This 47-year-old man developed a necrotic ulcer with eschar and purpuric borders following immunosuppression for an orthotopic liver transplant (HCV). The lesion was biopsied and sent for both histology and cultures. The clinical differential diagnosis included deep fungal infection and ecthyma gangrenosum. The histopathology showed scattered filamentous fungi within the areas of necrosis. The apparent aseptate and ribbon-like nature of the fungus is highly suggestive of zygomycosis (mucor, rhizopus, etc), however, degenerated Aspergillus species can look like this, and thus cultures are necessary for confirmation.
At high power, using a Periodic Acid Schiff (PAS) stain with a light green counterstain, the features of the fungal hyphae become more clear while in a background of necrotic debris. The ribbon-like hyphae do not have parallel borders, and fail to form distinct branching angles, rather wave and twist in different directions. Septation can be difficult to evaluate, but no clear evidence of septation is seen here.