What is the preferred imaging modality, ultrasound (US) or computed tomography (CT) scan of the neck, for detecting salivary gland stones?

Ultrasound vs CT for Salivary Gland Stone Detection

Ultrasound is the first-line imaging modality for detecting salivary gland stones due to its high sensitivity, non-invasive nature, absence of radiation exposure, and cost-effectiveness. 1

Diagnostic Approach to Salivary Gland Stones

Ultrasound as First-Line Imaging

• Ultrasound is recommended as the initial imaging modality by the American College of Radiology 1

• Advantages of ultrasound include:

  • Non-invasive nature
  • No radiation exposure
  • High accessibility and low cost
  • Excellent visualization of superficial structures
  • High sensitivity for stone detection (approximately 90%) 2
  • Can be repeated easily for follow-up 3
  • Allows assessment of gland morphology and surrounding inflammatory changes 1

• Recent meta-analysis (2022) confirms ultrasound's high diagnostic accuracy:

  • Sensitivity: 89.9%
  • Specificity: 96.6%
  • Positive predictive value: 98.5% 4

When to Use CT Scanning

CT with intravenous contrast is indicated in specific scenarios:

• When ultrasound results are inconclusive 1
• For suspected deep extension or bone involvement 1
• For visualization of:
  • Small or multiple calcifications
  • Deep structures not well-visualized by ultrasound
  • Stones in the deep lobe of parotid gland 1
  • Proximal duct system stones that may be missed by ultrasound 1

Anatomical Considerations

Ultrasound Performance by Gland Location

• Submandibular gland: Excellent visualization due to superficial location 1
• Parotid gland:
  • Superficial lobe: Well-visualized 1
  • Deep lobe: Limited visualization (consider CT) 1
• Sublingual gland: Limited visualization (consider CT) 1

The 2022 meta-analysis found that ultrasound of the parotid gland had the highest diagnostic accuracy with a negative predictive value of 93.9%, compared to 67.2% for the submandibular gland 4.

Common Pitfalls and Limitations

Ultrasound Limitations

• Limited visualization of:
  • Deep lobe of parotid gland
  • Sublingual gland
  • Stones in proximal duct system
  • Subtle ductal abnormalities 1
• Small stones (<2mm) may be difficult to detect due to absence of posterior acoustic shadowing 2
• Operator-dependent technique requiring experience

CT Limitations

• Radiation exposure
• Higher cost
• Less accessible than ultrasound
• Not ideal for repeated follow-up examinations

Clinical Algorithm for Salivary Stone Imaging

1. Start with ultrasound for all suspected salivary gland stones 1, 5
2. Proceed to CT if:
   • Ultrasound is inconclusive
   • Deep extension is suspected
   • Bone involvement is suspected
   • Stone is in deep lobe of parotid or sublingual gland
   • Multiple small stones are suspected 1
3. Consider sialography or MR sialography for detailed assessment of ductal anatomy if needed 6
4. Consider sialoendoscopy for both diagnostic confirmation and therapeutic intervention 1

Ultrasound remains the leading diagnostic tool for salivary gland diseases, including sialolithiasis, with CT serving as an excellent complementary modality when ultrasound findings are inconclusive or when deeper structures need evaluation 5, 1.