Imaging for Suspected Appendicitis
Direct Answer
In non-pregnant adults with suspected acute appendicitis, obtain CT scan with intravenous contrast as the initial imaging modality. 1
Adult Patients (Non-Pregnant)
Primary Recommendation
- CT abdomen with IV contrast is the preferred initial imaging test for adults with suspected appendicitis, offering superior diagnostic accuracy with sensitivity of 96-100% and specificity of 93-95%. 1, 2, 3
Why CT Over Ultrasound in Adults
- CT provides definitive results that rarely require additional imaging, whereas ultrasound in adults has significant limitations with sensitivity of only 74.3% and specificity of 53.0%. 4
- Ultrasound is highly operator-dependent and frequently yields equivocal results in adults, particularly in patients who are female, over age 30, or have elevated BMI. 4
- When ultrasound is definitively positive or negative, it can be accurate, but this occurs less reliably in adults compared to children. 1
Technical CT Considerations
- IV contrast is usually appropriate and increases sensitivity to 96% compared to 91% for unenhanced CT. 1, 3, 5
- CT without IV contrast maintains high diagnostic accuracy (sensitivity ~91%, specificity ~98%) and may be appropriate in certain situations. 1, 3
- Oral contrast is generally not necessary and may delay diagnosis without improving accuracy. 2, 3
- Low-dose CT has similar diagnostic performance to standard-dose CT (sensitivity 94% vs 95%), making it a reasonable radiation-sparing option. 5
Management After Negative CT
- If CT is negative but clinical suspicion persists, consider observation with supportive care, with or without antibiotics. 1
- If clinical suspicion is high despite negative imaging, surgical intervention may still be warranted. 1, 3
Pediatric Patients
Primary Recommendation
- Ultrasound should be the initial imaging modality in children and adolescents with suspected appendicitis due to lack of radiation exposure and good accuracy when results are definitive. 1, 6, 2
- Ultrasound in children has sensitivity of approximately 76% and specificity of 95%. 2
- Point-of-care ultrasound by experienced operators shows higher performance (sensitivity 91%, specificity 97%). 2
When Initial Ultrasound is Equivocal
- If ultrasound is equivocal or non-diagnostic and clinical suspicion persists, obtain MRI or CT rather than repeating ultrasound. 1, 6
- CT with IV contrast is usually appropriate for follow-up imaging after equivocal ultrasound. 1, 6
- MRI is a radiation-free alternative that should be considered when readily available, though it may require sedation in young children. 1, 6
Pregnant Patients
Primary Recommendation
- Ultrasound is the initial imaging modality of choice in pregnant patients with suspected appendicitis. 1, 2
When Initial Ultrasound is Equivocal
- If ultrasound is inconclusive, MRI without IV contrast is preferred over CT. 1, 2, 3
- MRI is readily available in many centers and would yield similar results to a conditional imaging strategy (ultrasound followed by MRI). 1
Key Diagnostic Findings
CT Findings Suggesting Appendicitis
- Appendiceal diameter >6 mm with wall thickening >2 mm 7
- Periappendiceal fat stranding 2, 7
- Findings suggesting complicated appendicitis: extraluminal appendicolith, abscess, extraluminal air, appendiceal wall enhancement defect 2
Ultrasound Findings
- Appendiceal diameter ≥7 mm 2
- Non-compressibility of the appendix 2
- Appendiceal tenderness during examination 2
Common Pitfalls and Caveats
Ultrasound Limitations in Adults
- Ultrasound accuracy is highly operator-dependent and has poor negative predictive value (12.2%) in adults. 2, 4
- Females, patients over age 30, and those with elevated BMI are significantly more likely to have indeterminate or false negative ultrasound results. 4
- These high-risk patients may benefit from proceeding directly to CT as their initial screening test. 4
Imaging Accuracy for Complicated Appendicitis
- Both MRI and ultrasound may incorrectly classify up to half of patients with perforated appendicitis as having simple appendicitis. 2
- CT is superior for identifying complicated appendicitis features. 2
Radiation Concerns
- While radiation exposure is a consideration, concerns should be balanced against the need for accurate and timely diagnosis, particularly in adults where diagnostic accuracy directly impacts morbidity and mortality. 2
- Low-dose CT protocols provide comparable diagnostic accuracy with reduced radiation exposure. 5