A 62-year-old man with a history of peptic ulcer disease presents with acute severe epigastric pain and rigid abdomen. Plain abdominal radiograph shows pneumoperitoneum. Which radiographic finding best distinguishes a perforated peptic ulcer from a perforated viscus due to bowel obstruction?

Explanation

## Distinguishing Perforated Peptic Ulcer from Perforated Bowel in Obstruction ### Key Radiographic Differences **Key Point:** The critical discriminator is the pattern of bowel gas and dilatation, not pneumoperitoneum alone — both conditions present with free air. | Feature | Perforated Peptic Ulcer | Perforated Bowel (Obstruction) | |---------|------------------------|--------------------------------| | **Pneumoperitoneum** | Present (often large volume) | Present (usually smaller) | | **Bowel Dilatation** | Minimal to absent | Marked (dilated loops) | | **Air-Fluid Levels** | Few or none | Multiple, prominent | | **Rigler's Sign** | Prominent (both sides of bowel wall) | May be present but with dilated loops | | **Onset** | Sudden (acute perforation) | Gradual (obstruction then rupture) | ### Clinical Pearl **Clinical Pearl:** In a perforated peptic ulcer, the stomach or duodenum perforates acutely, releasing a large bolus of gastric air into the peritoneum. The small bowel distal to the perforation remains relatively decompressed and non-dilated because there is no preceding obstruction. Rigler's sign (visualization of both sides of the bowel wall due to air on both luminal and peritoneal surfaces) is classically described with normal or minimally dilated bowel loops. In contrast, when a bowel loop perforates secondary to obstruction, the proximal bowel is already dilated with multiple air-fluid levels from the obstructive process. The pneumoperitoneum is usually smaller because perforation occurs late. ### High-Yield Mnemonic **Mnemonic:** **PUPU** — **P**erforated **U**lcer = **P**erforation **U**nexpected (no prior obstruction) → minimal dilatation, large free air. **Obstructed then ruptured** = dilated loops first, then rupture → multiple air-fluid levels. ### Why Rigler's Sign Matters Here Rigler's sign (double wall sign) is seen in both, but the presence of Rigler's sign **with normal bowel caliber and minimal air-fluid levels** is pathognomonic for perforated peptic ulcer. The absence of obstructive features is the key discriminator. [cite:Robbins 10e Ch 17]