A case of extramedullary plasmacytoma arising from the posterior mediastinum

Abstract

Plasmacytomas are a localized proliferation of plasma cells in the bone marrow, and are less frequently seen in extraosseous organs or tissues. Extramedullary plasmacytoma is a rare malignant neoplasm, and is especially uncommon when it arises from the mediastinum. Here, we report on a case of posterior mediastinal extramedullary plasmacytoma in a 64-year-old man. He was admitted with an asymptomatic right apical mediastinal mass, which was provisionally diagnosed as a neurogenic mass. However, a subsequent investigation revealed that this tumor was a rare case of IgG kappa type extramedullary plasmacytoma arising from the posterior mediastinum. The patient was treated with local radiation to the mediastinum and is doing well without further evidence of disease.

Figure 1

Plain chest roentgenography (A) showed a smooth, marginated 3×4 cm sized mass-like lesion on the right upper mediastinal area. Chest computed tomographic (CT) with enhancement (B) 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 thoracic vertebrae was noted.

Figure 2

Magnetic resonance imaging (MRI) revealed a tumor of homogeneous signal intensity with a signal intensity similar to that of muscle on T1-weighted images (A). Moderate heterogeneous enhancement was observed after introducing gadolinium contrast (B).

Figure 3

Microscopically, the tumor consisted of extensively infiltrating, diffuse sheets of mature and immature plasma cells with eccentric, pleomorphic nuclei, nucleoli, and variably stained cytoplasm (A) (Hematoxylin and eosin stain, ×400). Immunohistochemical staining showed that the neoplastic plasma cells were reactive for CD79a B-cell marker (B) and had kappa monoclonality (C). (Immunohistochemical stain: CD79a, ×400 and kappa light chain, ×400)