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.
A medium power look at the tissue using a modified silver stain (Grocott's Methenamine Silver, or GMS) demonstrates numerous fungal hyphae concentrated in the abscess cavity. These hyphae form unusual ribbon-like structures with large, bulbous "cysts" when cut en face. Background staining of elastic fibers is present in the superficial dermis.