Which radiological sign on plain abdominal X-ray is pathognomonic for closed-loop small bowel obstruction?

Explanation

## Radiological Signs of Bowel Obstruction **Key Point:** The **coffee bean sign** (or **loop sign**) is the most specific radiological finding for closed-loop obstruction, representing a loop of bowel twisted on its mesentery with a characteristic appearance on frontal radiographs. ### Pathognomonic and High-Yield Signs | Sign | Radiological Finding | Obstruction Type | Specificity | |------|----------------------|------------------|-------------| | **Coffee bean sign** | Twisted loop with dense central line | Closed-loop (volvulus) | Highly specific | | **Bird's beak sign** | Abrupt tapering at transition point | Volvulus (sigmoid) | Specific but not pathognomonic | | **Rigler's triad** | Pneumoperitoneum + small bowel obstruction + pneumatosis | Ischemic obstruction | Suggests advanced/ischemic disease | | **Valvulae conniventes** | Transverse mucosal folds in small bowel | Normal or partial obstruction | Not specific | **High-Yield:** Closed-loop obstruction is a surgical emergency because the trapped loop is at risk of ischemia and perforation. The coffee bean sign warrants urgent surgical evaluation. ### Why Coffee Bean Sign is Pathognomonic 1. **Mechanism:** A loop of bowel twisted 180–360° on its mesentery creates a characteristic "twisted" appearance on frontal view. 2. **Appearance:** Dense central line (mesentery) surrounded by the twisted bowel loop, resembling a coffee bean. 3. **Clinical Significance:** Indicates volvulus (usually sigmoid in adults) and demands urgent decompression or surgery. **Clinical Pearl:** Closed-loop obstruction progresses rapidly to ischemia and necrosis. Early recognition on imaging is critical for survival — do not delay surgical consultation if this sign is present. **Mnemonic:** **COFFEE BEAN = CLOSED LOOP** — remember that a twisted loop looks like a bean on X-ray, and closed-loop obstruction is the classic cause of this appearance.