What are the diagnostic criteria for appendicitis?

Diagnostic Criteria for Appendicitis

The diagnosis of appendicitis should be based on a combination of clinical assessment, laboratory findings, and appropriate imaging, with CT abdomen and pelvis with IV contrast being the most accurate diagnostic test for adults with suspected appendicitis. 1

Clinical Assessment

Key Clinical Findings

• Right lower quadrant (RLQ) pain, abdominal rigidity, and periumbilical pain radiating to the right lower quadrant are the most reliable signs for diagnosing appendicitis in adults 2
• Classic symptom progression includes:
  • Vague periumbilical pain
  • Anorexia, nausea, and/or vomiting
  • Migration of pain to the right lower quadrant
  • Low-grade fever 3
• In children, additional reliable signs include:
  • Absent or decreased bowel sounds
  • Positive psoas sign (pain with extension of right hip)
  • Positive obturator sign (pain with internal rotation of flexed right hip)
  • Positive Rovsing sign (pain in RLQ when pressing the left lower quadrant) 2

Clinical Scoring Systems

• Alvarado score and Appendicitis Inflammatory Response score can help stratify patients into low, moderate, or high risk categories 2
• These scoring systems incorporate:
  • Migration of pain to RLQ
  • Anorexia/nausea/vomiting
  • RLQ tenderness
  • Rebound tenderness
  • Elevated temperature
  • Leukocytosis
  • Shift to left (neutrophilia) 3, 2

Laboratory Evaluation

• White blood cell count - typically elevated (>10,000/mm³)
• C-reactive protein - often elevated
• Urinalysis - to rule out urinary tract infection 4, 3

Imaging Studies

For Adults:

• CT abdomen and pelvis with IV contrast is the first-line imaging modality for suspected appendicitis in adults with typical presentation 1

  • Sensitivity: 90.8%, Specificity: 94.2% 4
  • Key CT findings of appendicitis:
    • Appendiceal dilatation (≥7 mm diameter)
    • Appendiceal wall thickening
    • Periappendiceal fat stranding
    • Appendicolith (when present)
    • Wall enhancement defect (in perforation) 1

• Ultrasound may be used as initial imaging in adults, particularly in pregnant patients, with CT reserved for equivocal cases 1

  • Sensitivity: 87.1%, Specificity: 89.2% 4
  • Findings include:
    • Non-compressible appendix >6mm
    • Target appearance on cross-section
    • Periappendiceal fluid 5

For Children:

• Ultrasound is the recommended first-line imaging for children 1
• CT should be reserved for cases with equivocal ultrasound findings 1
• MRI without IV contrast is an alternative when ultrasound is non-diagnostic, especially to avoid radiation exposure 1

For Pregnant Patients:

• Ultrasound should be the initial imaging modality 1
• MRI without IV contrast is recommended when ultrasound is non-diagnostic 1
• CT should be avoided when possible due to radiation concerns 1

Diagnostic Criteria for Complicated Appendicitis

CT findings suggestive of perforation include:

• Extraluminal appendicolith
• Abscess formation
• Extraluminal air
• Appendiceal wall enhancement defect
• Periappendiceal phlegmon or fluid collection 1

Common Pitfalls and Caveats

• Relying solely on clinical assessment can lead to high negative appendectomy rates (up to 25% historically) 1
• Atypical presentations are common in:
  • Elderly patients - often have delayed diagnosis and higher rates of perforation 1
  • Young children - less reliable symptoms 1
  • Pregnant women - displaced appendix due to gravid uterus 1
• Appendicitis with perforation has significantly higher mortality in elderly patients (11.9-15% vs 1.52-3% for non-perforated) 1
• Non-visualization of the appendix on ultrasound is common (reported in up to 29.2% of cases) and requires additional imaging 1
• CT findings of appendicolith, mass effect, and appendix diameter >13mm are associated with higher failure rates of antibiotic-only treatment 3

Algorithmic Approach to Diagnosis

1. Initial clinical assessment:

   • Apply clinical scoring system (Alvarado or Appendicitis Inflammatory Response score)
   • Low risk: Consider observation or alternative diagnoses 2
   • Moderate to high risk: Proceed to imaging 1

2. Imaging selection based on patient population:

   • Adults: CT abdomen/pelvis with IV contrast 1
   • Children: Ultrasound first, followed by CT or MRI if ultrasound is equivocal 1
   • Pregnant patients: Ultrasound first, followed by MRI if ultrasound is equivocal 1
   • Elderly patients: CT with IV contrast recommended due to higher rates of atypical presentation and perforation 1

3. Definitive diagnosis is made when imaging demonstrates:

   • Appendiceal diameter ≥7mm
   • Wall thickening and enhancement
   • Periappendiceal inflammation 3