What is the most appropriate initial imaging study for a pediatric patient with severe abdominal pain, rebound tenderness, and mild grade fever, suspected of having appendicitis?

Ultrasound of the Abdomen is the Most Appropriate Initial Imaging Study

For a pediatric patient presenting with severe right lower quadrant abdominal pain, rebound tenderness, and fever—classic signs of acute appendicitis—ultrasound of the abdomen (US abdomen) is the recommended initial imaging modality. 1, 2

Rationale for Ultrasound as First-Line Imaging

• Ultrasound is the guideline-recommended initial imaging study for children with suspected appendicitis across all clinical risk categories where imaging is indicated, with sensitivity of 82-99% and specificity of 94-97%. 1, 2

• The clinical presentation described (severe pain, inability to stand straight, rebound tenderness, fever) places this patient in the intermediate-to-high risk category, where imaging provides diagnostic benefit and US is specifically recommended as the first imaging modality. 1, 2

• US avoids radiation exposure, which is particularly important in the pediatric population, while maintaining excellent diagnostic accuracy when performed with proper technique (graded compression). 1, 2

• The 2024 Infectious Diseases Society of America guidelines specifically recommend obtaining abdominal US as the initial imaging modality to diagnose acute appendicitis in children and adolescents. 1

Why Not CT Initially?

• CT should be reserved for equivocal or non-diagnostic ultrasound results, not as the first-line study, despite its high sensitivity (94%) and specificity (95%). 1, 3, 2

• CT involves radiation exposure (3-6 mSv with low-dose protocols, up to 11-24 mSv with standard protocols), which should be avoided when US can provide the diagnosis. 4

• The staged imaging approach (US first, then CT or MRI if equivocal) has been shown to be 94% accurate with 92% sensitivity and 95% specificity for appendicitis diagnosis. 1

Why Not MRI Initially?

• MRI has similar accuracy to CT (sensitivity 86-98%, specificity 94-97%) but is not readily available in most emergency settings and may require sedation in young children. 1, 2

• MRI is appropriately used as a second-line study after equivocal ultrasound, particularly when radiation avoidance remains a priority. 1, 3, 2

Why Not MRCP?

• MRCP (magnetic resonance cholangiopancreatography) is specifically designed for biliary and pancreatic pathology, not appendicitis, and would be inappropriate for this clinical presentation. 1

Critical Management Pathway

If the initial US is equivocal or non-diagnostic and clinical suspicion persists:

• Obtain CT abdomen/pelvis with IV contrast (91% sensitivity, 98% specificity following equivocal US) or MRI as the next step. 1, 3, 2
• Do not repeat ultrasound, as this is less likely to be diagnostic than proceeding to CT or MRI. 3, 2

Important caveat: US has limited sensitivity for detecting perforated appendicitis, which should be considered if nonoperative management is contemplated. 1, 2

Answer: B. US abdomen