Structure
Bile leaves the liver in the right and left hepatic ducts, which unite at the porta hepatis to form the common hepatic duct. The common hepatic duct runs down in the free edge of the lesser omentum and is joined from the right by the cystic duct. Below that junction the duct is the common bile duct.
Common bile duct
The common bile duct is described in four parts:
- Supraduodenal: in the free edge of the lesser omentum, to the right of the hepatic artery proper and in front of the portal vein.
- Retroduodenal: behind the first part of the duodenum, with the gastroduodenal artery to its left.
- Pancreatic: in a groove or tunnel on the back of the head of the pancreas.
- Intraduodenal: running obliquely through the wall of the second part of the duodenum, where it usually joins the main pancreatic duct.
The joined ducts form a short dilated channel, the hepatopancreatic ampulla (of Vater), which opens on the major duodenal papilla on the posteromedial wall of the second part of the duodenum. The hepatopancreatic sphincter (of Oddi) is smooth muscle around the ampulla, with separate sphincters around the terminal bile duct and pancreatic duct. The accessory pancreatic duct, when present, opens at the minor papilla slightly higher.
Gallbladder
The gallbladder is a pear-shaped sac in a fossa on the visceral surface of the liver, described as fundus, body and neck. The fundus projects below the inferior border of the liver. The neck narrows into the cystic duct, whose mucosa forms a spiral fold. A dilatation of the neck where stones often lodge is called Hartmann's pouch.
Relations and Calot's triangle
The hepatocystic triangle (Calot's triangle) is bounded by the cystic duct, the common hepatic duct and the inferior surface of the liver. It contains the cystic artery, the cystic lymph node and, often, the right hepatic artery. Calot's original description used the cystic artery rather than the liver as the upper border, which is why both versions appear in textbooks.
In the free edge of the lesser omentum, which forms the front of the epiploic foramen, the common bile duct lies on the right, the hepatic artery proper on the left and the portal vein behind both.
Behind the duodenum the duct is related to the inferior vena cava, and in the pancreatic head it lies close to the gastroduodenal and posterior superior pancreaticoduodenal arteries. The gallbladder lies against the first part of the duodenum and the transverse colon, which is where a gallstone fistula forms.
Blood supply and innervation
The gallbladder is supplied by the cystic artery, which usually arises from the right hepatic artery within Calot's triangle. Its origin is variable: it may come from the left hepatic, common hepatic or gastroduodenal artery, or be double. Cystic veins pass directly into the liver or join the portal vein.
The supraduodenal bile duct is supplied by small axial vessels running along its sides at roughly the 3 and 9 o'clock positions. Most of their flow comes from below, from the gastroduodenal and posterior superior pancreaticoduodenal arteries, so stripping tissue off the duct risks an ischaemic stricture.
Nerves reach the tree through the coeliac plexus, carrying sympathetic fibres and pain afferents, and from the vagus. Contraction of the gallbladder is mainly hormonal: cholecystokinin released by fat in the duodenum contracts it and relaxes the sphincter. Biliary pain is felt in the epigastrium and right upper quadrant, often radiating to the back near the right scapula.
Clinical relevance
Most clinical problems of the biliary tree come from gallstones and from injury during cholecystectomy.
- Bile duct injury: mistaking the common bile duct for the cystic duct is the classic error. The critical view of safety requires Calot's triangle to be cleared so that only two structures, the cystic duct and cystic artery, are seen entering the gallbladder.
- Anatomical variants include a low or parallel cystic duct insertion, a cystic duct draining into the right hepatic duct, and an aberrant right hepatic duct, all of which raise the risk of injury.
- Mirizzi syndrome is obstruction of the common hepatic duct by a stone impacted in Hartmann's pouch or the cystic duct.
- Gallstone pancreatitis follows a stone blocking the ampulla, where bile and pancreatic ducts share a channel.
- Courvoisier's law: in a jaundiced patient, a palpable non-tender gallbladder is unlikely to be due to stones and suggests a malignant distal obstruction.
- Hilar cholangiocarcinoma (Klatskin tumour) arises at the confluence of the hepatic ducts.
On the specimen
This station asks for the whole duct system from the hepatic ducts to the papilla, and it also uses a magnetic resonance cholangiopancreatography (MRCP) image.
- Find the cystic duct first. Above its junction the duct is the common hepatic duct; below it, the common bile duct. Pins on either side of the junction test exactly this.
- Right or left hepatic duct: the right is short and runs in from the right lobe; the left is longer and more horizontal, crossing under the quadrate lobe.
- Main pancreatic duct: runs through the length of the gland from tail to head and meets the bile duct at the duodenal wall.
- Second part of the duodenum: the descending C-shaped loop; the papilla and sphincter region sit on its medial wall.
On MRCP, which uses heavily T2-weighted images, still fluid is bright. The ducts appear as white branching tubes, the gallbladder as a bright pear-shaped sac and the pancreatic duct as a thin horizontal line crossing the head and body of the pancreas. Fluid in the duodenum may also be bright, which helps locate the papilla.