Intestinal Ultrasound: Technique, Bowel Wall Thickness, Crohn's Disease and Diverticulitis

Intestinal ultrasound directly assesses the bowel wall, and the central parameter is thickness: in Crohn's disease, the EFSUMB guideline uses above 3 mm when high sensitivity is wanted and above 4 mm when high specificity is wanted. Thickness, however, is not a diagnosis. A useful report states which segment is abnormal, over what length and with which associated signs.

Intestinal ultrasound technique

• Two transducers: low frequency for overview and for deep segments or obese patients; above 5 MHz to measure the wall, whose layers are usually under 1 mm.
• Graded compression: a normal loop compresses easily; a diseased loop, barely.
• Systematic sweep of the quadrants with anatomic landmarks: the iliopsoas muscle and iliac vessels help locate the terminal ileum on the right and the sigmoid on the left.
• Wall measurement with the beam perpendicular, in a representative stretch, from the lumen-mucosa interface to the serosa.
• Color or power Doppler for vascularity, and harmonics when available.

Bowel wall thickness and stratification

The normal wall has five layers of alternating echogenicity. Cut-offs vary across sources:

• Normal small bowel: below 2 mm is the reference attributed to EFSUMB in reviews; 3 mm is the most adopted cut-off for activity.
• Crohn's, in a meta-analysis of 15 studies: 3 mm had 89% sensitivity and 96% specificity; 4 mm, 87% and 98%.
• Diverticulitis: studies use above 4 or 5 mm in the segment with a diverticulum.

Crohn's disease

• Stratification: thickening with loss of layers is associated with a higher risk of surgery.
• Doppler: the Limberg scale goes from 1 (no signal) to 4 (signal in the wall and mesentery); above 2 is considered pathological.
• Inflammatory fat: hypertrophied mesenteric fat wrapping the loop.
• Stricture: narrowing with upstream dilation.
• Tracts and abscesses: hypoechoic tract, sometimes with air; abscess as a collection outside the wall, surrounded by inflamed fat. Complex fistulas call for enterography.

At follow-up, the 2025 international consensus defines response as a drop of at least 25% in thickness from baseline, or combined improvement in thickness with Doppler or another parameter. That is why the report should carry the prior value.

Diverticulitis

The most used criteria are an inflamed diverticulum with tenderness on compression, a thickened wall in the segment and echogenic pericolic fat. A 2025 meta-analysis (12 studies) found 92.5% sensitivity and 87.7% specificity. The meta-analysis in the Korean KASID guideline found 85% and 98% for ultrasound, against 96% and 98% for CT.

Guidelines differ on the role of the method. KASID recommends CT as the test of choice and ultrasound by an experienced examiner when CT is limited. EFSUMB places ultrasound at the base of the assessment and CT as backup, especially for the distal sigmoid, deep pelvic inflammation and poor windows.

What the report should include

• Segment, length and maximum thickness, compared with the prior study.
• Stratification, Doppler and adjacent fat.
• Stricture, upstream dilation, tracts and collections.
• In diverticulitis: segment, involved diverticulum, fat, collection and free fluid.
• Segments not assessed and why.

Common mistakes

• Writing "bowel loops unremarkable" without assessing the terminal ileum and sigmoid.
• Measuring the wall in a contracted loop without reassessing peristalsis.
• Calling thickening Crohn's disease without symptoms or confirmation.
• Not stating the limitation in the deep pelvis.
• Omitting the prior measurement at follow-up.

See also our articles on ultrasound in appendicitis and the abdominal ultrasound guide.

How Laudário helps

Laudário does not have a dedicated intestinal ultrasound template with activity scores. In the complete abdomen templates, the bowel loops tab offers:

• Crohn's disease with location, thickening, creeping fat, stricture and hyperemia.
• Diverticulitis with segment, length, thickness, fat and abscess.
• Appendix and right iliac fossa in the same place, plus epiploic appendagitis and mesenteric adenitis.

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References

• Maconi G, et al. EFSUMB Guidelines for GIUS in Inflammatory Bowel Diseases. Ultraschall Med 2018.
• Nylund K, et al. EFSUMB Recommendations and Guidelines for Gastrointestinal Ultrasound. Part 1: Examination Techniques and Normal Findings. Ultraschall Med 2017;38:273-284.
• Kucharzik T, et al. Intestinal ultrasound and management of small bowel Crohn's disease. Therap Adv Gastroenterol 2018;11.
• Dirks K, et al. EFSUMB Position Paper: Recommendations for GIUS in Acute Appendicitis and Diverticulitis. Ultraschall Med 2019;40:163-175.
• Lee, et al. KASID clinical practice guidelines for acute colonic diverticulitis. Intest Res 2026;24.