Michael Zapor, MD, PhD

Over the past 2 decades, there has been an alarming increase in opportunistic fungal infections with an associated rise in morbidity and mortality. This trend has been attributed to the growing number of patients who are immunocompromised because of bone marrow or solid organ transplant, immunosuppressive drugs, AIDS, and hematological malignancies. Advances in trauma and critical care medicine that lead to longer survival of more patients with immunocompromising conditions also play a role.

Filamentous fungi (molds) can be divided into 2 broad morphologically distinct groups: those that produce aseptate hyphae and those that produce aseptate (or rarely septated) hyphae. Identification of aseptate hyphae in tissue is virtually pathognomonic of zygomycosis (mucormycosis)-disease caused by fungi of the class Zygomycetes (order Mucorales). The discovery of septate hyphae in tissue is less diagnostic; septate hyphae may be caused by fungi that typically grow as yeasts (eg, Candida and Trichosporon) or a vast number of species of molds. The septate molds are often divided into those with darkly pigmented hyphae (phaeohyphomycetes) and those with pale or colorless (hyaline) hyphae (hyalohyphomycetes).