A 68-year-old man with a 10-year history of type 2 diabetes presents with painless jaundice and a 3-month history of 8 kg weight loss. On examination, a non-tender, palpable gallbladder is noted. Contrast-enhanced CT pancreas shows a hypodense mass in the pancreatic head with dilation of both the common bile duct and the pancreatic duct (double-duct sign). The structure marked **B** in the diagram represents the dilated pancreatic duct. Which of the following best explains why the pancreatic duct is dilated in this clinical scenario?

Explanation

## Why option 1 is correct The clinical presentation—painless obstructive jaundice, new-onset diabetes in an elderly patient, weight loss, Courvoisier sign (palpable non-tender gallbladder with jaundice), and the imaging finding of a hypodense pancreatic head mass with double-duct sign—is pathognomonic for pancreatic ductal adenocarcinoma. The structure marked **B** (dilated pancreatic duct) is dilated because the tumor obstructs the main pancreatic duct as it traverses the pancreatic head. Pancreatic ductal adenocarcinoma accounts for >85% of pancreatic cancers, with 70% arising in the head. The double-duct sign (simultaneous dilation of the CBD and pancreatic duct) is a classic radiological finding of pancreatic head cancer and is considered diagnostic until proven otherwise. [Harrison 21e Ch 81; Sabiston Surgery 21e] ## Why each distractor is wrong - **Option 2 (Acute pancreatitis)**: While acute pancreatitis can cause ductal dilation, it presents with acute epigastric pain and elevated amylase/lipase. This patient has a chronic presentation with weight loss, jaundice, and a discrete mass on imaging—not acute inflammation. Acute pancreatitis does not produce a hypodense mass or Courvoisier sign. - **Option 3 (Chronic alcohol-related pancreatitis)**: Chronic pancreatitis does cause pancreatic ductal dilation and atrophy, but the presence of a discrete hypodense mass, painless jaundice, and Courvoisier sign point to malignancy, not chronic pancreatitis. Chronic pancreatitis is a risk factor for pancreatic cancer but is not the diagnosis here. - **Option 4 (Pancreatic pseudocyst)**: A pseudocyst can compress the main pancreatic duct, but pseudocysts typically follow acute pancreatitis and present with pain and a fluid collection. This patient has a solid hypodense mass with obstructive jaundice and weight loss, consistent with malignancy, not a pseudocyst. **High-Yield:** Double-duct sign (dilated PD + CBD) = pancreatic head cancer until proven otherwise; painless jaundice + palpable GB = Courvoisier sign = malignant biliary obstruction. [cite: Harrison 21e Ch 81; Sabiston Surgery 21e]