Benign hyperplastic thymus is a rare but important differential diagnosis of anterior mediastinal lesions. Histological and radiological criteria are used to distinguish this benign condition from other malignant diseases but have their limitations, and biopsy of mediastinal masses can be risky. | Watchful waiting for some children with a mediastinal mass: The potential role for 18 F-fluorodeoxyglucose positron emission tomography: A case report and review of the literature