What are the criteria for ordering a thyroid ultrasound?

Criteria for Ordering a Thyroid Ultrasound

Thyroid ultrasound is the first-line imaging modality for evaluating palpable thyroid nodules, suspected goiter, and thyrotoxicosis in euthyroid or hyperthyroid patients, but should be preceded by TSH measurement to guide the appropriate diagnostic pathway. 1, 2

Clinical Scenarios Requiring Thyroid Ultrasound

Palpable Thyroid Nodule (Euthyroid State)

• Ultrasound is the preferred initial imaging test for any palpable thyroid nodule in patients with normal TSH levels 1
• Order ultrasound when the nodule is discovered on physical examination or incidentally on other imaging 1
• Ultrasound should be performed alongside fine-needle aspiration (FNA) of the nodule and clinically suspicious lymph nodes 1
• The study evaluates nodule characteristics that predict malignancy risk, including microcalcifications, irregular borders, hypoechogenicity, solid composition, and dimensions taller than wide 1, 3

High-Risk Clinical Features Mandating Ultrasound

Order thyroid ultrasound immediately when any of these features are present:

• Age younger than 15 years (higher malignancy risk) 1
• History of head and neck irradiation 1
• Family history of thyroid cancer or associated syndromes (familial adenomatous polyposis, Carney complex, Cowden's syndrome, MEN 2A or 2B) 1
• Concerning physical examination findings: very firm nodule, fixed to adjacent structures, rapidly growing, enlarged regional lymph nodes, vocal cord paralysis, or symptoms of neck structure invasion 1
• Male gender (higher malignancy risk compared to females) 1

Suspected Goiter

• Ultrasound is the first-line test to confirm the diagnosis and document size and extent 1
• Order when there is diffuse palpable thyroid abnormality or obstructive symptoms (dyspnea, orthopnea, obstructive sleep apnea, dysphagia, dysphonia) 1
• If substernal extension is suspected, add CT neck without IV contrast after ultrasound 1

Thyrotoxicosis (Low TSH)

• Ultrasound should be performed first to evaluate thyroid morphology and identify nodules 1, 2
• Follow with radioiodine uptake scan (I-123 preferred over I-131) to determine the cause of thyrotoxicosis 1, 2
• The combination helps differentiate Graves disease, toxic adenoma, toxic multinodular goiter, and subacute thyroiditis 1, 2

When NOT to Order Thyroid Ultrasound

Primary Hypothyroidism

• Imaging is not recommended for initial evaluation of primary hypothyroidism (elevated TSH without palpable abnormality) 1, 2

Euthyroid Patients Without Palpable Findings

• Do not order ultrasound as a screening test in asymptomatic patients with normal TSH and no palpable abnormality 1, 2

Critical Pitfalls to Avoid

TSH Must Be Checked First

• Always obtain TSH levels before selecting imaging modality to avoid unnecessary testing and radiation exposure 2
• The TSH result determines whether ultrasound alone is sufficient or if radionuclide scanning is needed 2

Do Not Use Radionuclide Scanning in Euthyroid Patients

• Radionuclide uptake scans have no role in determining malignancy in euthyroid patients with nodules 1, 2
• Although cold nodules are more likely malignant, most nodules are cold and most cold nodules are benign, resulting in low positive predictive value 1
• Radionuclide scanning should only be performed when TSH is suppressed (low) 2

Ultrasound Features That Guide Biopsy Decisions

Once ultrasound is performed, specific features determine biopsy necessity:

• Single high-risk feature (microcalcifications, size >2 cm, entirely solid composition) has sensitivity of 88% but high false-positive rate of 44% 3
• Two or more high-risk features significantly increase cancer likelihood (odds ratio 4.0), reducing unnecessary biopsies by 90% while maintaining low missed cancer risk 3
• Microcalcifications carry the highest malignancy risk (odds ratio 8.1), followed by solid composition (odds ratio 4.0) and size >2 cm (odds ratio 3.6) 3

Special Considerations for Pediatric Patients

• Pediatric thyroid nodules (age ≤21 years) carry higher malignancy risk than adult nodules 4
• Ultrasound features predictive of malignancy in this population include microcalcifications, abnormal lymph nodes, and taller-than-wide dimensions 4
• All patients with ≥3 malignant ultrasound features had thyroid cancer on final pathology 4
• All nine pediatric patients with abnormal lymph nodes on ultrasound had malignant disease 4