PMC3891389_01
Plain chest roentgenography (A) showed a smooth, marginated 3x4 cm sized mass-like lesion on the right upper mediastinal area. Chest computed tomographic (CT) with enhancement (B) revealed a 2.5x2 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.
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F1
The plain chest X-ray revealed a smooth marginated 3x4 cm sized mass-like lesion in the right upper mediastinal area (Figure 1A). Chest computerized tomographic (CT) studies, performed after the intravenous administration of a contrast agent, revealed a 2.5x2 cm sized, well defined, bilobed, homogeneously enhancing mass lesion in the right upper posterior mediastinum (Figure 1B).
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).
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F2
Moderate heterogeneous enhancement was noted with gadolinium-enhancement (Figure 2).
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, x400). Immunohistochemical staining showed that the neoplastic plasma cells were reactive for CD79a B-cell marker (B) and had kappa monoclonality (C). (Immunohistochemical stain: CD79a, x400 and kappa light chain, x400)
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F3
Histologically, the tumor was characterized by a well circumscribed proliferation of plasma cells (Figure 3A). Immunohistochemical staining was positive for IgG and kappa light chain (Figure 3C), but not for lambda chain. The tumor cells were positive for CD79a (a pan-B cell marker) (Figure 3B), and CD45, and were negative for CD3 (a pan-T cell marker) and cytokeratin, which was consistent with plasma cell differentiation.