Ultrasound findings in atresia
In infants with persistent conjugated hyperbilirubinemia, ultrasound is a critical diagnostic step. Typical sonographic findings include the following features:
- Triangular cord sign (triangular cord sign). This is a dense atretic fibrous plate in the area of the porta hepatis (porta hepatis). It represents nothing more than the sclerosed remnant of the extrahepatic biliary tract.
- Gallbladder abnormalities. The organ is typically small (about 10 mm), and its wall has altered structure.
- Absence of dilation. The biliary tract is not dilated.
- Vascular changes. A prominent hepatic artery is observed (diameter exceeding 2 mm in the porta hepatis region).
The clinical value of ultrasound is extremely high. If an infant under three months of age lacks the "triangular cord" sign and has normal gallbladder morphology, this provides a negative predictive value of over 90%. In other words, extrahepatic atresia can be excluded with a high degree of confidence.
Radioisotope studies
Radioisotope diagnostics (scintigraphy) has high sensitivity, but its application is limited by low specificity. False-positive results are recorded in more than 20% of cases.
The problem is that bile excretion and drainage can be impaired in numerous other pathologies unrelated to surgical obstruction. These include metabolic diseases, severe infections, persistent intrahepatic cholestasis, neonatal hepatitis, and the consequences of prolonged total parenteral nutrition.
Malformations and choledochal cysts
The differential diagnosis of atresia includes biliary malformations—conditions in which the ducts are abnormally dilated without signs of acute obstruction. These anomalies can fall within the fibropolycystic spectrum (fibropolycystic spectrum).
About 80% of cases manifest in childhood. Malignant transformation in childhood has not been reported. The overall incidence is 1:100,000 to 1:200,000, but in Japan it is an order of magnitude higher (up to 1:1,000).
For infants younger than 3 months with conjugated jaundice and extrahepatic dilation, a clear differential diagnostic scale based on duct diameter has been developed:
- Less than 3 mm — the pathology is non-surgical in nature.
- 3 to 4 mm — an intermediate value, often indicating inspissated bile syndrome (inspissated bile syndrome).
- Greater than 4 mm — a reliable sign of a choledochal malformation.
It is believed that the pathogenesis of malformations is based on the formation of a common pancreatobiliary channel (visible on ultrasound or MRCP). This anatomical deviation leads to the reflux of pancreatic secretion directly into the common bile duct.
MRCP classification of choledochal cysts
Magnetic resonance cholangiopancreatography (using heavily T2-weighted images) is used for precise anatomical mapping of the biliary tree. Four main types of malformations are distinguished:
- Type 1 (most common): fusiform (fusiform) or spherical dilation of the extrahepatic bile ducts.
- Type 2: a cystic diverticulum originating laterally from the common bile duct.
- Type 3: choledochocele (protrusion of the terminal part directly into the lumen of the duodenum).
- Type 4: combined dilation affecting both the common hepatic duct and the central intrahepatic ducts.
Briefly: answers to topical questions
What types of choledochal cysts are distinguished according to the Todani classification?
The Todani classification includes five main types of cystic biliary disease:
- Type I (Type I) — choledochal cyst presenting as a fusiform or saccular dilation of the common bile duct (the most common variant, accounting for 79%).
- Type II (Type II) — extrahepatic duct diverticulum (3%).
- Type III (Type III) — choledochocele, which is a cystic dilation of the intramural portion of the duct within the duodenal wall (4%).
- Type IV (Type IV) — multiple cysts, including a combination of intra- and extrahepatic ducts (13%).
- Type V (Type V) — Caroli disease, characterized by cystic dilation of the intrahepatic ducts (1%).
What anatomical types of biliary atresia are distinguished according to the Kasai classification?
The classification of biliary atresia identifies the following anatomical types:
- Type I (Type I) — atresia of the common bile duct with fully patent proximal segments.
- Type II (Type II) — atresia of the common hepatic duct.
- Type III (Type III) — atresia of the ducts at the porta hepatis, representing complete obstruction of the extrahepatic biliary tract (the most common variant, occurring in up to 90% of cases).
The "3-4 mm" rule for duct diameter in infants: up to 3 mm — search for a medical cause; greater than 4 mm — suspect a choledochal malformation.
Class and exam questions
What conditions should cystic formations in the porta hepatis of newborns be differentiated from?
Clinically, it is most crucial to rule out the cystic form of biliary atresia. The differential diagnosis also includes duodenal duplication cyst and lymphangioma.
Why do radioisotope studies yield a high rate of false-positive results in atresia?
Because decreased bile excretion occurs in many non-surgical conditions: metabolic diseases, neonatal hepatitis, infections, and during total parenteral nutrition.
What is the "triangular cord" sign?
This is a sonographic sign where a hyperechoic fibrous plate is visualized in the porta hepatis region, representing the remnant of sclerosed and atretic extrahepatic ducts.
What else to study on this topic
- Metabolic diseases and intrahepatic cholestasis in infants
- Inspissated bile syndrome
- Cystic form of biliary atresia
- Gastrointestinal duplication cysts and abdominal lymphangiomas
- Fibropolycystic liver disease spectrum
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