Choledochal cyst is a rare malformation characterized by congenital cystic dilatation of the bile ducts. Classified into 5 types by Todani classification: Type I (most common, 50-80%, fusiform dilatation of common bile duct), Type II (choledochal diverticulum), Type III (choledochocele), Type IV (intra+extrahepatic dilatations), Type V (Caroli disease — isolated intrahepatic). Ductal plate malformation and anomalous pancreaticobiliary junction (APBJ — long common channel) play roles in pathogenesis. Cholangiocarcinoma risk increases with age (10-30% lifetime risk). 3-4 times more common in women, higher prevalence in Asian populations.
Age Range
0-50
Peak Age
25
Gender
Female predominant
Prevalence
Rare
Two main mechanisms drive choledochal cyst formation: (1) Anomalous pancreaticobiliary junction (APBJ) — the pancreatic and bile ducts join outside the sphincter of Oddi creating a long common channel (>15 mm). This arrangement permits reflux of pancreatic fluid into the bile duct, and proteolytic enzymes weaken the duct wall causing cystic dilatation. Pancreatic enzyme reflux causes chronic inflammation and epithelial dysplasia, increasing cholangiocarcinoma risk. (2) Ductal plate malformation — embryonic bile duct remodeling defect causes congenital wall weakness. Imaging reflects fusiform dilatation, wall thickening (chronic inflammation), and enhancement (wall hypervascularity/fibrosis). In Type I, extrahepatic duct dilatation appears at fluid density/signal, while Type IV shows both intra and extrahepatic dilatations.
Fusiform spindle-shaped dilatation of common bile duct on MRCP — cystic dilatation communicating with the biliary tree, continuing with normal-caliber bile duct proximally and distally. Pathognomonic appearance for Todani Type I (most common, 50-80%). CBD diameter typically reaches 20-100+ mm.
Fusiform dilatation of common bile duct on MRCP — Type I shows smooth fusiform dilatation, cystic bile duct continues with normal-caliber duct proximally and distally. CBD diameter typically 20-100+ mm in Todani Type I. APBJ (long common channel) may be visible. MRCP demonstrates entire biliary tree anatomy and is the gold standard for surgical planning.
Report Sentence
MRCP demonstrates marked fusiform dilatation of the common bile duct, with the cyst continuing with normal-caliber bile duct proximally and distally; findings are consistent with Todani Type I choledochal cyst.
Cystic/fusiform dilatation of extrahepatic bile duct on portal venous phase — fluid density (0-20 HU), thin smooth wall, relationship with surrounding structures (duodenum, pancreatic head, portal vein) is evaluated. Thin wall enhancement may be seen. In complicated cases, wall thickening, intracystic debris or stones may be observed.
Report Sentence
Fusiform cystic dilatation of the extrahepatic bile duct with fluid density and smooth thin wall enhancement is noted; consistent with choledochal cyst.
Anechoic/hypoechoic cystic structure in porta hepatis region on US — communicates with bile ducts. Type I shows fusiform dilatation in CBD area, Type II lateral diverticulum, Type III duodenal intramural cystic structure. Secondary intrahepatic bile duct dilatation may be seen. Gallbladder must be separately identified (cyst is not the gallbladder). US is the preferred initial diagnostic method in neonates.
Report Sentence
Anechoic cystic structure communicating with the bile duct is seen in the porta hepatis region; consistent with choledochal cyst.
Markedly hyperintense fusiform dilatation of extrahepatic bile duct on T2-weighted images. Cyst content may be homogeneously hyperintense (clear bile) or heterogeneous (debris, stones, sludge). Cyst wall appears as T2 hypointense thin line. In Type IV, hyperintense dilatations are seen in both intra and extrahepatic portions. Thin-slice axial T2 sequences are important for APBJ evaluation.
Report Sentence
Markedly hyperintense fusiform cystic dilatation of the extrahepatic bile duct is seen on T2-weighted series; consistent with choledochal cyst.
Hyperdense stones or calcified debris within dilated choledochal cyst on non-contrast CT. Stones are usually calcium bilirubinate showing >100 HU density. Wall calcification reflects chronic inflammation. Pancreatic duct dilatation (APBJ related) or pancreatitis findings may accompany.
Report Sentence
Hyperdense stones are seen within the dilated choledochal cyst; consistent with complicated choledochal cyst.
