A 62-year-old man presents to the emergency department with a 3-day history of colicky abdominal pain, abdominal distension, and constipation. He had undergone an open appendectomy 35 years ago. On examination, his abdomen is distended with visible peristaltic waves. Bowel sounds are high-pitched and tinkling. Plain abdominal X-ray shows dilated small bowel loops with air-fluid levels in a stepladder pattern, and the transition point is clearly visible. There is no free air under the diaphragm. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Adhesive Small Bowel Obstruction ### Key Clinical Features **Key Point:** The combination of a remote surgical history (appendectomy 35 years ago), classic mechanical obstruction signs (colicky pain, distension, constipation), and characteristic radiological findings (stepladder air-fluid levels with a clear transition point) is pathognomonic for adhesive obstruction. ### Radiological Findings | Finding | Significance | |---------|-------------| | Dilated small bowel loops | Obstruction proximal to transition point | | Air-fluid levels in stepladder pattern | Hallmark of mechanical small bowel obstruction | | Transition point visible | Indicates complete obstruction | | No free air | Rules out perforation | ### Pathophysiology of Adhesions 1. **Formation mechanism:** Post-surgical trauma → peritoneal inflammation → fibrin deposition → collagen organization → mature adhesions 2. **Timing:** Can occur immediately post-op or decades later (as in this case) 3. **Incidence:** Responsible for 60–75% of mechanical small bowel obstructions in developed countries 4. **Risk factors:** Multiple prior abdominal surgeries increase risk exponentially ### Clinical Pearl **Clinical Pearl:** The "stepladder" appearance on X-ray occurs because each dilated bowel loop fills with fluid, and peristalsis pushes the fluid distally, creating successive levels of air-fluid interfaces that resemble a staircase. ### High-Yield Facts **High-Yield:** Adhesions are the most common cause of mechanical small bowel obstruction in patients with prior abdominal surgery. The obstruction can occur years or decades after the initial surgery due to gradual adhesion maturation and fibrosis. ### Management Approach **Tip:** Initial management is conservative (NPO, nasogastric decompression, IV fluids, electrolyte correction) in uncomplicated cases. Surgery is reserved for failed conservative management (typically after 48–72 hours) or signs of strangulation (fever, peritonitis, elevated lactate).