Plasmacytoma is characterized by infiltrates of plasma cells of diverse maturity. The cells have small, round, eccentric nuclei with clumped peripheral chromatin. The cytoplasm is abundant and basophilic, with a perinuclear halo, composed of the Golgi apparatus. Because benign reactive plasmacytosis, undifferentiated carcinomas, non-Hodgkin lymphoma, malignant melanomas, and esthesioneuroblastomas are histologically similar to plasmacytomas, differentiation represents a diagnostic challenge for head and neck pathologists. The pathologic features should be reviewed by a histopathologist with a special interest in lymphoproliferative disorders.1 Immunohistochemical studies are very helpful in making the diagnosis. Clonal expansion of the tumor can be demonstrated by staining of light-chain immunoglobulins. In the present case, the cytoplasm of all tumor cells was characteristically strongly positive for the immunoglobulin κ light chain. Therefore, the histopathologic results confirmed that the tumor was a monoclonal plasma cell neoplasm.
Pathology Quiz Case 2: Diagnosis. Arch Otolaryngol Head Neck Surg. 2006;132(11):1271. doi:10.1001/archotol.132.11.1271