Which microscopic feature is characteristic of Aspergillus in tissue?

Which microscopic feature is characteristic of Aspergillus in tissue?

• A. Non-septate hyphae with wide-angle branching
• B. Yeast forms
• C. Encapsulated bacteria
• D. Septated hyaline hyphae with 45-degree branching

Answer: (D)

The key microscopic feature is septate hyphae that are narrow and hyaline, with acute-angle branching around 45 degrees. This branching pattern—narrow, regular, and septate hyphae that branch at about 45 degrees—is characteristic of Aspergillus in tissue. It helps distinguish it from organisms like Mucorales, which show broad, non-septate hyphae with wide-angle (often near 90 degrees) branching. Yeast forms would point toward organisms such as Candida or Histoplasma, not filamentous molds, and encapsulated bacteria are not fungi. Special stains like Gomori methenamine silver or PAS can highlight these septate hyphae.

The key microscopic feature is septate hyphae that are narrow and hyaline, with acute-angle branching around 45 degrees. This branching pattern—narrow, regular, and septate hyphae that branch at about 45 degrees—is characteristic of Aspergillus in tissue. It helps distinguish it from organisms like Mucorales, which show broad, non-septate hyphae with wide-angle (often near 90 degrees) branching. Yeast forms would point toward organisms such as Candida or Histoplasma, not filamentous molds, and encapsulated bacteria are not fungi. Special stains like Gomori methenamine silver or PAS can highlight these septate hyphae.