In an adult with newly discovered thyroid nodules, what is the best imaging study?

Best Imaging Study for Thyroid Nodules

Thyroid ultrasound is the best and mandatory first-line imaging study for evaluating thyroid nodules in adults, performed after checking TSH levels. 1, 2

Diagnostic Algorithm

Step 1: Check TSH First

• Always measure TSH before ordering any imaging, as the TSH result determines the entire diagnostic pathway and imaging strategy 1, 2
• TSH measurement is the critical first step that guides whether additional functional imaging (radionuclide scanning) will be needed 1

Step 2: Perform Thyroid Ultrasound

• Ultrasound is the preferred first-line imaging modality for all thyroid nodules regardless of TSH status 1, 2
• Ultrasound provides superior morphological evaluation and structural assessment of nodules 1, 3
• It allows characterization using ACR TI-RADS criteria to assess malignancy risk 2, 4
• Ultrasound detects suspicious features including spiculated margins, microcalcifications, taller-than-wide shape, and marked hypoechogenicity 3
• It evaluates for cervical lymphadenopathy with superior specificity compared to CT 2
• Ultrasound guides fine-needle aspiration biopsy when indicated 2, 4, 3

Step 3: Consider Radionuclide Scanning (Only in Specific Circumstances)

• Thyroid scintigraphy should ONLY be performed when TSH is low (suppressed) 1, 4
• In hyperthyroid patients, radionuclide scanning differentiates between Graves' disease, toxic adenoma, toxic multinodular goiter, and thyroiditis 1
• Do NOT perform radionuclide scanning in euthyroid patients with nodules, as it has low positive predictive value for malignancy and does not help determine which nodules need biopsy 1, 2, 4

Why Ultrasound is Superior

• Ultrasound is the most complete and cost-effective imaging method for evaluating thyroid nodules 5
• It provides high-resolution imaging with remarkable clarity for visualizing nodule location, number, size, and consistency 6, 7
• Ultrasound has high sensitivity and specificity for distinguishing benign from malignant lesions when combined with clinical features 6
• It is safe, readily available, quick, and involves no radiation exposure 1

Critical Pitfalls to Avoid

• Never proceed directly to radionuclide scanning in euthyroid patients - this wastes resources and provides no useful information about malignancy risk 1, 2
• Never skip ultrasound evaluation, even if planning specialist referral, as it provides essential information that guides urgency and type of intervention 2
• Never use radionuclide scanning to determine malignancy in euthyroid patients - the decision to biopsy should be based on ultrasound features and clinical risk factors, not functional imaging 4, 7
• Never fail to check TSH before selecting imaging modality - this leads to unnecessary testing and potential radiation exposure 1
• Coexisting thyroid nodules requiring biopsy can be missed if ultrasound is skipped and the patient proceeds directly to uptake scan 1

Role of Fine-Needle Aspiration

• Ultrasound-guided FNA has supplanted imaging studies as the routine initial procedure for differentiating benign from malignant nodules 7
• FNA should be performed based on nodule size and suspicious sonographic features identified on ultrasound 4
• The combination of ultrasound and FNA is highly effective for definitive assessment 6