Diagnosis of Diverticulitis
Do not rely on clinical examination alone—obtain CT imaging with IV contrast to confirm the diagnosis of acute diverticulitis, as clinical diagnosis is correct in only 40-65% of cases. 1
Diagnostic Approach Algorithm
Initial Clinical Assessment
Clinical presentation alone is insufficient for diagnosis. The classic triad that suggests diverticulitis includes: 1
- Left lower quadrant tenderness (present in only 50% of elderly patients) 1
- CRP > 50 mg/L 1
- Absence of vomiting 1
When all three criteria are present, diagnostic accuracy reaches 97%, but this occurs in only 24% of patients. 1
Critical pitfall in elderly patients: Only 50% present with lower quadrant pain, only 17% have fever, and 43% lack leukocytosis—making clinical diagnosis even less reliable in this population. 1, 2
Laboratory Testing
Obtain the following baseline studies: 3, 4
- Complete blood count (WBC elevation)
- C-reactive protein (most useful inflammatory marker)
- Basic metabolic panel
- Urinalysis
CRP has prognostic value for severity: 1
- CRP < 170 mg/L suggests mild/uncomplicated diverticulitis (87.5% sensitivity, 91.1% specificity) 1
- CRP > 170 mg/L indicates higher probability of requiring surgery or drainage 1
- However, 39% of patients with complicated diverticulitis have CRP < 175 mg/L—do not use low CRP to exclude complications 1, 2
Imaging: The Definitive Diagnostic Step
CT abdomen/pelvis with IV and oral contrast is the gold standard imaging modality with sensitivity 95-100% and specificity 97-100%. 1, 2, 5
Mandatory CT indications: 1, 2
- No prior imaging-confirmed diagnosis of diverticulitis
- Severe presentation suggesting complications (abscess, perforation, peritonitis)
- Immunocompromised patients (chemotherapy, steroids, transplant recipients)
- Failure to improve with initial therapy
- Multiple recurrences when considering prophylactic surgery
- Elderly patients (>65 years) due to atypical presentations
CT changes management in 37% of patients and alters surgical decisions in 48% of elderly patients. 1, 2
CT Classification (WSES System)
Use CT findings to classify disease severity: 1
Uncomplicated (Stage 0):
- Diverticula, bowel wall thickening, increased pericolic fat density 1
Complicated:
- Stage 1a: Pericolic air bubbles or small fluid collection within 5 cm 1
- Stage 1b: Abscess ≤ 4 cm 1
- Stage 2a: Abscess > 4 cm 1
- Stage 2b: Distant gas (> 5 cm from inflamed segment) 1
- Stage 3: Diffuse fluid without distant free gas 1
- Stage 4: Diffuse fluid with distant free gas (generalized peritonitis) 1
Alternative Imaging Considerations
Ultrasound can be used as initial imaging only when performed by expert operators, with CT follow-up for inconclusive cases. 2 This is more commonly utilized in Europe. 1
MRI is very sensitive but less specific than CT and generally not used acutely. 1
Avoid CT in pregnancy—consider MRI or ultrasound as alternatives. 2
Post-Acute Colonoscopy Timing
Colonoscopy is mandatory after complicated diverticulitis to exclude malignancy (7.9% prevalence of colon cancer in complicated cases vs 1.3% in uncomplicated). 1
Timing: Delay colonoscopy by 6-8 weeks after symptom resolution, whichever is longer. 1
Can defer colonoscopy if high-quality colonoscopy performed within 1 year before the acute episode. 1
Key Clinical Pitfalls to Avoid
- Never diagnose based on clinical findings alone—positive predictive value is only 65%, while CT has 95% PPV 1
- Do not assume normal inflammatory markers exclude severe disease—up to 39% of complicated cases have CRP < 175 mg/L 1, 2
- Do not delay CT in high-risk patients (elderly, immunocompromised, severe presentation)—mortality increases significantly with delayed diagnosis 2
- Remember alternative diagnoses that mimic diverticulitis: ovarian pathology, leaking aortic/iliac aneurysm, ureterolithiasis, appendicitis, and colon cancer 2