## **Core Concept**
The main pancreatic duct (MPD) diameter is a key criterion in the diagnosis of chronic pancreatitis using endoscopic ultrasonography (USG). Chronic pancreatitis is characterized by inflammation and fibrosis of the pancreas, leading to ductal dilatation and parenchymal changes.

## **Why the Correct Answer is Right**
The correct answer, , indicates that a main pancreatic duct diameter of less than 2 mm is considered abnormal and suggestive of chronic pancreatitis when using endoscopic USG criteria. Normally, the main pancreatic duct diameter ranges from 3 to 4 mm. A diameter of less than 2 mm, particularly if associated with other features like hyperechoic foci, hyperechoic strands, and lobularity, supports the diagnosis of chronic pancreatitis.

## **Why Each Wrong Option is Incorrect**
* **Option A:** A diameter of more than 3 mm is generally considered within the normal range or not specifically diagnostic for chronic pancreatitis on its own, making it an incorrect criterion for the diagnosis.
* **Option B:** Similarly, a diameter of more than 2 mm but less than 3 mm might not be specifically diagnostic for chronic pancreatitis without other supporting features, making it less accurate.
* **Option D:** A diameter of more than 4 mm could indicate dilatation but is not specific to chronic pancreatitis alone and could be seen in other conditions like pancreatic obstruction.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that endoscopic USG is highly sensitive for detecting early changes of chronic pancreatitis that might not be evident on CT or MRI. The Rosemont criteria, which include features like hyperechoic foci, hyperechoic strands, lobularity, and ductal dilatation, are often used for the diagnosis. A main pancreatic duct diameter of less than 2 mm, in conjunction with these features, supports the diagnosis of chronic pancreatitis.

## **Correct Answer:** .