Nodules are cell clusters of different size and structure from the normal thyroid tissue formed within the thyroid gland. It is more common in women. Although 95% of thyroid nodules are benign, cancer cells can be found in around 5% of the nodules. Thyroid nodules are divided into two groups as thyroid hormone-secreting (hot) and non-hormone-secreting (cold) nodules according to their functions, and anatomically into two subgroups as single (solitary) nodules and multiple (multinodular) nodules. Whether the nodules are hot or cold nodules is determined by the examination called scintigraphy, and the number, size and contents are determined by ultrasonography.

Especially in single and non-hormone-secreting (solitary cold) nodules, the probability of thyroid cancer is higher than other nodule types, and this risk rises up to 15%. Ultrasound-guided fine-needle biopsy is necessary to determine whether this type of thyroid nodule is malignant. Cancer can be caught with this method. Periodic follow-up is recommended for small nodules without cancer. Surgery can be recommended for nodules that are large in size and cause cosmetic problems, continue to grow despite drug therapy, and no cancer is detected in fine needle biopsy, although ultrasound findings are suspicious for cancer.