18F-FDG PET/CT Detection of Extensive Pleural Metastasis in Rare Malignancy Thymoma

The majority of metastatic pleural lesions are caused by malignancies such as bronchogenic carcinoma (40%), breast cancer (20%), lymphoma (10%), and ovarian or gastric carcinomas (5%). However, pleural metastases from thymoma are extremely rare. In this report, we present the ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) imaging findings of a patient with thymoma and extensive pleural metastases. Although biopsy remains the gold standard for diagnosis, it is important to consider high grade thymoma in the differential diagnosis, as extensive pleural involvement observed on ¹⁸F-FDG PET/CT imaging can mimic both primary and metastatic pleural malignancies. Recognizing this possibility can assist in more accurate interpretation of imaging findings.