A 62-year-old man presents with acute onset abdominal distension, colicky pain, and vomiting for 8 hours. He has a history of two previous abdominal surgeries. On examination, the abdomen is distended with visible peristaltic waves and high-pitched bowel sounds. What is the investigation of choice to confirm the diagnosis and determine the level of obstruction?

## Investigation of Choice in Small Bowel Obstruction **Key Point:** Abdominal X-ray (erect and supine views) is the first-line and investigation of choice for suspected intestinal obstruction in acute settings. ### Why Plain Radiography? 1. **Rapid availability** — can be done at the bedside in acute care settings 2. **Cost-effective** — no contrast or special preparation required 3. **Diagnostic accuracy** — shows classic signs of obstruction: - **Valvulae conniventes** (mucosal folds) in small bowel obstruction - **Haustra** (incomplete colonic folds) in large bowel obstruction - **Air-fluid levels** on erect view (pathognomonic) - **Absence of colonic gas** in small bowel obstruction 4. **Determines level** — distribution of gas and fluid helps localize the obstruction ### Radiographic Signs of Small Bowel Obstruction | Sign | Appearance | Significance | |------|-----------|---------------| | Valvulae conniventes | Thin, complete mucosal folds crossing entire lumen | Diagnostic of SBO | | Air-fluid levels | Stepladder pattern on erect film | Confirms obstruction | | Dilated loops | Bowel diameter >3 cm | Indicates obstruction | | Transition point | Abrupt change from dilated to collapsed bowel | Locates obstruction | **Clinical Pearl:** In this patient with previous abdominal surgeries, adhesions are the most common cause of small bowel obstruction (60–75% of cases), and plain X-ray will demonstrate the characteristic findings. **High-Yield:** The erect view is essential because air-fluid levels are only visible on erect or lateral decubitus radiographs, not on supine films. ### When to Escalate to CT CT abdomen with IV contrast is reserved for: - Suspected strangulation (fever, peritonitis, elevated lactate) - Equivocal plain film findings - Recurrent obstruction requiring anatomical detail - Suspected closed-loop obstruction **Tip:** In acute uncomplicated obstruction, start with plain X-ray. CT is the next step if clinical suspicion for strangulation or if diagnosis remains unclear after plain films.