Intrahepatic ducts and branching variants
The architectonics of the biliary tract in the liver is described based on the Couinaud segment system and the Healey and Schroy classification. The classic pattern of common hepatic duct (CHD) formation is as follows: the right anterior and right posterior sectoral ducts merge to form the right hepatic duct (RHD). In turn, the RHD joins the left hepatic duct (LHD) to form the CHD.
However, a typical bifurcation is not always present. It is important for the radiologist to recognize the following anatomical variants:
- Trifurcation (about 12% of cases): simultaneous merging of the three main ducts at a single point.
- Aberrant drainage of the right sector (28% of cases): the right sectoral duct crosses the porta hepatis zone and drains directly into the left system. Most commonly, this is the right posterior duct (22%), less frequently the anterior one (6%).
- Low insertion: the right posterior duct descends parallel to the extrahepatic pathways and drains directly into the CHD or even into the cystic duct. This anatomical feature dramatically increases the risk of inadvertent duct transection during surgery.
Anatomy of the cystic duct and gallbladder
The cystic duct (ductus cysticus) normally connects with the middle third of the CHD, forming the common bile duct. On ultrasound, the border between them cannot always be clearly visualized, so the umbrella term "common duct" is frequently used. The cystic duct may join the common duct from the right, the left (encircling it anteriorly or posteriorly), and may also drain anomalously low, which can lead to its misidentification as the common bile duct.
Accessory ducts are of particular surgical importance:
- Luschka ducts (subvesical ducts): run in the liver parenchyma near the gallbladder fossa, lacking a connection to the portal vein.
- Cystohepatic ducts: directly drain bile from the liver into the gallbladder or its duct.
The gallbladder itself is also prone to anomalies. True duplication or agenesis are extremely rare (less than 0.1%). The "phrygian cap"—a septum in the fundus region—is detected much more frequently. Positional variants include intrahepatic localization (in acute cholecystitis, it can mimic a liver abscess) and a left-sided position (situs inversus, Winslow foramen hernias, or true location beneath the left lobe).
Diagnostic imaging methods
The choice of biliary tract imaging method depends on the clinical objective and preserved hepatocyte function.
- Ultrasound (US). First-line method. Performed after a 4-hour fast for adequate gallbladder filling. Dynamic evaluation with changes in body position helps differentiate mobile calculi from fixed polyps. The extrahepatic bile duct is visualized anteriorly to the portal vein as a tubular structure without blood flow on Doppler imaging.
- Contrast-enhanced ultrasound (CEUS). Based on the intravenous administration of gas microbubbles, which resonate and generate harmonic frequencies. The method is safe in renal failure, provides strong enhancement, and is ideal for the differential diagnosis of sludge and tumor.
- Magnetic resonance cholangiopancreatography (MRCP). A non-contrast technique based on heavily T2-weighted images, where stationary fluid (bile) produces a high signal. The main advantage is that the method is excretion-independent and performs exceptionally well in patients with jaundice.
- CT intravenous cholangiopancreatography (CT-IVC). Requires intravenous infusion of an iodine-containing agent excreted in bile. Provides direct visualization of bile fistulas. The main disadvantage: the method is uninformative in obstructive jaundice (if bilirubin levels exceed normal by two or more times).
Endoscopic retrograde cholangiopancreatography (ERCP) and percutaneous transhepatic cholangiopancreatography (PTC) have yielded their diagnostic role to MRCP in modern practice. Today, they are predominantly interventional methods.
Briefly: answers to topical questions
What is the normal diameter of the common bile duct in millimeters?
The normal diameter of the common bile duct (choledochus) is up to 8 mm. Its size varies considerably depending on the patient's age and history of prior surgeries. In patients with jaundice, a diameter greater than 7 mm often serves as a predictor of obstruction. In elderly individuals, a diameter greater than 8 mm is a common finding, and following cholecystectomy, the duct size frequently exceeds 10 mm.
How is the extrahepatic bile duct visualized on ultrasound in relation to the portal vein and the proper hepatic artery?
On ultrasound, the extrahepatic bile duct (extrahepatic bile duct) is visualized as a tubular structure located anterior to the portal vein (portal vein). When color Doppler mapping is applied, no blood flow is detected within this structure. Information regarding the visualization of the duct in relation to the proper hepatic artery is not provided in the supplied materials.
Which liver segments according to the Couinaud classification are drained by the left hepatic duct?
The left hepatic duct (left hepatic duct) drains bile from segments II, III, and IV of the liver. According to the Couinaud classification (Couinaud), the branching of the left intrahepatic bile duct system is formed precisely by the ducts of segments II, III, and IV. Knowledge of this segmental anatomy is paramount for diagnostics and surgical planning.
What types of bile duct cysts exist according to the Todani classification?
According to the Todani classification, five types of bile duct cysts are distinguished:
- Type I (choledochal cyst) — choledochal cyst, occurs in 79% of cases.
- Type II — diverticulum of the extrahepatic duct, accounts for 3%.
- Type III (choledochocele) — choledochocele, observed in 4% of cases.
- Type IV — multiple cysts, which can be both intrahepatic and extrahepatic (13%).
- Type V (Caroli disease) — Caroli disease, occurs in 1% of cases.
Class and exam questions
Which imaging modality should be chosen in severe obstructive jaundice?
The optimal method is non-contrast MRCP. Unlike CT cholangiography, it relies on the characteristics of the fluid itself (bile) in the T2 sequence and does not require the affected liver to secrete a contrast agent.
What are Luschka ducts and why must they be kept in mind?
These are subvesical intrahepatic bile ducts not accompanied by a portal vein branch. Due to their close proximity to the gallbladder fossa, they are frequently injured during cholecystectomy, leading to postoperative bile leakage.
What artifacts can simulate stones on MRCP?
Local signal loss due to metallic surgical clips, gas within the ducts, or rapid-flow artifacts from bile. However, flow artifacts are typically centrally located within the duct and have less distinct margins than true calculi.
What complication is the most frequent during ERCP?
The most frequent significant complication following endoscopic retrograde cholangiopancreatography is the development of acute pancreatitis.
What else to study on this topic
- Gallbladder diseases: imaging findings of acute cholecystitis
- Benign biliary pathology and strictures
- Tumor pathology: hilar cholangiocarcinoma
- Interventional methods in the biliary system
- Application of hepatobiliary contrast agents in MRI (gadoxetic acid disodium)
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