A 55-year-old woman with a history of peptic ulcer disease presents with sudden onset severe epigastric pain radiating to the back, followed by diffuse abdominal pain and rigidity. She is tachycardic (HR 110/min) and hypotensive (BP 95/55). An upright chest radiograph is obtained as part of the acute abdomen workup. What is the most important radiographic finding you would expect to see?

Explanation

## Clinical Presentation Analysis The patient presents with the classic triad of perforated peptic ulcer: 1. Sudden onset severe epigastric pain (often described as 'worst pain of life') 2. Peritoneal signs (rigidity, guarding) 3. Hemodynamic compromise (tachycardia, hypotension) ## Pathophysiology of Perforation **Key Point:** When a peptic ulcer perforates, gastric or duodenal contents (including air) spill into the peritoneal cavity, causing acute peritonitis and septic shock. The free air rises when the patient is upright, accumulating under the diaphragm. ## Radiographic Findings in Perforated Viscus | Sign | Finding | Sensitivity | Specificity | Timing | |------|---------|-------------|------------|--------| | **Free air under diaphragm** | Lucency on upright CXR or decubitus film | 60–80% | Very high | Immediate | | **Pneumoperitoneum** | Air outlining visceral organs | 70–90% | Very high | Within 1–2 hours | | **Rigler's triad** | Free air, pneumobilia, air-fluid levels | Specific for obstruction | N/A | Hours to days | | **Sentinel loop** | Localized dilated small bowel loop | Non-specific | Low | Variable | **High-Yield:** The **upright chest radiograph** is the gold standard initial imaging for detecting free air under the diaphragm in suspected perforated viscus. If upright CXR is not possible, a left lateral decubitus abdominal film is the alternative. ## Clinical Pearl About 10–15% of perforated peptic ulcers may not show free air on initial plain films, especially if the perforation is small or sealed by omentum. However, when present, free air is highly specific for perforation and mandates emergency surgical consultation. ## Mnemonic: PERFORATION Signs on Plain Film **P** — Pneumoperitoneum (free air under diaphragm) **E** — Epigastric pain (clinical clue) **R** — Rigidity and rebound (peritoneal signs) **F** — Free air (most important radiographic finding) **O** — Onset sudden **R** — Rigler's triad (if obstruction coexists) **A** — Air-fluid levels (variable) **T** — Thoracic imaging (upright CXR best) **I** — Immediate surgical intervention needed **O** — Often requires CT or laparoscopy if CXR negative **N** — Never delay surgery waiting for imaging [cite:Harrison 21e Ch 297]