OBSTRUCTIVE JAUNDICE BILIARY DUCT DILATATION
Category: Diagnostic Radiology
Abstract : OBSTRUCTIVE JAUNDICE AND BILIARY DUCT DILATATION Dilatation of all or part of
the biliary tree is usually the result of proximal obstruction. Less commonly
the biliary tree may be dilated but not obstructed. The most common causes of
obstruction are stones in the common duct or a neoplasm of the bile duct or head
of pancreas. The patient with obstructive jaundice may present with upper
OBSTRUCTIVE JAUNDICE AND BILIARY DUCT DILATATION
Dilatation of all or part of
the biliary tree is usually the result of proximal obstruction. Less commonly
the biliary tree may be dilated but not obstructed. The most common causes of
obstruction are stones in the common duct or a neoplasm of the bile duct or head
of pancreas.
The patient with obstructive jaundice may present with upper
abdominal pain, abnormal liver function tests (LFTs) and, if the obstruction is
not intermittent, the sclera of the eye and the skin adopt a yellow
tinge.
Assessment of the level of obstruction :
It is possible for the
sonographer to work out where the obstructing lesion is situated by observing
which parts of the biliary tree are dilated:
● Dilatation of the common bile
duct (that is, that portion of the duct below the cystic duct insertion) implies
obstruction at its lower end.
● Dilatation of both biliary and pancreatic
ducts implies obstruction distally, at the head of the pancreas or ampulla of
Vater. This is more likely to be due to carcinoma of the head of pancreas,
ampulla or acute pancreatitis than a stone. However, it is possible for a stone
to be lodged just distal to the confluence of the biliary and pancreatic
ducts.
● Dilatation of the gallbladder alone (that is without ductal
dilatation) is usually caused by, obstruction at the neck or cystic
duct.
To assess whether the gallbladder is pathologically dilated may be
difficult on ultrasound. The sonographer should look at both the size and shape;
the dilated gallbladder will have a rounded, bulging shape due to the increase
in pressure inside it. A gallbladder whose wall has become fibrosed from chronic
cholecystitis due to stones will often lose the ability to distend, so the
biliary ducts can look grossly dilated despite the gallbladder remaining
‘normal in size, or contracted.
Early ductal obstruction :
Beware
very early common duct obstruction, before the duct becomes obviously dilated.
The duct may be mildly dilated at the lower end, just proximal to a stone.
Likewise intermittent obstruction by a small stone at the lower end of the duct
may be nondilated by the time the scan is performed. A significant ultrasound
feature in the absence of any other identifiable findings is that of thickening
of the wall of the bile duct. This represents an inflammatory process in the
duct wall, which may be found in patients with small stones in a nondilated
duct, but is also associated with sclerosing cholangitis. It is sometimes
technically difficult in some patients (particularly those with diffuse liver
disease) to work out whether a tubular structure on ultrasound represents a
dilated duct or a blood vessel. Colour Doppler will differentiate the dilated
bile duct from a branch of hepatic artery or portal vein.
Assessment of
the cause of obstruction :
Frequently, ultrasound diagnoses obstruction but
does not identify the cause. This is a good case for perseverance by the
operator, as the lower end of the CBD is visible in the majority of cases once
overlying duodenum has been moved away. However, ultrasound is not generally
regarded as a reliable tool for identifying ductal stones and is ERCP, although
invasive, is a more accurate method of examining the CBD and will often identify
strictures or small calculi not visible on ultrasound. It has the advantage of a
therapeutic role in addition to its diagnostic capabilities, by allowing the
extraction of stones at the time of diagnosis. It is associated with a small
risk of complication, however, and its use is therefore increasingly limited in
favour of the non-invasive magnetic resonance cholangiopancreatography (MRCP).
