A small nodular shadow with a diameter of about 13mm is seen in the anterior superior mediastinum refers to a nodule of 13mm size found in the anterior superior mediastinum tissues during the imaging examination. Common causes include thymic lesions, enlarged lymph nodes, teratomas, and thyroid lesions. 1. Thymic lesions: mainly include thymoma and degenerative thymus, both of which will have nodular changes and need to be judged according to further examination and clinical symptoms. 2. Enlarged lymph nodes: mostly related to inflammation, but some enlarged lymph nodes may be related to tumor infiltration. 3. Teratoma: it is a common benign tumor in the anterior superior mediastinum, which is caused by the proliferation of abnormal cells remaining in the process of embryonic development. 4. Thyroid lesions: including retrosternal goiter and intrathyroidal occupations protruding into the mediastinum, with unclear demarcation between the lesion and the thyroid gland. Small nodular shadows, about 13mm in diameter, can be seen in the anterior superior mediastinum, which should be promptly followed to improve the relevant examinations and standardized treatment under the guidance of physicians.