Cool nodules are nodular tissues that do not absorb iodine, so there is no radioactivity at the nodule. About 20% of such nodules are cancerous. For those that are solitary and not very clearly demarcated from the surrounding tissues, cancer is more likely. Combined with the measurement of serum calcitonin, the diagnosis rate can be improved. Cool nodules are mostly seen in undifferentiated thyroid cancer, medullary carcinoma, cystic changes of thyroid and acute stage of subacute thyroiditis. Etiology: 1, autoimmune: patients with autoimmune thyroiditis are also prone to cool thyroid nodules. 2, excessive iodine intake: severe iodine deficiency can cause endemic goiter, but excessive iodine intake can also cause a variety of thyroid disorders, such as abnormal thyroid function and thyroid nodules. 3.Radiation exposure: History of radiation exposure is an important causative factor for thyroid cancer. Individuals who received irradiation doses of 10 to 1000 rad during childhood have a higher incidence of thyroid cancer.