A 68-year-old man presents to the emergency department with a 3-day history of abdominal pain, abdominal distension, and vomiting. He has a history of colorectal cancer treated with left hemicolectomy 5 years ago. On examination, his abdomen is distended with visible peristaltic waves. Bowel sounds are high-pitched and tinkling. His blood pressure is 100/65 mmHg, heart rate 108/min, and temperature 37.2°C. Plain abdominal X-ray shows dilated small bowel loops with air-fluid levels and a transition zone in the left lower abdomen. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Adhesive Small Bowel Obstruction ### Key Clinical Features **Key Point:** The patient has a history of abdominal surgery (left hemicolectomy) 5 years ago, which is the most common cause of small bowel obstruction in developed countries. **High-Yield:** In the post-operative patient with a history of abdominal or pelvic surgery, adhesions account for 60–75% of mechanical small bowel obstructions. The timing (years after surgery) and absence of signs of malignancy recurrence make adhesions the most likely diagnosis. ### Radiological Findings The plain abdominal X-ray findings are classic for small bowel obstruction: - Dilated small bowel loops (typically >3 cm diameter) - Air-fluid levels on upright film - Transition zone (abrupt change from dilated to collapsed bowel) - Absence of colonic gas (suggesting small bowel as the site of obstruction) **Clinical Pearl:** The presence of high-pitched, tinkling bowel sounds and visible peristaltic waves indicates the bowel is still contracting against the obstruction—consistent with mechanical obstruction rather than ileus. ### Why Adhesions Are Most Likely | Feature | Adhesions | Recurrent Cancer | Volvulus | Herniation | |---------|-----------|------------------|----------|------------| | **Timing after surgery** | Years later (common) | Variable | Acute, no surgery link | Variable | | **Presentation** | Gradual onset, recurrent episodes | Progressive, systemic signs | Acute, severe pain | Acute | | **Location** | Small bowel (80%) | Colon (left hemicolectomy site) | Sigmoid | Variable | | **Imaging pattern** | Transition zone in small bowel | Proximal obstruction + mass | Twisted mesentery sign | Closed-loop pattern | **Mnemonic: ADHESIONS** — **A**bdominal surgery history, **D**ilated small bowel, **H**igh-pitched sounds, **E**arly post-op or years later, **S**mall bowel transition, **I**ntestinal loops, **O**bstruction, **N**o recurrence signs, **S**urgery is the risk factor. ### Management Approach ```mermaid flowchart TD A[Suspected adhesive SBO]:::outcome --> B{Signs of peritonitis or shock?}:::decision B -->|Yes| C[Emergency surgical exploration]:::urgent B -->|No| D[Conservative management trial]:::action D --> E[NPO, IV fluids, NG tube]:::action E --> F{Resolution in 24-48 hrs?}:::decision F -->|Yes| G[Discharge with dietary advice]:::outcome F -->|No| H[Surgical adhesiolysis]:::action ``` **Key Point:** Most adhesive obstructions (70–80%) resolve with conservative management (bowel rest, nasogastric decompression, IV fluid resuscitation). Surgery is reserved for failed conservative management or signs of strangulation.