Gold Standard Imaging for Appendicitis
In non-pregnant adults with suspected appendicitis, CT abdomen/pelvis with intravenous contrast is the gold standard imaging modality, achieving sensitivity of 96-100% and specificity of 93-95%. 1
Adults (Non-Pregnant)
CT abdomen/pelvis with IV contrast should be obtained as the initial imaging study in adults with suspected acute appendicitis. 1
Technical Specifications for CT:
- IV contrast is strongly preferred and increases sensitivity to 96% compared to unenhanced CT (91% sensitivity). 1, 2
- Oral contrast is NOT necessary and should generally be avoided—it delays diagnosis by 40 minutes to 2+ hours without improving diagnostic accuracy. 3
- Low-dose CT performs equivalently to standard-dose CT with negligible differences in sensitivity and specificity, making it an acceptable alternative to reduce radiation exposure. 2
- CT without IV contrast maintains high accuracy (sensitivity ~91%, specificity ~98%) if contrast is contraindicated due to allergy or renal failure. 3, 2
Key Advantages of CT:
- No additional imaging is typically needed after CT due to its high accuracy—if CT is negative but clinical suspicion persists, proceed to observation with supportive care ± antibiotics rather than repeat imaging. 1
- CT identifies complicated appendicitis features including extraluminal appendicolith, abscess, extraluminal air, and periappendiceal fat stranding. 4
Children and Adolescents
Ultrasound should be the initial imaging modality in pediatric patients with suspected appendicitis (sensitivity 76%, specificity 95%). 1, 5
Rationale for Ultrasound First:
- Avoids radiation exposure, which is critical in children—CT delivers approximately 10 mSv of radiation. 5
- Point-of-care ultrasound by experienced emergency physicians or surgeons achieves higher accuracy (sensitivity 91%, specificity 97%) than radiology-performed ultrasound. 4, 5
- Key ultrasound findings include appendiceal diameter ≥7 mm, non-compressibility, and focal tenderness during examination. 4, 5
When Ultrasound is Equivocal:
If initial ultrasound is non-diagnostic and clinical suspicion persists, obtain CT abdomen/pelvis with IV contrast or MRI rather than repeating ultrasound. 1, 5
Critical Pitfall:
Ultrasound is highly operator-dependent and may incorrectly classify up to half of perforated appendicitis cases as simple appendicitis. 4, 5
Pregnant Patients
Ultrasound should be the initial imaging modality in pregnant patients with suspected appendicitis. 1
If Ultrasound is Inconclusive:
MRI without IV contrast is the preferred next step rather than CT, to avoid radiation exposure (sensitivity 94%, specificity 96%). 1, 4
- It would be reasonable to obtain MRI as the initial study if readily available, as the conditional strategy (ultrasound then MRI) yields similar results to MRI alone. 1
Common Pitfalls to Avoid
- Do not proceed directly to CT in children without attempting ultrasound first—this exposes them to unnecessary radiation when ultrasound may be diagnostic. 5
- Do not add oral contrast to CT studies—it provides no diagnostic benefit, delays care, and is poorly tolerated by patients with nausea and vomiting. 3
- Do not dismiss appendicitis based on negative imaging alone if clinical suspicion remains high—consider observation, antibiotics, or surgical consultation depending on clinical context. 1
- In elderly patients, proceed directly to CT with IV contrast due to higher rates of atypical presentations, complicated appendicitis, and mortality. 4