**Core Concept**
Kasai's procedure is a surgical intervention aimed at treating biliary atresia, a condition characterized by the obstruction or absence of the bile ducts. This procedure involves the resection of the affected ducts and the anastomosis of the liver to the intestine to restore bile flow.

**Why the Correct Answer is Right**
The Kasai procedure is specifically performed in infants with biliary atresia to prevent liver cirrhosis and to restore bile flow. The procedure involves the removal of the atretic portions of the bile ducts and the Roux-en-Y hepaticojejunostomy, which allows bile to drain into the intestine. The success of the procedure depends on the age of the patient, with the best outcomes achieved in infants under 3 months of age.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as the Kasai procedure is not performed in adults with biliary atresia. While adults can undergo surgical interventions for biliary atresia, the Kasai procedure is specifically designed for infants.
**Option B:** This option is incorrect as the Kasai procedure is not performed in patients with primary sclerosing cholangitis. While both conditions involve bile duct obstruction, the Kasai procedure is specifically designed to treat biliary atresia.
**Option C:** This option is incorrect as the Kasai procedure is not performed in patients with choledochal cysts. While both conditions involve bile duct abnormalities, the Kasai procedure is specifically designed to treat biliary atresia.

**Clinical Pearl / High-Yield Fact**
The Kasai procedure is most effective in infants under 3 months of age, and the success of the procedure is closely related to the age of the patient at the time of surgery.

**Correct Answer:** D.