The gallbladder lies at the equator between the right and left hemiliver, an imaginary line known as Cantlie’s line or the Rex-Cantlie line coursing between segments 4b and 5, through the bed of the gallbladder towards the vena cava posteriorly. The gallbladder is mostly peritonealized, except for its posterior surface which lies on the cystic plate, a fibrous area on the underside of the liver.

The proportion if its circumference varies, from a pedicled gallbladder with little to no contact with the cystic plate to a mostly intrahepatic gallbladder surrounded by liver parenchyma. The gallbladder carries no muscularis mucosa, no submucosa, and a discontinuous muscularis and only carries a serosa on the visceral peritonealized surface. These anatomical specificities facilitate the direct invasion of gallbladder cancer into the liver. This is why the surgical treatment of gallbladder cancer mandates a radical cholecystectomy, which includes resection of a wedge of segments 4b and 5, when the T stage is higher or equal to T1b. From the body of the gallbladder, a conical infundibulum becomes a cystic duct that extends as the lower edge of the hepatocystic triangle towards the porta hepatis and joins with the common hepatic duct (CHD) to form the CBD. As in the rest of the biliary system, variation is the rule when it comes to the cystic duct confluence with the CHD. It can variably run parallel to it for a distance prior to inserting or spiral behind it and insert on its medial aspect. It can variably insert into the RHD or the RPD, the latter in 4% of livers and particularly when the RPD inserts into the CHD (i.e., below the left-right ductal confluence). This configuration is notorious for exposing the RPD to a risk of injury at the time of cholecystectomy. Rare variations of gallbladder anatomy, including gallbladder duplication and gallbladder agenesis, are also described but are rare. The CBD courses anterolaterally within the hepatoduodenal ligament, usually to the right of the hepatic artery and anterolaterally to the portal vein. However, hepatic arterial anatomy can vary, and when an accessory or replaced hepatic artery is present arising from the superior mesenteric artery, the accessory or replaced vessel courses lateral to the CBD. In its conventional configuration, the right hepatic artery crosses posteriorly to the RHD as it heads towards the right liver, but 25% of the time it crosses anteriorly. These anatomical variants are all relevant to developing a sound surgical strategy to treat hilar CCA. Of note, while left hepatic artery anatomy can also be quite variable, rarely does it affect surgical decision-making in CCA to the same degree as right hepatic artery anatomy.

Distally, the CBD enters the head of the pancreas, joining the pancreatic duct to form the hepatopancreatic ampulla. Just distal to this is the sphincter of Oddi, which controls emptying of ampullary contents into the second portion of the duodenum. When the junction of the CBD and the pancreatic duct occurs before the sphincter complex, reflux of pancreatic enzymes into the biliary tree can lead to chronic inflammatory changes and anatomical distortion resulting in choledochal cysts, known risk factors for the development of CCA. Unlike the rest of the liver parenchyma, which receives dual supply from the arterial and portal venous circulation, the biliary tree is exclusively alimented by the arterial system. The LHD and RHD are alimented respectively by the left hepatic artery and right hepatic artery, which can frequently display replaced, accessory, and aberrant origins – the left artery arising conventionally from the hepatic artery proper but alternatively from the left gastric artery and the right hepatic artery arising from the hepatic artery proper but also variably from the superior mesenteric artery. In hilar CCA, variable combinations of hepatic arterial anatomy and tumor location can either favor resectability or make a tumor unresectable.

Within the hilum of the liver, a plexus of arteries connects the right and left hepatic arteries. Termed the “hilar epicholedochal plexus,” this vascular network provides collateral circulation that can maintain arterial supply to one side of the liver if the ipsilateral vessel is damaged. The preservation of arterial blood supply to the liver remnant is crucial, particularly when creating an enterobiliary anastomosis. Its absence leads to ischemic cholangiopathy and liver abscesses that can be difficult to treat. The CBD receives arterial supply inferiorly from paired arterioles arising from the gastroduodenal artery and the posterior superior pancreaticoduodenal artery, the most important and constant arterial supply to the distal CBD. Proximally the CBD is alimented by paired arterioles of the right hepatic artery. These vessels, known as the marginal arteries, run in parallel to the CBD, laterally and medially to it. Denuding the CBD of this arterial supply risks stricture formation after choledochoenteric anastomosis.

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References : https://bit.ly/3fOmcv2