Choledochal Cyst Classification
Choledochal cysts are classified according to the Todani classification system, which categorizes them into five main types based on their anatomical location, morphology, and distribution in the biliary tree. 1
Todani Classification of Choledochal Cysts
Type I (Most Common, 80-90% of cases)
- Type IA: Saccular dilatation of the extrahepatic bile duct
- Type IB: Segmental dilatation of the extrahepatic bile duct
- Type IC: Fusiform dilatation of the entire extrahepatic bile duct
- Type ID: A newer proposed variant involving dilatation of both common bile duct and central portion of cystic duct, giving a bicornal appearance 2
Type II (2-3% of cases)
- Isolated diverticulum protruding from the extrahepatic bile duct
- Appears as a true diverticulum with a narrow neck connection to the main bile duct
Type III (Choledochocele, 1-4% of cases)
- Dilatation of the intraduodenal portion of the common bile duct
- Protrudes into the duodenal lumen
- Often managed endoscopically rather than surgically 3
Type IV (15-20% of cases)
- Type IVA: Multiple cysts/dilatations in both intrahepatic and extrahepatic bile ducts
- Type IVB: Multiple cysts limited to the extrahepatic bile ducts only 1
Type V (Caroli Disease)
- Multiple cystic dilatations limited to the intrahepatic bile ducts
- Distinguished by the characteristic "central dot sign" on imaging, representing fibrovascular bundles within dilated intrahepatic ducts 4
- When associated with congenital hepatic fibrosis and kidney cysts, it's termed "Caroli syndrome" 4
Diagnostic Imaging
The diagnosis and classification of choledochal cysts rely heavily on imaging:
- Ultrasound: First-line imaging modality, especially useful for initial screening
- MRCP (Magnetic Resonance Cholangiopancreatography): Gold standard for diagnosis, providing detailed anatomy of the biliary tree 1
- CT scan: Helpful for evaluating complications and surrounding structures
- ERCP: Can be both diagnostic and therapeutic, especially for Type III cysts
Clinical Significance of Classification
The Todani classification is clinically important because treatment approaches differ based on cyst type:
- Types I and IV: Complete excision of the extrahepatic portion with Roux-en-Y hepaticojejunostomy is recommended due to high malignancy risk 1
- Type II: Complete cyst excision
- Type III: Often managed endoscopically rather than surgically
- Type V: Management depends on extent and complications, may require partial hepatectomy in severe cases
Malignancy Risk
All types of choledochal cysts carry a risk of malignant transformation (3-7.5%), with the highest risk in Types I and IV 5. This risk persists even after resection (approximately 5.6%), primarily during the first 20 years post-resection 1.
Limitations of Current Classification
Some cases of choledochal cysts do not fit neatly into the Todani classification, suggesting the need for potential revision of this system 6. Proper classification is essential for surgical planning and long-term management.
Long-term Surveillance
Due to the persistent risk of malignancy, long-term surveillance is recommended for all patients with choledochal cysts, including:
- Annual liver function tests for 20 years
- Annual CA19-9 measurement
- Biannual ultrasound for 20 years 1
The Todani classification system, while not perfect, remains the most widely used framework for categorizing choledochal cysts and guiding their management to prevent complications including the significant risk of malignant transformation.