Coccidioidomycosis and Histoplasmosis

Both of these diseases may present with a miliary pattern resembling miliary tuberculosis.

Figure 1. Miliary Coccidioidomycosis

HRCT shows numerous, bilateral, small, well-defined nodules, randomly distributed throughout the lung in an AIDS patient with disseminated coccidioidomycosis.

Figure 2. Miliary Coccidioidomycosis

Slice of lung from a similar patient showing the resemblance to miliary tuberculosis.

spherule

Figure 3. A Miliary Lesion

As with miliary tuberculosis, well-formed granulomas are absent. Note the spherule in the center of the exudate.

Find the spherule of Coccidioides immitis.

 

endospores

Figure 4. Maturing Sporangia and Spherules

This Gomori methenamine silver (GMS) stain shows spherules and enlarging, maturing sporangia without endospores. Contiguous maturing sporangia should not be confused with budding yeast of blastomycosis.

Only spherules with endospores are diagnostic, histologically.

Find the spherule that has just released its endospores.

Figure 5. Histoplasma capsulatum

This GMS stain shows multiple, intracellular and extracellular, small yeast forms of histoplasma in a non-granulomatous exudate from an immunocompromised patient.

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Spherule of Coccidioides immitis

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Endospores erupting from spherule

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