|
|
Anatomy relevant
to cholecystectomy
|
|
|
|
|
Nagral Sanjay
Department of GI Surgery, Jaslok
Hospital and Research Centre, G Deshmukh Marg, Mumbai, India
Correspondence
Address:
Nagral Sanjay
Department of GI Surgery, Jaslok Hospital and
Research Centre, G Deshmukh Marg,
Mumbai - 400 026
India
nagral@vsnl.com
Abstract
This review discusses anatomical facts that are of relevance to the
performance of a safe cholecystectomy.
Misinterpretation of normal anatomy and anatomical variations contribute to
the occurrence of major postoperative complications like biliary
injuries following a cholecystectomy, the incidence
being higher with laparoscopic cholecystectomy. A
look at the basic anatomy is therefore important for biliary
and minimally invasive surgeons. This includes normal anatomy and variations
of the biliary apparatus as well as the arterial
supply to the gallbladder. Specific anatomical distortions due to the
laparoscopic technique, their contribution in producing injury and a
preventive strategy based on this understanding are discussed. Investigative
modalities that may help in assessing anatomy are considered. Newer insights into the role of anatomic illusions as well as the
role of a system-based approach to preventing injuries is also
discussed.
Full Text
Knowledge of relevant anatomy is important for the safe execution of any
operative procedure. Specifically, in the context of a cholecystectomy,
it has been recognized since long that misinterpretation of normal anatomy as
well as the presence of anatomical variations contribute to the occurrence of
major postoperative complications especially biliary
injuries.[1] Such injuries in turn can cause significant morbidity and
occasionally even mortality. They are also one of the commonest causes of
litigation against abdominal surgeons in the developed world. There is now a
fair amount of data to suggest that the acceptance of laparoscopic cholecystectomy (LC) as the standard procedure, has led
to an increase in bile duct injuries.[2] This seems partly related to the
different anatomical exposure of the area around the gallbladder especially
the Calot's triangle during the laparoscopic
procedure as opposed to the open procedure.
Hence, it is important for biliary and minimally
invasive surgeons to appreciate basic anatomical facts as they apply to the
performance of cholecystectomy as well as
understand from literature how anatomical distortions or variations can
contribute to complications. This review attempts to address these issues. It
is not an exhaustive description of biliary anatomy
but discusses anatomical facts that are of relevance to the performance of a
safe cholecystectomy.
Gallbladder
The gallbladder is a pear shaped organ situated in a fossa
on the liver undersurface. It is variable in shape and volume. Normally
present at the junction of segments 4 and 5 (and at the lower limit of the
principal plane or Cantlie's line) its position in
relation to the liver may vary. For example, it may be partially or
completely embedded within the liver parenchyma, the so-called 'intrahepatic' gallbladder. This may create difficulties
in dissection and may increase the chance of intraoperative
injury to the liver. Although the main right pedicle is fairly deep in the
liver parenchyma, large portal, and hepatic venous branches traverse the
liver at a depth of around one cm from the gallbladder. Thus, a deep liver
tear during the dissection of the gallbladder off its fossa
can occasionally bleed profusely. Also, during the dissection it may be
important to err on the side of the gallbladder rather than the liver
parenchyma.
The gallbladder is divided into a fundus, a body
and a neck or infundibulum. The 'Hartmann's pouch'
an out pouching of the wall in the region of the neck is recognized more as
an outcome of pathology in the form of dilatation or presence of stones.[3]
This pouch is variable in size but a large Hartmann's pouch may obscure the
cystic duct and the Calot's triangle. This may be
result of plain enlargement or due to adherence to the cystic duct or bile
duct. Thus a small cystic duct can get completely hidden and traction on the
gallbladder can lead to the bile duct looking like the cystic duct. An
exaggerated form of the same process is the 'Mirizzi's
syndrome' in which a large stone in the Hartmann's pouch area is either
adherent to or erodes into the bile duct. This can create major difficulty
during a cholecystectomy.
Although the accessory ducts are discussed separately later in the article
the cholecysto-hepatic duct can join the
gallbladder at any point in its hepatic bed. The exact incidence of such
ducts is not well documented and in fact some authors question their
existence.[3] Thus, a duct encountered in the
gallbladder fossa is likely to be a small
superficial intrahepatic duct and can be ligated safely.
