How do you interpret the result of an ultrasound of the thyroid gland in an adult patient with no known history of thyroid disease?

How to Interpret Thyroid Ultrasound Results

Begin by checking the patient's TSH level before interpreting any thyroid ultrasound findings, as this determines the appropriate diagnostic pathway and whether additional imaging is needed. 1

Initial Assessment Framework

The interpretation of thyroid ultrasound in an adult with no known thyroid disease follows a systematic approach:

Step 1: Correlate with Thyroid Function Tests

• TSH measurement is the single most important test that must guide your ultrasound interpretation 1, 2
• If TSH is normal (euthyroid), ultrasound serves as the primary tool for morphological evaluation 1
• If TSH is low (suppressed), you will need to add radioiodine uptake scanning to determine the cause of thyrotoxicosis 3, 1
• If TSH is elevated (hypothyroidism), imaging generally provides no additional diagnostic value for determining the cause 1

Step 2: Evaluate Overall Thyroid Morphology

Document the following structural features systematically:

• Thyroid size and volume - assess for goiter (enlargement) 3, 4
• Echogenicity - normal thyroid is homogeneous and hyperechoic compared to adjacent neck muscles 5, 6
• Gland margins - should be smooth and well-defined 6
• Thyroid stroma pattern - assess for diffuse heterogeneity suggesting thyroiditis 6

Step 3: Identify and Characterize Any Nodules

When nodules are present, assess each one for suspicious ultrasound features that increase malignancy risk:

High-Risk Ultrasound Features (Require FNA if nodule >1 cm)

• Microcalcifications - the most specific feature for papillary thyroid carcinoma 3
• Hypoechogenicity - nodule appears darker than surrounding thyroid tissue 3, 2
• Irregular or infiltrative borders - suggests invasive growth 3
• Taller-than-wide shape (anteroposterior dimension exceeds transverse) 3, 2
• Solid composition - purely solid nodules carry higher risk than cystic 3, 2
• Central or intranodular vascularity on Doppler imaging 3, 2

Important Caveat About Ultrasound Features

• Each individual suspicious feature has poor predictive value when present alone 2
• Specificity increases substantially only when multiple suspicious features are present simultaneously 3, 2
• Ultrasound cannot definitively distinguish benign from malignant nodules - this requires fine-needle aspiration biopsy 4, 5

Step 4: Determine Need for Fine-Needle Aspiration

FNA is indicated for:

• Any nodule >1 cm with suspicious ultrasound characteristics 3, 2
• Nodules <1 cm if there is clinical suspicion (history of head/neck irradiation, family history of thyroid cancer, suspicious cervical lymphadenopathy) 3
• Ultrasound guidance improves FNA accuracy and should be used 3, 4

Step 5: Assess for Lymphadenopathy

• Examine central and lateral neck compartments for abnormal lymph nodes 3
• Suspicious lymph nodes should undergo FNA if clinically indicated 3

Common Pitfalls to Avoid

Do not order radioiodine uptake scanning in euthyroid patients - it has low positive predictive value for malignancy and does not help determine which nodules need biopsy 1, 2

Do not rely on ultrasound alone to exclude malignancy - even nodules with benign-appearing features can harbor cancer, which is why FNA remains the gold standard for tissue diagnosis 3

Do not skip TSH measurement - proceeding with ultrasound interpretation without knowing thyroid function status leads to inappropriate management decisions and unnecessary testing 1, 2

Do not assume all hypoechoic nodules are malignant - this finding alone has insufficient specificity and must be combined with other suspicious features 2

Avoid misidentifying adjacent anatomical structures (such as parathyroid glands, lymph nodes, or vascular structures) as thyroid nodules 6

Clinical Risk Factors That Modify Interpretation

Even with benign-appearing ultrasound features, maintain higher suspicion in patients with:

• Age <15 years or male gender - higher baseline malignancy risk 3
• History of head and neck irradiation - 7-fold increased risk if nodule is firm, fixed, or rapidly growing 3
• Family history of thyroid cancer or associated syndromes (MEN 2, familial adenomatous polyposis, Cowden syndrome) 3
• Rapidly growing nodule, vocal cord paralysis, or fixation to adjacent structures - these clinical features increase malignancy likelihood approximately 7-fold 3

When Additional Imaging Is Needed

• CT or MRI - reserved for evaluating substernal extension, retropharyngeal involvement, or tracheal compression in large goiters 3
• Radioiodine uptake scan - only indicated when TSH is suppressed to differentiate causes of thyrotoxicosis 3, 1
• FDG-PET/CT - not recommended for initial thyroid evaluation 3