Table 3. American Thyroid Association guidelines for fine needle aspiration recommendations with regards to clinical and sonographic features (adapted from [7]).

Nodule sonographic or clinical features	Recommended nodule threshold size for fine needle aspiration
High-risk history:
Thyroid cancer in first-degree relatives
External beam radiation as a child
Exposure to ionising radiation in childhood or adolescence
Previous thyroid cancer
FDG avidity on positron emission tomography scan
Nodule WITH suspicious sonographic features:	>5 mm
Microcalcifications, hypoechoic, increased nodular vascularity, infiltrative margins, taller than wide on transverse view
Nodule WITHOUT suspicious sonographic features	>5 mm
Abnormal cervical lymph nodes	All
Microcalcifications in nodule	≥1 cm
Solid nodule
AND hypoechoic	>1 cm
AND iso- or hyperechoic	≥1–1.5 cm
Mixed cystic-solid nodule
WITH any suspicious ultrasound features	≥1.5–2 cm
WITHOUT suspicious ultrasound features	≥2 cm
Spongiform nodule	≥2 cm
Purely cystic nodule	Fine needle aspiration not indicated