A 68-year-old man with a 40-pack-year smoking history and newly diagnosed type 2 diabetes presents with progressive painless jaundice, dark urine, pale stools, and 9 kg weight loss over 6 weeks. Examination reveals scleral icterus, a palpable non-tender distended gallbladder, and excoriations from pruritus. CA 19-9 is markedly elevated at 1,850 U/mL. Multiphasic contrast-enhanced CT of the abdomen is shown. The structure marked **A** in the diagram represents a hypoenhancing mass in the pancreatic head with ill-defined infiltrative margins. Based on the clinical presentation, imaging findings (including the double-duct sign), and the hypoattenuating nature of the structure marked **A**, what is the most likely diagnosis?

Question

Accepted Answer

B. Pancreatic adenocarcinoma with metastatic disease. ## Why Pancreatic adenocarcinoma with metastatic disease is right

The hypoenhancing (hypoattenuating) mass marked **A** in the pancreatic head, combined with the classic double-duct sign (simultaneous dilatation of the common bile duct and main pancreatic duct), progressive painless jaundice, markedly elevated CA 19-9 (>1,000 U/mL), Courvoisier sign (palpable gallbladder in jaundice), new-onset diabetes in an elderly patient, and imaging evidence of liver metastases and vascular encasement, is pathognomonic for pancreatic adenocarcinoma. The hypoattenuating appearance reflects the hypovascular nature of pancreatic ductal adenocarcinoma relative to normal pancreatic parenchyma. According to NCCN guidelines (Tempero et al. 2021), this constellation of findings—particularly the double-duct sign with a hypoenhancing head mass—is the classic imaging signature of pancreatic head cancer causing obstructive jaundice. EUS-guided FNA confirmed adenocarcinoma histologically.

## Why each distractor is wrong

- **Pancreatic neuroendocrine tumor with local invasion**: Neuroendocrine tumors typically enhance more homogeneously and avidly than adenocarcinoma; they do not classically present with the double-duct sign or such markedly elevated CA 19-9 (>1,000). They are also much rarer and less likely to cause painless obstructive jaundice with this clinical syndrome.
- **Acute pancreatitis with pseudocyst formation**: Acute pancreatitis presents with acute severe epigastric pain, elevated amylase/lipase, and diffuse pancreatic edema on imaging. A pseudocyst would not cause the double-duct sign, would not elevate CA 19-9 to 1,850 U/mL, and would not present with progressive painless jaundice over 6 weeks or liver metastases.
- **Pancreatic ductal obstruction from benign stricture**: Benign strictures (from chronic pancreatitis, trauma, or post-surgical changes) do not produce a discrete hypoenhancing mass, do not elevate CA 19-9 to oncologic levels (>1,000), and do not cause liver metastases or vascular encasement. The ill-defined infiltrative margins of structure **A** are incompatible with benign obstruction.

**High-Yield:** The double-duct sign (simultaneous CBD and MPD dilatation) + hypoattenuating head mass + painless jaundice + CA 19-9 >1,000 = pancreatic adenocarcinoma until proven otherwise.

[cite: Tempero MA et al. Pancreatic Adenocarcinoma, Version 2.2021, NCCN Clinical Practice Guidelines. J Natl Compr Canc Netw 2021;19(4):439-457.]

Answer

A. Pancreatic ductal obstruction from benign stricture

Answer

C. Pancreatic neuroendocrine tumor with local invasion

Answer

D. Acute pancreatitis with pseudocyst formation

Explanation

Why Pancreatic adenocarcinoma with metastatic disease is right

Why each distractor is wrong

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