Abnormal pigmentation of schwannoma attributed to excess production of neuromelanin-like pigment

Five cases of non-melanotic pigmented schwannoma with excess accumulation o f neuromelanin are presented. The tumors were composed basically of spindle or fusiform tumor cells, compatible with those of classical schwannoma, to gether with varying numbers of tumor cells containing various amounts of li ght brown or grayish pigment. Fontana-Masson stain demonstrated argentaffin granules in some tumor cells of each tumor and bleaching with potassium pe rmanganate abolished argentaffin reaction. Ultrastructural examination demo nstrated the granules contained fine particles with heterogeneous density, occasionally together with coarse granular materials or amorphous high-dens ity areas, indicating lysosome or autophagosome. Neither typical melanosome s nor neurosecretory granules were detected. In immunohistochemistry, neuro genic markers as well as CD68 were expressed in most tumor cells in each ca se and various numbers of tumor cells were positive for Leu7 and CD34, Lyso zyme was also frequently positive in tumor cells, especially in granular ce lls. HMB45 was not expressed in any of the cases. These findings indicate t hat these cases are schwannomas with abnormal accumulation of neuromelanin- like pigment.