Author: Assoc Prof Patrick Emanuel, Dermatopathologist, Auckland, New Zealand, 2013.
Mucormycosis is a fungal infection caused by organisms of the Mucorales order. Rhisopus is the most common organism. Absidia, Mucor, Rhizomycor are other less common causative moulds.
Histology of mucormycosis
The fungal forms of mucormycosis are broad, non-septate hyphae (figure 1). They are wider than Aspergillus species and branch irregularly. The angle of branching is greater than other organisms, and usually approaches 90° (figure 2, arrow)
Angioinvasion is common and may elicit intravascularthrombosis. There is often a marked inflammatory response which may be neutrophilic and granulomatous. Sometimes, there is minimal inflammatory response, particularly in immunosuppressed individuals.
Mucormycosis organisms may easily be seen on haematoxylin and eosin sections (figure 1). Special stains with PAS (figure 2) or GMS can be used to highlight the organisms and allow a clearer assessment of the morphology.
Differential diagnosis of mucormycosis pathology
Aspergillus – Aspergillus species are thinner, septate, with regular branching and they branch at acute angles (45° as opposed to 90°).