Background: The Fontana-Masson stain can be used to detect melanin of dematiaceous fungi such as Curvularia lunata and Bipolaris hawaiiensis in tissue. This stain is often used to identify fungi that may not have an evident brown color in hematoxylin-eosin-stained sections. However, it is not clear whether hyphae of nondematiaceous fungi can be stained with the Fontana-Masson procedure.
Methods: Paraffin sections from culture-proven mycoses caused by species of Aspergillus, Candida, Fusarium, Pseudallescheria, Trichosporon, zygomycetes, and dematiaceous fungi were stained by the Fontana-Masson procedure. Extent of stain intensity and its distribution in fungal elements in tissue were evaluated by means of an intensity scale based on Cryptococcus neoformans as a positive control.
Results: Many Aspergillus spp, some zygomycetes, and all of the dematiaceous fungi showed strong intensity, whereas other fungi showed either weak intensity or no staining.
Conclusion: Fungal hyphae other than dematiaceous fungi occasionally can be stained with the Fontana-Masson procedure. The morphology of positively stained hyphae must be carefully evaluated, especially when they are hyaline in hematoxylin-eosin-stained tissue sections.