From the Guidelines
Thyroid nodules with specific ultrasound findings, such as hypoechogenicity, microcalcifications, absence of peripheral halo, irregular borders, solid aspect, intranodular blood flow, and shape (taller than wide), should undergo fine needle aspiration (FNA) when they measure >1 cm, as these features are associated with an increased risk of malignancy 1. When multiple patterns suggestive of malignancy are simultaneously present in a nodule, the specificity of US increases, but the sensitivity becomes unacceptably low 1. Key ultrasound findings that indicate FNA include:
- Hypoechogenicity
- Microcalcifications
- Absence of peripheral halo
- Irregular borders
- Solid aspect
- Intranodular blood flow
- Shape (taller than wide) These findings should prompt FNA in nodules >1 cm, regardless of other clinical or ultrasonographic factors 1. In addition to these ultrasound findings, other factors that may prompt FNA include:
- Clinical suspicion of malignancy, such as a history of head and neck irradiation, family history of thyroid cancer, or suspicious features at palpation
- Cervical adenopathy
- Multinodular goiter with suspicious features at US It is essential to note that FNA is a sensitive tool for the differential diagnosis of benign and malignant nodules, but it has limitations, such as inadequate samples and follicular neoplasia 1. Molecular testing for thyroid nodules (BRAF, RAS, RET/PTC, and PAX8/PPARγ mutations) may also be useful in identifying nodules with a high risk of malignancy, as the presence of any mutation is a strong indicator of cancer 1.
From the Research
Thyroid Ultrasound Findings Indicating Fine Needle Aspiration (FNA)
The following ultrasound findings indicate the need for fine needle aspiration (FNA) of thyroid nodules:
- Microcalcifications 2, 3
- Irregular or microlobulated margin 2
- Marked hypoechogenicity 2, 3
- Shape that is more tall than it is wide 2, 3
- Hypoechogenicity 3
- Coarse calcification 3
- Spiculated margin 3
- Irregular shape 3
Nodule Size and FNA Indication
Nodule size is also an important factor in determining the need for FNA:
- Nodules larger than 15 mm have a higher rate of Bethesda category I results 4
- Nodules with a size range of 5 to 10 mm have the best diagnostic accuracy 4
- Nodules with a size range of 5 to 15 mm have better sensitivity, accuracy, positive predictive value (PPV), and likelihood ratio (LR) for negative US-guided FNA results 4
Ultrasound Features and FNA Results
Certain ultrasound features are associated with false-negative or false-positive FNA results:
- Nodules with circumscribed margins and those that are nonsolid and nonhypoechoic and have no microcalcifications are more likely to have Bethesda I FNA results 4
- Nodules with circumscribed margins and those that are nonsolid, heterogeneous, and nonhypoechoic and have increased vascularity are more likely to have false-negative FNA results 4
- Borders are correlated with Bethesda I false-negative and false-positive FNA results 4
- Tiny nodules (≤5 mm) with obscure borders tend to yield false-positive FNA results 4
- Large nodules (>20 mm) with several US features tend to yield false-negative FNA results 4