Choledochal cyst in childhood: US and MRI findings

A 4-year-old female presented to the Emergency Department (ED) for cramp-like abdominal pain in right upper quadrant lasting for two months, getting worse a few weeks before. No jaundice. No palpable abdominal mass.

The patient underwent ultrasound (US) scan in the ED showing common bile duct dilation with a maximum calibre of 24 mm and marked gallbladder ectasia. Not remarkable intrahepatic biliary tree dilation. No ascites. (Fig.1)

After surgical consult, she underwent a Magnetic Resonance Cholangiopancreatography (MRCP) with intravenous sedation and no contrast agent injection. The exam identified a fusiform dilation of the distal tract of the common bile duct and ectatic common hepatic duct without a definite cause of obstruction, dilation of the gallbladder and mild dilated cystic duct with tortuous course. In the lumen of the fusiform distal tract dilation, a small amount of sludge was identified. No lesions of pancreas head, liver, kidney, adrenal glands and spleen were shown. No increased lymph nodes. No ascites. (Fig 2)

Then the patient underwent surgical removal of the common bile duct dilatation, cholecystectomy and reconstruction of the common bile duct.  A follow-up US scan revealed no remarkable findings and normal diameter of the intrahepatic bile ducts.

Choledochal cysts are a group of rare congenital diseases that manifest as focal or diffuse cystic dilation of the biliary tree. Approximately 75% of the patients are diagnosed in childhood and the female-to-male ratio is 3-1 [1,2]. The origin of this disorder is related to anomalies of the pancreaticobiliary ductal junction.

The most widely used classification system divides choledochal cyst into five subtypes according to Todani and it is based on cholangiographic morphology [3]. In our case, we report a Type Ia, which represent the most common subtype and is characterized by fusiform dilation of the entire extrahepatic bile duct, along with cylindric dilation of hepatic common duct and cystic duct [4].

Abdominal pain, jaundice and abdominal mass it the classic triad of symptoms, present in 19-60% of cases [5].

US is regarded as the best initial technique to evaluate any patient with jaundice, regardless of age, being able to visualize both intrahepatic and extrahepatic biliary tree. Sonography typically shows a choledochal cyst as a cyst or fusiform structure at the porta hepatis, separate from gallbladder and may show mild ectasis of intrahepatic biliary ducts. The cyst may also contain sludge and stones due to cholestasis or even rarely a solid neoplasm. Use of various scanning and angles allows for depiction of the relationship with the biliary tract, differentiating it from pancreatic pseudocyst or enteric duplication [6].

Computed Tomography (CT) determines the extent of the cyst more accurately than US, but is desirable to save ionizing radiation exposure in childhood [5].

MRCP findings are similar to US with the advantage of better anatomical delineation of the structure of choledochal cyst and biliary ducts before surgery and it is even a suitable replacement for Endoscopic Retrograde Cholangiopancreatography (ERCP). In our case MRCP was helpful to examine biliary tree anatomy and thus reporting a Type I choledochal cyst [6,7].

Surgical resection is advocated because there is a risk of cholangiocarcinoma, as well as stone formation, pancreatitis and bile peritonitis due to cyst rupture. Our patient underwent a Roux-en-Y hepaticojejunostomy through robot-assisted laparoscopy, which is considered the procedure of choice for reconstruction of the common biliary tract in the case of anomalies of the pancreaticobiliary ductal union [6].

In conclusion, Radiologists should be aware of the causes of biliary tree dilation and keep in mind both intrinsic and extrinsic causes, especially neoplasms, and congenital anomalies, which can also occur several years after birth. For this reason, careful US observation of the bile duct is crucial to detect choledochal cysts. MRI findings help to clarify subtypes and are mandatory for surgical planning, with the advantage to avoid ERCP or CT, especially in children [7].