[Foreign body granuloma with positive 18-fluorodeoxyglucose positoron emission tomography( FDGPET)3 years after thymectomy].

A seventies year-old woman underwent thymo-thymectomy through a median sternotomy for type B2 thymoma. Annual screening with fluorodeoxyglucose positron emission tomography (FDG-PET) and computed tomography( CT) did not show any abnormality until 3 years after surgery, when a FDG-positive lesion, 1.5 cm in diameter, was found in the top of the anterior mediastinum. The lesion was resected under the diagnosis of thymoma recurrence, but was pathologically diagnosed as a foreign body granuloma including a suture thread. False-positive results with FDG-PET are related to FDG-uptake by inflammatory cells (e.g. macrophages and lymphocytes in the granuloma). Although FDG-PET is useful for diagnosing the postoperative recurrence of tumors, it should be noted that a foreign body granuloma and local recurrence of tumor have similar growth rates and both appear positive on FDGPET.