T. Fukuda et al., Abnormal pigmentation of schwannoma attributed to excess production of neuromelanin-like pigment, PATHOL INT, 50(3), 2000, pp. 230-237
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.