In a 23-year-old male with terminal ileal ulcers and patchy colonic inflammation being evaluated for Crohn’s disease, should magnetic resonance enterography (MRE) be performed with intravenous gadolinium-based contrast?

MRE Traditionally Includes IV Contrast, But It May Be Omitted for Detecting Active Inflammation in the Terminal Ileum and Colon

In this 23-year-old patient with terminal ileal ulcers and patchy colonic inflammation being evaluated for Crohn's disease, MRE should be performed WITH intravenous gadolinium contrast to maximize detection of penetrating complications (fistulae, abscesses), though IV contrast may be omitted if the primary goal is solely to assess active inflammation in the terminal ileum and colon.

Standard MRE Protocol

According to the 2022 ACR Appropriateness Criteria, MRE traditionally includes the use of IV contrast, with the enteric phase (45-70 seconds after injection) being most commonly used to assess for mural hyperenhancement accompanying active bowel inflammation 1. The standard protocol combines:

• Large volume oral contrast (biphasic agent for bowel distension)
• IV gadolinium-based contrast
• Standard pulse sequences (T2-weighted, balanced steady-state free precession, diffusion-weighted imaging)
• Optional hypoperistaltic medication (glucagon or hyoscine butylbromide)

When IV Contrast Adds Value vs. When It Can Be Omitted

IV Contrast IS Important For:

Detecting penetrating complications - Recent evidence indicates that IV contrast improves MRE sensitivity for detecting penetrating Crohn's disease complications including fistulae, abscesses, sinus tracts, and inflammatory masses 1. In your patient with suspected Crohn's disease at initial diagnosis, these complications would significantly alter management (e.g., fistulae may indicate need for biologic therapy; abscesses may require drainage).

A 2018 pediatric study found that 3 out of 5 cases with perianal penetrating disease were not recognized on pre-contrast MRE 2. This is clinically significant because missing these complications could lead to inappropriate treatment decisions.

IV Contrast May Be Omitted For:

Detecting active inflammation in the terminal ileum and colon - Multiple recent studies show similar performance for detection of active inflammation without IV contrast 1. The same ACR guidelines note that "similar performance for detection of active inflammation in the terminal ileum and colon without IV contrast administration" has been demonstrated 1.

A 2016 prospective study showed that DWI without IV contrast was noninferior to contrast-enhanced MRE for evaluating small-bowel inflammation in Crohn's disease, with 91.8% agreement and correlation coefficient of 0.937 3. However, this study specifically noted that DWI and contrast-enhanced MRE "concurred in the diagnosis of penetrating complications in only five of eight segments," highlighting the limitation for penetrating disease.

Another 2018 pediatric study found no significant increase in diagnostic performance with IV contrast for assessment of small or large bowel inflammation, but noted potential for missing perianal complications without IV contrast 2.

Practical Algorithm for Your Patient

Given this is an initial diagnostic evaluation in a young patient with terminal ileal ulcers and patchy colonic inflammation:

1. Perform MRE WITH IV gadolinium contrast because:

   • This is the first cross-sectional imaging study
   • Need to comprehensively evaluate for penetrating complications that would alter initial treatment strategy
   • The patient is young (23 years old), making MRE preferable to CT to avoid radiation
   • Terminal ileal disease has high risk for penetrating complications

2. For future surveillance imaging (if diagnosis confirmed and monitoring response to therapy):

   • Consider non-contrast MRE with DWI if the sole goal is assessing mucosal inflammation
   • This minimizes cumulative gadolinium exposure in a young patient who will require repeated imaging
   • Maintain low threshold to add IV contrast if any concern for complications develops

Important Caveats

• Diffusion-weighted imaging (DWI) can substitute for IV contrast in detecting inflammatory wall thickening and lesion detection with comparable performance 1, but has moderate sensitivity and low specificity, leading to increased false positives 4

• Non-contrast MRE performs worse when bowel distension is suboptimal or in patients with limited mesenteric fat (though less of a concern in a 23-year-old) 1

• The 2018 consensus recommendations note that while MRE can be performed without IV contrast, the current consensus is that there is likely improved performance with post-IV contrast series 4