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