A 58-year-old man with chronic NSAID use presents to the emergency department with sudden-onset severe generalised abdominal pain that began 4 hours ago. He lies completely still, is shocked (BP 88/52, HR 124), and has a rigid, board-like abdomen with generalised tenderness, guarding, and rebound tenderness. Bloods show WBC 24,000/mm³, lactate 5.8 mmol/L, and metabolic acidosis. An erect posteroanterior chest radiograph is obtained. The structure marked **A** in the diagram shows crescentic free air beneath both hemidiaphragms. What is the most likely diagnosis and primary pathology?

Question

Accepted Answer

B. Perforated peptic ulcer causing pneumoperitoneum and generalised peritonitis. ## Why "Perforated peptic ulcer causing pneumoperitoneum and generalised peritonitis" is right

The clinical presentation of sudden-onset severe epigastric pain that rapidly spreads to the entire abdomen (especially right lower quadrant due to gastric contents tracking down the right paracolic gutter), combined with signs of peritonitis (rigid board-like abdomen, guarding, rebound tenderness, absent bowel sounds), septic shock (fever, tachycardia, hypotension, elevated lactate and WBC), and the erect chest radiograph finding of crescentic free air beneath both hemidiaphragms (marked **A**) is pathognomonic for hollow viscus perforation. In a patient with a 20-year history of chronic NSAID use and a previous endoscopic diagnosis of gastric ulcer, perforated peptic ulcer is the most likely diagnosis. The erect posteroanterior chest radiograph is the most sensitive plain film for detecting free intraperitoneal gas (capable of detecting as little as 1 mL of air after 5–10 minutes of upright positioning), and the sharply delineated crescentic lucency beneath both hemidiaphragms (marked **A**) is the classic radiological sign of pneumoperitoneum. Management requires emergency exploratory laparotomy with omental patch repair and peritoneal lavage (Sartelli M et al. WSES guidelines for management of intra-abdominal infections. World J Emerg Surg 2017;12:29).

## Why each distractor is wrong

- **Acute pancreatitis with retroperitoneal gas dissection**: Acute pancreatitis does not typically cause pneumoperitoneum (free intraperitoneal air). Gas dissection in pancreatitis is retroperitoneal and would not produce the bilateral crescentic free air pattern beneath both hemidiaphragms. Additionally, the clinical presentation of sudden-onset epigastric pain with rapid spread to the entire abdomen and signs of generalised peritonitis is more consistent with hollow viscus perforation than pancreatitis alone.

- **Boerhaave syndrome with oesophageal perforation**: While oesophageal perforation can cause pneumoperitoneum and presents with sudden severe chest/epigastric pain, it typically follows forceful vomiting or retching and is associated with subcutaneous emphysema and mediastinitis. The patient's history of NSAID use with a known gastric ulcer, and the clinical picture of peritonitis with septic shock, makes perforated peptic ulcer far more likely.

- **Ruptured abdominal aortic aneurysm with gas-forming organism infection**: While a ruptured AAA can present with shock and abdominal pain, pneumoperitoneum from gas-forming organisms is rare and would require a pre-existing infection. The clinical context of chronic NSAID use with a known peptic ulcer history makes peptic ulcer perforation the far more likely diagnosis.

**High-Yield:** Erect posteroanterior chest radiograph is the most sensitive plain film for pneumoperitoneum; crescentic free air beneath both hemidiaphragms (marked **A**) is the classic sign of hollow viscus perforation, most commonly perforated peptic ulcer in NSAID users.

[cite: Sartelli M et al. WSES guidelines for management of intra-abdominal infections. World J Emerg Surg 2017;12:29.]

Answer

A. Ruptured abdominal aortic aneurysm with gas-forming organism infection

Answer

C. Boerhaave syndrome with oesophageal perforation

Answer

D. Acute pancreatitis with retroperitoneal gas dissection

Explanation

Why "Perforated peptic ulcer causing pneumoperitoneum and generalised peritonitis" is right

Why each distractor is wrong

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