Cool nodules are nodules in which the tissue does not absorb iodine, so the nodules are not radioactive. About 20% or so of such nodules are cancerous. Cancer is more likely in those that are solitary and not very well demarcated from the surrounding tissue. In conjunction with serum calcitonin measurement, the diagnostic rate can be improved. Cool nodules are a very common case, especially in middle-aged women. There are two major categories: benign and malignant. Benign nodules account for the majority of cases and are completely curable. Cool nodules can be single or multiple, and the incidence of multiple nodules is higher than that of single nodules, but the incidence of thyroid cancer is higher in single nodules. There are many causes of cool nodules, and several common causes are as follows: 1. Nodular goiter: it is more common in middle-aged women. It is the more common cause of cool nodules in the thyroid gland. Nodules are developed in the process of proliferation and compensation of the gland, most of them are multinodular goiter, and a few of them are single nodular. In the case of relative deficiency of thyroid hormone in the body, the pituitary gland secretes more TSH, and the thyroid gland is stimulated by this increased TSH for a long period of time, which leads to uneven enlargement of the thyroid gland and nodular changes after repeated or continuous hyperplasia. 2.Nodular toxic goiter: this disease starts slowly, often occurs in patients who have nodular goiter for many years, mostly at the age of 40~50 years old, more common in women, can be accompanied by hyperthyroidism symptoms and signs, thyroid function test shows that thyroid hormone in the blood is elevated, by the function of autonomic nodules caused by the person, the nuclide scan shows “hot nodules “Inflammatory nodules: subtle nodules. 3, inflammatory nodules: subacute thyroiditis, chronic lymphocytic thyroiditis, invasive fibrous thyroiditis can cause thyroid cool nodules. 4, thyroid cysts: the vast majority are formed by the degenerative changes of goiter nodules or adenomas, the cysts contain blood or slightly mixed fluid, clear borders with the surrounding, hard texture, generally no pressure pain, nuclear scanning shows “cold nodules”. A few patients are caused by congenital thyroglossal cysts or remnants of the fourth gill slit. 5.Thyroid tumor: due to multiple colloid nodules or thyroid adenomas, single or multiple, which may coexist with goiter or appear alone. They include benign thyroid tumors, thyroid carcinoma and metastatic carcinoma.