A 62-year-old man presents with acute onset abdominal distension, colicky pain, and vomiting for 8 hours. On examination, there is abdominal distension with visible peristaltic waves and hyperactive bowel sounds. Plain abdominal radiograph shows dilated small bowel loops with air-fluid levels and a transition zone. What is the investigation of choice to confirm the diagnosis and identify the cause of obstruction?

Explanation

## Investigation of Choice for Small Bowel Obstruction **Key Point:** CT abdomen and pelvis with IV contrast is the gold standard investigation for suspected small bowel obstruction, providing both diagnosis confirmation and identification of the underlying cause. ### Why CT is Superior **High-Yield:** CT has: - **Sensitivity and specificity >90%** for detecting small bowel obstruction - **Ability to identify the transition zone** — the exact point where obstruction occurs - **Determination of etiology** — adhesions, hernia, malignancy, volvulus, intussusception - **Assessment of bowel viability** — presence of free fluid, bowel wall enhancement, mesenteric stranding (signs of ischemia) - **Rapid acquisition** — critical in acute obstruction where time matters ### Clinical Pearl In acute small bowel obstruction with clinical signs (visible peristaltic waves, hyperactive bowel sounds, transition zone on plain film), CT with IV contrast should be obtained urgently to guide management — whether conservative (nasogastric decompression, fluids) or surgical intervention. ### Comparison with Other Modalities | Investigation | Sensitivity | Specificity | Identifies Cause | Assesses Viability | Time-Efficient | |---|---|---|---|---|---| | **CT (IV contrast)** | >90% | >90% | Yes | Yes | Yes | | Barium studies | 60–80% | Variable | Limited | No | No (delayed) | | Ultrasound | 70–80% | 80–90% | Limited | No | Yes | | MRI | High | High | Yes | Possible | No (prolonged) | **Key Point:** Barium studies are contraindicated in complete obstruction due to risk of barium impaction and perforation. ### Diagnostic Criteria on CT 1. **Transition zone** — abrupt change from dilated to collapsed bowel 2. **Bowel dilation** — small bowel >3 cm diameter 3. **Air-fluid levels** — on plain film; CT shows distribution 4. **Mesenteric stranding** — suggests ischemia or inflammation 5. **Free fluid** — may indicate perforation or ischemia **Warning:** Do not delay CT in a patient with signs of peritonitis or ischemia — proceed directly to surgery if clinical deterioration occurs.