Is thyroid ultrasound (US) more sensitive than computed tomography (CT) soft tissue imaging for detecting thyroid nodules?

Thyroid Ultrasound vs CT for Detecting Thyroid Nodules

Thyroid ultrasound is significantly more sensitive than CT for detecting thyroid nodules, with superior specificity for cervical lymph node evaluation and better ability to characterize nodule features. 1

Comparative Sensitivity of Imaging Modalities

• Ultrasound is the first-line and preferred imaging modality for evaluating thyroid structure and detecting thyroid nodules due to its high sensitivity, safety, and cost-effectiveness 2, 3
• Ultrasound demonstrates superior sensitivity for detecting calcifications in thyroid nodules compared to CT (92.5% vs 53.3%, p<0.0005) 4
• Ultrasound shows significantly higher agreement with pathologic findings for calcification detection than CT (87.9% vs 81.9%, p=0.018) 4

Specific Advantages of Ultrasound

• Ultrasound provides excellent resolution for evaluating nodule characteristics including composition, echogenicity, margins, calcifications, and shape 3, 5
• Ultrasound is highly effective for characterizing palpable abnormalities in the neck and detecting deeper neck masses that may not be palpable 1, 6
• For cervical lymph node evaluation, ultrasound demonstrates similar sensitivity to CT but with much greater specificity (sensitivity 75% and specificity 92% for US versus sensitivity 80% and specificity 25% for CT) 1

Limitations of Ultrasound

• Ultrasound cannot visualize retrosternal extension of thyroid nodules or structures in the mediastinum 7
• Ultrasound has limitations in evaluating the inferior border of disease and determining the extent of mediastinal structure involvement in cases with significant caudal spread 1
• Ultrasound may miss lymph node metastases in the central compartment and retropharyngeal space, where CT has higher sensitivity 1

When CT is Preferred

• CT is recommended as an adjunct to ultrasound for patients with clinical suspicion of advanced disease, including invasive primary tumor or clinically apparent multiple or bulky lymph node involvement 1
• CT is superior for delineating the extent of laryngeal, tracheal, esophageal, or vascular involvement 1
• CT is the preferred imaging modality for evaluating substernal extension of thyroid nodules and defining the degree of tracheal compression 7

Clinical Approach to Thyroid Nodule Imaging

• Begin with ultrasound as the first-line imaging for all thyroid nodules 2, 3
• Use the American College of Radiology TI-RADS criteria to characterize nodules and determine which require fine-needle aspiration biopsy 3
• Add CT with contrast when there are concerns about:
  • Substernal extension 7
  • Tracheal compression 7
  • Invasive features 1
  • Bulky nodal disease 1

Common Pitfalls to Avoid

• Failing to use ultrasound as the initial imaging modality for thyroid nodule evaluation 2, 5
• Relying solely on CT for thyroid nodule characterization, which may miss important features like microcalcifications 4
• Not obtaining CT when there are signs of retrosternal extension or compression of vital structures, where ultrasound has limitations 7
• Performing routine thyroid cancer screening with imaging in low-risk individuals, as this has not been shown to improve survival 8