Plasma cell granuloma of the lung (inflammatory pseudotumor).

A case of plasma cell granuloma (PCG) of the lung in a 54-year old man is reported. PCG is a rare benign lesion that usually presents as a solitary nodule in the lung (coin lesion) at routine X-ray examination. Microscopically it consists of a granulomatous tissue where the major components are mature plasma cells. The immunohistochemical demonstration of polyclonality of plasma cells, excluding the diagnosis of plasmacytoma, confirms the inflammatory pseudotumoral nature of this lesion, although the etiology remains obscure. The presence of lymphocytes, histiocytes, macrophages, blood vessels with prominent endothelial cells and peripheral sclero-hyalinized connective tissue may pose problems in the differential diagnosis with sclerosing hemangioma, pseudolymphoma, nodular amyloidosis, pulmonary hyalinizing granuloma, chronic abscess and neoplasms of true histiocytic origin. The term inflammatory pseudotumor is preferable in describing this type of lesion.