Normal anatomy and imaging technique
To obtain a high-quality image of the hepatobiliary area, preparation is critical: preliminary fasting allows the gallbladder to expand maximally and reduces the volume of interfering gas in the stomach and intestines.
Normally, the ductal system has a typical branching pattern: the right posterior and anterior sectoral ducts (RPSD and RASD) merge into the right hepatic duct (RHD). This, in turn, joins the left hepatic duct (LHD), which collects bile from segments II, III, and IV. Together they form the common hepatic duct (CHD). Anatomical variations sometimes occur, such as trifurcation or aberrant drainage of the posterior duct directly into the left system.
During scanning, the extrahepatic bile ducts appear as tubular structures without internal blood flow (confirmed by Doppler), located anterior to the portal vein. Local tenderness upon probe pressure in this projection is classified as a positive US Murphy's sign.
Diagnosis of cholelithiasis
Gallstones (gallstones) are found in approximately 15% of adult patients, while in the vast majority of cases (about 80%) they are asymptomatic. Most often they consist of cholesterol, and less frequently of calcium bilirubinate (pigment stones).
Ultrasound diagnostics demonstrate a sensitivity of over 95% in detecting calculi. The main diagnostic criteria are:
- Presence of hyperechoic foci in the lumen.
- A clear acoustic shadow forms behind the foci.
- The formations shift when the patient's body position changes (gravitational mobility).
If the gallbladder is entirely packed with stones, the "double-arc" sign (double-arc shadow) is formed on the screen: two curved parallel echo lines separated by a fluid strip, followed by a dense acoustic shadow.
Another distinct entity is LPAC syndrome — cholelithiasis associated with low phospholipid levels. This is a genetic defect (ABCB4 gene mutation) that leads to reduced cholesterol solubility. The disease often manifests before the age of 40 and is characterized by a recurrent course with intrahepatic stone formation.
Congenital anomalies: cysts and biliary atresia
In infants with prolonged jaundice, ultrasound helps exclude critical malformations. In biliary atresia, the intrahepatic ducts are not dilated, and a fibrous cord—the so-called triangular cord sign—is visualized in the porta hepatis. Meanwhile, the gallbladder itself is small (about 10 mm), and the hepatic artery is dilated to over 2 mm.
Another group of pathologies is choledochal malformations associated with pancreatic juice reflux due to a common channel. An extrahepatic duct diameter greater than 4 mm in an infant is a marker of surgical pathology.
| Classification type | Ultrasound and MRI findings |
|---|---|
| Type 1 | Fusiform or saccular dilation of the extrahepatic ducts |
| Type 2 | Diverticulum-like cystic protrusion from the common bile duct |
| Type 3 | Choledochocele (protrusion into the duodenal lumen) |
| Type 4 | Combined dilation of the intrahepatic and extrahepatic bile ducts |
Complications in immunocompromised children
Pediatric oncology patients undergoing therapy frequently develop specific hepatobiliary tract disorders.
Gallbladder changes: sludge or freely mobile stones that may resolve spontaneously are often detected. When inflammation develops, acalculous cholecystitis is typically diagnosed—edema and wall thickening accompanied by local tenderness.
Liver and vascular changes:
- Steatosis: focal hyperechoic areas, often clustered around the porta hepatis.
- Fibrosis and siderosis: increased overall echogenicity of the parenchyma; siderosis also yields low signal intensity on MRI due to iron overload.
- Veno-occlusive disease: a severe syndrome involving the sinusoids. On ultrasound, it manifests as hepatomegaly, reversed portal flow, periportal edema, and high resistance indices (RI) in the arteries.
Additionally, neutropenic patients may develop typhlitis (inflammation of the cecum), where ultrasound clearly visualizes the thickened intestinal wall.
To differentiate structures of the porta hepatis, always use color Doppler: the extrahepatic bile duct is located anterior to the portal vein and never shows color flow since it contains no blood flow.
Class and exam questions
What is the "double-arc" sign?
This is the classic sonographic appearance of a gallbladder entirely filled with calculi. Two parallel curved hyperechoic lines (the wall and stone surface) with a thin fluid layer between them and a strong shadow behind are visible on the monitor.
Which ultrasound finding is considered key for biliary atresia in infants?
The most specific is the triangular cord sign—the presence of dense fibrous tissue in place of undeveloped extrahepatic ducts in the porta hepatis region.
What does lymphomatous involvement of the liver look like on ultrasound?
The picture is extremely non-specific, however, hepatosplenomegaly and a mottled parenchymal pattern often described as a "salt-and-pepper appearance" may be observed.
What else to study on this topic
- Magnetic resonance cholangiopancreatography (MRCP) in choledochal cysts
- Assessment of the biliary confluence using CT cholangiography
- Endoscopic ultrasound (EUS) to search for distal causes of obstruction
- Radioisotope hepatobiliary scintigraphy with HIDA agents
- Follow-up T-tube cholangiography after surgical revision of the common bile duct
- Abdominal manifestations of cystic fibrosis: meconium ileus and viscous secretions
Master the entire topic in the "Diagnostic Radiology" course
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- Complete study guide on "Liver and Gallbladder Ultrasound" and 2,199 more pages of the subject
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Other topics in the section "Diagnostic Radiology of the Abdominal Organs"
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.