**Core Concept**
The Schwartz operation, also known as the Schwartz procedure, is a surgical technique used to manage a specific type of congenital anomaly involving the biliary system. It involves the creation of a new biliary-enteric anastomosis to restore bile flow.

**Why the Correct Answer is Right**
The Schwartz operation is specifically performed in cases of choledochal cysts, a rare congenital condition characterized by the dilation of the bile ducts. This procedure involves the complete removal of the choledochal cyst and the creation of a Roux-en-Y hepaticojejunostomy to ensure proper bile drainage into the small intestine. The Schwartz procedure is a preferred method for managing choledochal cysts due to its low risk of complications and high success rate in preventing recurrence.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the Schwartz operation is not typically performed for gallstones, which are a separate entity that may require cholecystectomy or other treatments.
**Option B:** This option is incorrect because the Kasai procedure is a different surgical technique used for the treatment of biliary atresia, not choledochal cysts.
**Option C:** This option is incorrect because the hepaticojejunostomy is indeed a component of the Schwartz procedure, but it is not the primary reason for performing the surgery; rather, it is a key step in restoring bile flow.

**Clinical Pearl / High-Yield Fact**
It's essential for surgeons to carefully evaluate patients with suspected choledochal cysts, as these anomalies are often associated with an increased risk of malignancy and other complications.

**Correct Answer:** D