Thymic nodule 13mm is not necessarily thymoma, the determination of thymoma is not only diagnosed according to the size of the nodule, the diagnosis of thymoma is mainly based on imaging examination and surgical biopsy. 1. Imaging examination: X-ray shows widening of the mediastinum, and post-thoracic hyperdensity can be seen in lateral view; CT helps to determine the range of thymoma, but it cannot determine the benign or malignant nature of thymoma, and the foci are mostly round tissue density foci, and some of them can show cystic lesions, and most of them are solid and uniformly intensified foci. 3. Surgical biopsy: it is the gold standard for diagnosing thymoma and its benign or malignant nature, and it shows atypical hyperplasia as malignant lesion. It is suggested that patients should go to the hospital for detailed examination and early treatment to avoid delaying the condition.