Identification of the asexual state of Rhizopus species on histologic tissue sections in a patient with rhinocerebral mucormycosis.

Mucormycosis is an infection caused by a group of fungi in the order Mucorales in the phylum Zygomycota. The most well-known form of this disease is rhinocerebral mucormycosis, which usually develops in diabetic or immunocompromised patients. The fungal hyphal elements are easily detected in biopsy specimens by direct or histologic examination. However, the confirmatory identification of the genus or species requires culture of the specimen. This article presents a case of rhinocerebral mucormycosis in which presumptive identification of the genus was made without microbiologic cultures and was based on the extraordinarily rare appearance of fungal sporangia and sporangiospores in histologic tissue sections. Identification of these structures allowed an early and accurate diagnosis of rhinocerebral invasive mucormycosis.

Giant forms of Blastomyces dermatitidis in the pulmonary lesions of blastomycosis. Potential confusion with Coccidioides immitis.

Typical yeast-phase cells of Blastomyces dermatitidis have a characteristic appearance in tissue sections. Fungal morphologic variation occurs infrequently in the lesions of blastomycosis, yet it can complicate the differential diagnosis, particularly if fresh tissue is not available for microbiologic culture. The authors report a case of pulmonary blastomycosis, confirmed by culture and direct immunofluorescence, in which some of the yeast-like cells were abnormally large. These giant yeast-like cells exceeded the size range accepted for the tissue forms of B. dermatitidis; therefore, coccidioidomycosis was considered initially in the differential diagnosis. Otherwise characteristic morphologic features of these cells, in particular multinucleation and the production of broad-based blastoconidia, helped resolve the differential diagnosis. The diagnosis can be confirmed by direct immunofluorescence or microbiologic culture.