Can a contrast‑enhanced computed tomography (CT) scan of the abdomen and pelvis accurately diagnose acute appendicitis in an adult presenting with right lower quadrant pain, fever, and leukocytosis?

Can CT Scan Diagnose Appendicitis?

Yes—contrast-enhanced CT of the abdomen and pelvis is highly accurate for diagnosing acute appendicitis, with sensitivity ranging from 85.7% to 100% and specificity from 94.8% to 100%, making it the gold standard imaging modality for adults presenting with suspected appendicitis. 1

Diagnostic Performance of CT

CT demonstrates exceptional diagnostic accuracy that far exceeds clinical examination alone:

• Sensitivity: 85.7–100% across multiple studies 1
• Specificity: 94.8–100% 1
• Overall accuracy: 90–98.5% 2, 3
• Negative predictive value: 95–100% 3, 4

For context, clinical assessment alone misdiagnoses appendicitis in 34–68% of cases, with negative appendectomy rates reaching 25% when imaging is omitted. 5 Using preoperative CT reduces the negative appendectomy rate dramatically to 1.7–7.7%. 1

Optimal CT Protocol

The American College of Radiology recommends CT abdomen and pelvis with IV contrast only (no oral contrast required) for rapid, accurate diagnosis: 1, 5

• IV contrast alone achieves sensitivity of 90–100% and specificity of 94.8–100% 1
• Eliminates the 1-hour delay required for oral contrast administration 4
• Provides excellent visualization of appendiceal wall enhancement and periappendiceal inflammation 1

Unenhanced CT has lower sensitivity (91% vs. 96% for contrast-enhanced) and is limited in characterizing complications such as perforation and abscess formation. 1 Enhanced CT is superior across all age groups and should be performed unless IV contrast is contraindicated. 6

Key CT Diagnostic Findings

CT identifies appendicitis through multiple imaging signs: 1

• Maximal outer diameter >6 mm (optimal cutoff 8.2 mm for highest accuracy) 1, 7
• Periappendiceal fat stranding 1
• Appendiceal wall enhancement after IV contrast 5
• Absence of intraluminal gas 1
• Presence of appendicoliths (increases perforation risk) 7

When two or more signs are present, the odds ratio for appendicitis is 6.8. 1

Critical Value Beyond Appendicitis Diagnosis

CT identifies alternative diagnoses in 23–45% of patients presenting with right lower quadrant pain and suspected appendicitis, fundamentally changing management: 1, 5

• Gynecologic pathology: 21.6% of alternative diagnoses (ovarian torsion, ruptured cyst, ectopic pregnancy, PID) 5
• Gastrointestinal conditions: 46% of alternative diagnoses (right-sided diverticulitis, Crohn's disease, bowel obstruction) 5
• Genitourinary pathology: ureteral stones, pyelonephritis 5
• Right colonic diverticulitis: 8% of cases 5

Performance in Equivocal Clinical Presentations

CT is particularly valuable when clinical findings are uncertain:

• In patients with equivocal clinical exams, CT achieves 92% sensitivity, 85% specificity, and 90% overall accuracy 3
• After an equivocal ultrasound, CT demonstrates 91% sensitivity and 98% specificity 1
• A staged ultrasound-then-CT algorithm achieves 99% sensitivity and 91% specificity 1, 5

CT is significantly more sensitive and accurate than ultrasound (92% vs. 30% sensitivity; 88% vs. 69% accuracy, P<0.01). 3

Detection of Complications

CT reliably identifies complications of appendicitis: 1

• Perforation
• Abscess formation
• Bowel obstruction
• Periappendiceal phlegmon

This broad field of view allows comprehensive assessment of complications extending beyond the right lower quadrant, which focused imaging may miss. 1

Common Clinical Pitfalls to Avoid

Do not exclude appendicitis based on absence of fever—fever is absent in approximately 50% of appendicitis cases. 5

Do not rely on normal inflammatory markers—normal WBC and CRP are common in early appendicitis and do not rule out the diagnosis. 5

Do not assume a normal CT completely excludes appendicitis—sensitivity ranges from 85.7–100%, meaning early appendicitis may occasionally lack classic CT findings. 5 However, the negative predictive value remains excellent at 95–100%. 3, 4

Special Populations

In pregnant women, MRI should be used instead of CT, achieving 96% sensitivity and specificity with similar accuracy for detecting perforation. 1, 5

In children, the American College of Radiology recommends starting with ultrasound to avoid radiation, then proceeding to CT if ultrasound is nondiagnostic or equivocal. 1 A staged approach achieves 99% sensitivity and 91% specificity. 1

In reproductive-age women, transvaginal ultrasound may be performed first to evaluate gynecologic causes, but if nondiagnostic, proceed directly to contrast-enhanced CT. 5