**Core Concept**
A choledochal cyst is a congenital anomaly of the bile duct characterized by a cystic dilatation of the intrahepatic or extrahepatic bile ducts. The treatment of choice involves surgical excision to prevent complications such as malignancy, infection, and pancreatitis.

**Why the Correct Answer is Right**
The surgical excision of a choledochal cyst involves a complete resection of the cystic structure along with a Roux-en-Y hepaticojejunostomy to restore bile flow. This approach minimizes the risk of malignancy and reduces the incidence of future complications. The excision should be performed by experienced surgeons, often in a pediatric or general surgical department, as it requires a thorough understanding of the anatomy and potential complications.

**Why Each Wrong Option is Incorrect**
**Option A:** **Cystic drainage and internal stenting** may be a temporary measure to alleviate symptoms but is not a definitive treatment for choledochal cysts.
**Option B:** **Endoscopic retrograde cholangiopancreatography (ERCP)** can be used for diagnostic purposes but is not suitable for definitive treatment due to the risk of bile duct injury.
**Option C:** **Watchful waiting** is not recommended as it can lead to complications such as cholangitis, pancreatitis, and malignancy.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that a choledochal cyst should be treated surgically, ideally within the first two years of life to prevent potential complications. The surgical approach should be tailored to the individual patient based on the location, size, and complexity of the cyst.

**Correct Answer:** C. Surgical excision with Roux-en-Y hepaticojejunostomy.