What is the recommended diagnostic approach using CT scan for an adult patient suspected of having diverticulitis?

CT Scan for Suspected Diverticulitis

In non-pregnant adults with suspected acute diverticulitis, obtain an abdominal CT scan with intravenous contrast as the initial diagnostic imaging modality. 1

Recommended CT Protocol

CT abdomen and pelvis with IV contrast is the gold standard, demonstrating exceptional diagnostic accuracy with sensitivity of 92-99% and specificity of 97-100%. 1, 2, 3

Contrast Administration

• IV contrast is usually appropriate and should be administered to characterize bowel wall abnormalities, detect subtle inflammation, and identify complications such as abscess formation. 1
• CT without IV contrast may be acceptable when IV contrast is contraindicated (severe renal disease or contrast allergy), though diagnostic accuracy is reduced. 1
• Oral contrast may improve abscess detection by distinguishing abscess from adjacent bowel loops, though unenhanced CT with oral contrast remains less accurate than contrast-enhanced CT with oral contrast. 1

Key Diagnostic Advantages

CT provides multiple critical functions beyond diagnosis:

• Distinguishes complicated from uncomplicated diverticulitis, directly impacting treatment decisions. 1, 2
• Identifies alternative diagnoses (neoplasm, inflammatory bowel disease, appendicitis, ischemic colitis) with sensitivity ranging 50-100%, significantly higher than ultrasound (33-78%). 1, 4
• Detects complications including abscess, perforation, fistula, and obstruction with 96-98% accuracy. 1, 4
• Guides interventional procedures such as percutaneous drainage for abscesses ≥3-4 cm. 1, 5

Alternative Imaging When CT Unavailable or Contraindicated

Ultrasound

If CT is unavailable or contraindicated, ultrasound or MRI can be considered as alternatives, though with important limitations. 1

• Ultrasound has sensitivity >90% and positive predictive value >90% in meta-analyses, but pooled specificity (90%) is significantly lower than CT (96%). 1, 2
• Major limitations include: diminished accuracy in obese patients, reduced detection of distal sigmoid diverticulitis, inability to identify alternative diagnoses as effectively as CT, and requirement for high operator expertise (minimum 500 examinations for competency). 1, 2
• A step-up approach is reasonable: perform ultrasound first, then CT if ultrasound is inconclusive or negative. 1

MRI

• MRI demonstrates sensitivity of 94% and specificity of 88%, though evidence quality is low due to limited studies. 1, 2
• Motion artifact may limit image quality in acutely ill patients unable to remain still during acquisition. 1

Special Population: Pregnant Patients

In pregnant adults with suspected diverticulitis, ultrasound or MRI should be considered to avoid radiation exposure, though insufficient evidence exists to recommend one over the other. 1, 2

Special Population: Elderly Patients

CT scan with IV contrast should be performed in ALL elderly patients with suspected diverticulitis regardless of laboratory values (CRP, leukocyte count). 1

Critical Rationale

• Clinical presentation is atypical in elderly patients: only 50% have lower quadrant pain, only 17% have fever, and 43% lack leukocytosis. 1
• CT changed unsuspected diagnoses in 43% of elderly patients presenting with acute abdominal pain and influenced treatment plans in 65% overall. 1
• Low CRP does not exclude complicated diverticulitis: 39% of patients with complicated disease had CRP below the optimal threshold of 175 mg/L. 1

Contrast-Induced Nephropathy Prevention

The prevalence of chronic kidney disease in patients >60 years is 39.4%, but the diagnostic benefit of CT with contrast generally justifies the risk. 1, 6

For patients with GFR <40-45 mL/min/1.73 m², initiate isotonic saline hydration at 1 mL/kg/hour for 12 hours before and after contrast administration. 6

Imaging NOT Recommended

Plain radiography is not useful as the initial imaging test because it cannot detect extramucosal inflammation, has poor sensitivity for small amounts of free air, and misses abscess formation. 1

Contrast enema is not recommended for acute diverticulitis due to increased perforation risk with colonic distention and inability to visualize extraluminal pathology. 1

Common Pitfalls to Avoid

• Do not rely on clinical signs and laboratory tests alone to diagnose or exclude diverticulitis, especially in elderly patients. 1
• Do not skip CT imaging based on normal inflammatory markers—12 cases of perforation would have been missed if CT was performed only when CRP >50 mg/L. 1
• Do not perform biphasic imaging (unenhanced plus contrast-enhanced CT)—this is unnecessary and not recommended. 1
• Do not perform colonoscopy during acute flare-up due to increased perforation risk; delay endoscopic evaluation 6 weeks after symptom resolution. 5, 7