MRCP has been found to be highly effective in the diagnosis of CBD stones24 and
can potentially avoid the use of purely diagnostic ERCP. CT and MRI are useful
for staging purposes if the obstructing lesion is malignant. Cholangiocarcinomas
spread to the lymph nodes and to the liver and small liver deposits are
particularly difficult to recognize on ultrasound if the intrahepatic biliary
ducts are dilated. In hepatobiliary scintigraphy, technetium99mlabelled
derivatives of iminodiacetic acid are excreted in the bile and may help to
demonstrate sites of obstruction, for example in the cystic duct, or abnormal
accumulations of bile, for example choledochal cysts. Courvoisiers law, to
which there are numerous exceptions, states that if the gallbladder is dilated
in a jaundiced patient, then the cause is not due to a stone in the common duct.
The reason for this is that, if stones are or had been present, then the
gallbladder would have a degree of wall fibrosis from chronic cholecystitis
which would prevent it from distending. In fact there are many exceptions to
this law which include the formation of stones in the duct, without
gallbladder stones, and also obstruction by a pancreatic stone at the
ampulla.
Thus:
● Do not assume that obstructive jaundice in a patient
with gallstones is due to a stone in the CBD. The jaundice may be attributable
to other causes.
● Do not assume that obstructive jaundice cannot be due to a
stone in the CBD if the gallbladder does not contain stones. A solitary stone
can be passed into the duct from the gallbladder or stones can form within the
duct.
Causes of biliary duct dilatation
Intrinsic
Stones
Carcinoma of the ampulla of Vater
Cholangiocarcinoma
Stricture
(associated with chronic pancreatitis)
Biliary atresia/choledochal
cyst
Post-liver-transplantation bile duct stenosis (usually
anastomotic)
Parasites
Age-related or post-surgical mild CBD
dilatation
Extrinsic
Carcinoma of the head of pancreas
Acute
pancreatitis
Lymphadenopathy at the porta hepatis
Other masses at the
porta, e.g. hepatic artery aneurysm, gastrointestinal tract mass
Intra-hepatic tumours (obstruct distal segments)
Diffuse hepatic
conditions
Sclerosing cholangitis
Carolis disease
Management
of biliary obstruction :
Management of biliary obstruction obviously depends
on the cause and the severity of the condition. Removal of stones in the CBD may
be performed by ERCP with sphincterotomy. Elective cholecystectomy may take
place if gallstones are present in the gallbladder. Laparoscopic ultrasound is a
useful adjunct to surgical exploration of the biliary tree and its accuracy in
experienced hands equals that of X-ray cholangiography. It is rapidly becoming
the imaging modality of choice to examine the ducts during laparoscopic
cholecystectomy. Endoscopic ultrasound can also be used to examine the CBD,
avoiding the need for laparoscopic exploration of the duct when performed in the
immediate preoperative stage. The treatment of malignant obstruction is
determined by the stage of the disease. Accurate staging is best performed using
CT and/or MRI. If surgical removal of the obstructing lesion is not a suitable
option because of local or distant spread, palliative stenting may be performed
endoscopically to relieve the obstruction and decompress the ducts. The patency
of the stent may be monitored with ultrasound scanning by assessing the degree
of dilatation of the ducts. Clinical suspicion of early obstruction should be
raised if the serum alkaline phosphatase is elevated, (often more sensitive in
the early stages than a raised serum bilirubin). In the presence of ductal
dilatation on ultrasound, further imaging, such as CT or MRCP, may then refine
the diagnosis.
Intrahepatic tumours causing biliary obstruction
:
Focal masses which cause segmental intrahepatic duct dilatation are usually
intrinsic to the duct itself, for example cholangiocarcinoma. It is also
possible for a focal intrahepatic mass, whether benign or malignant, to compress
an adjacent biliary duct, causing subsequent obstruction of that segment. This
is not, however, a common cause of biliary dilatation and occurs most usually
with hepatocellular carcinomas. Most liver metastases deform rather than
compress adjacent structures and biliary obstruction only occurs if the
metastases are very large and/or invade the biliary tree. A hepatocellular
carcinoma or metastatic deposit at the porta hepatis may obstruct the common
duct by squeezing it against adjacent extrahepatic structures. Benign
intrahepatic lesions rarely cause ductal dilatation, but occasionally their
sheer size obstructs the biliary tree.
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