How should inflammatory colitis identified on CT scan be evaluated and managed?

Evaluation and Management of Inflammatory Colitis on CT Scan

When inflammatory colitis is identified on CT scan, the immediate priority is to determine the specific etiology through targeted diagnostic testing—including stool studies for infectious causes and consideration of endoscopic evaluation—while simultaneously assessing for complications that require urgent intervention.

Initial Diagnostic Workup

Mandatory Stool Testing

• Obtain comprehensive stool studies immediately, including Clostridioides difficile toxin assay, bacterial cultures (Salmonella, Shigella, Campylobacter, E. coli), and ova/parasites when clinically indicated 1, 2
• Measure stool inflammatory markers (lactoferrin or calprotectin) to stratify severity and guide need for endoscopy; stool lactoferrin demonstrates 90% sensitivity for histologic inflammation 1

Laboratory Assessment

• Order baseline labs including complete blood count, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), electrolytes, liver function tests, albumin, and magnesium 2
• Consider CMV testing in immunocompromised patients or those with severe disease refractory to initial therapy 1, 2

CT Interpretation for Etiology Clues

Location-based differential diagnosis:

• Isolated right colon/ascending colon involvement suggests ischemic colitis, C. difficile infection, Crohn's disease, or medication-related colitis 3
• Left-sided predominance is typical for ulcerative colitis, diverticulitis, or ischemic colitis 1
• Pancolitis can occur with C. difficile (look for "accordion sign" or marked wall thickening >15 mm), severe ulcerative colitis, or Crohn's disease 3, 4

Pattern-based differential diagnosis:

• Symmetric circumferential thickening (mean 7.8 mm) with "target sign" and perirectal fat proliferation suggests ulcerative colitis 5
• Asymmetric thickening (mean 13 mm) with mesenteric fat stranding and engorged vasa recta indicates Crohn's disease 1, 3, 5
• Segmental involvement is most common in C. difficile colitis (66% of cases), with rectum and sigmoid most frequently affected 4

Risk Stratification for Severe Disease

Immediate Hospitalization Criteria

Admit any patient meeting criteria for acute severe colitis:

• Temperature >37.8°C, heart rate >90 bpm, hemoglobin <105 g/L, or CRP >30 mg/L 2
• ≥6 bloody stools per day with any systemic toxicity 2
• Pericolic fluid on CT is a marker of severe inflammation requiring immediate inpatient care and surgical consultation 2

High-Risk CT Features Requiring Urgent Intervention

• Colonic wall thickness >4 mm with pericolic fat stranding or ascites predicts higher mortality 2
• Pneumatosis intestinalis or free intraperitoneal air indicates perforation requiring emergency surgery 3, 2
• Colonic dilation >5.5 cm suggests toxic megacolon 1, 2
• Peritoneal signs (severe pain, rebound tenderness, guarding) mandate emergency surgical evaluation 2

Endoscopic Evaluation Strategy

When to Perform Endoscopy

• Flexible sigmoidoscopy is preferred over full colonoscopy in acute severe colitis due to lower perforation risk; approximately 95% of inflammation is visible in the left colon 1
• Perform within 48 hours if acute severe colitis is suspected to obtain biopsies for histology, assess for CMV, and identify deep ulceration (poor prognostic marker) 2
• Consider endoscopy when stool inflammatory markers are elevated, symptoms persist despite treatment, or differential diagnosis remains unclear 1
• Avoid full colonoscopy in fulminant colitis or when toxic megacolon is suspected 1, 2

Histologic Differentiation

Biopsies allow definitive diagnosis:

• Crohn's disease: transmural inflammation with granulomas 3
• Ulcerative colitis: mucosal-limited inflammation 3
• Ischemic colitis: ghost cells and hyalinized lamina propria 3
• CMV colitis: viral inclusions on tissue biopsy 3

Treatment Algorithm by Etiology

Clostridioides difficile Colitis

• Initiate empiric oral vancomycin 125 mg four times daily while awaiting test results in severe presentations 2
• If confirmed on steroids, add oral vancomycin 500 mg every 6 hours for 10 days while continuing corticosteroids 2
• Discontinue inciting antibiotics whenever feasible 2

Acute Severe Ulcerative Colitis

• Start intravenous corticosteroids immediately: hydrocortisone 100 mg every 6 hours OR methylprednisolone 60-80 mg daily 2
• Provide thromboprophylaxis with low-molecular-weight heparin for all admitted patients 2
• Withhold 5-ASA agents during the acute phase 2
• Day-3 response assessment: >8 bowel movements/day OR 3-8 movements/day with CRP >45 mg/L predicts ~85% steroid failure, indicating need for rescue therapy (infliximab or cyclosporine) 2

Immune Checkpoint Inhibitor Colitis

• Grade 1 symptoms: low-fiber diet and close monitoring 1
• Grade 2 or higher: systemic corticosteroids 0.5-2 mg/kg prednisone equivalent daily with 4-6 week taper 1
• Steroid-refractory disease (no response within 72 hours or incomplete response within 1 week): add infliximab or vedolizumab 1
• Colonic ulceration predicts need for second-line immunosuppression 1

Crohn's Disease

• Mild to moderate: oral mesalamine and topical mesalamine 2
• Moderate to severe: systemic corticosteroids and biologic therapy with infliximab or vedolizumab 2

Ischemic Colitis

• Conservative management first-line: bowel rest, IV fluids, broad-spectrum antibiotics 2
• Ultrasound-measured bowel wall thickness >10 mm associates with 60% mortality versus 4.2% when ≤10 mm 2

Essential Supportive Care

All Patients Require

• Adequate hydration and electrolyte replacement (potassium, magnesium) 2
• Maintain hemoglobin >10 g/dL 2
• Avoid antiperistaltic agents and opiates to prevent toxic megacolon 2
• Avoid NSAIDs as they exacerbate colonic inflammation 3, 2
• Daily abdominal examinations; obtain imaging if transverse colon diameter exceeds 5.5 cm 2

Emergency Surgical Indications

Consult surgery immediately for:

• Free air indicating perforation 2
• Toxic megacolon (radiologic dilation with severe systemic inflammation) 2
• Hemodynamic instability or septic shock despite optimal medical therapy 2
• Serum lactate >5.0 mmol/L (marker of severe disease) 2
• Clinical deterioration after 3-5 days of maximal medical treatment 2

Common Pitfalls to Avoid

• Do not delay treatment while awaiting stool culture results if acute severe colitis is suspected 2
• Do not perform full colonoscopy in fulminant colitis due to perforation risk 1, 2
• Do not rely on CT alone for diagnosis; sensitivity ranges only 53-85% for immune checkpoint inhibitor colitis, and patterns are indistinguishable between infectious, ischemic, and inflammatory etiologies 1
• Do not use empiric antibiotics in suspected inflammatory bowel disease flares once infection is excluded, as they may worsen outcomes 3
• Do not miss diverticulitis follow-up: colonoscopy should be performed 6-8 weeks after resolution to exclude underlying malignancy 6

Prognostic Markers

• Low hemoglobin, albumin <30 g/L, and elevated lactate predict higher surgery rates, ICU admission, and mortality 2
• CRP/albumin ratio >0.85 with stool frequency >3/day confers 74% risk of treatment failure 2
• Pericolic fluid with distant free air carries 57-60% failure rate with conservative management 2
• Endoscopic deep ulceration predicts poorer outcomes and increased colectomy rates 2