A 58-year-old man from Delhi presents to the emergency department with acute onset severe epigastric pain radiating to the back, associated with nausea and vomiting. He has a history of peptic ulcer disease treated irregularly. On examination, he is in severe distress, with rigid abdomen and rebound tenderness. Blood pressure is 95/60 mmHg, heart rate 118/min. Erect chest X-ray shows pneumoperitoneum. Which of the following imaging findings on CT abdomen would be most specific for perforated peptic ulcer?

Explanation

## Imaging Findings in Perforated Peptic Ulcer ### CT Abdomen Findings **Key Point:** The **triangular shaped air collection anterior to the liver** (also called the "sentinel clot sign" variant or **"air in the lesser sac"**) with a **focal wall defect** in the gastric antrum or pyloric region is the most specific finding for perforated peptic ulcer disease. ### Characteristic Features of Perforated PUD | Feature | Finding | Specificity | |---------|---------|-------------| | **Air location** | Anterior to liver, lesser sac, along lesser omentum | High | | **Wall defect** | Focal defect in antrum/pylorus (90% of cases) | Very high | | **Associated findings** | Sentinel clot, fat stranding, fluid collection | Moderate | | **Timing** | Air visible within minutes; may be reabsorbed in 24-48 hrs | Clinical correlation needed | ### Why This Finding Is Most Specific 1. **Anatomical containment**: Air from gastric perforation is initially contained by the lesser omentum and anterior peritoneal layer, creating a characteristic triangular or crescentic collection anterior to the liver dome. 2. **Direct visualization of defect**: CT can directly visualize the focal perforation site in the gastric wall, which is pathognomonic. 3. **Peptic ulcer location**: Perforations occur at the anterior wall of the antrum or pylorus (gastric antrum in ~90%, duodenal bulb in ~10%), and this location is uniquely identifiable on CT. ### Other Perforation Types and Their Imaging Patterns ```mermaid flowchart TD A[Hollow Viscus Perforation]:::outcome --> B{Location?}:::decision B -->|Gastric/Duodenal| C[Air anterior to liver<br/>Focal wall defect<br/>Lesser sac involvement]:::action B -->|Colon| D[Air in paracolic gutters<br/>Diverticular site or wall defect<br/>Feculent material]:::action B -->|Small bowel| E[Air diffuse throughout peritoneum<br/>Mesenteric stranding<br/>Bowel wall thickening]:::action C --> F[Perforated PUD]:::outcome D --> G[Perforated diverticulitis]:::outcome E --> H[Perforated enteritis/trauma]:::outcome ``` **Clinical Pearl:** In perforated peptic ulcer, the **sentinel clot sign** (a blood clot at the perforation site) is often visible on CT and helps localize the defect. However, the **triangular air collection with focal wall defect** is the single most specific imaging finding. **High-Yield:** Approximately 70–80% of perforated peptic ulcers can be managed conservatively (without surgery) if diagnosed early and the patient is hemodynamically stable. CT imaging allows this risk stratification by showing the size and containment of the perforation. ### Differential Imaging Findings - **Pneumoperitoneum without focal defect**: Non-specific; could be post-surgical or from any perforation. - **Diffuse peritoneal air**: Suggests more extensive contamination (larger perforation or delayed diagnosis). - **Loculated collections**: Suggest walled-off perforation or abscess formation (later stage).