**Question:** Saccular diverticulum of extrahepatic bile duct in choledochal cyst is classified as

A. Type I - Takao
B. Type II - Caroli
C. Type III - Alonso-Lej
D. Type IV - Todani

**Correct Answer:** D. Type IV - Todani

**Core Concept:** Choledochal cysts are rare congenital anomalies characterized by the dilation of the extrahepatic bile ducts. These cysts are classified into types based on their anatomical features and distribution.

**Why the Correct Answer is Right:**
Type IV choledochal cysts are a subset of Todani's classification, which is a comprehensive system for classifying choledochal cysts. This classification is based on the extent of involvement of the bile ducts, including the intrahepatic and extrahepatic areas. In Type IV choledochal cysts, the cyst extends into the pancreatic duct and/or involves the common bile duct.

**Why Each Wrong Option is Incorrect:**
A. Type I - Takao: This classification involves cysts limited to the extrahepatic bile ducts without involvement of the pancreatic duct.
B. Type II - Caroli: This classification is for cysts limited to the intrahepatic bile ducts without involvement of the extrahepatic ducts.
C. Type III - Alonso-Lej: This classification is for cysts involving both the intrahepatic and extrahepatic bile ducts but not the pancreatic duct.

**Clinical Pearl:** Understanding the various classifications of choledochal cysts is crucial for proper diagnosis and management. Knowledge of the classification systems helps in determining the extent of involvement and informs surgical planning, such as whether to perform a simple cyst excision or a more complex Whipple's procedure.