Colitides

Key radiological signs of inflammation

The main marker of the inflammatory process in cross-sectional imaging is bowel wall thickening (4 mm or more). With intravenous contrast administration (optimally in the enteral phase, at 45–50 seconds), the wall actively enhances.

A layered pattern (layered pattern) is frequently identified: central and peripheral enhancement with a hypodense zone between them. This is a non-specific sign found in infections, ischemic injury, and IBD.

The advantage of tomography over conventional barium enema lies in the visualization of surrounding tissues. The methods allow the detection of:

• Phlegmons — inflammatory infiltrates without clear borders in the adjacent omentum or mesentery.
• Abscesses — walled-off collections of low density (10–30 HU) that may contain gas bubbles due to gas-forming bacteria or communication with the bowel lumen.

On ultrasound during an acute process, the wall thickens but often preserves layer differentiation (characteristic of ulcerative colitis), whereas in chronic Crohn's disease, stratification may be lost.

IBD: Ulcerative Colitis and Crohn's Disease

Despite their common nature, the radiological presentation of these two diseases has significant differences:

1. Ulcerative Colitis (UC): inflammation always starts in the rectum and continuously spreads proximally. Involvement is symmetric and limited to the mucosa. Wall thickness is typically 5–8 mm. A typical sign is reflux ileitis (reflux ileitis): gaping of the ileocecal valve with inflammation of the distal 10–15 cm of the ileum (completely disappears after colectomy).
2. Crohn's Disease (CD): involvement is focal and asymmetric. Inflammation is transmural in character (affecting all layers of the wall), leading to deep slit-like ulcers and fistula formation. The wall is significantly thicker (averaging 11 ± 5.1 mm). Aphthoid ulcerations (aphthoid ulceration) are visualized on the mucosa. The rectum is involved in only about half of patients.

In acute extensive colitis, the mucosa can be virtually destroyed, leaving only edematous areas—pseudopolyposed elevations. As healing occurs, thread-like or bridge-like structures form, known as post-inflammatory polyps (post-inflammatory polyps).

Assessment of disease activity in IBD

The use of potent therapy (e.g., TNF-alpha inhibitors) requires a precise understanding: is the inflammatory process active now, or is this a consequence of scarring?

Signs of active inflammation:

• Pronounced wall thickening with layered enhancement.
• High signal intensity on T2-weighted MRI images, directly reflecting tissue edema.
• «Comb sign» (comb sign) — increased vascularization of the mesentery.
• Presence of free fluid, mesenteric edema, and enlarged lymph nodes.

Signs of chronic fibrosis:

• Heterogeneous but moderate contrast enhancement.
• Low MR signal on T2-WI.
• Specific adipose tissue proliferation: increase in submucosal fat in UC or proliferation of fibro-fatty mesenteric and presacral tissue in CD.

Ischemic and radiation colitis

• Ischemic colitis is more common in patients over 60 years of age (in younger patients, causes may include vasculitis, cocaine use, or hypercoagulable states). The typical localization is the splenic flexure. Radiography sometimes reveals the thumbprinting sign. CT visualizes a low-density target sign caused by submucosal edema. Transmural necrosis (mesenteric stranding, portal venous gas, pneumatosis) requires emergency surgery.
• Radiation colitis occurs as a late complication of radiation therapy (at doses >45 Gy), most commonly in pelvic oncology. The rectum is primarily affected. It is characterized by generalized wall thickening, mesorectal fat fibrosis, widening of the presacral space, and the risk of rectovaginal fistula formation.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Modern methods for the differential diagnosis of strictures (ultrasound elastography, magnetization transfer MRI).
• Specific radiological patterns of infectious colitis (CMV, Chlamydia, Salmonella).
• Features of bowel involvement in Behçet's syndrome.
• Colorectal cancer in the setting of long-standing total ulcerative colitis: pathogenesis and screening.
• Dependence of colitis localization on the etiological factor (diffuse, right-sided, and left-sided involvement).

Other topics in the section "Diagnostic Radiology of the Abdominal Organs"

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