CT Enterography is the Most Appropriate Investigation
For a young woman with suspected small bowel Crohn disease presenting with chronic diarrhea, weight loss, right lower quadrant pain, and positive fecal occult blood test, CT enterography (CTE) is the most appropriate initial investigation. 1
Rationale for CT Enterography
The 2025 ECCO-ESGAR-ESP-IBUS guideline establishes that cross-sectional imaging with either MRE or CTE is essential for accurate phenotyping and staging of Crohn disease at initial diagnosis 2. The 2018 consensus recommendations specifically address when to select CTE versus MRE, and several factors in this case favor CTE:
- First cross-sectional enterography exam in an acutely symptomatic patient - CTE is specifically recommended for this scenario 1
- Need to rule out other diseases causing diarrhea - The differential diagnosis remains broad, and CTE excels at evaluating alternative pathology 1
- Suspected complex disease - Right lower quadrant pain with positive fecal occult blood suggests potential complications that CTE can rapidly assess 1
Why Not the Other Options
Flexible Sigmoidoscopy Alone (Option B) - Inadequate
Sigmoidoscopy only visualizes the rectum and sigmoid colon, missing the suspected small bowel involvement entirely. While ileocolonoscopy remains important, the guideline emphasizes that cross-sectional imaging is necessary because ileocolonoscopy cannot adequately assess the proximal small bowel 2. In fact, imaging studies demonstrate that 20 cm of proximal terminal ileum with active inflammation can be completely missed on normal ileocolonoscopy 1.
Abdominal Radiography (Option C) - Obsolete
Plain radiography has no role in diagnosing Crohn disease. It cannot detect mucosal inflammation, wall thickening, or other diagnostic features of inflammatory bowel disease.
24-Hour Esophageal pH Monitoring (Option D) - Irrelevant
This test evaluates gastroesophageal reflux disease and has no application in suspected small bowel Crohn disease.
The Complete Diagnostic Algorithm
After CTE establishes the diagnosis and maps disease extent:
Ileocolonoscopy with biopsies should follow to confirm inflammation histologically and assess the terminal ileum and colon 2
If CTE and ileocolonoscopy are negative but suspicion remains high, capsule endoscopy becomes the next appropriate test 2. Research shows capsule endoscopy has 93% sensitivity for small bowel Crohn disease when standard tests are negative 3, though it should not be used if strictures are present due to retention risk 4
Important Caveats
Age consideration: While MRE is generally preferred in patients under 35 years old due to radiation concerns 1, CTE remains appropriate for the first examination in an acutely symptomatic patient regardless of age, particularly when using low-dose CT techniques 1.
MRE advantages: If this patient were not acutely symptomatic or if this were a follow-up examination, MRE would be preferred given her young age 1, 2. The METRIC trial demonstrated that MRE has 97% sensitivity and 96% specificity for detecting active small bowel disease, with superior accuracy for assessing disease extent (80% sensitivity, 95% specificity) compared to ultrasound 2.
What CTE reveals: Look for asymmetric wall thickening, hyperenhancement, mural stratification, comb sign (engorged vasa recta), and perienteric fat stranding - these findings indicate active inflammatory Crohn disease 1. CTE also identifies complications including strictures, fistulas, abscesses, and penetrating disease that would alter management 1.