What is the best initial diagnostic step for a pediatric patient suspected of having appendicitis with right lower quadrant pain and a normal white blood cell (WBC) count?

Ultrasound Abdomen is the Best Initial Step for This 9-Year-Old

In a 9-year-old child with right lower quadrant pain, normal WBC, and atypical presentation for appendicitis, obtain an abdominal ultrasound as the initial imaging study rather than admitting for observation or proceeding directly to CT. 1

Rationale for Ultrasound-First Approach

The 2024 Infectious Diseases Society of America guidelines explicitly recommend ultrasound as the initial imaging modality for all children and adolescents with suspected acute appendicitis, regardless of laboratory values. 1 This recommendation prioritizes:

• Zero radiation exposure in a pediatric patient who may require serial imaging 1
• High diagnostic accuracy when definitive (sensitivity 82-99% when positive or negative, though lower when equivocal results included) 1
• Ability to identify alternative diagnoses including gynecologic pathology, intussusception, mesenteric adenitis, and ovarian pathology 2, 3

Why the Clinical Picture Does NOT Rule Out Appendicitis

This patient's presentation is concerning despite the reassuring features:

• Normal WBC occurs in up to 30% of pediatric appendicitis cases and has a negative predictive value of only 89.5-95.6% in children 4, 2
• Absence of fever is common in early appendicitis and does not exclude the diagnosis 2
• Classic symptoms occur in only ~50% of appendicitis cases 5, 2
• Absence of rebound tenderness does not rule out appendicitis, particularly in early presentations 2

The combination of RLQ pain alone warrants imaging evaluation rather than clinical observation or discharge. 5, 2

Why NOT to Admit for 24-Hour Observation (Option A)

Admitting for observation without imaging is outdated and potentially dangerous:

• Clinical examination alone has unacceptably poor diagnostic accuracy with negative appendectomy rates as high as 25% when relying on clinical assessment 2
• Delayed diagnosis increases perforation risk, which is already higher in pediatric patients 1, 3
• Observation without imaging does not improve diagnostic accuracy and merely delays definitive diagnosis 2

Why NOT to Proceed Directly to CT (Option B)

While CT has excellent diagnostic accuracy (90-94% sensitivity, 94% specificity), it is not the appropriate first-line test in children: 1

• Radiation exposure is particularly concerning in pediatric patients (effective dose ~10 mSv per abdominal CT) 1
• Guidelines explicitly recommend ultrasound first to minimize radiation burden 1
• CT should be reserved for equivocal ultrasound results when clinical suspicion persists 1

Why NOT to Discharge (Option C)

Discharging this patient would be inappropriate and potentially negligent:

• RLQ pain with normal labs does not exclude surgical pathology 5, 2
• CT identifies non-appendiceal causes requiring intervention in 22% of RLQ pain cases 5
• Missing early appendicitis leads to perforation and increased morbidity 1, 3

Algorithmic Management Approach

Step 1: Obtain abdominal ultrasound with graded compression of the RLQ 1

Step 2: If ultrasound is definitively positive → Surgical consultation for appendectomy 3

Step 3: If ultrasound is definitively negative → Consider alternative diagnoses; may discharge with strict return precautions if clinical suspicion is low 1

Step 4: If ultrasound is equivocal/non-diagnostic and clinical suspicion persists → Obtain MRI abdomen/pelvis (preferred) or CT abdomen/pelvis with IV contrast 1

Step 5: If MRI/CT unavailable and clinical suspicion high → Admit for observation with surgical consultation 1

Critical Pitfalls to Avoid

• Never rely on normal WBC alone to exclude appendicitis – it has insufficient negative predictive value in children 2, 4
• Do not skip imaging based on "atypical" presentation – atypical presentations are common in pediatric appendicitis 2, 3
• Avoid CT as first-line imaging in children unless ultrasound is unavailable or contraindicated 1
• Do not discharge without imaging when appendicitis remains in the differential diagnosis 5, 2