From the Guidelines
Fungal organisms are characterized by distinctive microscopic features, including hyphae that can be septate or non-septate, with specific branching patterns, such as the uniform width and acute-branching septate hyphae of Aspergillus species, and the non-septate hyphae with wide angle branching of Zygomycetes. The microscopic features of fungal organisms are crucial for their identification and classification. According to the european position paper on rhinosinusitis and nasal polyps 2020 1, the most common causative pathogens of invasive fungal rhinosinusitis are the Zygomycetes (Rhizopus, Mucor, Rhizomucor) and the Aspergillus species. Key features of these pathogens include:
- Septate hyphae with uniform width and acute-branching patterns, often branching at 45 degrees, characteristic of Aspergillus species
- Non-septate hyphae with wide angle branching, characteristic of Zygomycetes
- Angioinvasion of fungal hyphae, producing thrombosis and mucosal infarction, and subsequent tissue necrosis, as seen in invasive fungal rhinosinusitis 1. These microscopic features are essential for the diagnosis and treatment of fungal infections, and for understanding the pathophysiology of diseases such as invasive fungal rhinosinusitis.
From the Research
Microscopic Features of Fungal Organisms
The microscopic features of fungal organisms are not always specific and can be similar across different species.
- Fungal infections can be diagnosed using microscopic examination, but this method has its limitations 2, 3.
- The morphology of fungi in tissue is not always reliable for species-level identification, and other methods such as culture, immunohistochemistry, in situ hybridization, and PCR may be needed to determine the specific agent present 2, 3, 4.
- Some fungal organisms, such as hyaline molds, are not reliably differentiated based on their morphology in tissue, and microbiologic diagnosis via culture or molecular-based methods is necessary to guide antifungal management and inform prognosis 4.
- Deep fungi can be identified by clinical and histological features, as well as serological evaluation and culture, and species-specific syndromes may be recognized 5.
Limitations of Microscopic Examination
- Microscopic examination of tissue alone is not sufficient for species-level diagnosis of fungi, and correlation with laboratory studies is necessary 3.
- The accuracy of histopathologic identification of fungi can be high, but incorrect morphologic diagnoses can occur, particularly with Aspergillus spp. and Mucorales 3.
- Education and knowledge of mycology are essential for accurate diagnosis and identification of fungal organisms 3.