The echogenicity of a thyroid nodule refers to the echo level of the solid component of the nodule relative to the thyroid parenchyma and the cervical band muscles, and can be categorized into several types: hyperechoic, isoechoic, hypoechoic, very hypoechoic, and anechoic. Hypoechoic means that the echo is higher than the surrounding thyroid parenchyma; isoechoic means that the echo is similar to the surrounding thyroid parenchyma; hypoechoic means that the echo is lower than the surrounding thyroid parenchyma; very hypoechoic means that the echo is lower than the cervical strap muscles; and anechoic is seen in cystic nodules. Hypoechoic or very hypoechoic echoes are generally considered to be suspicious malignant ultrasound features. If hypoechoicity is used as a diagnostic criterion, the sensitivity of diagnosis is higher and the specificity is lower; if very low echo is used as a diagnostic criterion, the sensitivity of diagnosis is lower and the specificity is higher. Thyroid nodules are detected and should be treated under the supervision of a physician.