Solitary dural plasmacytoma with conspicuous cytoplasmic inclusions

A solitary intracranial plasmacytoma originated from the left parietal meninges of a 67-year-old woman; the patient had a four-month history of generalized seizures. Immunoelectrophoresis, performed nine months after surgery, revealed a monoclonal IgG band in the cerebrospinal fluid (CSF) but not in the blood. A peculiar feature of the tumor cells was the presence of abundant hyaline, eosinophilic cytoplasmic inclusions. Ultrastructurally, these inclusions consisted of electron-dense floccular material within distended cisterns of endoplasmic reticulum (ER). These ultrastructural features resemble "thesaurocytes" originally described by Paraskevas et al. in IgA myeloma. Tumors composed mainly of such inclusion-bearing cells are extremely rare. Only a fraction of the tumor cells stained positively for IgG with the immunoperoxidase technique; most inclusion-bearing cells did not stain. It is therefore unlikely that the electron-dense material is stored immunoglobulins.