Biliary Normal Variants and Artifacts

Published on 18/07/2015 by admin

Filed under Radiology

Last modified 22/04/2025

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 Left hepatic duct formed by segmental branches from segments II-IV

image Right hepatic duct has 2 branches, including a horizontally oriented anterior branch draining segments V and VIII and a vertically oriented posterior branch draining segments VI and VII
image Right and left hepatic ducts converge at porta hepatis to form common hepatic duct (CHD)
image Cystic duct usually joins CHD just below confluence of right and left hepatic ducts
image Only central intrahepatic ducts seen normally (measuring ≤ 3 mm): Visualization of ↑ intrahepatic ducts concerning for dilated ducts or strictures
• Most common variants

image Usually aberrant right posterior branch which can drain into left hepatic duct (“crossover anomaly”), CHD, common bile duct (CBD), cystic duct, or gallbladder (GB)
image Most frequent: Right posterior duct drains into left duct
image 2nd most common is right posterior duct fusing with lateral (right) aspect of right anterior duct

TOP DIFFERENTIAL DIAGNOSES

• MRCP artifacts may simulate or obscure pathology

image Reconstruction artifacts (with MIP reconstructions)
image Respiratory motion artifacts
image Partial volume effect
image Overestimation of ductal narrowing
image Susceptibility artifacts (e.g., surgical clips, coils)
image Pulsatile vascular compression
image Intraductal mimics of gallstones (gas, flow artifact)
image Spasm of sphincter of Oddi

CLINICAL ISSUES

• Normal biliary variants are common (42% of population)
• No clinical significance unless surgery is planned
• Risk of injury if surgeon is unaware (especially anomalies of cystic duct and right hepatic duct)
image
(Left) Upper left-hand graphic (A) shows the conventional arrangement of the bile ducts. Variations are common, especially with aberrant insertion of the right posterior duct, as seen in figures D-F. This may lead to inadvertent ligation or transection at surgery.

image
(Right) Graphic shows common variations in the course and insertion of the cystic duct, leading to difficulty in isolation and ligation at cholecystectomy. The cystic duct may be mistaken for the common hepatic or common bile duct.
image
(Left) Intraoperative cholangiogram shows a peculiar bilobed cystic dilation of the distal common duct image, presumably a type 3 choledochal cyst or choledochocele. Also noted is aberrant drainage of the posterior lobe bile duct image into the common hepatic duct.

image
(Right) Coronal MRCP with MIP reconstruction demonstrates separate origins of the right anterior and posterior ducts from the common duct. MRCP has a very high concordance with ERCP for identifying biliary tree variants.

TERMINOLOGY

Definitions

• Variants and artifacts that may simulate pathology or potentially complicate hepatobiliary surgical procedures

IMAGING

General Features

• Normal biliary anatomy

image Right hepatic duct (which is typically relatively short) has 2 branches

– Anterior (ventrocranial) branch drains segments VI and VIII and has horizontal course extending lateral and towards right from right hepatic duct
– Posterior (dorsocaudal) branch drains segments VI and VII and has vertical course extending upward from right hepatic duct
– Right posterior duct fuses to right anterior duct from medial approach
image Left hepatic duct formed by segmental branches from segments II-IV
image Bile duct from caudate lobe can join origin of left or right hepatic ducts
image Right and left hepatic ducts converge at porta hepatis to form common hepatic duct (CHD)
image Cystic duct usually joins CHD just below confluence of right and left hepatic ducts
image Only central intrahepatic ducts seen on MRCP in normal patients (≤ 3 mm): Visualization of too many intrahepatic ducts raises concern for ductal strictures or dilatation
• Most common variants

image Most common anatomic variants involve aberrant right hepatic duct

– Occurs in > 10% of general population
– Usually aberrant posterior branch, which can drain into left hepatic duct (“crossover anomaly”), CHD, common bile duct (CBD), cystic duct, or gallbladder (GB)

image Most frequent is right posterior duct draining into left hepatic duct (13-19% of population)
image 2nd most common variant is right posterior duct fusing with lateral (right) aspect of right anterior duct (∼ 12% of population)
– May complicate or preclude living donor right liver transplantation
– May result in bile leak or stricture following cholecystectomy
image Abnormal junction of hepatic ducts

– Trifurcation pattern (“triple confluence”), with single junction of left hepatic duct with anterior and posterior branches of right hepatic duct (11% of population)

image Right hepatic duct nonexistent in this pattern
image Accessory hepatic ducts seen in 2% of patients
image Anomalous insertion of cystic duct

– Low insertion into common duct (10% of population)
– May insert into right hepatic duct
– May insert into medial aspect of common duct
– May follow parallel course to CHD over several cm
– Must be recognized at cholecystectomy to avoid iatrogenic biliary injuries
• Uncommon or rare variations

image Duplication of cystic duct or CBD
image Agenesis of GB (rare, ± other anomalies in 75%)
image Duplication of GB (very rare)
image Cholecystomegaly (enlarged GB)

