Immunohistochemical and clonal analysis of minute pulmonary meningothelial-like nodules

The histogenesis of meningothelial-like nodule or so-called minute pulmonar y chemodectoma remains unclear, with various immunohistochemical analyses g iving inconsistent results. We performed an immunohistochemical and clonal analysis of minute pulmonary meningothelial-like nodules. Thirty-one histol ogically defined meningothelial-like nodules in 14 cases were stained immun ohistochemically. One case had multiple lesions with brown pigment granules , which were positively stained with Berlin blue method, indicating the pre sence of hemosiderin. All meningothelial-like nodules were positive for vim entin and epithelial membrane antigen (EMA), but not for S-100 protein, chr omogranin A, or synaptophysin. Five of 13 cases (13 of 28 lesions) were pos itive for CD68 by KP-I. Ten cases (24 lesions) stained for CD68 by PG-M1 we re weakly positive. All lesions were negative for lysozyme, myosin, actin, keratin, and melanoma-associated antigen. Alveolar macrophages were intense ly positive for CD68 and lysozyme in all examined cases. We analyzed the cl onality of 11 minute pulmonary meningothelial-like nodule lesions in two fe male cases based on an X-chromosome-linked polymorphic marker, the human an drogen receptor gene (HUMARA). The HUMARA was found to be amplified with or without prior digestion by the methylation-sensitive restriction endonucle ase HpaII. Six of 11 lesions showed monoclonal expansion. Five lesions in a multiple case showed different patterns of monoclonality. Our findings sho wed that minute pulmonary meningothelial-like nodules have meningothelial-l ike and phagocytic characteristics but no muscular phenotype. Furthermore, some minute pulmonary meningothelial-like nodules may show monoclonal expan sion, whereas others are polyclonal. Our data indicate that minute pulmonar y meningothelial-like nodules are reactive rather than neoplastic. Copyrigh t (C) 1999 by W.B. Saunders Company.