Clinical management of thyroid nodules should be based on ultrasound and FNAB findings. Thyroid ultrasound should be performed when the patient is at risk for thyroid malignancy, has palpable nodules, a multinodular goiter, or enlarged lymph nodes of suspected malignancy. Based on the findings, the need for ultrasound-guided fine-needle aspiration biopsy is determined. During ultrasonography, FNAB is recommended for nodules with the following conditions: ① Solid hypoechoic nodules larger than 10 mm in diameter. ②Thyroid nodules of any size with suspicion of extracapsular growth or cervical lymph node metastasis on ultrasonography. ③Patients with a history of neck radiation exposure in childhood or adolescence; first-degree relatives of patients with papillary thyroid carcinoma (PTC), medullary thyroid carcinoma, or multiple endocrine adenomatosis type 2; those with a history of thyroid cancer surgery; and those with elevated calcitonin levels measured in the absence of any interfering factors. ④Nodules that are less than 10 mm in diameter but have signs associated with malignant lesions on ultrasonography [hypoechoic and/or irregular borders, elongated shape, microcalcifications, or disturbance of blood flow signal within the nodule]. For multinodular goiter: ① When the nodules are consistent with the above-mentioned malignant signs on ultrasonography, FNAB is rarely required for more than 2 nodules; ② When the isotope scan shows “hot” nodules, FNA biopsy cannot be performed; ③ If there is suspicious lymphadenopathy, FNA biopsy should be performed on both the enlarged lymph nodes and the suspicious nodes. (3) In case of suspected lymphadenopathy, FNA biopsy should be performed on both the enlarged lymph node and the suspected node. For mixed (cystic-solid) thyroid nodules: ① UGFNAB is performed on the solid part of the nodule; ② cytology is performed on both the FNAB sample and the aspirated fluid specimen.