Pneumoperitoneum: NEET PG Radiology
1. Classic Radiographic Signs
- Rigler’s Sign (Double-Wall Sign): Air is visible on both the inner and outer sides of the bowel wall, making the wall appear abnormally thin and sharply defined.
- Cupola Sign: A crescent-shaped lucency seen over the liver on a supine abdominal X-ray, representing air collecting under the diaphragm.
- Football Sign: A large amount of free air in the peritoneal cavity outlines the entire abdominal cavity, making it look like a football (the falciform ligament is often seen as the “seam”).
- Falciform Ligament Sign: Free air outlines the falciform ligament, which is usually invisible.
2. High-Yield Clinical Context
| Imaging Method | High-Yield Detail |
|---|---|
| Erect Chest X-ray | The most sensitive view for detecting small amounts of free air (seen as a crescent under the diaphragm). |
| Left Lateral Decubitus | Performed if the patient cannot stand; air collects between the liver and the abdominal wall. |
| CT Scan | The gold standard can detect even tiny amounts of free air (pneumoperitoneum) that are missed on plain X-rays. |
3. Examination Pearls
- Clinical Correlation: Most common cause is a perforated peptic ulcer (PPU). Always look for “board-like rigidity” on abdominal exam.
- Chilaiditi Syndrome: A common mimicker where a segment of the colon interposes between the liver and the diaphragm, creating a false appearance of free air. Key distinction: Haustral markings are visible in the interposed colon, whereas free air is featureless.
- Post-Surgical: A small amount of pneumoperitoneum is normal for up to 5–7 days following laparoscopic surgery.