How do I assess for thyroiditis based on ultrasound results?

Assessing Thyroiditis on Ultrasound

Thyroiditis can be reliably assessed on ultrasound by identifying characteristic findings including hypoechogenicity, heterogeneous echotexture, pseudolobulation, and increased or decreased vascularity depending on the type of thyroiditis. 1, 2

Key Ultrasound Features of Thyroiditis

Hashimoto's/Lymphocytic Thyroiditis

• Primary findings:
  • Diffusely reduced echogenicity (hypoechoic appearance)
  • Heterogeneous echotexture
  • Pseudolobulated gland margins
  • Normal or slightly enlarged thyroid volume
  • Occasionally micronodular appearance

Subacute (De Quervain's) Thyroiditis

• Primary findings:
  • Focal or multiple hypoechoic areas
  • Poorly defined hypoechoic lesions
  • Correlation between hypoechoic area size and pain location 3
  • Initially enlarged thyroid that reduces in size during recovery (up to 68% reduction) 4

Additional Assessment Parameters

• Vascularity assessment:
  • Hashimoto's: Normal or increased vascularity
  • Subacute thyroiditis: Reduced vascularity in affected areas
• Margins and borders:
  • Ill-defined borders of hypoechoic areas
  • Pseudolobulated appearance of the gland

Diagnostic Accuracy and Correlation

The presence of diffuse reduction in thyroid echogenicity has a high positive predictive value (88.3%) and negative predictive value (93.0%) for autoimmune thyroid disease 5. When ultrasound findings suggest thyroiditis, confirmation by fine needle aspiration biopsy (FNAB) can increase the diagnostic accuracy to 81.8% 2.

Recommended Approach to Ultrasound Assessment

1. Evaluate overall echogenicity:

   • Compare to surrounding neck muscles (thyroid should normally be more echogenic)
   • Assess for diffuse or focal hypoechogenicity

2. Assess parenchymal texture:

   • Look for heterogeneity throughout the gland
   • Identify any micronodular pattern

3. Examine gland size and shape:

   • Measure dimensions and calculate volume
   • Note any pseudolobulation of margins

4. Evaluate vascularity with Doppler:

   • Assess for increased, normal, or decreased blood flow
   • Compare with surrounding tissues

5. Look for associated findings:

   • Enlarged regional lymph nodes
   • Presence of nodules requiring further evaluation

Integration with Clinical and Laboratory Assessment

For comprehensive evaluation, correlate ultrasound findings with:

• Thyroid function tests (TSH, FT4)
• Thyroid antibodies (anti-TPO, anti-Tg)
• Clinical symptoms (pain, tenderness)

Quantitative ultrasound features have been shown to correlate with antibody levels and may predict the presence of thyroid antibodies 6.

Pitfalls and Caveats

• Hypoechogenicity alone is not specific to thyroiditis and may be seen in other conditions
• Some thyroid malignancies can mimic thyroiditis on ultrasound 1
• Follow-up ultrasound is recommended as thyroiditis may evolve over time
• Persistent morphological abnormalities may remain even after clinical resolution 4

For suspicious findings or inconclusive ultrasound results, ultrasound-guided FNAB should be performed to confirm the diagnosis and rule out malignancy 1, 2.