are not unusual. The exact
mechanism responsible for the genesis of multiseptation is not clear. However,
it is speculated that wrinkling and infolding seen in the gallbladder buds of cat
and guinea-pig embryos or formation of the so-called Phrygian cap in human
embryos may be related to this phenomenon.
Figure 6: Ultrasonography showing some locules formed by the transversal septas.
CONCLUSION
Radiological diagnosis of biliary anomalies is an important part of
abdominal imaging. In daily practice, biliary anatomy may be demonstrated
with a wide range of techniques, such as high resolution US, multislice CT
and MRCP. Preoperative awareness of any variation minimizes the chance
of an unexpected situations during cholecystectomy, and helps avoiding
any unwanted damage to the biliary tract.
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