– Acquired anomaly
– Seen in patients with diabetes, sickle cell disease, or pregnancy, as well as after truncal vagotomy
image Microgallbladder

– Acquired, most often in cystic fibrosis patients
• Pancreaticobiliary junction variants

image Separate entrance of CBD and main pancreatic duct into duodenum
image Long (> 8 mm) common channel of distal CBD and pancreatic duct
image CBD may enter side of pancreatic duct

– > 1.5 cm proximal to ampulla of Vater
– Commonly seen in type I choledochal cyst
– Associated with higher prevalence of cholangiocarcinoma, gallbladder carcinoma, choledocholithiasis, and chronic pancreatitis
• Persistent postoperative dilation of bile ducts

image Affects common duct more commonly than intrahepatic ducts
image Common duct > 8 mm in diameter
image Most common in elderly patients following cholecystectomy
image Especially common in patients who had choledocholithiasis and dilated common duct prior to surgery

– Also seems to occur without precholecystectomy dilation (controversial)

Imaging Recommendations

• Best imaging tool

image ERCP or MRCP

– MRCP is noninvasive but more susceptible to artifacts, which can result in misinterpretation
image CT cholangiography may be performed to define biliary anatomy prior to living right lobe liver transplant donation

– 1st- and 2nd-order bile duct branch opacification diminishes with hepatic dysfunction, increased liver volume, body mass index

DIFFERENTIAL DIAGNOSIS

MRCP Artifacts and Pitfalls

• Reconstruction artifacts

image Frequently a problem with maximum intensity projection (MIP) reconstructions
image Partial volume averaging may obscure small filling defects (e.g., gallstones or polypoid tumors)
image Careful evaluation of source thin-section images can prevent misdiagnosis
image Reviewing thin-section source 3D MRCP images rather than MIP reconstructions or thick-slab 2D MRCP increases accuracy in identifying subtle abnormalities
• Respiratory motion artifacts

image More common in 3D thin-section MRCP due to longer acquisition times

– Particularly problematic on MIP reconstructions
image CBD or main pancreatic duct may appear disconnected, stenotic, dilated, or duplicated due to motion artifact
image Single-shot fast spin echo (SSFSE) images acquired using a much shorter acquisition time and have fewer motion artifacts
• Flow artifact

image Low-signal focus in center of bile duct (rare location for stone)
image Often within dilated duct (such as at point of cystic duct insertion) due to swirling or helical flow of bile
image More common when using single-shot fast spin echo sequences (i.e., HASTE) and less common on sequences acquired with T2 FSE or SSFP technique
image Any potential filling defect should be confirmed on multiple sequences
• Susceptibility artifacts

image Susceptibility artifact from metallic foreign bodies (such as surgical clips, endovascular coils, stents, etc.) produces adjacent signal loss, potentially mimicking stone or filling defect within biliary tree

– New titanium clips do not create susceptibility artifact
image Gas in stomach and duodenum can cause large signal void, covering middle and lower CBD, mimicking biliary stone or obstruction
image Careful evaluation of coronal source images and in-phase gradient echo images (which highlight susceptibility artifact) can prevent misdiagnosis
• Pulsatile vascular compression

image Pulsatile compression of biliary tree by adjacent artery occurs during systole, causing pseudocalculus defect

– Hepatic, cystic, and gastroduodenal arteries traverse biliary tree in their courses
– Most commonly seen due to right hepatic artery crossing CHD or left hepatic duct
– Can also result from motion of anterior wall of IVC near extrahepatic bile duct
image Usually a band-like defect in duct without dilatation of upstream biliary tree
image Most commonly affected sites are CHD, left hepatic duct, and mid CBD
• Fluid in GI tract

image Fluid in stomach or duodenum may overlap biliary tree, obscuring biliary lesions
image Negative oral contrast media (such as ferumoxsil) or routinely acquiring 2D thick-slab MRCP from multiple different angles can help avoid problems
• Intraductal mimics of gallstones

image Pneumobilia, hemobilia, and debris have low signal intensity on MRCP, mimicking gallstones

– T1WI images may be helpful to differentiate among them
– Air-fluid level within duct suggests pneumobilia
• Spasm of sphincter of Oddi

image May simulate distal CBD stone
image Routinely acquiring multiple sequential 2D thick-slab MRCP acquisitions in succession can distinguish true stenosis (which will be unchanged over multiple acquisitions) from temporary spasm (which will open on at least 1 acquisition)
• Overestimation of ductal narrowing

image Due to reconstruction artifact and limited spatial resolution of MRCP
image MRCP depicts biliary tree in physiologic state vs. ERCP depiction of biliary tree under supraphysiologic distention
• Pseudostenosis of pancreatic duct

image In fasting patients, secretion of pancreas is reduced, and normal pancreatic duct may be collapsed segmentally