Cystic duct
The cystic duct joins the gallbladder to the bile duct and is one of the
important structures needing proper identification and division during a
standard cholecystectomy. The cystic duct may run a
straight or a fairly convoluted course. Its length is variable and usually
ranges from 2 to 4 cm.[3] Around 20% of cystic ducts
are less than 2 cm. Hence there may be very little space to put clips or
ligatures. True absence of the cystic duct is extremely rare[3]
and if the duct is not seen is more likely to be hidden. The cystic duct is
usually 2-3 mm wide. It can dilate in the presence of pathology (stones or
passed stones). The normal bile duct is also around 5 mm and hence can look
like a mildly dilated cystic duct. In general a cystic duct larger than 5 mm
(or the need to use a very large clip to completely occlude the duct) should
arouse a suspicion of mistaken identity with the bile duct before it is
clipped or ligated.
The cystic duct joins the gallbladder at the neck and this angle may be
fairly acute. Also the mode of joining may be smooth tapering or abrupt. On
the bile duct side its mode of union shows significant variations [Figure 1].
Since such variations are not uncommon it may not be safe to try and dissect
the cystic duct to its junction with the bile duct. It is important to
remember that even in the low insertion variety the cystic duct rarely goes
behind duodenum and therefore a ductal structure passing behind the duodenum
is more likely to be the bile duct itself. Double cystic ducts are described
but are exceedingly rare and therefore two ductal structures entering the
gallbladder should always be viewed with suspicion. Also the cystic duct does
not have vessels traveling on its surface whereas the bile duct has such
visible vessels.[2]
Cystic artery and right hepatic artery
The cystic artery is a branch of the right hepatic artery (RHA) and is
usually given off in the Calot's triangle. It has a
variable length and enters the gallbladder in the neck or body area. The
course and length of the cystic artery in the Calot's
triangle is variable. Although classically the artery traverses the triangle
almost in its center, it can occasionally be very close or even lower than
the cystic duct.
It usually gives off an anterior or superficial branch and a posterior or
deep branch. This branching usually takes place near the gallbladder. When
the point of dissection is very close to the gallbladder as in a LC or the
branching is proximal, one may have to separately ligate
the two branches [Figure 2]. Also if the presence of a posterior branch is
not appreciated it can cause troublesome bleeding during posterior dissection.
In addition the cystic artery gives of direct branches to the cystic duct.
These small vessels have been better appreciated in the era of LC and need to
be divided to obtain a length of cystic duct before division.
The RHA normally courses behind the bile duct and joins the right pedicle
high up in the Calot's triangle. It may come very
close to the gallbladder and the cystic duct in the form of the 'caterpillar'
or 'Moynihan's' hump [Figure 3]. Although the incidence of this variation is
variable it seems common enough to merit detailed description and may be as
high as 50%.[3] If such a hump is present, the
cystic artery in turn is very short. In this situation the RHA is either
liable to be mistakenly identified as the cystic artery or torn in attempts
to ligate the cystic artery. The ensuing bleeding
in turn predisposes to biliary injury.
There are a fair number of other arterial variations of the cystic artery
also described [Figure 3]. Many of these are unlikely to cause confusion if
the artery is divided very close to the gallbladder wall. There is a 2-15%
incidence of double cystic artery. Therefore it may be occasionally necessary
to ligate two arteries to the gallbladder. When the
cystic artery is given off not from the RHA but from other vessels like the
common hepatic artery or the left hepatic artery (2-5%) it crosses the bile
duct anteriorly and may be prone to injury. Also
the superior mesenteric artery may give off the cystic artery in which case
it ascends to the gallbladder below the cystic duct. An accessory or replaced
RHA from superior mesenteric artery which is a variation seen in almost 15%
of individuals the RHA courses thru the Calot's
triangle (and therefore nearer the gallbladder) and in turn has a shorter
cystic artery.
Accessory and aberrant ducts
There are a large number of accessory ducts described in the biliary drainage network of the liver. However, the
accessory ducts likely to be encountered during a cholecystectomy
are those draining parts of the right lobe. These ducts are typically small
and course through the Calot's triangle (and
therefore closer to the gallbladder) before they enter the common hepatic
duct separately below the confluence of the right and left duct at variable
distances. Sometimes the cystic duct may actually join the accessory duct.
Some of the variations of relevance to cholecystectomy
are shown [Figure 4].
