Biliary Atresia Indicators - When Bile Ducts Are Not Dilated

If bile ducts are not dilated, the following ultrasound features should be assessed for biliary atresia:

• Hilar plaque: A hyperechoic triangular area at the bile duct confluence with a thickness >4 mm, representing fibrosis and obliteration of the extrahepatic bile ducts.
• Gallbladder abnormalities: Small gallbladder (<15 mm), thickened and possibly irregular wall, or a complete absence of the gallbladder on imaging.
• Hilar cystic anomalies: Microcyst at the hilar plaque or macrocyst within the hepatic pedicle, which may indicate residual cystic structures within an atretic biliary system.
• Polysplenia syndrome anomalies: Associated anomalies include polysplenia or asplenia, preduodenal portal vein, inferior vena cava abnormalities, situs inversus, midline liver, and short pancreas. 

Differential Diagnoses - When Bile Ducts Are Dilated

• Biliary Lithiasis:
  • Can occur at any age, including intrauterine life.
  • Risk factors: Hemolysis (sickle cell disease, hereditary spherocytosis), infection, dehydration, cirrhosis, cystic fibrosis, Wilson's disease, parenteral nutrition, and certain medications such as ceftriaxone.
  • Sonographic findings: Hyperechoic foci with posterior acoustic shadowing within the bile ducts.
  • Complications: Cholecystitis, bile duct obstruction, and biliary pancreatitis. 
• Biliary Malformations and Choledochal Cysts:
  • Result from a biliopancreatic junction anomaly characterized by an abnormally long junction, leading to cystic dilation of the common bile duct.
  • Classified into Todani types; type I (saccular/fusiform dilation) is most common in children, while type IV (multiple cystic dilations) can extend into the intrahepatic ducts.
  • Best visualized on US and confirmed by MRCP.
  • Complications: Biliary stasis, stone formation, pancreatitis, and an increased risk of cholangiocarcinoma in later life.
• Extrinsic Compression and Intrabiliary Tumors:
  • Bile ducts may be compressed by external structures such as a digestive duplication cyst, pancreatic pseudocyst, or lymphadenopathy.
  • Tumors (rare in children) include rhabdomyosarcoma, which may present as an intraductal mass causing obstruction.
  • Imaging with US and MRCP aids in differentiating extrinsic versus intrinsic causes. Contrast-enhanced MR imaging may be required for characterization.
• Cholangitis:
  • Can occur in association with inflammatory bowel disease, Langerhans cell histiocytosis, or autoimmune hepatitis.
  • Ultrasound findings include bile duct wall thickening and increased periductal echogenicity.
  • Primary sclerosing cholangitis (PSC), although rare in young children, may present with beading and irregularity of the bile ducts, best assessed by MRCP.

Management and Prognosis

Biliary atresia, if suspected, necessitates urgent surgical intervention with Kasai portoenterostomy to establish bile flow. If successful, it delays the need for liver transplantation; however, many children eventually require transplantation due to progressive cirrhosis.

Choledochal cysts often require surgical excision with bile duct reconstruction to prevent complications such as cholangitis and malignancy.

Gallstones in children may be managed conservatively unless symptomatic, requiring cholecystectomy.