What is the biliary anatomy and its clinical significance?

Biliary Anatomy and Clinical Significance

Anatomical Classification of the Biliary Tree

The biliary system is anatomically divided into intrahepatic and extrahepatic components, with the intrahepatic bile ducts classified by their relationship to hepatic segments and the extrahepatic ducts defined by their position relative to the cystic duct insertion. 1

Intrahepatic Bile Ducts

• Intrahepatic cholangiocarcinoma (iCCA) arises from bile ductules proximal to the second-order bile ducts (segmental bile ducts). 1
• The intrahepatic biliary tree includes large bile ducts (right and left hepatic ducts and their first to third order branches), septal and interlobular bile ducts, and bile ductules, classified by size and location relative to hepatic lobules. 2
• The right and left hepatic ducts converge at the hepatic hilum to form the common hepatic duct. 1

Extrahepatic Bile Ducts

• Perihilar cholangiocarcinoma (pCCA) arises in the right and/or left hepatic duct and/or at their junction (perihilar bile ducts). 1
• Distal cholangiocarcinoma (dCCA) arises from the epithelium distal to the insertion of the cystic duct. 1
• The extrahepatic bile ducts are composed of dense fibrous duct walls lined by columnar biliary epithelium. 2
• The common bile duct extends from the cystic duct insertion to the ampulla of Vater, where it joins the pancreatic duct. 3

Anatomical Variations and Their Frequency

Anatomical variations of the biliary tree occur in approximately 40-50% of patients, with significant implications for surgical safety and diagnostic accuracy. 4, 5

Right Hepatic Duct Variations

• Type A1 (normal anatomy): 61.3% - right anterior and posterior hepatic ducts join to form the right hepatic duct. 6
• Type A2: 14.5% - trifurcation where the right hepatic duct is absent and right anterior and posterior hepatic ducts join directly to the confluence with the left hepatic duct. 6
• Type A3: 13.3% of cases. 6
• Type A4: 6.1% of cases. 6
• Atypical branching patterns occur in 14% of cases. 6

Left Hepatic Duct Variations

• Type B1 (normal anatomy): 76.2% of cases. 6
• Type B2: 15% of cases. 6
• Type B3: 3.7% of cases. 6
• Atypical branching patterns occur in 8% of cases. 6
• Segment IV drainage to both left and right hepatic ducts represents one of the most common variations. 6

Cystic Duct Variations

• Typical cystic duct anatomy is present in only 53.2% of patients. 4
• Variations in cystic duct insertion and course are critical to recognize during cholecystectomy to prevent bile duct injury. 1, 7

Clinical Significance for Surgical Safety

Understanding biliary anatomy is critical for preventing bile duct injury (BDI) during cholecystectomy, which occurs in approximately 0.3-0.7% of laparoscopic cases, with only 25% recognized intraoperatively. 1, 7

The Critical View of Safety (CVS)

The CVS is the gold standard technique for preventing BDI and consists of three mandatory steps: 1

1. Visualization of the hepatocystic triangle with no exposure of the common bile duct. 1
2. Exposure of the lower part of the gallbladder and its separation from the liver bed. 1
3. Visualization of only 2 structures entering the gallbladder: the cystic duct and the cystic artery. 1

High-Risk Anatomical Scenarios

• A short cystic duct increases the risk of common bile duct injury during dissection. 1
• A second cystic artery or large artery posterior to the cystic duct indicates aberrant vascular anatomy requiring careful identification. 1
• Bile draining from a tubular structure other than the gallbladder suggests accessory bile ducts (ducts of Luschka) or aberrant anatomy. 1

Approaches for Exposing Proximal Bile Ducts in Complex Cases

When severe scarring or inflammation obscures the hepatic hilum, four systematic approaches can be used to identify the proximal bile duct stumps: 1

1. Hilar Plate Approach

• Cutting the hilar plate along the posterior edge of liver segment IVb in the hilar transverse groove reveals the top of the hepatic duct junction. 1

2. Upper Hepatic Portal Approach

• When severe scarring prevents hilar plate dissection, dissect through the posterior margin of liver segment IVb superior to the transverse sulcus, extending deeply into liver parenchyma until reaching the hepatic duct confluence. 1

3. Umbilical Vein Fissure Approach

• Cut the liver bridge in the Rex recess after dissecting the umbilical vein plate, exposing the portal vein sagittal plane and cutting the right posterior umbilical vein panel to reveal the left hepatic duct. 1

4. Posterior Hepatic Portal Approach

• Dissect the portal vein from the posterolateral hepatoduodenal ligament, following the anterior wall of the portal vein to the right hepatic pedicle, where the enlarged right proximal hepatic duct is located above this anatomical plane. 1

Vascular Supply and Its Clinical Relevance

The biliary tract is supplied by the peribiliary vascular plexus, with afferent vessels deriving from hepatic arterial branches and drainage into the portal venous system or hepatic sinusoids. 2

• Isolated right hepatic artery injury during cholecystectomy should not be systematically repaired immediately; the benefit/risk ratio must be carefully evaluated. 1
• Vascular injury combined with bile duct injury (vasculobiliary injury) requires delayed repair and should not be attempted intraoperatively. 1

Peribiliary Glands

• Peribiliary glands are found along extrahepatic and large intrahepatic bile ducts, secreting mucinous and serous substances into bile. 2
• Intramural glands drain directly into the bile duct lumen, while extramural glands drain via their own conduits. 2

Ampulla of Vater Anatomy

The ampulla of Vater represents the junction of the pancreatic and distal common bile ducts, with two distinct histological subtypes: 3

• Pancreatobiliary type: arises from biliary epithelium with characteristics similar to cholangiocarcinoma. 3
• Intestinal type: originates from small bowel epithelium with features similar to duodenal or colorectal adenocarcinoma. 3
• These subtypes have distinct clinical courses and management approaches. 3

Imaging Considerations for Biliary Anatomy

MRI/MRCP is superior to ultrasound for detecting biliary pathology and delineating anatomical variations, with sensitivity advantages for cholangiocarcinoma detection. 1

• Advanced imaging with three-dimensional CT reconstructions can accurately define biliary anatomy preoperatively. 8
• Age correlates significantly with common bile duct diameter, an important consideration for interpreting imaging studies. 4

Common Pitfalls in Biliary Surgery

The most critical error is persisting with dissection when anatomy cannot be clearly defined rather than converting to open surgery or using bailout techniques such as subtotal cholecystectomy. 7

• Missing independent openings of the right posterior hepatic duct during high-level bile duct repair causes postoperative recurrent cholangitis requiring reoperation. 1
• Following the principle of "bile duct is three rather than two" prevents missing the right posterior hepatic duct during complex reconstructions. 1
• Conversion to open surgery is not a failure but a valid surgical decision prioritizing patient safety when anatomical clarity cannot be achieved. 7