These ducts may drain substantial portions of the right lobe of the liver,
either one of the sectors (two segments) or a segment and may in fact be the
sole drainage of that part of the liver in which case they are more precisely
termed as 'aberrant' ducts. It has been suggested that most such ducts are
aberrant rather than accessory[3] in which case it
is even more important to safeguard them. Cholangiographic
studies have shown that there is almost a 20% incidence of the right anterior
or the right posterior ducts joining the common hepatic duct separately
rather than in the form of a right duct. If such a duct is injured it can
lead to substantial biliary stasis or leak. The
size of the duct may be an indirect indicator of the amount of liver it
drains. It has hence been recommended that in case of injury if the duct is
more than 3 mm it should always be drained into a Roux loop.[3]
Alternatively one can perform a cholangiogram
through the duct to assess the amount of liver it drains as well as whether
it is accessory or aberrant. With increasing recognition of injury to such
ducts these have now been grouped into separate type in the recent Strasberg classification[2] of
bile duct injuries.
Calot's triangle
This famous triangle was described as bound by the cystic duct, the bile duct
and the cystic artery in its original description by Calot
in 1891. In its present interpretation the upper border is formed by the
inferior surface of the liver with the other two boundaries being the cystic
duct and the bile duct [Figure 5]. Its contents usually include the RHA, the
cystic artery, the cystic lymph node (of Lund), connective tissue, and lymphatics. Occasionally it may contain accessory hepatic
ducts and arteries as discussed previously. It is this triangular space,
which is dissected in a cholecystectomy to identify
the cystic artery and cystic duct before ligation
and division. In reality, it may be a small potential space rather than a
large triangle making the dissection of its contents without damaging the
bordering structures the most challenging step of a cholecystectomy.
In addition the space may be obscured and shrunken by various mechanisms. The
left (or medial) boundary of the triangle formed by the bile duct is the most
important structure, which needs to be safeguarded.
The advent and popularity of LC has led to a new look and insights into biliary anatomy especially of the Calot's
triangle area and the term 'laparoscopic anatomy' has actually found a place
even in anatomy texts. Although a detailed discussion of all the factors
peculiar to laparoscopy that contribute to an increased incidence of injuries
is beyond the purview of this review, the different anatomical 'laparoscopic
view' of the area around the gallbladder especially the Calot's
triangle does contribute to misidentification of structures. The method of
retraction during the laparoscopic procedure tends to distort the Calot's triangle by actually flattening it rather than
opening it out.[2] Also, the reluctance to (or difficulty in) performing a fundus first cholecystectomy
during the laparoscopic procedure as opposed to the open procedure also contributes
to the same lack of exposure of the Calot's
triangle. Finally, the 'posterior' or 'reverse' dissection of the Calot's triangle, which is popular during an LC, again
gives a different view of the area and since the gallbladder is flipped over
during this method may lead to further anatomical distortion. The Rouviere's sulcus is a fissure
on the liver between the right lobe and caudate process and is clearly seen
during a LC during the posterior dissection in a majority of patients[4] [Figure 6]. It corresponds to the level of the
porta hepatis where the
right pedicle enters the liver. It has hence been recommended that all
dissection be kept to a level above (or anterior) to this sulcus[4] to avoid injury
to the bile duct. Also, this being an 'extrabiliary'
reference point it does not get affected by distortion due to pathology.
Similarly, a clear delineation of the junction of the cystic duct with the
gallbladder along with the demonstration of a space between the gallbladder
and the liver clear of any other structure other than the cystic artery
(safety window or critical view) is also recommended as an essential step to
prevent bile duct injury[2] [Figure 7].
Investigations to assess the anatomy
Drawings of the Calot's triangle from anatomy texts
are very different from the anatomy seen during the performance of a cholecystectomy. In the first place all the structures
forming the boundaries of the Calot's triangle are
not seen during surgery as they are covered with tissue. Also, in a
significant number of individuals since the cholecystectomy
is performed for pathology in the form of cholecystitis the anatomy is
obscured by inflammation, edema, adhesions, fibrosis, and presence of stones.
In view of the importance of anatomy and it's variations in injuries caused
during cholecystectomy it is logical to look at the
possibility of assessing the anatomy accurately with the help of imaging
before or during the performance of a cholecystectomy.
