A 58-year-old man presents to the emergency department with acute onset severe epigastric pain and vomiting. Plain radiograph of the abdomen shows pneumoperitoneum. What is the most common cause of perforation in this clinical presentation?

Explanation

## Most Common Cause of Pneumoperitoneum **Key Point:** Perforated peptic ulcer disease (PUD) accounts for approximately 70–80% of all cases of pneumoperitoneum in developed countries and remains the leading cause globally. ### Clinical Context The acute epigastric pain with vomiting and sudden onset of symptoms is classic for peptic ulcer perforation. The presence of pneumoperitoneum on plain radiograph confirms a hollow viscus perforation. ### Imaging Findings in PUD Perforation - **Free air under diaphragm** on upright CXR or left lateral decubitus view (most sensitive sign) - **Rigler's triad** on abdominal radiograph: 1. Pneumoperitoneum (free air) 2. Mediastinal emphysema (air in mediastinum) 3. Subcutaneous emphysema (air in soft tissues) - **CT abdomen** (gold standard): Air in peritoneal cavity, often with focal defect in anterior wall of stomach or duodenum - Duodenal perforations (more common than gastric) may show air tracking into retroperitoneum ### Epidemiology of Perforation Causes | Cause | Frequency | Geographic Variation | |-------|-----------|----------------------| | Peptic ulcer | 70–80% | Higher in developed nations; declining with PPI use | | Appendicitis | 5–10% | Varies with appendicitis incidence | | Diverticulitis | 5–10% | More common in elderly | | Typhoid enteritis | 5–15% | Endemic in South Asia, Africa | | Malignancy | 2–5% | Rare | | Trauma | Variable | Context-dependent | **High-Yield:** In India and endemic regions, typhoid perforation is more common (10–15%), but peptic ulcer remains the leading cause overall. ### Clinical Pearl The **location of free air** can hint at the source: retroperitoneal air suggests duodenal perforation; free intraperitoneal air suggests gastric or antral ulcer. **Mnemonic: PERFORATED** — **P**eptic ulcer (most common), **E**nteric (typhoid), **R**uptured viscus, **F**oregut pathology, **O**ther (malignancy, trauma), **R**etroperitoneal, **A**ppendix, **T**rauma, **E**sophageal, **D**iverticular. [cite:Harrison 21e Ch 297]