Do jejunal loops appear thickened on MRI when not properly inflated with contrast?

Jejunal Loop Appearance on MRI with Inadequate Distension

Yes, jejunal loops can appear falsely thickened on MRI when they are not properly distended with oral contrast, making this a critical technical pitfall that can lead to misdiagnosis of inflammatory bowel disease.

Why Underdistension Causes Apparent Wall Thickening

Wall thickness measurements are only valid in properly distended bowel loops. 1 The consensus guidelines from the American Gastroenterological Association and Society for Abdominal Radiology explicitly state that wall thickness should "only be measured or estimated in bowel loops distended by enteric contrast." 1

When jejunal loops are collapsed or underdistended:

• The bowel wall appears artificially thickened due to accordion-like folding of the wall layers 1
• Mural hyperenhancement may also appear more prominent in contracted segments, mimicking inflammation 1
• This creates a false-positive appearance that can be mistaken for pathology

Critical Distinction: Hyperenhancement Without Wall Thickening

Mural hyperenhancement without wall thickening is a nonspecific imaging sign that may reflect contraction or underdistension rather than true inflammation. 1 The guidelines emphasize that hyperenhancement becomes diagnostically meaningful only when combined with wall thickening in a properly distended segment. 1

The differential diagnosis for hyperenhancement in underdistended bowel includes:

• Physiologic contraction 1
• Underdistension artifact 1
• True inflammation (Crohn's disease, infectious enteritis) 1
• Other pathologic processes (ischemia, vasculitis, NSAID enteropathy) 1

How to Avoid This Pitfall

Adequate luminal distension is essential for accurate MR enterography interpretation. 2 Studies comparing different CT enterography techniques demonstrate that jejunal distension quality varies significantly by protocol, with CT enteroclysis achieving optimal jejunal distension (median diameter 27 mm) compared to other oral contrast methods. 2

Key technical considerations:

• Assess multiple pulse sequences or serial images to determine if narrowing is fixed or related to peristalsis 1
• Compare the suspected abnormal segment to adjacent well-distended loops 1
• Look for additional features that suggest true pathology rather than artifact 1

Features That Indicate True Pathology vs. Artifact

When wall thickening is real inflammation rather than underdistension artifact, additional specific findings should be present:

True inflammatory wall thickening typically shows:

• Asymmetric involvement (mesenteric border more affected than antimesenteric border) - highly specific for Crohn's disease 1, 3
• Stratified enhancement pattern (bi- or tri-laminar) with submucosal edema 1, 3
• Intramural T2 hyperintensity on fat-saturated sequences, indicating edema 1, 3
• Restricted diffusion on high b-value images when combined with other inflammatory findings 1
• Mesenteric findings such as comb sign, lymphadenopathy, or fat stranding 1

Special Note on Diffusion-Weighted Imaging

Diffusion restriction can occur in normal jejunum without any pathology, particularly in underdistended loops. 4 A pediatric study found that 38.5% of patients with normal MR enterography and no clinical evidence of bowel disease demonstrated jejunal diffusion restriction, with no correlation to luminal distension, age, or magnetic field strength. 4 This reinforces that diffusion restriction alone, without other inflammatory features, should not be interpreted as pathologic in collapsed bowel segments.

Practical Measurement Guidelines

When bowel loops are adequately distended, wall thickness classification is:

• Normal: <3 mm 1, 3
• Mild thickening: 3-5 mm 1, 3
• Moderate thickening: 5-9 mm 1, 3
• Severe thickening: ≥10 mm 1, 3

These measurements are invalid in collapsed or underdistended segments and should not be reported. 1