Histoplasmosis: Tissue Reactions and Morphologic Variations of the Fungus

Abstract

From the study of autopsy material from 22 cases of disseminated histoplasmosis and lesions obtained surgically in nondisseminated cases, several different types of histologic reactions were observed. Histiocytomycotic lesions occurred in 19 of the 22 cases which came to autopsy. Epithelioid cell graaulomatous reactions in 10 cases resembled the lesions of tuberculosis or Boeck''s sarcoid. Often, with a special fungus stain, Histoplasma could be demonstrated in noncaseous epithelioid cell granulomas. In an increasing number of cases histologic study with special fungus stains has revealed Histoplasma in the necrotic centers of pulmonary "tuberculomas." Histoplasmosis of the adrenal gland occurred in 21 of the 22 cases. Often the glands were greatly enlarged and necrotic. In this series necrotizing lesions of renal medulla were observed in 3, brain "abscess" in 2, and endocarditis in 3 cases. There were 6 instances of enlarged spleen due to epithelioid granulomas, suggestive of Boeck''s sarcoid or tuberculosis. Extracellular forms of Histoplasma capsulatum in necrotic tissue differ from the intracellular forms in viable tissue by exhibiting: poor or no staining with hematoxylin and eosin, distorted and large forms, and occasional hyphae. In 2 of the 3 cases with endocarditis a mycelial growth was demonstrated in the valvular thrombi. There appeared to be transitions from acceptable yeast forms to hyphae. In the valvular thrombus of the 3rd case large cells were producing abortive hyphae. Although cultures were not made directly from the endocardial lesions, on the basis of the histologic evidence, the large forms and the hyphae were interpreted as phases of Histoplasma developing under unusual environmental conditions.