Paediatric Imaging

Choledochal cyst

developmental anomalies of the extrahepatic biliary tract, leading to focal or generalised dilatation of the common duct. They are not associated with generalized abnormalities of the liver parenchyma. The aetiology is controversial; some may be congenital and others arise because of abnormalities of the insertion of the pancreatic duct into the distal bile duct, allowing reflux of pancreatic secretions into the common bile duct and so causing inflammation and ectasia.

Presentation is either in infancy following antenatal diagnosis or with obstructive jaundice, or later in childhood with jaundice, pain and sometimes a palpable mass. Sonography will demonstrate a cystic structure related to the porta hepatis and often its relationship to the common duct. It is thin walled and is anechoic unless sludge, calculi or infection supervene. There may be minor dilatation of the proximal parts of the left and right hepatic ducts but there is no significant dilatation of the intrahepatic bile ducts. The size of the cyst is variable.

Cholangiography (Fig.1) (percutaneous, endoscopic retrograde or MRCP) will demonstrate focal or generalized dilatation of the bile duct and its relationship to the intrahepatic and pancreatic ducts. Cross-sectional imaging shows a cystic structure in the right upper quadrant (Fig.2).

Choledochal cysts have several typical appearances and have been classified into three main types. A type 1 cyst involves fusiform dilatation of the whole of the common bile duct; a type 2 cyst focal ectasia or diverticulum formation in part of the common duct; and type 3 a cystic structure in the medial wall of the duodenum. See cyst choledochal

Treatment is surgical and is performed because of the risk of complications which increase with age and include infection and calculus formation because of biliary stasis. There is a small but definite risk of malignant bile duct tumours in patients with choledochal cysts. Treatment involves resection of the affected portion of the duct, with an appropriate anastomosis.

DG

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Fig.1

Radiograph taken after percutaneous cholangiography. Note the fusiform (type 1) dilatation of the right and left hepatic ducts and two thirds of the common bile duct and normal intrahepatic ducts. In this child, the pancreatic duct is inserted into the distal common bile duct.
Choledochal cyst, Fig.1
Choledochal cyst, Fig.2