The risk of malignancy is increased in thyroid nodules with the following features: hypoechoic, microcalcifications, poorly defined or irregular borders, and color Doppler ultrasound showing increased and irregular blood flow signals. It is important to note that no single ultrasound feature is unique to benign or malignant thyroid nodules, and a comprehensive analysis is required to help differentiate between benign and malignant nodules. The following is an analysis of some of the major ultrasound features of thyroid nodules in terms of their significance in identifying benign and malignant thyroid nodules. Single versus multiple nodules: In the past, malignant thyroid nodules were considered to be single solid nodules, while multiple nodules were commonly found in benign lesions. High-frequency color Doppler ultrasonography is now used to detect small nodules that cannot be detected by clinical palpation. Benign and malignant nodules can coexist, and it is no longer reliable to distinguish benign and malignant nodules by the feature of single or multiple nodules. In addition, about 10%-20% of papillary carcinomas are multicentric in origin. Therefore, it is now emphasized that the ultrasound characteristics of each node should be analyzed individually during ultrasound examination in order to screen for malignant nodes in multiple nodes. Intranodal calcifications: Calcifications can be detected in about 10% of thyroid nodules. Peripheral annular calcifications and gross calcifications are most often seen in benign nodules, whereas gritty microcalcifications are more often seen in malignant nodules, especially in the primary foci of papillary carcinoma and its cervical lymph node metastases. Small foci of calcification are also commonly seen within the primary foci of medullary carcinoma and metastatic nodes in the neck. Echo levels within nodules: Thyroid nodules can be hypoechoic, moderately echogenic, or hyperechoic, and the level of echogenicity of thyroid nodules can also help to differentiate between benign and malignant nodules. Current studies have shown that more malignant nodules are hypoechoic, while hyperechoic nodules are less likely to be malignant and moderate echogenic nodules are somewhere in between. The peripheral halo of a thyroid nodule on ultrasound images refers to the hypoechoic band around the nodule, which is the envelope of the thyroid nodule or the compressed thyroid parenchyma or blood vessels. If the nodule has a complete and regular peripheral halo, it is more likely to be benign (studies have shown that the nodule is 12 times more likely to be benign than malignant); even if the peripheral halo is incomplete, it is still 4 times more likely to be benign than malignant. It should be noted that 15%-30% of malignant nodules also have peripheral halos, so it is not possible to determine the benignity or malignancy of a nodule by the feature of peripheral halos alone, but must be analyzed and judged comprehensively. Intra-nodal dotted strong echogenicity with comet tail sign: When dotted strong echogenicity with posterior comet tail is present in thyroid nodules, it is often a dense colloid, which is characteristic of benign thyroid nodules. Color Doppler flow imaging: Color Doppler flow distribution of thyroid nodules is also helpful in determining the benignity or malignancy of the nodule. There are three patterns of flow distribution in thyroid nodules: (1) no flow signal inside or around the nodule; (2) flow signal around the nodule; and (3) abundant and disorganized flow signal inside the nodule with or without flow signal around the nodule. Pattern (3) is usually characteristic of malignant nodules, while patterns (1) and (2) are mostly characteristic of benign nodules.