A 58-year-old man presents to the emergency department with a 3-day history of colicky abdominal pain, abdominal distension, and absolute constipation. He has a past surgical history of open appendicectomy 15 years ago. On examination, he is afebrile, blood pressure 110/70 mmHg, and the abdomen is distended with visible peristaltic waves. Bowel sounds are high-pitched and tinkling. Laboratory investigations show normal WBC and serum electrolytes. Plain abdominal X-ray reveals dilated small bowel loops with air-fluid levels and a transition zone in the mid-ileum. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Adhesive Small Bowel Obstruction ### Key Clinical Features **Key Point:** Adhesions account for 60–75% of mechanical small bowel obstructions in the developed world and are the most common cause in patients with prior abdominal surgery. This patient presents with the classic triad of mechanical small bowel obstruction: 1. **Colicky abdominal pain** — intermittent, crampy, due to peristaltic attempts to overcome the obstruction 2. **Abdominal distension** — from accumulation of gas and fluid proximal to the obstruction 3. **Absolute constipation** — no flatus or stool passage ### Radiological Findings | Feature | Significance | |---------|-------------| | Dilated small bowel loops | Proximal to obstruction | | Air-fluid levels | Indicate mechanical obstruction | | Transition zone | Marks the site of obstruction | | Normal WBC | Rules out perforation/peritonitis | **High-Yield:** The combination of prior abdominal surgery + mechanical obstruction signs + normal inflammatory markers = adhesive obstruction until proven otherwise. ### Why Adhesions Are the Diagnosis 1. **Prior surgical history** — appendicectomy 15 years ago is the strongest risk factor for adhesion formation 2. **Gradual onset** — adhesions typically present with insidious symptoms over days (not acute volvulus) 3. **Stable vital signs** — no signs of strangulation or perforation 4. **Transition zone on imaging** — characteristic of adhesive obstruction; volvulus would show a "whirlpool" or "barber pole" sign ### Management Approach ```mermaid flowchart TD A[Adhesive SBO]:::outcome --> B{Signs of strangulation?}:::decision B -->|No| C[Conservative management]:::action C --> D[NPO, NG tube, IV fluids]:::action D --> E{Resolution in 48-72 hrs?}:::decision E -->|Yes| F[Discharge, counseling]:::outcome E -->|No| G[Surgical exploration]:::action B -->|Yes: fever, peritonitis, shock| H[Emergency laparotomy]:::urgent H --> I[Adhesiolysis ± resection]:::action ``` **Clinical Pearl:** Up to 50% of adhesive obstructions resolve with conservative management (NPO, nasogastric decompression, IV fluid resuscitation). Surgery is reserved for failed conservative management or signs of strangulation. **High-Yield:** Strangulation signs include fever, leukocytosis, severe pain, peritoneal signs, and shock — this patient lacks these, making conservative management appropriate initially.