When suspecting Crohn's Disease, do you initially investigate with a colonoscopy or an MR (Magnetic Resonance) enterography?

Diagnostic Approach for Suspected Crohn's Disease: Colonoscopy First, Then MR Enterography

For suspected Crohn's disease, ileocolonoscopy with biopsies should be performed as the first-line investigation, followed by MR enterography to assess small bowel involvement beyond the reach of the colonoscope. 1

Rationale for This Approach

Step 1: Ileocolonoscopy with Biopsies

• Ileocolonoscopy with segmental biopsies is established as the first-line investigation for suspected Crohn's disease 1
• Allows direct visualization and histological assessment of the colon and terminal ileum
• Provides definitive diagnosis through histological confirmation
• Enables assessment of disease severity and extent in the colon and terminal ileum
• High diagnostic yield when endoscopic abnormalities are present (84% with "ileitis" and 69% with ulcers/erosions) 2

Step 2: MR Enterography

• Should be performed after ileocolonoscopy to assess small bowel involvement beyond the reach of the colonoscope 1
• Up to 20% of patients have isolated proximal small bowel disease that would be missed by ileocolonoscopy alone 1
• MRE is preferred over CT enterography in younger patients (<35 years) to avoid radiation exposure 1
• MRE provides excellent visualization of small bowel inflammation, strictures, and penetrating complications 1

Important Clinical Considerations

When to Consider MR Enterography First

• In patients with obstructive symptoms or known stenosis, MR enterography should be the initial method of choice before endoscopic evaluation 1
• When there is concern for complex intra-abdominal penetrating disease requiring intervention 1
• In patients with perianal fistula or perianal sepsis 1

Limitations of Ileocolonoscopy Alone

• Terminal ileum intubation may not always be possible during colonoscopy 1
• Cannot visualize proximal small bowel disease beyond the reach of the scope 1
• In a cohort study, 36 out of 150 Crohn's disease patients had active small bowel disease diagnosed by cross-sectional imaging despite a normal ileocolonoscopy 1

Complementary Nature of Both Modalities

• Ileocolonoscopy and cross-sectional imaging are complementary in diagnosing Crohn's disease 1
• MRE can detect inflammation in segments not accessible or visualized during endoscopy 1
• Figure 10 from consensus guidelines shows cases where normal-appearing terminal ileum on ileoscopy had significant inflammation in more proximal segments detected only by cross-sectional imaging 1

Special Situations

Small Bowel Capsule Endoscopy

• May be considered as an initial diagnostic modality for small bowel evaluation if ileocolonoscopy is negative and there are no obstructive symptoms or known stenosis 1
• Higher diagnostic yield for small bowel lesions compared to ileocolonoscopy, small bowel follow-through, and CT enterography 1
• Caution: Small lesions detected by capsule may not be specific for Crohn's disease 1

When to Consider CT Enterography Instead of MRE

• In acutely symptomatic patients or when sepsis is suspected 1
• In older patients (>35 years old) 1
• When MRI is contraindicated (claustrophobia, implanted devices) 1
• When rapid diagnosis is needed 1

Conclusion

The optimal diagnostic approach for suspected Crohn's disease begins with ileocolonoscopy with biopsies, followed by MR enterography to assess small bowel involvement. This combined approach provides the most comprehensive evaluation for accurate diagnosis, disease extent assessment, and detection of complications.