I. Causes of calcification Malignant tumors of thyroid gland cause calcification due to rapid growth of cancer cells and proliferation of blood vessels and fibrous tissues in the tumor, which can easily lead to calcium salt deposition. In addition, calcification can also be caused by the secretion of some substances, such as glycoproteins and mucopolysaccharides, by the tumor itself. Calcification of thyroid can occur in malignant nodules as well as benign nodules, but the chance of calcification in malignant nodules is higher, 26%~54% in the former and 8%~32% in the latter. Calcification typing by ultrasound ① Microcalcifications: multiple strong echogenic dots (less than 2 m m ) in clusters or scattered distribution, with or without acoustic shadowing. When both microcalcifications and coarse calcifications are present in the nodule, the nodule is classified as a microcalcification type. (ii) Coarse calcification: a strong echogenic spot larger than 2 mm inside the nodule with acoustic shadowing. (iii) Peripheral calcification: coarse calcification surrounding the nodule in a circular or curved shape. ④ Isolated calcified spot: a single coarse calcification with no surrounding thyroid nodule. The relationship between calcification and benign and malignant nodules Microcalcifications are usually considered to be the most reliable indicator for the diagnosis of thyroid cancer, basically reflecting the “sand bodies” in the pathology. Sandy bodies are characteristic of papillary thyroid carcinoma and can also be seen in follicular thyroid carcinoma, nodular goiter, follicular adenoma, and chronic lymphocytic thyroiditis. Peripheral calcification, coarse calcification, and isolated calcification are usually considered indicators of benign thyroid tumors and are seen in benign diseases such as thyroid adenoma and nodular goiter, but all three can also occur in malignant nodules. In conclusion, calcification on ultrasound is a specific indicator for the diagnosis of thyroid cancer, but it does not necessarily mean that the presence of calcification is malignant.