**Question:** Most commonly seen Choledochal cyst

**Core Concept:** Choledochal cyst is a rare cystic dilatation of the common bile duct (CBD) caused by the accumulation of bile in the cyst. This condition can lead to complications like cholangitis, pancreatitis, and liver cirrhosis.

**Why the Correct Answer is Right:** Type I choledochal cyst is the most common form, accounting for approximately 80-90% of cases. It is a complete cyst that involves the entire length of the extrahepatic bile ducts (CBD). The cyst typically arises from the right hepatic duct and communicates with the cystic duct.

**Why Each Wrong Option is Incorrect:**

A. Type II cyst: This variant involves the left hepatic duct but not the right. It is less common (10-20% of cases) and does not communicate with the cystic duct.
B. Type III cyst: This type is uncommon (5-10% of cases) and involves both the right and left hepatic ducts. It does not communicate with the cystic duct.
C. Type IV cyst: This variant involves the cystic duct only, and accounts for <5% of cases. D. Type V cyst: This is a combination of Type II and Type IV cysts, which is very rare (1-2% of cases) and accounts for <2% of cases. **Clinical Pearl/High-Yield Fact:** Radiological imaging modalities like ultrasound, MRI, and CT scans are essential in diagnosing choledochal cyst. Surgical management is the gold standard for treating choledochal cyst, which typically involves excision and primary anastomosis or Roux-en-Y hepaticojejunostomy. Early diagnosis and intervention prevent complications like cholangitis, pancreatitis, and liver cirrhosis.