A Case of Posterior Mediastinal Plasmacytoma Confounded by Community-Acquired Pneumonia.

Plasmacytomas are extramedullary accumulations of plasma cells originating from soft tissue. Mediastinal plasmacytoma is a rare presentation. A 67-year-old man recovered after antibiotic treatment for community-acquired pneumonia. However, on convalescent chest radiography after 3 months, mass like lesion at the right lower lung field was newly detected. Follow-up chest computed tomography (CT) revealed an increase in the extent of the right posterior mediastinal mass that we had considered to be pneumonic consolidations on previous CT scans. Through percutaneous needle biopsy, we diagnosed IgG kappa type extramedullary plasmacytoma of the posterior mediastinum.