Thymic Carcinoma Unexpected Detected by FDG-PET in a Patient with Elevated serum Carbohydrate Antigen 19-9

摘要

Thymic carcinoma defined as primary thymic epithelial neoplasms showing overt cytologic features of malignancy is rare. A 66-year-old female with persistent elevation of serum carbohydrate antigen 19-9 levels was arranged a FDG-PET study because ultrasound, MRI, and colonscopy examinations focusing on the digestive systems got negative finding. FDG-PET revealed a focal area with increased FDG uptake in the anterior aspect of superior mediastinum. The lesion was pathologically proven to be thymic carcinoma after surgical resection. The thymus can be distinguished from superior mediastinal adenopathy by its characteristic of inverted V shape. Mildly increased FDG uptake into thymus is not uncommonly found in children and young adults. In adult, increased uptake can be seen in thymic hyperplasia. Soon after chemotherapy or radiotherapy, thymic uptake is sometimes seen. If an increased focal uptake (greater than that of liver uptake) in the thymus or if the thymic shape is distorted, the possibility of malignancy is considered.