Most cholecystectomies are performed after
identification of gallstone disease on ultrasound examination. Although on
occasion an ultrasound examination can predict gross distortions of anatomy
like the Mirizzi syndrome, in the usual case it
does not throw any light on anatomical relations. Thus knowledge of the
specific anatomy in that individual is not available to the surgeon
preoperatively as a routine. If a cholangiogram in
the form of a magnetic resonance cholangio pancreatography (MRCP) or an endoscopic
retrograde cholangiopancreatography (ERCP) has been performed for some
reason, it may reveal anomalies like the presence of accessory ducts or a low
insertion of cystic duct.
Methods to assess anatomy during the surgery are perhaps more relevant. The
first and foremost (and perhaps the most reliable) is clean dissection and
accurate visual identification of the contents of the Calot's
triangle especially the cystic artery and duct. The role of a routine intraoperative cholangiogram in
delineating biliary anatomy and in turn preventing
misidentification has been a subject of a long and intense debate amongst biliary surgeons but there is conflicting evidence on its
value.[2] In reality most biliary
surgeons do not perform a routine intraoperative cholangiogram but use it selectively. In any case, unless
it is performed through the gallbladder, once a duct has been opened for a cholangiogram in case it is the bile duct this actually
constitutes a partial injury. Also a cholangiogram
may not delineate all aberrant ducts and does not provide any insight into
arterial anatomy.
Recently, there have been sporadic reports of the use of newer sophisticated
technology to identify biliary as well as arterial
anatomy during the performance of a cholecystectomy.
This has included the use of laparoscopic ultrasound for identification of
structures, laparoscopic Doppler for identification of arteries and the use
of an instrument called the tactile sensor probe. Some recent reports
describe innovative methods such as the injection of a dye called methelenum coeruleum into the
gallbladder which gives a blue color to the biliary
system and the introduction of a small optical fiber thru ampulla
of vater which illuminates the entire biliary tree during the cholecystectomy
a procedure called 'light cholangiography.'[5] Most
of these methods rely on costly technology, are largely unavailable and have
not been scientifically validated. Thus, it seems that presently there is no
good alternative to meticulous dissection in a planned manner with precise
identification of structures before they are divided.
Finally, an interesting recent study has shown that 'anatomic illusions' to
which everyone is susceptible are the primary cause of bile duct injuries;
experience, knowledge, and technical skill by themselves may not be adequate
protection against such illusions and the resultant complications.[6] The
study also suggests that the current incidence of bile duct injury may be
nearing the upper limits of human performance and that the most useful
corrective strategy may lie outside the individual in changes in the
processes or technology. Another similar study recommends that surgeons
performing cholecystectomies should have an intraoperative protocol that is similar to navigation
principles used in the aviation and maritime industry.[7]
The number of cholecystectomies, especially LCs, being performed in India has increased phenomenally
in the last few years. Although there is no large population-based data there
is some evidence that the incidence of biliary
injuries is increasing as referral units including ours are treating an
increasing number of patients every year. While there has been a lot of focus
on technology and technical skills, discussions on anatomy and it's relevance
in prevention of injuries also deserve space in the future.
References
|
1
|
Eisendrath
DN. Anomalies of the bile ducts and blood vessels as the cause of accidents
in biliary surgery. JAMA 1918;71:864-7.
|
|
2
|
Strasberg
SM, Hertl M, Soper NJ.
An analysis of the problem of biliary injury
during laparoscopic cholecystectomy. J Am Coll Surg 1995; 180:101-25.
|
|
3
|
Adams
DB. The importance of extra hepatic biliary
anatomy in preventing complications at laparoscopic cholecystectomy.
Surg Clin N America 1993;73:861-71.
|
|
4
|
Hugh TB, Kelly MD, Mekisic A. Rouviere's sulcus; a useful
landmark in laparoscopic cholecystectomy. Br J Surg 1997;84:1253-4.
|
|
5
|
Xu F, Xu CG, Xu DZ. A new method of
preventing bile duct injury in laparoscopic cholecystectomy.
World J Gastroenterol 2004;10:2916-8.
|
|
6
|
Way LW, Stewart L, Gantert W, Liu K,
Lee CM, Whang K, Huntyer
JG. Causes and prevention of laparoscopic bile duct injuries. Analysis of
252 cases from a human Factors and cognitive psychology perspective. Ann Surg 2003;237:460-9.
|
|
7
|
Hugh TB. New strategies to prevent laparoscopic bile duct
injury-surgeons can learn from pilots. Surgery 2002;132:826-35.
|
|