Fine-needle aspiration cytology of a mediastinal seminoma associated with multilocular thymic cyst

Multiloculated thymic cysts are uncommon lesions that carl be either acquir ed or associated with malignancies. This report describes the fine-needle a spiration (FNA) cytology of a mediastinal seminoma with prominent cystic ch ange, confirmed by surgical pathology examination and ancillary studies per formed on both the cytology and tissue specimens. The FNA cytology revealed clusters of malignant oval-to-polygonal-shaped cells with large oval nucle i possessing prominent nucleoli set in a pale-to-eosinophilic cytoplasm. Th ese cells were surrounded by a dense lymphoid infiltrate along with a few n oncaseating granulomas. The large malignant seminoma cells stained positive for placental alkaline phosphatase (PLAP) and negative for both low molecu lar and broad-spectrum cytokeratin. The differential diagnosis of malignanc ies associated with thymic cysts is presented To the best of our knowledge, this is the first report of aspiration cytology of a mediastinal seminoma associated with a multilocular cyst. (C) 1999 Wiley-Liss, Inc.