How to diagnose appendicitis with Point-of-Care Ultrasound (POCUS)?

Diagnosing Appendicitis with Point-of-Care Ultrasound (POCUS)

POCUS is the recommended first-line diagnostic imaging tool for suspected appendicitis in both adults and children when imaging is clinically indicated, offering satisfactory sensitivity and specificity when performed by an experienced operator. 1

Diagnostic Criteria for Appendicitis on POCUS

Key Sonographic Findings

• Appendix diameter >6-7 mm (primary criterion) 2, 3
• Appendix wall thickness >2 mm 3
• Loss of compressibility of the appendix
• Hyperemia on color Doppler (in uncomplicated appendicitis) 2
• Visualization of the appendix tip 3
• Periappendiceal fluid (suggests progression toward complicated appendicitis) 2, 3
• Sonographic McBurney's sign (pain when pressing with the ultrasound probe) 3

Pathologic Continuum Assessment

• Uncomplicated appendicitis: Enlarged appendix with intact echogenic submucosal layer and hyperemia on color Doppler 2
• Gangrenous appendicitis: Loss of the echogenic submucosal layer with absent color Doppler flow 2
• Perforated appendicitis: Loculated pericecal fluid, prominent pericecal fat, and circumferential loss of the submucosal layer 2

POCUS Technique

1. Patient positioning: Supine position

2. Probe selection: Linear high-frequency transducer (7.5-10 MHz) for thin patients; curvilinear probe (3.5-5 MHz) for larger patients

3. Scanning approach:

   • Begin at point of maximal tenderness
   • Use graded compression technique to displace bowel gas and simulate clinical palpation 1
   • Scan both right lower quadrant AND right upper quadrant (retrocecal appendicitis may be found in the right upper or periumbilical region) 4
   • Apply gentle but firm pressure to compress normal bowel loops while visualizing the appendix

4. Anatomical landmarks:

   • Identify the cecum (gas-filled, non-peristaltic pouch)
   • Follow the cecum to the appendiceal origin
   • Trace the appendix from base to tip

Clinical Pearls and Pitfalls

Strengths of POCUS for Appendicitis

• No radiation exposure (especially important for children and pregnant patients) 1
• Can be performed at bedside for rapid decision-making 1
• High sensitivity when the appendix is visualized (100% in some studies) 3
• Excellent negative predictive value when appendix is visualized and normal 3

Limitations to Consider

• Operator-dependent technique requiring specific training 1
• Visualization rate varies (lower in North America compared to Europe/Asia) 1
• Patient factors affecting visualization:
  • Obesity
  • Bowel gas
  • Patient discomfort limiting compression
  • Retrocecal position of appendix

Diagnostic Algorithm

1. Clinical assessment first to determine if imaging is indicated
2. POCUS as first-line imaging when available with trained operator 1
3. If POCUS is positive (meets criteria above): Proceed with appropriate management
4. If POCUS is non-diagnostic or negative but clinical suspicion remains high:
   • In adults: Proceed to CT scan (preferably low-dose with IV contrast) 1
   • In children: Consider MRI as next step to avoid radiation 1
   • In pregnant patients: Proceed to MRI 1

Special Populations

Children

• POCUS is particularly valuable due to radiation concerns 1
• First-line imaging modality recommended 1
• If POCUS is equivocal, MRI is preferred as second-line imaging 1

Pregnant Patients

• POCUS recommended as initial imaging modality 1
• If inconclusive, MRI is recommended rather than CT 1

Conclusion

POCUS represents an effective first-line imaging approach for diagnosing appendicitis when performed by trained operators. Its high sensitivity and negative predictive value make it particularly valuable for ruling out appendicitis when the appendix is visualized and normal. The technique requires attention to proper scanning methodology, including examination of both the right lower and upper quadrants to identify potentially retrocecal appendicitis.