[Deep seated mycosis diagnosed at hospital pathology division]

A pathological diagnosis can be a decisive diagnosis for deep-seated mycosis. HE stain is used to look for structural changes of the infected lesion and then various special stains are used to visualize the fungus in sections. When viability of the fungus is low, it is faintly stained with HE or PAS. Grocott stain can clearly demonstrate the fungus regardless of viability. Overstaining and understaining sometimes occur. Grocott stain is not suitable to detect structural changes of an infected lesion. Cell walls of Cryptococcus and dematiaceous fungi are stained brown with Fontana-Masson stain because of the existence of melanin. However, it is noteworthy that some Aspergillus and zygomycetes also turn brown with this stain. Fungiflora Y with a fluorescence microscope can readily demonstrate most fungal hyphae except zygomycetes. Immunohistochemistry with antibody against various fungi and in situ hybridization are useful to confirm a fungal genus on paraffin sections. Furthermore, probes to detect specific species of Aspergillus for in situ hybridization are now available.