Which radiological sign on plain abdominal X-ray is pathognomonic for hollow viscus perforation?

Explanation

## Double Wall Sign (Rigler's Sign): Pathognomonic for Hollow Viscus Perforation **Key Point:** The **Double Wall Sign** (also called **Rigler's Sign**) — Option A — is the radiological sign on plain abdominal X-ray that is considered pathognomonic for hollow viscus perforation. It occurs when free intraperitoneal air outlines the *outer* wall of the bowel, while intraluminal air outlines the *inner* wall — making **both walls of the bowel loop visible simultaneously**. ### Mechanism Normally, only the inner (mucosal) surface of the bowel is visible on X-ray due to intraluminal gas. When a hollow viscus perforates, free air escapes into the peritoneal cavity and surrounds the outer bowel wall, rendering it visible as well. This dual visibility of the bowel wall is the **Double Wall Sign (Rigler's Sign)**. ### Why Not the Other Options? | Sign | What It Indicates | Pathognomonic for Perforation? | |------|-------------------|-------------------------------| | **Double Wall Sign (Rigler's Sign)** | Free air outlines outer bowel wall simultaneously with intraluminal air | **Yes — pathognomonic for pneumoperitoneum/perforation** | | **Thumbprinting** | Submucosal edema/hemorrhage in bowel wall | No — sign of ischemic colitis or inflammatory bowel disease | | **Rigler's Triad** | Pneumoperitoneum + Pneumatosis intestinalis + Portal venous gas | Highly specific for advanced bowel ischemia/necrosis, but a *triad* of three findings, not a single pathognomonic sign | | **Sentinel Loop** | Localized ileus adjacent to inflamed organ (e.g., pancreatitis, appendicitis) | No — sign of adjacent inflammation, not perforation | **High-Yield:** The **Double Wall Sign (Rigler's Sign)** is the single, specific plain X-ray finding pathognomonic for free intraperitoneal air from hollow viscus perforation. It is most useful in **supine patients** where subdiaphragmatic free air (the most common upright finding) may not be apparent. **Note on Rigler's Triad (Option C):** Rigler's Triad refers to the combination of **pneumoperitoneum + pneumatosis intestinalis + portal venous gas** — a triad associated with advanced bowel ischemia and necrosis. It is NOT a single sign and is NOT synonymous with Rigler's Sign (the Double Wall Sign). These are distinct entities and must not be confused. **Clinical Pearl:** On an upright X-ray, free air under the diaphragm is the most *common* finding in perforation. However, the **Double Wall Sign** is the *pathognomonic* sign, particularly valuable in supine patients. [cite: Sutton's Textbook of Radiology and Imaging, 7th ed.; Grainger & Allison's Diagnostic Radiology, 6th ed.]