Extrahepatic biliary structures

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  Gallbladder (GB)

  
  
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  Cystic duct (CD)

  
  
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  Right hepatic (RH) and left hepatic (LH) ducts

  
  
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  Common hepatic duct (CHD)

  
  
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  Common bile duct (CBD)

Proximal/distal biliary tree (follows direction of flow)

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  Proximal refers to portion of biliary tree that is closer in proximity to liver and hepatocytes

  
  
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  Distal refers to caudal end closer to ampulla and bowel

Central/peripheral

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  Central refers to biliary ducts close to porta hepatis

  
  
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  Peripheral refers to higher-order branches of intrahepatic biliary tree extending into hepatic parenchyma

Biliary ducts carry bile from liver to duodenum

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  Bile is produced continuously by liver, stored and concentrated by GB, and released intermittently by GB contraction in response to presence of fat in duodenum

  
  
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  Hepatocytes form bile → bile canaliculi → interlobular biliary ducts → collecting bile ducts → right and left hepatic ducts → CHD → CBD → intestines

CBD

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  Forms in free edge of lesser omentum by union of CD and CHD

  
  
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  Length of duct: 5-15 cm, depending on point of junction of cystic and CHD

  
  
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  Descends posterior and medial to duodenum, lying on dorsal surface of pancreatic head

  
  
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  Joins with pancreatic duct to form hepaticopancreatic ampulla of Vater

  
  
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  Ampulla opens into duodenum through major duodenal (hepaticopancreatic) papilla

  
  
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  Distal CBD is thickened into sphincter of Boyden and hepaticopancreatic segment is thickened into sphincter of Oddi

  
  
  
  
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    Contraction of these sphincters prevents bile from entering duodenum; forces it to collect in GB

    
    
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    Relaxation of sphincters in response to parasympathetic stimulation and cholecystokinin (released by duodenum in response to fatty meal)

  
  

Vessels, nerves, and lymphatics

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  Arteries

  
  
  
  
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    Hepatic arteries supply intrahepatic ducts

    
    
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    Cystic artery supplies proximal common duct

    
    
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    RH artery supplies middle part of common duct

    
    
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    Gastroduodenal and pancreaticoduodenal arcade supply distal common duct

    
    
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    Cystic artery supplies GB (usually from RH artery; variable)

  
  
  
  
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  Veins

  
  
  
  
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    From intrahepatic ducts → hepatic veins

    
    
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    From common duct → portal vein (in tributaries)

    
    
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    From GB directly into liver sinusoids, bypassing portal vein

  
  
  
  
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  Nerves

  
  
  
  
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    Sensory: Right phrenic nerve

    
    
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    Parasympathetic and sympathetic: Celiac ganglion and plexus; contraction of GB and relaxation of biliary sphincters is caused by parasympathetic stimulation, but more important stimulus is from hormone cholecystokinin

  
  
  
  
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  Lymphatics

  
  
  
  
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    Same course and name as arterial branches

    
    
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    Collect at celiac lymph nodes and node of omental foramen

    
    
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    Nodes draining GB are prominent in porta hepatis and around pancreatic head

  
  

Gallbladder

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  ~ 7-10 cm long, holds up to 50 mL of bile

  
  
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  Lies in shallow fossa on visceral surface of liver

  
  
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  Vertical plane through GB fossa and middle hepatic vein divides LH and RH lobes

  
  
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  May touch and indent duodenum

  
  
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  Fundus is covered with peritoneum and relatively mobile; body and neck attached to liver and covered by hepatic capsule

  
  
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  Fundus: Wide tip of GB, projects below liver edge (usually)

  
  
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  Body: Contacts liver, duodenum, and transverse colon

  
  
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  Neck: Narrowed, tapered, and tortuous; joins CD

  
  
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  CD: 3-4 cm long, connects GB to CHD; marked by spiral folds of Heister; helps to regulate bile flow to and from GB

Normal measurements

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  CBD/CHD

  
  
  
  
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    < 6-7 mm in patients without history of biliary disease in most studies

    
    
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    Controversy about dilatation related to previous cholecystectomy and old age

  
  
  
  
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  Intrahepatic ducts

  
  
  
  
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    Normal diameter of 1st and higher-order branches < 2 mm or < 40% of diameter of adjacent portal vein

    
    
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    1st- (i.e., LH duct and RH duct) and 2nd-order branches are normally visualized

    
    
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    Visualization of 3rd and higher-order branches is often abnormal and indicates dilatation

  
  

Patient should fast for at least 4-6 hours prior to US examination to ensure GB is not contracted after meal, ideally fasting for 8-12 hours (overnight)

Complete assessment includes scanning liver, porta hepatis region, and pancreas in sagittal, transverse, and oblique views

