**Core Concept**
ERCP (Endoscopic Retrograde Cholangiopancreatography) is an endoscopic procedure used to diagnose and treat problems in the bile and pancreatic ducts. Urgent ERCP is indicated in specific situations where there is a high risk of complications or the need for immediate intervention.

**Why the Correct Answer is Right**
The correct answer is **B. Walled-off necrosis**. Walled-off necrosis is a complication of acute pancreatitis where a collection of dead pancreatic tissue is walled off by a fibrotic capsule. This can lead to infection and abscess formation, which may require urgent drainage. ERCP with stent placement can be used to drain the collection and prevent further complications.

**Why Each Wrong Option is Incorrect**
**Option A:** Pancreatic pseudocyst is not an indication for urgent ERCP, as it can be managed conservatively or with endoscopic or surgical drainage.

**Option C:** Gallstones are a common cause of pancreatitis, but they are not an indication for urgent ERCP unless there is a biliary obstruction or suspected bile duct injury.

**Option D:** Hyperamylasemia is a marker of pancreatitis, but it is not an indication for urgent ERCP.

**Clinical Pearl / High-Yield Fact**
Walled-off necrosis is a complication of acute pancreatitis that requires urgent intervention to prevent infection and abscess formation. ERCP with stent placement can be used to drain the collection and prevent further complications.

**Correct Answer: B. Walled-off necrosis**