S11C18aP13a-Histoplasmosis

S11C18aP13a-1: In this field of a cutaneous lesion of histoplasmosis, small organisms are numerous and intracellular.

S11C18aP13a-2: The organisms are small and basophilic; they are outlined by a halo. The organisms have a thin cell wall (histoplasmosis).

S11C18aP13a-3: This cystic lesion is rounded and expansile. Its lumen contains cellular debris. The gross characteristic of the material in the lumen probably would have been in the nature of pus, or caseous material. The lesion has a thick fibrous wall. Along the luminal surface, there are palisades of histocytes (phaeohyphomycotic abscess).

S11C18aP13a-4: Fungal hyphae mostly are vertically oriented along the lumen of the cyst; they are interspersed among radially arranged histiocytes. Some are faintly pigmented (brown). Degree of pigmentation is variable in this category of organisms. Perhaps, some of the variation has to do with the vitality of the organisms. In this field, hyphal forms are numerous.

S11C18aP13a-5: Pigmented hyphal forms are numerous (PAS stain).

S11C18aP13a-6: At the periphery of this “abscess,” giant cells are a prominent feature.

S11C18aP13a-7: The hyphal forms in the wall of the abscess are heavily pigmented.

S11C18aP13a-8: Yeast and hyphal forms are represented (phaeohyphomycotic abscess).

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