Ultrasound malignancy risk stratification of thyroid nodules based on the degree of hypoechogenicity and echotexture

Objectives The ultrasound (US) lexicon of nodule echogenicity and echotexture is one of the major differences among various risk stratification systems of thyroid nodules. This study aimed to stratify the US malignancy risk of thyroid nodules based on their degree of hypoechogenicity and echotexture. Material and methods This retrospective study included a total of 2255 consecutive thyroid nodules (≥ 1 cm) with final diagnoses (malignancy rate, 13%) from 2011 to 2016. Thyroid nodules were stratified according to the US degree of hypoechogenicity (mild, moderate, or marked hypoechogenicity) and echotexture (homogeneous vs. heterogeneous). The calculated malignancy risk was compared between each category. Results There was no significant difference of malignancy risk between the homogeneous markedly hypoechoic and moderately hypoechoic nodules ( p ≥ .18). However, the malignancy risks of markedly and moderately hypoechoic nodules were significantly higher than those of mildly hypoechoic nodules ( p < .001). Heterogeneous predominantly hypoechoic thyroid nodules showed a significantly higher malignancy risk than predominantly iso- or hyperechoic thyroid nodules ( p < .001). There were no significant differences of malignancy risk between heterogeneous predominantly hypoechoic and homogeneous hypoechoic nodules according to the degree of hypoechogenicity ( p ≥ .12) and between heterogeneous predominantly iso- or hyperechoic nodules and homogeneous iso- or hyperechoic thyroid nodules ( p = .36). Conclusions The malignancy risk of nodule hypoechogenicity is stratified as mild vs. moderate to marked hypoechogenicity, and the malignancy risk of nodules with heterogeneous echotexture is stratified by the predominant echogenicity of the nodules. Key Points • Thyroid nodule echogenicity is categorized as marked, moderate, or mild hypoechogenicity and iso- or hyperechogenicity with the reference standard of adjacent thyroid tissue and anterior neck muscles. • The malignancy risk of thyroid nodule echogenicity is stratified as iso- or hyperechoic vs. mild vs. moderate or marked hypoechogenicity. • The malignancy risk of nodules with heterogeneous echotexture is stratified by the predominant echogenicity.