What is the best initial imaging modality, ultrasound or abdominal x-ray (abdominal radiograph), to check for appendicitis?

Ultrasound vs. Abdominal X-ray for Appendicitis Diagnosis

Ultrasound should be used as the first-line imaging modality for suspected appendicitis, while abdominal x-ray has no significant role in the diagnosis of appendicitis. 1, 2, 3, 4

Initial Imaging Approach by Patient Population

Adults

• CT abdomen with IV contrast is recommended as the initial imaging modality in non-pregnant adults with suspected acute appendicitis due to its high sensitivity (96-100%) and specificity (93-95%) 2
• However, ultrasound should be considered first in young adults to minimize radiation exposure, with CT reserved for cases with equivocal ultrasound results or atypical presentations 3, 5
• When ultrasound results are definitive (either positive or negative), sensitivity approaches 99% with excellent specificity 1

Children

• Ultrasound is strongly recommended as the first-line imaging study in children with suspected appendicitis due to:
  • Absence of radiation exposure
  • Wide availability
  • Good diagnostic accuracy when results are definitive 1
• If ultrasound results are equivocal and clinical suspicion persists, MRI or CT imaging should be considered as the next step rather than repeating ultrasound 1

Pregnant Women

• Abdominal ultrasound is the recommended initial imaging modality for pregnant women with suspected appendicitis 2, 6
• Ultrasound avoids radiation exposure to the fetus but has a high rate of equivocal results in pregnant women (median 95% in studies) 6
• If ultrasound is inconclusive or negative but clinical suspicion remains high, MRI should be the next imaging modality 2, 6

Limitations and Considerations

Ultrasound Limitations

• Ultrasound is operator-dependent and may result in non-visualization of the appendix 5, 4
• In adults, ultrasound has shown sensitivity of 74.3% and specificity of 53.0% with high positive predictive value (95.9%) but low negative predictive value (12.2%) 7
• Risk factors for false negative or indeterminate ultrasound results include:
  • Female sex
  • Age >30 years
  • Elevated BMI 7

Management of Equivocal Results

• When ultrasound findings are equivocal or there is clinico-radiological dissociation, follow-up imaging with CT or MRI is recommended 5
• In pediatric and pregnant patients with inconclusive ultrasound, MRI is the preferred next option 5
• If there is strong clinical suspicion after equivocal imaging, exploratory laparoscopy may be considered if subsequent imaging would delay appropriate management 1

Role of Abdominal X-ray

• Abdominal radiography has practically no role in the diagnosis and management of acute appendicitis 5
• Neither the American College of Radiology nor other major medical societies recommend abdominal x-ray for suspected appendicitis 1, 2, 6

Cost and Efficiency Considerations

• Despite the potential for inconclusive results, ultrasound-first imaging is more time-efficient and less costly than starting with MRI 8
• A stepwise approach starting with ultrasound, followed by CT or MRI only when necessary, reduces overall radiation exposure and healthcare costs 5, 4