Hypodense foci of the thyroid is not a disease, it is a pathologic manifestation of the thyroid gland found on imaging and is more common. It can be seen in a variety of thyroid diseases, such as thyroid nodules, etc. It also needs to be combined with other results of imaging tests and thyroid function tests to make a comprehensive diagnosis. 1. Thyroid nodule: it is an abnormal mass in the thyroid gland caused by various reasons, with both benign and malignant possibilities. Imaging examination can show low-density foci, and pathologic examination is necessary to clarify the benign or malignant nature of the nodule. If the nodule is benign and there is no obvious discomfort, regular review is enough; if the nodule is malignant, it is recommended to treat it as soon as possible, including surgery, drugs and other methods. 2. Thyroid cyst: It is a benign thyroid lesion, which may have neck mass, difficulty in swallowing, pain, hoarseness, dyspnea and other symptoms, or no obvious symptoms. If the patient’s physical examination found that the thyroid gland has a low density foci performance, do not panic, timely consultation, identify the cause of symptomatic treatment.