Thyroid parenchymal lesions, i.e., pathological changes in the parenchymal structure of the thyroid gland, are usually detected on ultrasonography and may be diffuse or nodular, and the diagnosis can be made by combining other findings of ultrasonography and thyroid function tests. The thyroid gland is an important endocrine organ in the human body, located in the neck near the thyroid cartilage, with the role of regulating calcium and phosphorus metabolism, promoting the growth and development of the brain in children, and maintaining the metabolic level of the body. The physiologic structure of the thyroid gland includes parenchyma and interstitium, and parenchymal lesions are often diffuse or nodular. Diffuse lesions may indicate Graves’ disease or thyroiditis. Nodular lesions are often suggestive of thyroid adenomas and papillary thyroid carcinoma. Parenchymal thyroid lesions should be actively sought for diagnosis and prompt treatment under the guidance of a doctor.