**Core Concept**
The patient's condition is likely due to a choledochal cyst, a congenital anomaly of the bile ducts leading to dilation and increased risk of cholangitis. Treatment involves surgical intervention to correct the anomaly and prevent future complications.

**Why the Correct Answer is Right**
The treatment of choice for choledochal cysts is surgical excision of the cyst, typically via a Roux-en-Y hepaticojejunostomy. This procedure involves removing the cyst and reconnecting the bile duct to a loop of jejunum, allowing bile to drain normally. This approach prevents the risk of future cholangitis and malignancy associated with the cyst. The surgery is performed to eliminate the cyst and prevent long-term complications.

**Why Each Wrong Option is Incorrect**
**Option A:** ERCP with sphincterotomy may be used to manage symptoms in the short term but is not a definitive treatment for choledochal cysts.
**Option B:** Liver transplant may be considered in cases of advanced disease or malignancy but is not the primary treatment for choledochal cysts.
**Option C:** Conservative management with antibiotics and supportive care may be used in the short term but does not address the underlying anatomical issue and is not a long-term solution.

**Clinical Pearl / High-Yield Fact**
Choledochal cysts are congenital anomalies that can be associated with an increased risk of malignancy, and surgical excision is the treatment of choice to prevent future complications.

**Correct Answer:** C. Roux-en-Y hepaticojejunostomy.