The clinical question is not "is there disease" but whether it is ACTIVE INFLAMMATION or FIBROSIS — and those have opposite treatments.
Orient first
- ACTIVE INFLAMMATION versus FIBROSTENOTIC disease is the whole point of the study, because one is treated medically and the other surgically or endoscopically. Reporting "wall thickening" without saying which is not an answer.
- ACTIVE disease shows high mural T2 signal (oedema), restricted diffusion, mural hyperenhancement often with stratification, engorged vasa recta (the comb sign) and adjacent fat stranding.
- FIBROTIC disease shows a thickened wall with LOW T2 signal, no restriction, and homogeneous delayed enhancement, usually with upstream dilatation.
- Most strictures are MIXED, and the honest report states the dominant component and the proportion rather than forcing one label.
- PENETRATING complications — sinus tract, fistula, phlegmon, abscess — change management immediately and must be searched for specifically.
Acquire the study
- Adequate ORAL contrast, taken over about an hour, is what makes the study interpretable; poor distension is the commonest cause of a non-diagnostic examination and mimics disease.
- Antispasmodic to reduce peristalsis, which otherwise blurs the wall.
- Coronal and axial T2 with and without fat suppression, DWI with ADC, and dynamic post-gadolinium including a delayed phase.
- CINE sequences to assess whether a narrowed segment is fixed or simply peristalsing.
- Confirm which sequence you are on before judging any signal — see the MRI sequence primer.
The manoeuvre
- Assess DISTENSION first and say whether it was adequate — an underdistended loop cannot be assessed and must not be called abnormal.
- Identify every abnormal segment and state its location and LENGTH.
- Measure wall thickness on a well-distended, correctly-oriented section.
- Assess mural T2 signal on fat-suppressed images to separate oedema from fibrosis.
- Review DWI and confirm any restriction on the ADC map.
- Assess the enhancement pattern and its timing, including the delayed phase.
- Assess the mesentery for the comb sign, fat proliferation, fluid and nodes.
- Search for PENETRATING disease: sinus tracts, fistulae, phlegmon and abscess, and describe their course.
- For any stricture, state the luminal calibre, the length, whether there is upstream dilatation, and whether the narrowing is FIXED on cine.
- Give a conclusion in terms of ACTIVITY and the dominant component.
What confirms it
- Active inflammation is mural thickening WITH high T2 signal, restricted diffusion and mural hyperenhancement, with mesenteric change.
- A fixed narrowing with upstream dilatation on cine imaging is a true stricture rather than peristalsis.
What licenses you to exclude it
- ⚠️ An underdistended study cannot exclude small bowel disease. Report it as limited and recommend a repeat rather than issuing a normal study.
- MR enterography assesses the small bowel well and the colon and rectum poorly — it does not replace colonoscopy.
- Absence of penetrating complications on a motion-degraded study is not an exclusion.
The classic misread
- Reporting wall thickening without classifying activity.
- Calling a peristaltic narrowing a stricture without cine confirmation.
- Assessing an underdistended loop.
- Missing a fistula by not following the tract on more than one plane.