Extramedullary plasmacytoma of the tonsil diagnosed by fine-needle aspiration cytology.

A case of tonsillar extramedullary plasmacytoma in a 53-year-old man with a complaint of lump sensation in the throat is presented. Examination of the oral cavity showed enlargement of the left tonsil. Magnetic resonance imaging demonstrated a solid mass, measuring 3.2 x 2.0 x 3.8 cm, in the left tonsil. Cytologic smear obtained by fine-needle aspiration biopsy appeared highly cellular and was composed of clusters of plasma cells with varying maturity. Atypical plasma cells had prominent eccentric nuclei with nucleoli and finely granular cytoplasm. Binucleated cells and mitotic figures were also identified. The cytoplasm of mature-looking small plasma cells was also finely granular without a perinuclear halo. A cytologic diagnosis of plasmacytoma was made. Excisional biopsy showed sheets of plasmacytoid cells with abundant eosinophilic granular cytoplasm. Occasional binucleated and pleomorphic cells with giant nuclei and prominent nucleoli were observed. These plasmacytoid cells were diffusely immunoreactive for lambda light chain and IgG, partially positive for epithelial membrane antigen. Metastatic examination finding was negative for multiple myeloma, and the patient was diagnosed as having extramedullary plasmacytoma. Although the diagnosis of plasmacytoma on cytologic smear may be difficult, in the current case, fine-needle aspiration cytology provided a rapid and accurate diagnosis.