IBD Ultrasound

Simplified IBD US Severity Assessment

Based on bowel wall thickness, doppler activity, wall stratification, and inflammatory fat

Generalized Severity Grading

Start
Suspected active IBD
Perform ultrasound
↓
Step 1
BWT ≥3 mm?
↓
No
Inactive / remission
Yes
Proceed
↓
Step 2
Doppler ≥2?
↓
No
Mild disease
Yes
Proceed
↓
Step 3
Loss of stratification
and/or inflammatory fat?
↓
Partial
Moderate disease
Yes
Severe disease
↓
Override
Stricture, fistula, abscess,
phlegmon, dilation?
↓
Yes
Severe / complicated
Feature Mild Moderate Severe
BWT >3–4 mm thicker very thick
Doppler none/minimal focal diffuse ± mesenteric
Stratification preserved partial loss complete loss
Fat none mild marked

How to do it

  • Fasting ~6–8 hrs (optional but improves views)
  • Supine positioning
  • Use curvilinear (deep) + linear (high-res) probes
  • Scan systematically: terminal ileum → proximally or full abdominal sweep

What you measure

  • Bowel wall thickness (BWT)
  • Doppler vascularity
  • Wall stratification
  • Peristalsis + compressibility
  • Luminal narrowing / dilation
  • Extramural findings (fat, nodes, abscess)

Bowel wall layers

  • Mucosa → submucosa → muscularis → serosa

Bowel wall thickness

  • Measure perpendicular to wall
  • Longitudinal + transverse views
  • Use most abnormal segment
    • Normal: <3 mm
    • Active inflammation: ≥3 mm

Doppler grading (Limberg)

In general ≥2 = active inflammation

  • 0 → no flow
  • 1 → thickened wall, no flow
  • 2 → spotty flow
  • 3 → diffuse intramural flow
  • 4 → flow into mesentery

Bowel wall stratification (BWS)

Loss of stratification = deeper, transmural inflammation

  • 0 → normal (clear layered pattern)
  • 1 → uncertain
  • 2 → focal loss ≤3 cm
  • 3 → extensive loss >3 cm

Inflammatory fat (i-fat)

Mesenteric fat hypertrophy adjacent to inflamed bowel (“creeping fat”). Appears hyperechoic surrounding affected segment. It is a marker of transmural inflammation and more common in Crohn's disease. Associated with stricturing and penetrating disease.

  • 0 → absent
  • 1 → uncertain
  • 2 → present

Features of active disease

  • BWT ≥3 mm
  • Increased Doppler signal
  • Loss of wall stratification
  • Inflammatory fat (creeping fat)
  • Mesenteric lymph nodes

Validated Scoring systems

Ulcerative Colitis

  • Milan Ultrasound Criteria (MUC)
    • MUC = 1.4 × BWT + 2 × Doppler
    • >6.2 → active disease
  • UC-IUS index (0-7)
    • BWT
    • Doppler
    • Haustration
    • Fat

Crohn’s disease

  • IBUS-SAS
    • BWT
    • BWS
    • CDS
    • I-fat

References

  1. Kucharzik, T., Tielbeek, J., Carter, D., Taylor, S. A., Tolan, D., Wilkens, R., Bryant, R. V., Maconi, G., Maaser, C., Panes, J., Rimola, J., Rieder, F., & Sturm, A. (2025). ECCO-ESGAR-ESP-IBUS guideline on diagnostics and monitoring of inflammatory bowel disease. Journal of Crohn’s and Colitis. https://doi.org/10.1093/ecco-jcc/jjaf108
  2. Maaser, C., Sturm, A., Vavricka, S. R., Kucharzik, T., Fiorino, G., Annese, V., Calabrese, E., Baumgart, D. C., Bettenworth, D., Borralho Nunes, P., Burisch, J., Castiglione, F., Eliakim, R., Ellul, P., González-Lama, Y., Gordon, H., Halligan, S., Katsanos, K., Kopylov, U., ... Stoker, J. (2019). ECCO-ESGAR guideline for diagnostic assessment in IBD part 1: Initial diagnosis, monitoring of known IBD, detection of complications. Journal of Crohn’s and Colitis, 13(2), 144–164. https://doi.org/10.1093/ecco-jcc/jjy113
  3. Novak, K. L., Nylund, K., Maaser, C., Petersen, F., Kucharzik, T., Lu, C., Allocca, M., Maconi, G., Panaccione, R., Ghosh, S., & Wilkens, R. (2021). Expert consensus on optimal acquisition and development of the International Bowel Ultrasound Segmental Activity Score [IBUS-SAS]: A reliability and inter-rater variability study on intestinal ultrasonography in Crohn’s disease. Journal of Crohn’s and Colitis, 15(4), 609–616. https://doi.org/10.1093/ecco-jcc/jjaa216
  4. Bots, S., Nylund, K., Löwenberg, M., & Gecse, K. B. (2021). Intestinal ultrasound to assess disease activity in ulcerative colitis: Development of a novel UC-ultrasound index. Journal of Crohn’s and Colitis, 15(8), 1264–1271. https://doi.org/10.1093/ecco-jcc/jjab002
  5. Allocca, M., Filippi, E., Costantino, A., Bonovas, S., Fiorino, G., Furfaro, F., Peyrin-Biroulet, L., & Danese, S. (2021). Milan ultrasound criteria are accurate in assessing disease activity in ulcerative colitis: External validation. United European Gastroenterology Journal, 9(4), 438–442. https://doi.org/10.1177/2050640620980203
  6. Maaser, C., Petersen, F., Helwig, U., Fischer, I., Roessler, A., Rath, S., Lang, D., Kucharzik, T., & German IBD Study Group. (2020). Intestinal ultrasound for monitoring therapeutic response in patients with ulcerative colitis: Results from the TRUST&UC study. Gut, 69(9), 1629–1636. https://doi.org/10.1136/gutjnl-2019-319451