What is the recommended approach for thyroid imaging?

Recommended Approach for Thyroid Imaging

Ultrasound is the first-line imaging modality for evaluating thyroid disease, with additional imaging modalities selected based on specific clinical scenarios. 1, 2

Initial Thyroid Imaging

• Ultrasound is the most appropriate initial imaging for palpable thyroid nodules in euthyroid patients without goiter due to its superior sensitivity and specificity for nodule detection and characterization 1, 2
• Ultrasound is highly effective for characterizing palpable abnormalities in the neck and detecting deeper neck masses that may not be palpable 2
• Ultrasound should be used to evaluate nodule characteristics using the ACR TI-RADS criteria to determine which nodules require fine-needle aspiration biopsy (FNAB) based on their size and suspicious features 2

Imaging for Specific Clinical Scenarios

Goiter Evaluation

• Ultrasound is the first-line imaging for suspected goiter to confirm thyroid origin and characterize goiter morphology 1, 3
• CT without IV contrast should be added when there is suspicion for substernal extension, as CT is superior for evaluating the extent of tracheal compression 1, 3
• MRI is an alternative to CT for goiter evaluation but is less preferred due to greater respiratory motion artifact 1, 3

Thyrotoxicosis Evaluation

• Three equivalent first-line imaging options for thyrotoxicosis include: 1
  1. Thyroid ultrasound
  2. I-123 radionuclide uptake and scan
  3. I-131 radionuclide uptake with Tc-99m pertechnetate scan
• Radionuclide uptake confirms that the entire goiter consists of thyroid tissue and helps identify hypofunctioning or isofunctioning nodules for biopsy 1

Primary Hypothyroidism

• No imaging is recommended for the initial evaluation of primary hypothyroidism 1
• Imaging does not help differentiate among causes of hypothyroidism, and all causes will have decreased radioiodine uptake 1

Thyroid Cancer Evaluation

• Ultrasound is the most appropriate preoperative imaging for differentiated thyroid cancer 1
• CT with IV contrast should be added for higher-stage disease or when there are concerns about invasive features or bulky nodal disease 1, 2
• For suspected recurrence of differentiated thyroid cancer, both ultrasound and I-123 whole-body scan are recommended as complementary procedures 1

Advantages and Limitations of Imaging Modalities

Ultrasound

• Advantages:

  • Most sensitive for detecting thyroid nodules 2, 4
  • Superior specificity for cervical lymph node evaluation (92% specificity vs 25% for CT) 2
  • Better characterization of nodule features that suggest malignancy (blurred margins, irregular shape, solid echo structure, hypoechogenicity, absent halo, fine calcifications) 5
  • Cost-effective and non-invasive 4, 6

• Limitations:

  • Limited in evaluating inferior disease borders and mediastinal structure involvement 2
  • May miss lymph node metastases in the central compartment and retropharyngeal space 2

CT Scan

• Indications:
  • Evaluation of substernal goiter extension 3
  • Assessment of tracheal compression 3
  • Evaluation of invasive primary tumors 2
  • Assessment of bulky lymph node involvement 2
  • Delineation of laryngeal, tracheal, esophageal, or vascular involvement 2

Nuclear Medicine Imaging

• Provides functional information about the thyroid gland and nodules 7
• Useful for determining the cause of thyrotoxicosis 1
• Helpful in detecting functioning distant metastases from differentiated thyroid cancers 7

Common Pitfalls to Avoid

• Do not rely solely on CT or MRI to differentiate between benign and malignant nodules, as these modalities have limited utility for this purpose 8
• Avoid using imaging alone to predict malignancy; techniques that combine ultrasound features and FNA cytology are most accurate 5
• Remember that ultrasound-guided FNA is superior to palpation-guided technique, particularly for nonpalpable, multiple, or heterogeneous nodules 5
• Do not order imaging for primary hypothyroidism as it provides no clinical benefit 1