S11C18P13Fungus



S11C18P13-1 a&b: On the left in a lesion of cryptococcosis, organisms are numerous and inflammatory cells sparse. This is common feature of this fungus infection. In some examples in which the host immune response is better developed, lesions tend to be localized, and to show well-developed granulomatous features. In this example, a prominent, rounded, clear halo surrounds each of the organisms. The clear space is representative of a mucinous capsule. In contrast to the organisms of blastomycosis, those of cryptococcosis often are only faintly, but uniformly, stained with hematoxylin. The organisms generally are smaller than those of blastomycosis. The buds from organisms in a lesion of cryptococcosis have narrow bases (arrows in field on right) (PAS stain). The capsule of a organism in cryptococcosis is mucicarminophilic.

S11C18P13-2: In this example of disseminated cryptococcosis, the inflammatory infiltrate is clearly granulomatous. Histiocytes have epithelioid qualities, but the infiltrates are diffuse; histiocytes are not clustered in discrete tubercle-like aggregates. The small organisms tend to cluster in the rounded, cytoplasmic defects. The organisms are intra-cellular in the cytoplasm of histiocytes; they have been phagocytized.

S11C18P13-3: In this example of disseminated histoplasmosis, activated histiocytes form diffuse sheets; tubercle-like aggregates are not a feature. Small organisms are intra-cellular in the cytoplasm of the histiocytes (small arrows). They appear as small blue dots with a peripheral clear halo. The organisms, in contrast to those of leishmaniasis, would react in a positive fashion on a PAS stain.

S11C18P13-4 a& b: Two additional fields are representative of lesions of disseminated histoplasmosis. The small organisms are intra-cellular. The infiltrates are composed of sheets of histiocytes.

S11C18P13-5: In this lesion of histoplasmosis, small, silver-impregnated organisms are numerous (Gomori silver methenamine).

S11C18P13-6: With a Gomori silver methenamine stain, the organisms of histoplasmosis appear somewhat larger than they would on a PAS stained section; the impregnation of silver on the surface increases the visual dimensions of the organisms. The buds of scattered organisms have narrow bases. The bud of the organism next to the red arrow farthest to the right is somewhat cigar-shaped.

S11C18P13-7: The granuloma is a diffuse infiltrate of closely spaced, activated histiocytes. The infiltrates do not nest in well-defined patterns; tubercle-like qualities are not a feature. The granulomatous infiltrate is not associated with a significant background infiltrate of lymphoid cells, The patient is probably immuno-suppressed, but this lesion predates the AIDS epidemic.

S11C18P13-8: The diffuse, unorganized character of the infiltrate is evident at higher magnification; the lesion is tumoral.

S11C18P13-9: At higher magnification, many of the histiocytes contain intra-cellular, small organisms. An organisms are recognized as a central blue punctum that is outlined by a clear halo (disseminated histoplasmosis) (see S11C18aP13a-1).

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