Thyroid Ultrasound Findings in Hashimoto Thyroiditis
The classic ultrasound appearance of Hashimoto thyroiditis shows a diffusely enlarged thyroid gland with heterogeneous echotexture and multiple small hypoechoic areas (micronodulation), without discrete nodules—classified as C-TIRADS 1. 1
Primary Sonographic Features
Parenchymal Changes
- Diffuse heterogeneous echotexture is the hallmark finding, representing lymphocytic infiltration and fibrosis throughout the gland 1, 2
- Multiple tiny hypoechoic areas (micronodulation) measuring 1-6 mm, surrounded by echogenic rims, are highly characteristic—these represent accentuated lobulation and have a 94.7% positive predictive value for Hashimoto thyroiditis 3
- The thyroid parenchyma may appear hypoechoic relative to adjacent strap muscles in most cases, though it can occasionally be isoechoic or even hyperechoic 4
Gland Size and Margins
- Diffuse thyroid enlargement is common, particularly in earlier stages of disease 5
- Undulation of gland margins (irregular, wavy borders) is a specific finding that helps distinguish Hashimoto thyroiditis from normal thyroid tissue 6
- Internal septations may be visible, representing fibrous bands within the parenchyma 6
Vascular Changes
- Increased vascularity on Doppler imaging is frequently present, reflecting the inflammatory process 2, 6
- Power Doppler demonstrates diffusely increased blood flow throughout the gland 6
Associated Lymph Node Changes
- Infrathyroidal and/or pretracheal reactive lymph nodes are commonly seen and support the diagnosis 6
Critical Distinction: Pseudonodules vs. True Nodules
The multiple small hypoechoic areas in Hashimoto thyroiditis are "pseudonodules" and do NOT require fine-needle aspiration. 2 These diffuse changes are classified as C-TIRADS 1 (no nodule present), indicating benign thyroid parenchyma with no malignancy risk 1
When to Pursue Further Evaluation
- FNA is reserved only for discrete nodules ≥10 mm with suspicious sonographic features (solid composition, vertical orientation, irregular margins, microcalcifications, marked hypoechogenicity) 2
- Discrete nodules should be evaluated using standard TIRADS criteria, independent of the background Hashimoto changes 1
- When nodule echogenicity is assessed in the setting of Hashimoto thyroiditis, it should still be compared to the surrounding thyroid parenchyma (even though that parenchyma is abnormal), and the report should note the altered background echotexture 1
Diagnostic Performance
Combining all ultrasound parameters (nodularity, margin undulation, septations, reactive lymph nodes, and increased vascularity) yields 90% sensitivity, 84.8% specificity, and 87.2% accuracy for diagnosing Hashimoto thyroiditis in anti-thyroid antibody-positive patients with normal thyroid hormone levels 6
Common Pitfalls to Avoid
- Do not mistake the diffuse hypoechoic micronodulation for multiple discrete thyroid nodules requiring biopsy—this is the most important distinction to prevent unnecessary invasive procedures 2, 3
- Do not routinely repeat ultrasound unless a new palpable discrete nodule appears on physical examination 2
- Be aware that ultrasound findings do not correlate with thyroid function status in serial examinations—patients can be euthyroid, hypothyroid, or even transiently thyrotoxic with similar imaging appearances 4
- In patients with more advanced disease and atrophy, the gland may be small rather than enlarged, with persistent heterogeneity 5
Severity Grading
Sonographic patterns correlate with disease severity: higher-grade patterns show larger glands, higher antithyroid antibody titers, lower T4, higher TSH levels, and increased incidence of hypothyroidism 5. This allows ultrasound to predict which patients may require treatment and to identify those with functional impairment 5.