Rebound thymic hyperplasia after pneumonectomy and chemotherapy for primary synovial sarcoma

Thymic hyperplasia occurs in a small proportion of patients receiving chemotherapy for various malignancies. It likely results from an immunologic rebound phenomenon. Fluorodeoxyglucose positron emission tomography-computed tomography is an important tool for staging malignant neoplasms. We report a case of rebound thymic hyperplasia manifesting as a hypermetabolic mass on fluorodeoxyglucose positron emission tomography-computed tomography after pneumonectomy and chemotherapy for primary pulmonary synovial sarcoma. We highlight the importance of recognizing the phenomenon of rebound thymic hyperplasia, as it can mimic residual or recurrent malignancy, especially in the setting of altered chest anatomy.