A 50-year-old man with a heavy alcohol history presents 6 weeks after an episode of acute pancreatitis with persistent epigastric fullness and early satiety. Trans-abdominal ultrasound shows a well-defined, round, anechoic collection (4.5 × 4 cm) with a thin echogenic wall and posterior acoustic enhancement in the lesser sac, as marked **A** in the diagram. CT confirms a fluid-attenuation collection with an enhancing rim and no necrotic debris. Which of the following best describes the pathological composition of the structure marked **A**?

Question

Accepted Answer

D. Fibrous wall of granulation tissue without epithelial lining surrounding pancreatic juice. ## Why "Fibrous wall of granulation tissue without epithelial lining surrounding pancreatic juice" is right

The structure marked **A** is a mature pancreatic pseudocyst, which by definition (Revised Atlanta Classification) forms >4 weeks after acute pancreatitis. The pathophysiology is ductal disruption leaking pancreatic juice into peripancreatic spaces; over 4–6 weeks a fibrous wall of granulation tissue forms around the collection. The critical high-yield distinguishing feature is that a pseudocyst has NO EPITHELIAL LINING — this is what separates it from a true cyst. The clinical presentation (6 weeks post-pancreatitis, imaging showing mature wall with no necrotic debris) confirms pseudocyst rather than acute peripancreatic fluid collection or walled-off necrosis.

## Why each distractor is wrong

- **True cyst with a complete epithelial lining and serous fluid**: True cysts (congenital or acquired) have an epithelial lining; pseudocysts do not. This is the fundamental pathological distinction. True cysts are not associated with pancreatitis.
- **Acute peripancreatic fluid collection with necrotic debris and inflammatory exudate**: At 6 weeks post-pancreatitis, the collection has matured beyond the acute phase (<4 weeks). An acute peripancreatic fluid collection (APFC) lacks necrotic material; if necrosis were present, it would be an acute necrotic collection (ANC). Neither term applies after 4 weeks—the collection becomes a pseudocyst (no necrosis) or walled-off necrosis (with necrosis). The CT here shows no necrotic debris, confirming pseudocyst.
- **Cystic neoplasm with mucinous epithelium and peripheral eggshell calcification**: Mucinous cystic neoplasms are unrelated to pancreatitis and have characteristic imaging (eggshell calcification, high CEA in fluid). The clinical context (pancreatitis 6 weeks prior) and imaging (no calcification, enhancing rim, no solid component) exclude neoplasm.

**High-Yield:** Pseudocyst = fibrous wall WITHOUT epithelial lining; forms >4 weeks post-pancreatitis; true cyst = epithelial lining (not pancreatitis-related).

[cite: Revised Atlanta Classification; ACG Pancreatitis Guidelines]

Answer

A. True cyst with a complete epithelial lining and serous fluid

Answer

B. Acute peripancreatic fluid collection with necrotic debris and inflammatory exudate

Answer

C. Cystic neoplasm with mucinous epithelium and peripheral eggshell calcification

Explanation

Why "Fibrous wall of granulation tissue without epithelial lining surrounding pancreatic juice" is right

Why each distractor is wrong

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