A 58-year-old man with a history of previous abdominal surgery presents with acute onset colicky abdominal pain and abdominal distension. Plain abdominal radiograph shows dilated small bowel loops with air-fluid levels. Which radiological feature best distinguishes adhesive small bowel obstruction from mechanical obstruction due to an internal hernia?

Explanation

## Distinguishing Adhesive SBO from Internal Hernia Obstruction ### Key Radiological Features **Key Point:** The clustered, centrally located dilated loops with concertina-like (accordion-like) appearance is the hallmark of internal hernia obstruction, distinguishing it from adhesive obstruction. ### Comparison Table | Feature | Adhesive SBO | Internal Hernia SBO | | --- | --- | --- | | **Loop distribution** | Scattered throughout abdomen | Clustered, central location | | **Loop appearance** | Dilated, separated loops | Concertina/accordion pattern | | **Transition zone** | May be present but often gradual | Abrupt transition common | | **Associated findings** | Often multiple transition zones | Single focal area of crowding | | **CT appearance** | Loops in various locations | Clustered loops with mesenteric vessels converging | ### Pathophysiology 1. **Adhesive obstruction:** Bowel loops are tethered at multiple points by adhesions, resulting in scattered dilated segments throughout the abdomen with variable transition zones. 2. **Internal hernia:** Bowel becomes incarcerated within a peritoneal defect (congenital or post-surgical), causing loops to bunch together in a specific anatomical location, creating the characteristic concertina appearance. **High-Yield:** The concertina sign (also called "accordion sign") on CT is virtually pathognomonic for internal hernia obstruction and helps differentiate it from adhesions, which typically show more dispersed, scattered loops. **Clinical Pearl:** Internal hernias are more common through the foramen of Winslow, paraduodenal defects, and post-bariatric surgery defects. The clustered appearance reflects the anatomical constraint of the hernia orifice. ### Why Other Features Are Less Discriminating - **Transition zone, collapsed distal bowel, air-fluid levels:** These are present in both adhesive and internal hernia obstructions and do not reliably distinguish between them.