Enhancement of choledochal cyst wall on contrast-enhanced T1-weighted series — thin smooth enhancement suggests chronic inflammation, thick nodular enhancement suggests malignant transformation (cholangiocarcinoma). Wall thickness <3 mm with smooth enhancement is benign, >3 mm with irregular nodular enhancement is suspicious for malignant transformation. Increasing wall enhancement on delayed phase reflects fibrosis.
Report Sentence
Thin smooth enhancement of the choledochal cyst wall is seen on contrast-enhanced series with no evidence of malignant transformation.
Color Doppler US evaluates relationship of cystic structure with vascular structures (portal vein, hepatic artery) and displacement pattern. Choledochal cyst displaces portal vein posteriorly and hepatic artery laterally. Increased vascularity in cyst wall suggests inflammation, irregular neovascularity suggests malignancy.
Report Sentence
Doppler US shows the cystic structure displacing portal vein posteriorly and hepatic artery laterally; consistent with choledochal cyst location.
Criteria
Fusiform (Ia), cystic (Ib), or saccular (Ic) dilatation of common bile duct. Most common type (50-80%). Entire extrahepatic bile duct may be involved. CBD diameter 20-100+ mm. APBJ present in 50-80% of cases.
Distinct Features
Smooth fusiform dilatation on MRCP, gallbladder normal or drains into cyst, progressive tapering of distal CBD.
Criteria
Saccular dilatation arising as a lateral diverticulum from common bile duct. Rare (2-3%). Cyst connects to main bile duct via a stalk. CBD caliber is usually normal.
Distinct Features
Saccular cystic structure extending laterally from CBD on MRCP, main duct caliber preserved.
Criteria
Cystic dilatation of distal CBD herniating into (intramural) duodenal wall. Rare (1-5%). Shows protrusion toward duodenal lumen. Usually small (<30 mm). May be endoscopically visible as cystic structure at papilla.
Distinct Features
Intramural cystic structure within duodenal wall on CT/MRI, communicates with CBD lumen.
Criteria
Cystic dilatation of both intra and extrahepatic bile ducts. Subdivided into Type IVa (intra+extrahepatic, common — 15-35%) and Type IVb (multiple extrahepatic only, rare). Highest cholangiocarcinoma risk is seen in this type.
Distinct Features
Cystic dilatations in both intra and extrahepatic bile ducts on MRCP, distinguished from Caroli disease by presence of extrahepatic component.
Distinguishing Feature
Caroli disease (Todani V) shows isolated intrahepatic saccular dilatation + central dot sign, extrahepatic duct is normal. Choledochal cyst (Todani I-IV) involves extrahepatic duct dilatation.
Distinguishing Feature
In choledocholithiasis, CBD dilatation is secondary to stone obstruction and acquired, usually not fusiform. Choledochal cyst shows congenital fusiform dilatation, APBJ association, and childhood diagnosis as distinguishing features.
Distinguishing Feature
Distal cholangiocarcinoma shows obstructive biliary dilatation + irregular wall thickening/mass in duct. In choledochal cyst, dilatation is congenital, wall is smooth and thin (unless malignant transformation). Nodular wall enhancement suggests malignant transformation.
Distinguishing Feature
Biliary cystadenoma is an intrahepatic multilocular cystic mass without direct communication with biliary tree. Choledochal cyst is dilatation of the bile duct itself and continues with the biliary tree.
Urgency
urgentManagement
surgicalBiopsy
Not NeededFollow-up
specialist-referralTreatment of choledochal cyst is surgical excision + hepaticojejunostomy (Roux-en-Y) with biliary diversion. Cyst should not be left in place — cholangiocarcinoma risk is 10-30% increasing with age. Simple drainage/marsupialization is inadequate and contraindicated. Complete cyst excision is performed in Types I and IVa. Endoscopic sphincterotomy may suffice for Type III. Hepatic resection may be needed in Type IVa. Postoperative follow-up includes annual US/MRI and liver function tests. CA 19-9 monitoring is used for malignant transformation screening.
Choledochal cyst requires surgical excision due to cholangiocarcinoma risk (2.5-28% risk). Standard treatment is cyst excision + hepaticojejunostomy (Roux-en-Y). Drainage alone is insufficient as carcinoma risk persists. Classic triad in children: jaundice, RUQ mass, and abdominal pain.