Mucormycosis (zygomycosis) is an opportunistic mycosis caused by a number of molds classified in the order Mucorales of the Phylum Glomerulomycota and Subphylum Mucoromycotina. These fungi are ubiquitous thermotoler ant saprobes. The leading pathogens among this group are species of the genera Rhizopus (see Figure 1), Rhizomucor, Lichtheimia, Cunninghamella (see Figure 2), Mucor, etc. The most prevalent agent is Rhizopus oryzae. The conditions that place patients at risk include acidosis—especially that associated with diabetes mellitus—leukemias, lymphoma, corticosteroid treatment, severe burns, immunodeficiencies, and other debilitating diseases as well as dialysis with the iron chelator deferoxamine.
Fig1. Rhizopus. The sporangium of this mold has released its sporangiospores but remains attached to the supporting sporangiophore, and rhizoids are apparent at the base of the sporangiophore. 200×.
Fig2. Cunninghamella bertholletiae. The sporangiospores are produced within sporangiola that are attached to a vesicle and supported by a sporangiophore. 400×.
The major clinical form is rhinocerebral mucormycosis, which results from germination of the sporangiospores in the nasal passages and invasion of the hyphae into the blood vessels, causing thrombosis, infarction, and necrosis. The disease can progress rapidly with invasion of the sinuses, eyes, cranial bones, and brain. Blood vessels and nerves are damaged, and patients develop edema of the involved facial area, a bloody nasal exudate, and orbital cellulitis. Thoracic mucormycosis follows inhalation of the sporangiospores with invasion of the lung parenchyma and vasculature. In both locations, ischemic necrosis causes massive tissue destruction. Less frequently, this process has been associated with contaminated wound dressings and other situations.
Direct examination or culture of nasal discharge, tis sue, or sputum will reveal broad hyphae (10–15 µm) with uneven thickness, irregular branching, and sparse septations (Figure 3). These fungi grow rapidly on laboratory media, producing abundant cottony colonies. Identification is based on the sporangial structures. Treatment consists of aggressive surgical debridement, rapid administration of amphotericin B, and control of the underlying disease. Many patients survive, but there may be residual effects such as partial facial paralysis or loss of an eye.
Fig3. Mucormycosis A: Broad, ribbon-like sparsely septate hyphae (10–15 µm in width) of Rhizopus oryzae in lung tissue. H&E 400×. B: Similar histopathologic specimen, stained with Gomori methenamine silver. 1000×.
