A 35-year-old man with known Crohn's disease presents with fever, right lower quadrant pain, and a palpable mass. Laboratory tests show elevated inflammatory markers. Abdominal examination suggests a possible fistula. Which investigation is most appropriate to confirm the presence of an enterocutaneous fistula and assess its anatomy?

Question

Accepted Answer

A. Magnetic resonance enterography with fistulography. ## Investigation of Choice for Fistula Assessment in Crohn's Disease

### Why MR Enterography with Fistulography is Superior

**Key Point:** Magnetic resonance enterography (MRE) with fistulography is the gold standard for detecting and characterizing fistulas in Crohn's disease. It provides excellent soft tissue contrast without radiation and defines fistula anatomy, branching, and relationship to surrounding structures.

### Advantages of MRE with Fistulography

| Feature | MRE with Fistulography | Barium Follow-Through | CT Enterography |
|---------|------------------------|----------------------|------------------|
| **Radiation** | None | Yes | Yes |
| **Soft tissue detail** | Excellent | Poor | Good |
| **Fistula detection** | 90-95% sensitivity | 60-70% | 85-90% |
| **Abscess detection** | Excellent | Poor | Good |
| **Functional assessment** | Yes (diffusion) | No | Limited |
| **Small bowel detail** | Excellent | Good | Good |

**High-Yield:** MRE is the imaging modality of choice for:
  - Detecting fistulas and sinus tracts
  - Assessing fistula complexity (simple vs. complex)
  - Identifying associated abscesses
  - Evaluating small bowel disease extent
  - Pre-operative surgical planning

### Fistula Classification (Relevant to Crohn's)

1. **Simple fistula:** Single tract, no abscess
2. **Complex fistula:** Multiple tracts, branching, associated abscess, or horseshoe configuration

**Clinical Pearl:** MRE with fistulography uses gadolinium-enhanced sequences and T2-weighted imaging to visualize fistula tracts as high-signal-intensity lines. This is superior to barium studies, which may miss internal fistulas entirely.

**Warning:** Barium studies can cause peritonitis if perforation is present — they are contraindicated in acute complicated Crohn's disease. MRI is safer in this context.

![Inflammatory Bowel Disease diagram](https://mmcphlazjonnzmdysowq.supabase.co/storage/v1/object/public/blog-images/explanation/3004.webp)

Answer

B. Plain abdominal radiograph

Answer

C. Abdominal ultrasound with Doppler

Answer

D. Barium follow-through study

Explanation

Investigation of Choice for Fistula Assessment in Crohn's Disease

Why MR Enterography with Fistulography is Superior

Advantages of MRE with Fistulography

Fistula Classification (Relevant to Crohn's)

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Feature	MRE with Fistulography	Barium Follow-Through	CT Enterography
Radiation	None	Yes	Yes
Soft tissue detail	Excellent	Poor	Good
Fistula detection	90-95% sensitivity	60-70%	85-90%
Abscess detection	Excellent	Poor	Good
Functional assessment	Yes (diffusion)	No	Limited
Small bowel detail	Excellent	Good	Good