Gastrointestinal and Hepatobiliary · Biliary tract · Todani 1977 with 2003 refinement

Todani Classification of Choledochal Cysts

An anatomical classification of congenital bile duct cysts based on the site, extent and morphology of intrahepatic and extrahepatic biliary dilatation.

Purpose

To classify congenital bile duct cysts according to the anatomical distribution and morphology of biliary dilatation, thereby guiding imaging description and surgical planning.

Type	Distribution	Morphology	Key distinction
IA	Extrahepatic bile duct	Marked cystic dilatation of the entire extrahepatic bile duct	Intrahepatic ducts are not primarily involved
IB	Focal segment of the extrahepatic bile duct	Localised segmental or saccular dilatation	Normal-calibre extrahepatic duct is present proximal and distal to the cyst
IC	Entire extrahepatic bile duct	Smooth fusiform or cylindrical dilatation	Often associated with pancreaticobiliary maljunction and may extend smoothly towards the hepatic ducts
II	Extrahepatic bile duct	True diverticulum arising from the duct wall	Communicates with an otherwise normal-calibre bile duct through a neck
III	Intramural distal common bile duct	Cystic dilatation protruding into the duodenum	Also called a choledochocele
IVA	Intrahepatic and extrahepatic bile ducts	Multiple cystic, fusiform or irregular dilatations	Both components of the biliary tree are involved
IVB	Extrahepatic bile ducts only	Multiple segmental or cystic dilatations	No primary intrahepatic duct involvement
V	Intrahepatic bile ducts only	Segmental or diffuse saccular intrahepatic duct dilatation	Corresponds to Caroli disease; association with congenital hepatic fibrosis denotes Caroli syndrome

How to use it

Type I is subdivided into IA, IB and IC according to the morphology and extent of extrahepatic duct dilatation.
Type III is an intraduodenal choledochocele rather than a conventional extrahepatic duct cyst.
Type IVA involves both intrahepatic and extrahepatic ducts, whereas type IVB is confined to multiple extrahepatic segments.
Type V represents communicating intrahepatic duct ectasia and should be distinguished from non-communicating hepatic cysts.
MRCP is generally preferred for non-invasive demonstration of the full biliary distribution and pancreaticobiliary junction.

Common mistake

Do not label every case with intrahepatic duct dilatation as type IVA. Type IVA requires true cystic or disproportionate intrahepatic duct involvement accompanying an extrahepatic cyst; ordinary upstream dilatation caused by distal obstruction does not establish type IVA.

Exam pearl

Remember the anatomical sequence: type I is a single extrahepatic dilatation, type II a diverticulum, type III a choledochocele, type IV multiple dilatations and type V isolated intrahepatic disease.

Viva questions

What is the basis of the Todani classification?: It classifies congenital bile duct cysts according to the site, extent and morphology of intrahepatic and extrahepatic biliary dilatation.
What are the principal Todani types?: Type I is extrahepatic duct dilatation, type II is an extrahepatic diverticulum, type III is a choledochocele, type IV comprises multiple biliary dilatations and type V is isolated intrahepatic duct ectasia.
How are type I choledochal cysts subdivided?: Type IA is marked cystic dilatation of the entire extrahepatic duct, type IB is a focal segmental dilatation and type IC is diffuse fusiform or cylindrical extrahepatic duct dilatation.
What is a type III choledochal cyst?: Type III is cystic dilatation of the intramural distal common bile duct protruding into the duodenum, termed a choledochocele.
How do type IVA and type IVB differ?: Type IVA involves multiple dilatations of both the intrahepatic and extrahepatic ducts, whereas type IVB has multiple dilatations confined to the extrahepatic ducts.
What is Todani type V disease?: Type V is segmental or diffuse saccular dilatation confined to the intrahepatic bile ducts and corresponds to Caroli disease.
What is the difference between Caroli disease and Caroli syndrome?: Caroli disease denotes isolated intrahepatic bile duct ectasia, whereas Caroli syndrome combines this duct abnormality with congenital hepatic fibrosis.
What is an important imaging pitfall when diagnosing type IVA disease?: Secondary intrahepatic duct dilatation caused by distal obstruction should not be mistaken for type IVA. True type IVA shows intrinsic cystic or disproportionate involvement of both the intrahepatic and extrahepatic ducts.