A 62-year-old man presents to the emergency department with acute onset abdominal pain, abdominal distension, and vomiting for 8 hours. He has a history of previous abdominal surgery 15 years ago. On examination, the abdomen is distended with visible peristaltic waves. Bowel sounds are high-pitched and tinkling. Plain radiograph of the abdomen shows dilated small bowel loops with valvulae conniventes crossing the entire width of the bowel, and a transition zone is identified. CT abdomen with IV contrast shows clustered small bowel loops in the center of the abdomen with a transition point. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Adhesive Small Bowel Obstruction ### Key Clinical Features **Key Point:** Adhesive small bowel obstruction (SBO) is the most common cause of mechanical SBO in the developed world, accounting for 60–75% of cases. It typically occurs after abdominal or pelvic surgery. ### Imaging Findings **High-Yield:** The imaging triad of adhesive SBO includes: 1. **Dilated small bowel loops** (diameter >3 cm) proximal to the obstruction 2. **Transition zone** — abrupt change from dilated proximal bowel to collapsed distal bowel 3. **Valvulae conniventes** — plicae circulares crossing the entire width of the small bowel (distinguishes small bowel from colon) ### Radiological Characteristics | Feature | Adhesive SBO | Volvulus | Internal Hernia | Crohn's Stricture | |---------|--------------|----------|-----------------|-------------------| | **Transition zone** | Sharp, focal | Twisted appearance | Abrupt | Gradual | | **Bowel wall** | Normal thickness | Normal initially | Normal | Thickened, inflamed | | **History** | Prior surgery | None typically | May be subtle | Chronic diarrhea | | **CT appearance** | Clustered loops centrally | Whirled mesentery | Hernia defect visible | Long segment narrowing | | **Valvulae conniventes** | Preserved | Preserved | Preserved | Destroyed | **Clinical Pearl:** The "clustered small bowel loops" sign on CT — where multiple dilated loops are tightly grouped in the center of the abdomen — is highly suggestive of adhesive obstruction. This reflects the mechanical constraint imposed by adhesions. ### Why Adhesive SBO Here? - **Prior abdominal surgery** 15 years ago is the strongest risk factor - **Acute presentation** with high-pitched tinkling bowel sounds (mechanical obstruction) - **Transition zone** on imaging is the hallmark - **Normal bowel wall** thickness and no inflammatory changes - **Central clustering** of dilated loops on CT is pathognomonic for adhesions ### Management Implications **Key Point:** Most adhesive SBOs (60–80%) resolve with conservative management (nasogastric decompression, IV fluids, bowel rest). Surgery is reserved for: - Failed conservative management (>5–7 days) - Signs of strangulation (fever, peritonitis, elevated lactate) - Recurrent episodes [cite:Robbins 10e Ch 17]