Thymic Hyperplasia and Graves Disease: A Nonincidental Association

We present 2 cases referred for evaluation of Graves disease (GD) associated with an incidental mediastinal mass. Chest computed tomography (CT) scans showed a 1.2 × 2.4 × 4.3 cm and a 5.7 × 2.6 × 7 cm thymic enlargement, respectively, consistent with thymic hyperplasia (TH) in the 2 patients. Patient 1 had been assessed by thoracic surgery for the mediastinal mass, and thymectomy had been performed to exclude thymoma, with an anatomopathological diagnosis consistent with thymic hyperplasia. Patient 2 was treated with methimazole. CT scan was repeated after he maintained a euthyroid state, which revealed total regression of the mass. There is a well-documented association between these 2 entities, but it is often underdiagnosed and unrecognized in routine clinal practice. The benign evolution, as evidenced by regression of thymic hyperplasia after resolution of the hyperthyroidism, is characteristic. These cases highlight the importance of recognizing the association of GD and TH and warrant a conservative approach, preventing unnecessary thymic evaluation and surgery.