Unusual histopathology of mucormycosis in acute myelogenous leukemia

Mucormycosis is a mycotic disease caused by certain genera of the class Zygomycetes (order Mucorales). It is usually a rapidly progressive opportunistic infection characterized by vascular invasion, neutrophilic response, and intravascular thromboses. Entomophthoromycosis describes another disease caused by Zycomycetes, but of the order Entophthorales. In contrast to mucormycosis, entomophthoromycosis is not associated with underlying disease. Vascular invasion by the hyphae does not occur, and the hyphae are surrounded by eosinophilic sheathes. These sheathes are regarded as one form of the Splendore-Hoeppli phenomenon. The authors report an unusual case of mucormycosis in a severely pancytopenic patient dying of acute myelogenous leukemia. At autopsy, eosinophilic sheathes with radiating fibrils were seen about intravascular hyphae, simulating entomophthoromycosis. This pseudo-Splendore-Hoeppli phenomenon appears to be caused by adsorption of plasma and fibrin to the hyphal walls in the absence of both neutrophilic response and extensive fibrin clotting.