Choledochal Cyst

Diagnosis requires excluding other causes of biliary dilatation, including tumor, stone, or stricture

Commonly associated with cholelithiasis, cystolithiasis, choledocholithiasis, and hepatolithiasis

• Classified into 5 types based on Todani classification

Type I: Fusiform/cystic dilation of extrahepatic duct

Type II: True diverticulum of supraduodenal ED

Type III: Dilation limited to intraduodenal segment of ED (a.k.a. choledochocele), with dilated segment of duct located within duodenal wall

Type IV: Presence of multiple biliary cysts, at least 1 of which must involve extrahepatic bile duct

Type V: Single or multiple intrahepatic biliary cysts, with multiple intrahepatic cysts known as Caroli disease

PATHOLOGY

• Etiology may be related to anomalous pancreaticobiliary junction or congenital ductal plate malformation

CLINICAL ISSUES

• Most common in female patients, often of Asian descent

• Usually diagnosed in infancy and childhood

• Classic triad of symptoms: Recurrent RUQ pain, jaundice, and palpable mass

• Complications: Stones, cholangitis, pancreatitis, or malignant degeneration (cholangiocarcinoma or gallbladder cancer)

• Treatment varies depending on type of choledochal cyst, but type I and IV cysts typically undergo surgical excision and reconstruction by Roux-en-Y hepaticojejunostomy

(Left) This graphic shows the Todani classification of choledochal cysts. Note that type I is fusiform dilation of the extrahepatic duct (ED). Type II is a true diverticulum of the supraduodenal ED. Type III is an isolated choledochocele. Type IV is fusiform dilation of the extrahepatic duct and intrahepatic ducts, and type V is synonymous with Caroli disease.

(Right) Coronal CECT reformation of a type I choledochal cyst shows fusiform dilatation of the extrahepatic duct . Type I lesions are the most common type of choledochal cyst.

(Left) Curved multiplanar CECT reformation along the length of the extrahepatic duct shows a small choledochocele protruding into the duodenal lumen and mild dilation of the common bile duct . This is either a type III or IVb choledochal cyst, depending on whether the ED is considered to be involved.

(Right) Coronal MRCP in the same patient nicely shows the choledochocele protruding into the duodenal lumen and the mildly dilated extrahepatic duct , along with numerous stones in the gallbladder .

TERMINOLOGY

Synonyms

• Biliary cyst

Definitions

• Congenital segmental cystic dilatation of intrahepatic or extrahepatic bile ducts, most commonly affecting main portion of extrahepatic duct (ED)

IMAGING

General Features

• Best diagnostic clue

MR cholangiopancreatography (MRCP): Fusiform dilatation of bile duct

• Location

Most commonly affects extrahepatic CD (80-90%)

• Size

Varies from 2-15 cm

• Morphology

• Rare disorder usually diagnosed in infancy and childhood, but is most common congenital lesion of large bile ducts

Often coexists with other cystic and fibrotic disorders of liver (e.g., Caroli disease, biliary hamartomas, congenital hepatic fibrosis)

• Segmental cystic dilatation of bile ducts with dilated segments maintaining communication with biliary tree

Diagnosis requires excluding other causes of biliary dilatation, including tumor, stone, or stricture

Commonly associated with cholelithiasis, cystolithiasis (stones within choledochal cyst), choledocholithiasis, and hepatolithiasis

Most commonly classified into 5 different types based on Todani classification

– 2003 modification of Todani classification incorporates presence of abnormal pancreaticobiliary junction (APBJ)

– Type I: Solitary fusiform or cystic dilation of extrahepatic bile duct (ED)

Type Ia: Cystic dilation of entire ED; associated with abnormal pancreaticobiliary junction (APBJ)

Type Ib: Focal dilation of ED (often distal); no association with APBJ

Type Ic: Fusiform dilation of entire ED; associated with APBJ

Most common type, constituting 50-85% of choledochal cysts

Much more common in females than males (3:1) and may present with pain, jaundice, or gallstone formation (due to bile stasis)

Differentiate from distal obstruction of ED (e.g., stone or tumor) or mild normal dilatation of ED after cholecystectomy

Mild dilation of right and left ducts may blur distinction with type IVa

– Type II: True diverticulum of supraduodenal ED

Very rare, accounting for only 2% of cases

Only a few reports of type II choledochal cysts in literature

– Type III: Dilation limited to intraduodenal segment of ED (a.k.a. choledochocele), with dilated segment of ED located within duodenal wall

Type IIIa: Cystic dilation of intraduodenal ED

Type IIIb: Diverticulum of intraduodenal ED

Constitutes 1-5% of cases

Cyst may be lined by either duodenal or biliary epithelium

Large choledochoceles may obstruct duodenum, present with jaundice, or cause pancreatitis

– Type IV: Presence of multiple biliary cysts, at least 1 of which must involve extrahepatic bile duct

IVa: Involvement of both intrahepatic and extrahepatic ducts; 2nd most common overall, comprising 40% of cases diagnosed in adults

IVb: Multiple extrahepatic cysts with no intrahepatic cysts

Constitutes 15-35% of cases

– Type V: Single or multiple intrahepatic biliary cysts, with presence of multiple intrahepatic cysts known as Caroli disease

No involvement of extrahepatic duct

Radiographic Findings

• Radiography

Upper gastrointestinal series

– Anterior displacement of 2nd part of duodenum and antrum

– Inferior displacement of duodenum

– Widening of duodenal sweep

• ERCP: Considered gold standard modality for diagnosis of choledochal cysts

Accurate means of evaluating pancreaticobiliary junction

May have trouble delineating some portions of biliary tree in cases with coexistent strictures

CT Findings

• Nonenhancing cystic structure (types I, II, or IV) in porta hepatis contiguous with biliary tree

Multiplanar images critical for establishing contiguity of cyst with biliary tree

• Cystic intramural mass within wall of proximal duodenum communicating with CBD (type III)

• Multiple intrahepatic cysts in close contiguity with intrahepatic bile ducts (type IV)

MR Findings

• Best noninvasive modality for assessing biliary tree, choledochal cysts, and anomalous pancreaticobiliary junction

• MRCP images nicely demonstrate cystic dilatation of biliary tree and relationship (and communication) of cysts with adjacent bile ducts

• Choledochal cysts should mirror signal intensity of normal bile ducts (hypointense on T1WI, hyperintense on T2WI, and no perceptible wall enhancement on T1WI C+)

• Presence of abnormal wall hyperenhancement or thickening should raise concern for superinfection or malignancy (particularly with nodular or irregular wall thickening)