A 68-year-old man presents to the emergency department with acute onset severe abdominal pain, abdominal distension, and vomiting for 6 hours. He has a history of previous abdominal surgery. On examination, the abdomen is distended and tympanitic with visible peristaltic waves. A plain abdominal radiograph shows multiple loops of small bowel with a 'stacked coin' or 'string of pearls' appearance and air-fluid levels at different heights. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis The patient presents with classic signs of acute mechanical obstruction: sudden onset pain, vomiting, distension, and visible peristaltic waves. ## Radiographic Findings Interpretation **Key Point:** The 'stacked coin' or 'string of pearls' appearance is pathognomonic for small bowel obstruction. This sign represents valvulae conniventes (plicae circulares) that are compressed by fluid, creating a characteristic linear pattern on the anteroposterior view. **High-Yield:** Air-fluid levels at different heights within dilated small bowel loops are a hallmark of mechanical small bowel obstruction. The small bowel typically measures ≤3 cm in diameter when obstructed. ## Differential Diagnosis | Finding | Small Bowel Obstruction | Colonic Obstruction | Paralytic Ileus | Perforation | |---------|------------------------|-------------------|-----------------|-------------| | **Onset** | Acute, sudden | Gradual | Insidious | Acute, severe | | **Peristaltic waves** | Visible, prominent | Absent | Absent | Absent | | **Air-fluid levels** | Multiple, different heights | Haustra pattern | Absent or minimal | Free air present | | **Bowel caliber** | Small bowel ≤3 cm | Colon >6 cm | Variable | Variable | | **String of pearls** | Present | Absent | Absent | Absent | ## Clinical Pearl The history of previous abdominal surgery is a major risk factor for adhesions, which are the most common cause of small bowel obstruction in developed countries. The acute presentation with visible peristaltic waves indicates the bowel is still attempting to overcome the obstruction (mechanical, not paralytic). ## Mnemonic: SOAP for Small Bowel Obstruction Signs **S** — String of pearls (valvulae conniventes) **O** — Obstruction (mechanical, acute) **A** — Air-fluid levels (multiple, different heights) **P** — Previous surgery (adhesions) [cite:Robbins & Cotran 10e Ch 17]