Malignancy Risk Stratification of Thyroid Nodules According to Echotexture and Degree of Hypoechogenicity: A Multicenter Validation Study

Abstract Purpose Various risk stratification systems show some discrepancies in the ultrasound (US) lexicon of nodule echotexture and hypoechogenicity. This study aimed to determine the malignancy risk of thyroid nodules according to their echotexture and degree of hypoechogenicity in a multicenter dataset.Methods From June to September 2015, 5,601 thyroid nodules (≥ 1.0 cm) in 4,989 consecutive patients who underwent thyroid US and with a final diagnoses from 26 institutions were evaluated. Thyroid nodules were stratified according to the US echotexture (homogeneous vs. heterogeneous) and degree of hypoechogenicity (mild, moderate, or marked). We then calculated malignancy risk and compared four subgroups stratified with nodule composition and presence of suspicious features.Results Heterogeneous hypoechoic nodules showed a significantly higher malignancy risk than heterogeneous isoechoic nodules (P ≤ 0.017) except in partially cystic nodules. There was no significant difference in malignancy risk between homogeneous vs. heterogeneous hypoechoic nodules (P ≥ 0.086) and between homogeneous vs. heterogeneous iso- or hyperechoic nodules (P ≥ 0.05) except in partially cystic nodules without suspicious features. The malignancy risks of both homogeneous and heterogeneous iso- or hyperechoic nodules were low to intermediate, depending on the presence of suspicious features. Regarding the degree of hypoechogenicity, there was no significant difference in malignancy risk between markedly and moderately hypoechoic nodules in all subgroups (P ≥ 0.48). Marked or moderately hypoechoic nodules showed a significantly higher risk than mild hypoechoic (P ≤ 0.016) and iso- or hyperechoic (P < .001) nodules. Conclusions The predominant echogenicity effectively stratifies the malignancy risk of nodules with heterogeneous echotexture. For malignancy risk stratification, the degree of nodules’ hypoechogenicity could be grouped as mild vs. moderate to marked hypoechogenicity.