A 42-year-old woman with a history of adhesions presents with acute onset colicky abdominal pain, abdominal distension, and vomiting. Plain abdominal radiograph shows multiple dilated small bowel loops with air-fluid levels and a transition zone. Which is the most appropriate next investigation to confirm the diagnosis and assess for strangulation?

Explanation

## Investigation of Choice for Small Bowel Obstruction with Suspected Strangulation **Key Point:** CECT abdomen and pelvis is the gold standard for confirming small bowel obstruction, identifying the cause, and detecting signs of strangulation (ischemia, perforation risk). ### Why CECT is Superior for SBO Evaluation **High-Yield:** CECT abdomen and pelvis with oral and IV contrast is the investigation of choice because it: - Confirms small bowel obstruction with high sensitivity (>95%) - Identifies the site and cause of obstruction (adhesions, hernia, malignancy, volvulus) - Detects signs of strangulation: - Bowel wall thickening (>3 mm) - Mesenteric edema - Ascites - Reduced or absent bowel wall enhancement (ischemia) - Free air (perforation) - Guides management: conservative vs. surgical - Sensitivity for strangulation: 80–90% ### Plain Radiograph Limitations While plain radiograph shows: - Dilated small bowel loops - Air-fluid levels - Transition zone It CANNOT: - Reliably identify the cause - Detect strangulation (ischemia, perforation) - Show mesenteric vascularity - Assess bowel wall viability ### Comparison Table: Investigations for Small Bowel Obstruction | Investigation | Sensitivity | Specificity | Identifies Cause | Detects Strangulation | Guides Management | |---|---|---|---|---|---| | Plain radiograph | 60–70% | Moderate | Poor | No | Limited | | SBFT (barium) | 70–80% | Moderate | Moderate | No | Limited | | CECT with contrast | >95% | >90% | Yes | Yes (80–90%) | Yes | | Ultrasound | 60–70% | Moderate | Poor | Poor | Limited | **Clinical Pearl:** Signs of strangulation on CT (bowel wall thickening, mesenteric edema, ascites, reduced enhancement) indicate urgent surgical intervention. Plain radiograph cannot reliably detect these findings. **Warning:** Do not delay CECT in suspected strangulation. Delay in diagnosis increases morbidity and mortality. Plain radiograph alone is insufficient for management decisions. **Mnemonic: CECT for SBO — Cause, Enhancement, Complication, Transition** - **C**ause of obstruction (adhesions, hernia, malignancy) - **E**nhancement pattern (normal = viable; reduced = ischemic) - **C**omplications (strangulation, perforation, peritonitis) - **T**ransition zone and site of obstruction ### Management Algorithm ```mermaid flowchart TD A[Suspected SBO on plain radiograph]:::outcome --> B[CECT abdomen/pelvis with oral + IV contrast]:::action B --> C{Signs of strangulation?}:::decision C -->|Yes| D[Urgent surgical exploration]:::urgent C -->|No| E{Partial or complete?}:::decision E -->|Partial| F[Conservative management: NG tube, fluids, monitor]:::action E -->|Complete| G{Cause identified?}:::decision G -->|Adhesions/benign| H[Trial of conservative management, then surgery if fails]:::action G -->|Hernia/malignancy| I[Surgical intervention]:::action ``` [cite:Harrison 21e Ch 287]