– No dilatation of upstream pancreatic duct is identified
• Pseudodilatation of CBD

image Long cystic duct running parallel to CHD may be confused for common duct
image Cystic duct and common duct together may appear to represent dilated duct on MIP reconstructions
image Error most common on MIP reconstructions (review source images to prevent misdiagnosis)
image Error can be avoided by reviewing source images (rather than just MIP reconstructions)
• Iodinated contrast material

image Low signal intensity on T2WI and not visualized on MRCP
image Performing MRCP immediately after ERCP may lead to nonvisualization of extrahepatic bile duct and GB
• Impacted distal CBD stone

image Can be missed on MRCP images due to lack of bile around stone
image Ampulla is known difficult location for MRCP, but axial images or MRCP in different planes may help overcome this pitfall

CLINICAL ISSUES

Demographics

• Epidemiology

image Normal biliary variants are common: 42% of population (23% of cholangiograms)
image Do not correlate with hepatic arterial or portal venous anomalies

Natural History & Prognosis

• Usually no clinical significance unless surgery is planned

image Risk of injury if surgeon is unaware (especially anomalies of cystic duct and right hepatic duct)
image Aberrant right hepatic duct may disqualify potential right lobe liver donor

Treatment

• No treatment

DIAGNOSTIC CHECKLIST

Consider

• MIP reconstructions may obscure small biliary filling defects due to partial volume effect 

image MIP reconstructions may also overestimate degree of ductal narrowing and create pseudostenoses
image Image interpretation should not be solely based on MIP reconstructions but also on review of thin-section images as well
• Pulsation artifact from right hepatic artery may mimic stenosis in CHD or left hepatic duct
• Flow artifacts are more common with single-shot fast spin-echo sequences and can mimic stone in center of duct

image Any potential ductal filling defect should be confirmed on other sequences
• MRCP may be difficult to interpret following placement of internal stents or drains, as ducts may be collapsed, filled with gas or blood, or obscured by artifacts from stent

Image Interpretation Pearls

• Careful depiction of biliary anatomy is crucial for planning partial liver transplantation
• Pseudocalculi and other artifacts are common in biliary tree, making familiarity with artifacts critical to avoid unnecessary intervention

image CT may provide complementary information (e.g., presence of gas, clips, vessels in or near bile ducts)

Reporting Tips

• Dilated bile ducts in elderly, post cholecystectomy patient should be correlated with clinical or biochemical evidence of biliary obstruction

image If neither is present, probably no need for additional imaging evaluation
image
(Left) Intraoperative cholangiogram obtained prior to right lobe liver donation shows insertion of the right posterior duct image into the proximal left bile duct image.

image
(Right) Coronal MRCP with MIP reconstruction demonstrates the right posterior duct image arising from the left hepatic duct. This is the most common biliary anatomic variant, and is found in 13-19% of the population.
image
(Left) Coronal 3D reconstruction CT cholangiogram of a potential liver donor shows trifurcation of the common duct into left image, right anterior image, and right posterior image ducts. This anatomy may require more complex biliary reconstruction during transplantation or may preclude donation.

image
(Right) Axial T2WI shows a small signal void in the middle of the distal common duct image. There was no proximal ductal dilation. Flow artifacts like these are more common when using single-shot technique.
image
(Left) Coronal MRCP shows a signal void image in the common hepatic duct that simulates a stone. Note the absence of dilation of the ducts upstream from this point.

image
(Right) MR cholangiogram performed after administration of Eovist in a potential right lobe liver donor shows drainage of the right posterior duct image into the proximal left hepatic duct. Note the pulsation artifact proximal to the bifurcation image and a motion-reconstruction artifact along the mid common duct image.
image
Upper left-hand graphic shows the conventional arrangement of the bile ducts image. Variations are common, especially with aberrant insertion of the right posterior duct, as seen in the other 3 graphics. This may lead to inadvertent ligation or transection at surgery.

image
ERCP cholangiogram shows a low insertion of the cystic duct image into the distal common duct. Note the valves of Heister that impart a “corrugated” appearance of the cystic duct near its junction with the gallbladder.
image
Longitudinal ultrasound image demonstrates a low insertion of the cystic duct image into the distal common bile duct image, very close to the ampulla.
image
Coronal thick-slab MRCP shows low insertion of the cystic duct image into the medial inferior aspect of a choledochal cyst image.
image
Coronal thick-slab MRCP shows a filling defect within the common duct image, above the cystic duct stump image. The signal void is caused by adjacent cholecystectomy clip susceptibility artifact. Note trifurcation of the common hepatic duct.
image
Coronal MRCP shows signal drop-out at the duct bifurcation image due to pulsation artifact from the adjacent right hepatic artery. Note the absence of intrahepatic biliary ductal dilatation.
image
A film from a cholecystogram shows a filling defect image in the distal common duct that simulates a stone. However, a repeat film moments later showed a normal duct. This was caused by a spasm of the sphincter of Oddi.
image
Coronal MRCP with MIP reconstruction demonstrates a band-like defect image in the proximal common duct with no proximal biliary dilatation, characteristic of pulsation artifact from the right hepatic artery.

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