What is the diagnostic approach for acute diverticulitis?

Diagnostic Approach for Acute Diverticulitis

Begin with clinical assessment combining history, physical examination, and laboratory markers, but do not rely on clinical findings alone—proceed to CT imaging when diagnostic uncertainty exists, as clinical diagnosis is correct in only 40-65% of cases. 1, 2

Initial Clinical Assessment

Key Clinical Features to Identify

• Left lower quadrant pain (acute or subacute onset) is the most common presenting symptom 2
• Fever is frequently present 2
• Nausea without vomiting is characteristic (absence of vomiting is actually a positive predictor) 1, 2
• Change in bowel habits 2
• Direct tenderness localized to the left lower quadrant on physical examination 1

Laboratory Markers

• Elevated white blood cell count and C-reactive protein (CRP) are typical findings 2
• CRP >50 mg/L combined with left lower quadrant tenderness and absence of vomiting has 97% positive predictive value for diverticulitis 1
• CRP >170 mg/L discriminates severe from mild diverticulitis with 87.5% sensitivity and 91.1% specificity 1
• Leukocyte count >13.5 × 10⁹ cells/L predicts progression to complicated disease 1

Critical Clinical Decision Rule

If all three criteria are present, diagnosis can be made clinically in 97% of cases: 1

1. Direct tenderness only in the left lower quadrant
2. CRP >50 mg/L
3. Absence of vomiting

When to Proceed to Imaging

Obtain CT imaging in the following situations—do not rely on clinical assessment alone: 1, 2

• No prior imaging-confirmed diagnosis of diverticulitis 2
• Diagnostic uncertainty based on clinician experience 1
• First episode without previous documentation 2
• Symptoms >5 days before presentation 1, 2
• Signs suggesting complications: perforation, bleeding, obstruction, or abscess 1, 2
• Severe presentation or failure to improve with therapy 2
• Immunocompromised patients 2
• Patients without all three clinical decision rule criteria 1
• Alternative diagnoses suspected: cancer, gynecologic causes, renal causes, inflammatory bowel disease 1

Imaging Modality Selection

First-Line: CT Abdomen/Pelvis with IV Contrast

CT with intravenous contrast is the gold standard diagnostic test with 95-99% sensitivity and 99-100% specificity. 1, 2, 3

CT findings confirming diverticulitis: 1, 2

• Colonic wall thickening
• Increased density of pericolic fat
• Inflammatory changes
• Edema in the root of the sigmoid mesentery
• Absence of pericolonic lymphadenopathy (>1 cm suggests cancer instead) 2

CT findings for staging complications: 1

• Stage 0 (uncomplicated): Diverticula, wall thickening, pericolic fat stranding only
• Stage 1a: Pericolic air bubbles or small fluid collection (<5 cm from bowel)
• Stage 1b: Abscess ≤4 cm
• Stage 2a: Abscess >4 cm
• Stage 2b: Distant gas (>5 cm from inflamed segment)
• Stage 3: Diffuse fluid without distant free gas
• Stage 4: Diffuse fluid with distant free gas (generalized peritonitis)

Alternative Imaging When CT Cannot Be Obtained

If CT with IV contrast is contraindicated (severe renal disease, contrast allergy): 1, 2

1. Abdominal ultrasonography as first alternative 1, 2

   • Sensitivity varies widely (operator-dependent) 1
   • Some studies show comparable sensitivity to CT, others significantly lower 1

2. MRI if ultrasonography is inconclusive 1, 2

   • Sensitivity 86-94%, specificity 88-92% 1
   • Useful in obese patients or those with extensive bowel gas 1

3. CT without IV contrast as last resort 1

Critical Pitfalls to Avoid

Do Not Diagnose on Clinical Grounds Alone in Elderly Patients

In elderly populations, clinical signs, symptoms, and laboratory tests alone are insufficient—always obtain imaging regardless of leukocyte or CRP values if there is abdominal guarding or left lower quadrant pain. 1

Rule Out Colorectal Cancer

Colorectal cancer mimics diverticulitis clinically and radiographically. 2

CT findings suggesting cancer rather than diverticulitis: 2

• Pericolonic lymphadenopathy >1 cm in short axis
• Lymphadenopathy with or without pericolonic edema

Colonoscopy is mandatory: 2

• After all episodes of complicated diverticulitis (7.9% cancer risk)
• After first episode of uncomplicated diverticulitis (1.3% cancer risk)
• Delayed 6-8 weeks or until complete symptom resolution
• May be deferred if high-quality colonoscopy performed within 1 year

Avoid Plain Radiography

Conventional abdominal radiographs have limited diagnostic value and rarely change management—they are normal in 79% of diverticulitis cases. 1, 4

Avoid Endoscopy During Acute Episode

Do not perform colonoscopy during acute diverticulitis—perforation/abscess must be excluded before any endoscopic evaluation. 5

Radiation Exposure Considerations

• Abdominal CT delivers approximately 10 mSv effective radiation dose (compared to 3 mSv annual background radiation) 1
• Balance radiation risk against the 40-65% misdiagnosis rate with clinical assessment alone 2
• Consider ultrasonography first in younger patients when expertise is available 1