A 52-year-old man with a history of abdominal tuberculosis presents with abdominal distension, colicky pain, and vomiting for 3 days. On examination, visible peristaltic waves are noted. Plain abdominal X-ray shows dilated small bowel loops with air-fluid levels in a stepladder pattern. What is the investigation of choice to confirm the diagnosis and determine the level of obstruction?

## Investigation of Choice for Small Bowel Obstruction **Key Point:** CT abdomen with IV contrast is the gold standard investigation for confirming small bowel obstruction and determining the exact level, cause, and presence of complications (ischemia, perforation). ### Why CT Abdomen with IV Contrast is Superior 1. **Diagnostic accuracy**: >95% sensitivity and specificity for small bowel obstruction 2. **Identifies cause**: Can detect adhesions (most common cause), malignancy, volvulus, intussusception, and strictures 3. **Determines level**: Precisely localizes the obstruction site 4. **Detects complications**: Can identify bowel ischemia (wall enhancement abnormalities), perforation, and peritonitis 5. **Guides management**: Helps differentiate between partial and complete obstruction, influencing conservative vs. surgical approach ### Comparison of Investigations | Investigation | Sensitivity | Specificity | Can determine level? | Detects ischemia? | Identifies cause? | | --- | --- | --- | --- | --- | --- | | **CT with contrast** | >95% | >95% | Yes | Yes | Yes | | Plain X-ray | 60–70% | 60–70% | No | No | No | | Ultrasound | 70–80% | 80–90% | Limited | No | Limited | | Barium follow-through | 70–80% | 70–80% | Yes | No | Limited | | MRI | 90–95% | 90–95% | Yes | Yes | Yes | **Clinical Pearl:** In acute obstruction with signs of peritonitis or sepsis, CT with IV contrast is preferred over MRI because it is faster and can detect free air and perforation more reliably. **High-Yield:** Plain X-ray is useful for initial screening and detecting free air (perforation), but CT is mandatory for confirmation and surgical planning in all cases of suspected mechanical obstruction. **Mnemonic: CT SCAN** — **C**ause identified, **T**ype (partial/complete), **S**ite of obstruction, **C**omplications (ischemia/perforation), **A**ccuracy >95%, **N**ext step (medical vs. surgical).