On plain abdominal radiograph, what is the significance of the 'double wall sign' (or 'double contour sign') in acute abdomen?

Explanation

## The Double Wall Sign: Free Air Outlining Bowel **Key Point:** The double wall sign (also called the double contour sign or Rigler's sign — not to be confused with Rigler's triad) is a radiological finding where free air in the peritoneal cavity outlines **both the inner and outer surfaces of the bowel wall**, creating a distinctive double-line appearance. ### Pathophysiology **High-Yield:** Normally, the bowel wall is visible on X-ray because it is surrounded by soft tissue (mesentery, peritoneal fat). When **pneumoperitoneum** (free air) is present, air outlines both sides of the bowel wall: - **Inner surface:** air within the bowel lumen - **Outer surface:** free air in the peritoneal cavity This creates the characteristic "double wall" or "double contour" appearance. ### Clinical Significance **Clinical Pearl:** The double wall sign indicates **perforation of a hollow viscus** (most commonly perforated peptic ulcer, perforated appendix, or perforated diverticulitis). This is a **surgical emergency** requiring immediate intervention. ### Comparison with Other Pneumoperitoneum Signs | Sign | Appearance | Sensitivity | |------|-----------|-------------| | **Double wall sign** | Free air outlining both surfaces of bowel wall | Moderate (more specific than Rigler's sign) | | **Rigler's sign** | Free air outlining inner surface of bowel wall only | High (more sensitive but less specific) | | **Subdiaphragmatic air** | Lucent crescent under diaphragm on upright film | High (most common finding) | | **Falciform ligament sign** | Free air outlining the falciform ligament | Specific but uncommon | **Warning:** Do not confuse the double wall sign with the **double bubble sign** (seen in duodenal atresia or pyloric stenosis in infants) — completely different entity. ### Diagnostic Algorithm ```mermaid flowchart TD A[Acute abdomen with suspected perforation]:::outcome --> B[Upright CXR or erect abdominal X-ray]:::action B --> C{Free air visible?}:::decision C -->|Yes - subdiaphragmatic| D[Perforation confirmed]:::outcome C -->|Yes - double wall sign| E[Viscus perforation with peritonitis]:::urgent C -->|No| F[Consider CT abdomen/pelvis]:::action E --> G[Emergency surgical consultation]:::action ``` [cite:Sabiston Textbook of Surgery Ch 45]