**Core Concept**
Choledochal cysts are congenital anomalies of the biliary tree, characterized by a dilatation of the intrahepatic or extrahepatic bile ducts. The pathophysiology involves a developmental defect in the formation of the bile ducts, leading to cystic dilatation.

**Why the Correct Answer is Right**
Excision of the choledochal cyst is considered the ideal treatment due to the risk of malignant transformation and recurrent cholangitis associated with the cyst. This surgical approach involves complete removal of the cyst and repair of the bile ducts to prevent future complications. The goal is to eliminate the cystic structure and prevent its recurrence. In some cases, a Roux-en-Y hepaticojejunostomy may be performed to reconstruct the bile ducts.

**Why Each Wrong Option is Incorrect**
**Option A:** Excision is not always an extrahepatic treatment, as some choledochal cysts may be intrahepatic and require a different surgical approach.
**Option B:** Cystojejunostomy involves creating a connection between the cyst and the jejunum, which is not an ideal treatment as it does not eliminate the cystic structure and may lead to recurrent cholangitis.
**Option D:** Drainage may provide temporary relief but is not a definitive treatment for choledochal cysts, as it does not address the underlying cause of the cystic dilatation.

**Clinical Pearl / High-Yield Fact**
A key aspect of choledochal cyst management is the importance of complete excision to prevent malignant transformation and recurrent cholangitis. This highlights the need for a thorough understanding of the underlying pathophysiology and a meticulous surgical approach.

✓ Correct Answer: C. Excision is ideal t/t.