A 50-year-old man with a history of abdominal surgery presents with abdominal distension, bilious vomiting, and obstipation. Erect abdominal X-ray shows multiple air-fluid levels in dilated small bowel loops with a 'step-ladder' pattern. Supine film shows valvulae conniventes crossing the entire width of the bowel loop. These findings indicate:

• A Large bowel obstruction
• B Paralytic ileus
• C Volvulus
• D Small bowel obstruction ✓

Explanation

Small bowel obstruction on plain radiograph shows dilated small bowel loops (>3 cm) with multiple air-fluid levels in a step-ladder pattern and valvulae conniventes (plicae circulares) that cross the entire width of the lumen. Large bowel obstruction shows peripheral dilated colon with haustra that do not cross completely. Paralytic ileus shows diffuse gas in both small and large bowel. Volvulus shows a single dilated loop.

Reference: Grainger and Allison's Diagnostic Radiology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.