A Case of Extramedullary Plasmacytoma Arising from the Posterior Mediastinum
A 64-year-old man was referred to the pulmonary department of Korea University Ansan Hospital for an evaluation of a lung mass. He had received a medical checkup 1 month previously, when the mass-like lesion was incidentally found on plain chest X-ray. He was asymptomatic and had well controlled hypertension and diabetes; he also had a smoking history of 40 pack-years. On physical examination, no palpable lymphadenopathy or other abnormality was noted. His hemoglobin, white cell count, platelets, urea and electrolytes, glucose, liver function tests, and serum calcium were normal. The plain chest X-ray revealed a smooth marginated 3×4 cm sized mass-like lesion in the right upper mediastinal area (). Chest computerized tomographic (CT) studies, performed after the intravenous administration of a contrast agent, revealed a 2.5×2 cm sized, well defined, bilobed, homogeneously enhancing mass lesion in the right upper posterior mediastinum (). No definite evidence of bony erosion of the thoracic vertebrae was observed. On magnetic resonance imaging (MRI), the tumor was visualized as a homogeneous signal intensity mass with a signal intensity similar to muscle on T1-weighted images, whereas on T2-weighted images, the signal intensity was moderately higher than that of muscle. Moderate heterogeneous enhancement was noted with gadolinium-enhancement ().\nA provisional diagnosis of neurogenic tumor was made and percutaneous needle aspiration was performed for diagnosis. However, the histologic examination showed aggregates of small round cells. Therefore, a right lateral mediastinotomy was performed for a confirmatory diagnosis. Histologically, the tumor was characterized by a well circumscribed proliferation of plasma cells (). Immunohistochemical staining was positive for IgG and kappa light chain (), but not for lambda chain. The tumor cells were positive for CD79a (a pan-B cell marker) (), and CD45, and were negative for CD3 (a pan-T cell marker) and cytokeratin, which was consistent with plasma cell differentiation. Based on these findings, the tumor was diagnosed as a plasmacytoma. We investigated the possibility of multiple myeloma. Serum protein electrophoresis analysis showed a monoclonal gamma globulin peak of 1.8 g/dL (0.6~1.7 g/dL), and serum immunoelectrophoresis revealed IgG kappa type monoclonal gammopathy, but this was insufficient to meet the diagnostic criteria of multiple myeloma. Surveys for a skeletal lesion, bone marrow biopsy, and Bence-Jones protein in urine were all normal. 99mTc-scintigraphy did not detect any other systemic lesions. Accordingly, multiple myeloma was ruled out, and the patient was finally diagnosed as having EMP of the posterior mediastinum. The patient received treatment with 40 Gy of radiation for five consecutive weeks to a field covering the right upper mediastinum. Six months after his diagnosis, the patient is doing well without further evidence of disease.