Todani Classification for Choledochal Cysts
The Todani classification is a five-type anatomical system that categorizes choledochal cysts based on the location and morphology of biliary dilatations, with Type I (extrahepatic fusiform dilatation) and Type IV (multiple intra- and extrahepatic cysts) being most common, and Type V representing Caroli disease (isolated intrahepatic bile duct dilatations). 1
Classification System Overview
The Todani classification, which modified the original Alonso-Lej system in 1977, remains the current standard for categorizing bile duct cysts despite some limitations 2, 3, 4. This anatomical framework divides choledochal cysts into five distinct types:
Type I: Extrahepatic Bile Duct Cysts
- Most common type (approximately 80% of cases)
- Fusiform or saccular dilatation of the extrahepatic bile duct
- High malignancy risk (3-7.5%)
- Requires complete surgical excision 3, 4
Type II: Extrahepatic Bile Duct Diverticulum
- True diverticulum arising from the extrahepatic bile duct
- Rare presentation
- Some advocate including cystic duct cysts as a subtype here rather than as a separate Type VI 2
Type III: Choledochocele
- Dilatation of the intraduodenal portion of the common bile duct
- Often managed endoscopically rather than surgically
- Lower malignancy risk compared to Types I and IV 5
Type IV: Multiple Cysts
- Type IV-A: Multiple intra- and extrahepatic cysts (second most common overall)
- Type IV-B: Multiple extrahepatic cysts only
- Requires complete excision of extrahepatic components due to malignancy risk 3, 4, 6
Type V: Caroli Disease
- Isolated intrahepatic bile duct dilatations appearing as saccular or fusiform cystic areas
- Distinguished from Caroli syndrome (which includes congenital hepatic fibrosis and renal cysts)
- Characterized by the "central dot sign" on imaging (fibrovascular bundles within dilated ducts)
- Requires surveillance for cholangiocarcinoma with MRCP every 12 months 1
Clinical Significance and Limitations
While the Todani classification clusters different diseases with varying epidemiology, pathogenesis, and malignancy risk, it remains clinically useful because it is simple, reproducible, and universally recognized 2. This allows for:
- Standardized communication between gastroenterologists, radiologists, and surgeons
- Appropriate comparative analysis between patient series
- Guidance for surgical planning based on anatomical distribution
Key Diagnostic Considerations
The classification guides imaging interpretation, particularly with MRCP being the gold standard for visualizing the complete biliary tree and accurately determining cyst type 1. However, preoperative misdiagnosis occurs frequently, with intraoperative findings sometimes revealing cysts that don't fit neatly into the classification 7.
Management Implications by Type
- Types I and IV: Complete cyst excision mandatory due to high malignancy potential (3-7.5% risk)
- Type III: Endoscopic management often sufficient
- Type V: Surveillance-based approach with annual MRCP for cholangiocarcinoma screening 1, 3, 5
Important Caveats
The classification does not account for differences in pathogenesis, clinical presentation, or therapeutic approaches across types, which has led some clinicians to question its clinical viability 2. Additionally, rare variants like cystic duct cysts were not originally included, creating ongoing debate about whether they constitute a Type VI or should be reclassified as Type II subtypes 2.
Despite these limitations, the Todani classification remains the standard framework for diagnosis, surgical planning, and long-term surveillance of choledochal cysts 2, 3, 7, 5.