Diagnostic Ultrasound - Abdomen and Pelvis

Biliary System
Anatomy: Abdomen
TERMINOLOGY
Abbreviations
• Extrahepatic biliary structures
○ Gallbladder (GB)
○ Cystic duct (CD)
○ Right hepatic (RH) and left hepatic (LH) ducts
○ Common hepatic duct (CHD)
○ Common bile duct (CBD)
Definitions
• Proximal/distal biliary tree
○ Proximal refers to portion of biliary tree that is in closer
in proximity to liver and hepatocytes
○ Distal refers to caudal end closer to ampulla and bowel
• Central/peripheral
○ Central refers to biliary ducts close to porta hepatis
○ Peripheral refers to higher-order branches of
intrahepatic biliary tree extending into hepatic
parenchyma
IMAGING ANATOMY
Overview
• Biliary ducts carry bile from liver to duodenum
○ 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
○ Hepatocytes form bile → bile canaliculi → interlobular
biliary ducts → collecting bile ducts → right and left
hepatic ducts → common hepatic duct → common bile
duct → intestines
• Common bile duct forms in free edge of lesser omentum
by union of cystic duct and common hepatic duct
○ Length of duct: 5-15 cm, depending on point of junction
of cystic and common hepatic ducts
○ Descends posterior and medial to duodenum, lying on
dorsal surface of pancreatic head
○ Joins with pancreatic duct to form hepaticopancreatic
ampulla of Vater
○ Ampulla opens into duodenum through major duodenal
(hepaticopancreatic) papilla
○ Distal common bile duct is thickened into sphincter of
Boyden and hepaticopancreatic segment is thickened
into a sphincter of Oddi
– Contraction of these sphincters prevents bile from
entering duodenum; forces it to collect in GB
– Relaxation of sphincters in response to
parasympathetic stimulation and cholecystokinin
(released by duodenum in response to fatty meal)
• Vessels, nerves, and lymphatics
○ Arteries
– Hepatic arteries supply intrahepatic ducts
– Cystic artery supplies proximal common duct
– RH artery supplies middle part of common duct
– Gastroduodenal and pancreaticoduodenal arcade
supply distal common duct
– Cystic artery supplies GB (usually from right hepatic
artery; variable)
○ Veins
– From intrahepatic ducts → hepatic veins
– From common duct → portal vein (in tributaries)
– From GB directly into liver sinusoids, bypassing portal
vein
○ Nerves
– Sensory: Right phrenic nerve
– 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
○ Lymphatics
– Same course and name as arterial branches
– Collect at celiac lymph nodes and node of omental
foramen
– Nodes draining GB are prominent in porta hepatis and
around pancreatic head
• Gallbladder
○ ~ 7-10 cm long, holds up to 50 mL of bile
○ Lies in shallow fossa on visceral surface of liver
○ Vertical plane through GB fossa and middle hepatic vein
divides left and right hepatic lobes
○ May touch and indent duodenum
○ Fundus is covered with peritoneum and relatively
mobile; body and neck attached to liver and covered by
hepatic capsule
○ Fundus: Wide tip of GB, projects below liver edge
(usually)
○ Body: Contacts liver, duodenum, and transverse colon
○ Neck: Narrowed, tapered, and tortuous; joins cystic duct
○ Cystic duct: 3-4 cm long, connects GB to common
hepatic duct; marked by spiral folds of Heister; helps to
regulate bile flow to and from GB
• Normal measurement limits of bile ducts
○ CBD/CHD
– < 6-7 mm in patients without history of biliary disease
in most studies
– Controversy about dilatation related to previous
cholecystectomy and old age
○ Intrahepatic ducts
– Normal diameter of 1st and higher-order branches < 2
mm or < 40% of diameter of adjacent portal vein
– 1st (i.e., LH duct and RH duct) and 2nd-order branches
are normally visualized
– Visualization of 3rd and higher-order branches is often
abnormal and indicates dilatation
ANATOMY IMAGING ISSUES
Imaging Recommendations
• Patient should fast for at least 4 hours prior to US
examination to ensure GB is not contracted after a 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
20