Answer: Histoplasmosis

Histology: none provided

Discussion: The lesion shows characteristic caseating granulomatous inflammation with a peripheral rim of pallisading histiocytes and central areas of debris with polymorphonuclear cell infiltrate. The GMS stain shows small budding yeast forms consistent with Histoplasma infection. The differential diagnosis would include mycobacterial infection and special stains should resolve that issue. Other considerations would be less likely, but include Wegener’s granulomatosis in which there would be an angry red “necrobiotic” appearance to the areas of necrosis and granulomatous inflammation. Sarcoid granulomas can have focal areas of fibrinoid necrosis, but lack the central massive necrosis with polymorphonuclear cell infiltrate seen here.