This 51-year-old woman had chronic ulcers of her lower extremities. Botryomycosis is an unusual finding in skin biopsies. The lesions are similar to mycetoma, but the the central areas are bacterial colonies (often Staphylococcus aureus) and not filamentous fungi. Immunoglobulin is abundant within the concretions. These structures have a characteristic brightly eosinophilic peripheral band, the Splendore-Hoeppli phenomenon.
Histologic sections of skin show a mixed inflammatory infiltrate, extending from an ulcerated epidermis to the subcutaneous tissue. There are zones of necrosis and abundant neutrophils. Scattered within the infiltrate are basophilic concretions with a brightly eosinophilic rim.