How can ultrasound identify benign and malignant thyroid nodules? In today’s society, the incidence of various thyroid diseases is gradually increasing, especially in this era when tumors are everywhere, and thyroid nodules also make many patients “fearful of nodules”, thinking that nodules are equivalent to malignant tumors. In fact, there is no need to worry about this, as only about 5% of all thyroid nodules are malignant tumors, while the other 95% can be degenerative, inflammatory, benign tumors, calcifications, fibrous scar tissue, hematomas, cysts or nodular goiter. Thyroid nodules are lumps caused by cellular hyperplasia that appear in the normal thyroid gland and differ from the normal thyroid gland in texture, shape, and blood supply. Approximately 80% or more of thyroid nodules are detected by ultrasound examination. What features of the ultrasound report are helpful in identifying the benignity or malignancy of thyroid nodules? The first thing to look for is the presence or absence of calcification in the nodule. Since calcification is present in about 80% of malignant tumors and only in about 50% of benign nodules, calcification is an important marker of a thyroid cancer. Of course, not all types of calcifications are indicative of thyroid cancer, which can be subdivided into: 1) Microcalcifications: they appear as posterior dots with or without acoustic shadowing, mostly calcifications and fibrosis secondary to amyloid deposits within the sarcoid or medullary carcinoma, and can be found in about 40% to 60% of thyroid cancers; 2) Marginal calcifications: they are calcifications located at the margins of thyroid nodules. It is common in nodular goiter and is a sign of benign nodules. 3. Coarse calcification and calcified spots: refers to a single coarse calcified foci and no thyroid nodules are shown on ultrasound in the area of calcification, which is common in benign thyroid lesions, such as nodular goiter, hyperthyroidism and other diffuse thyroid lesions. Many older adults have coarse calcification, marginal calcification, or calcified spots in the thyroid gland, mostly due to degeneration of thyroid tissue, inflammation, and malnutrition. It has been reported in the literature that there is a significant difference in the incidence of calcification and benign malignancy in thyroid nodules using 45 years as the age cut-off (p=0.002). That is, young patients (<45< span=""> years) with calcified thyroid nodules should be highly alert to the possibility of malignancy. In addition to calcification within the nodule that can be identified, a number of other nodule features are also diagnostically significant, including: 1. Ill-defined nodule borders. About 80% to 90% of malignant thyroid tumors have unclear or poorly defined borders, while most benign nodules have very clear borders, with only about 15% having unclear borders. 2. Uneven echogenicity. It is found that >90% of malignant tumors have uneven echogenicity. Although there are 2/3 of benign nodules with uneven echogenicity, once the nodules found by ultrasound have uniform echogenicity, it can be basically considered that their malignancy may be very small. 3. Uneven cystic component. In general, the more cystic components there are, the greater the likelihood of benign nodules. Those nodules with multi-housed cystic and “honeycomb” images containing fiber separation are basically benign nodules. Small cystic nodules with strong echogenicity and posterior enhancement, i.e., cystic nodules with “comet tail” artifacts, are also characteristic of benign nodules. The possibility of malignancy should be highly suspected in cystic nodules with mixed cystic and solid components, especially those with nodular bulge in the cyst wall and uneven cyst wall thickness. 4. Hypoechoic nodules. Almost all malignant nodules and most benign nodules (about 90%) are hypoechoic nodules. Once the echogenicity of the nodule is found to be isoechoic or hyperechoic, it can be treated as benign nodules. 5. Blood flow in nodules. All kinds of benign and malignant nodules will have blood flow performance, but malignant nodules still have their own specificity. Generally, the blood flow in malignant nodules is shown on color Doppler ultrasound to be of the multiple blood supply type, and the blood flow in the nodule is disorganized. Nodular goiter is characterized by blood flow that is seen to travel through and around the nodules; while the internal blood flow signal of the adenoma is distributed in a dotted or striped bundle pattern; when the blood flow signal around the adenoma is found to be richer, it generally suggests a cystic adenoma. 6. Enlarged lymph nodes in the neck. In addition to the characteristic manifestations of the thyroid nodule itself, the lymph nodes in the neck are also a very important differential evidence. Generally, normal enlarged lymph nodes appear as oval-shaped on ultrasound, and lymphatic portals or umbilical structures are visible. If a thyroid nodule is found to be accompanied by enlarged lymph nodes in the neck, and the enlarged lymph node has lost its lymph node gate structure, has cystic changes, or has microcalcifications in the lymph node and disturbed blood flow signals, this suggests that the node is malignant and has metastatic lymph nodes. It should be noted that ultrasound is more sensitive to lymph nodes metastasizing around the blood vessels in the neck, but not to lymph nodes metastasizing around the thyroid gland (central group lymph nodes), which may be related to the working principle of ultrasound. Collectively, if a thyroid nodule is found to be a hypoechoic solid nodule with microcalcifications, poorly defined borders, heterogeneous echogenicity, and blood flow disturbances, the likelihood of it being malignant will be over 90%. If enlarged lymph nodes in the neck with abnormal lymphatic structures are also found, malignancy should be highly suspected and the diagnosis can be confirmed by direct surgery if necessary. If a nodule is found to be hyperechoic, with clear borders, homogeneous echogenicity, more cystic components and no abnormalities in the lymph nodes of the neck, the likelihood of it being a benign nodule will also be more than 90%. In the literature, it has been reported that almost 100% of purely cystic nodules and nodules with multiple small vesicles occupying more than 50% of the nodule volume and showing spongy changes are benign. Finally, it should be noted that the benignity or malignancy of thyroid nodules is not directly related to the size of the nodule. It is not uncommon to find nodules less than 1 cm in diameter or even 1-2 mm in diameter that are malignant. The malignancy of nodules is also not related to the palpability of the nodules, which is only related to the site of nodule growth. Although the malignancy rate of single nodules is higher than that of multiple nodules, it is not uncommon to see multiple foci of thyroid cancer in our clinical practice.