A 58-year-old man from Delhi presents to the emergency department with acute onset severe epigastric pain radiating to the back, accompanied by vomiting. He has a history of peptic ulcer disease treated intermittently. On examination, he is febrile (38.5°C), tachycardic (110/min), and has severe epigastric tenderness with guarding. An upright chest X-ray is obtained. What is the most characteristic radiological finding that would support the diagnosis of perforated peptic ulcer?

Explanation

## Radiological Diagnosis of Perforated Peptic Ulcer ### Classic Imaging Finding **Key Point:** Pneumoperitoneum (free air under the diaphragm) on upright chest X-ray or erect abdominal X-ray is the hallmark radiological sign of hollow viscus perforation, particularly perforated peptic ulcer. ### Why This Finding Occurs When a peptic ulcer perforates through the anterior wall of the duodenum or stomach, gastric and duodenal contents (including swallowed air) escape into the peritoneal cavity. This free intraperitoneal air rises and collects under the diaphragm due to gravity when the patient is upright. ### Imaging Technique and Sensitivity | Finding | Sensitivity | Best View | Notes | |---------|-------------|-----------|-------| | Pneumoperitoneum | 70–85% | Upright CXR or erect abdominal X-ray | May be subtle; requires careful inspection | | Rigler's sign | High specificity | Supine abdominal X-ray | Air outlines both sides of bowel wall | | Falciform ligament sign | Specific | CT abdomen | Air outlines falciform ligament | | CT abdomen | >95% | Axial images | Gold standard; detects even small amounts | **High-Yield:** Upright CXR is the first-line imaging study in suspected perforation. Even 1–2 cm of free air can be detected as a lucent crescent under the diaphragm. ### Clinical Correlation **Clinical Pearl:** In this patient, the acute onset of severe epigastric pain with peritoneal signs (guarding) and fever strongly suggests perforated peptic ulcer. The upright CXR demonstrating pneumoperitoneum confirms the diagnosis and mandates urgent surgical intervention. **Tip:** If upright CXR is equivocal or negative but clinical suspicion is high, proceed directly to CT abdomen/pelvis with IV contrast, which has >95% sensitivity for pneumoperitoneum and can also identify the perforation site and assess for peritonitis. ### Why Not the Other Options - **Pleural effusion with mediastinal widening:** Suggests esophageal rupture (Boerhaave syndrome) or aortic pathology, not peptic ulcer perforation. - **Ground-glass opacity:** Indicates pulmonary edema or ARDS, not a direct sign of perforation. - **Dilated small bowel loops:** Suggests bowel obstruction, not perforation (though late perforation may cause obstruction).