Subcostal and right intercostal transverse views help align bile ducts and GB along imaging plane for optimal visualization

Usually structures are better assessed and imaged with patient in full-suspended inspiration and in left lateral oblique position

Harmonic imaging provides improved contrast between bile ducts and adjacent tissues, leading to improved visualization of bile ducts, luminal content, and wall

For imaging of gallstone disease, special maneuvers are recommended

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  Move patient from supine to left lateral decubitus position

  
  
  
  
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    Demonstrates mobility of gallstones

    
    
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    Gravitates small gallstones together to appreciate posterior acoustic shadowing

  
  
  
  
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  Set focal zone at level of posterior acoustic shadowing

  
  
  
  
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    Maximizes effect of posterior acoustic shadowing to confirm gallstone(s)

  
  

Overall gain is often lowered to remove reverberation artifact from GB; however, do not set gain too low such that true intraluminal echoes are obscured

Transabdominal US is ideal initial investigation for suspected biliary tree or GB pathology

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  Cystic nature of bile ducts and GB (especially if these are dilated) provides inherently high-contrast resolution

  
  
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  Acoustic window provided by liver and modern state-of-the-art US technology provides good spatial resolution

  
  
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  Common indications of US for biliary and GB disease include

  
  
  
  
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    Right upper quadrant/epigastric pain

    
    
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    Abnormal liver function test or jaundice

    
    
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    Suspected gallstone disease

    
    
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    Pancreatitis

  
  
  
  
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  US plays key role in multimodality evaluation of complex biliary problems

Supplemented by various imaging modalities, including MR/MRCP and CT

Common pitfalls in evaluation of GB

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  Posterior shadowing may arise from GB neck, Heister valves of CD, or adjacent gas-filled bowel loops

  
  
  
  
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    May mimic cholelithiasis

    
    
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    Scan after repositioning patient in prone or left lateral decubitus positions

    
    
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    Make sure to increase transducer frequency when evaluating GB after evaluation of liver

  
  
  
  
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  Food material within gastric antrum/duodenum

  
  
  
  
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    Mimics GB filled with gallstones or GB containing milk of calcium

    
    
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    During real-time scanning, carefully evaluate peristaltic activity of involved bowel with oral administration of water

  
  

Common pitfalls in evaluation of biliary tree

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  Redundancy, elongation, or folding of GB neck on itself

  
  
  
  
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    Mimics dilatation of CHD or proximal CBD

    
    
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    Avoided by scanning patient in full-suspended inspiration

    
    
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    Careful real-time scanning allows separate visualization of CHD/CBD medial to GB neck

  
  
  
  
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  Presence of gas-filled bowel loops adjacent to distal extrahepatic bile ducts

  
  
  
  
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    Obscure distal biliary tree and render detection of choledocholithiasis difficult

    
    
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    Scan with patient in decubitus positions or after oral intake of water

  
  
  
  
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  Gas/particulate material in adjacent duodenum and pancreatic calcification

  
  
  
  
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    Mimic choledocholithiasis within CBD

  
  
  
  
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  Presence of gas within biliary tree

  
  
  
  
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    May mimic choledocholithiasis, differentiated by presence of reverberation artifacts

    
    
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    Limits US detection of biliary calculus

  
  

Direct venous drainage of GB into liver bypasses portal venous system, often results in sparing of adjacent liver from generalized steatosis (fatty liver)

Nodal metastasis from GB carcinoma to peripancreatic nodes may simulate primary pancreatic tumor

Sonography: Optimal means of evaluating GB for stones and inflammation (acute cholecystitis); best done in fasting state (distends GB)

Intrahepatic bile ducts follow branching pattern of portal veins

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  Usually lie immediately anterior to portal vein branch; confluence of hepatic ducts just anterior to bifurcation of right and main portal veins

In patients with obstructive jaundice, US plays key role

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  Differentiates biliary obstruction from liver parenchymal disease

  
  
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  Determines presence, level, and cause of biliary obstruction

Common variations of biliary arterial and ductal anatomy result in challenges to avoid injury at surgery

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  CD may run in common sheath with bile duct

  
  
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  Anomalous RH ducts may be severed at cholecystectomy

Close apposition of GB to duodenum can result in fistulous connection with chronic cholecystitis and erosion of gallstone into duodenum

Obstruction of CBD is common

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  Gallstones in distal bile duct

  
  
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  Carcinoma arising in pancreatic head or bile duct

  
  
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  Result is jaundice due to back up of bile salts into bloodstream

Abnormal embryological development of fetal ductal plate can lead to spectrum of liver and biliary abnormalities, including

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  Polycystic liver disease

  
  
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  Congenital hepatic fibrosis

  
  
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  Biliary hamartomas

  
  
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  Caroli disease

  
  
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  Choledochal cysts