What is the hallmark histologic feature of Aspergillus species in tissue?

• A. Septate hyphae with acute-angle branching
• B. Broad non-septate hyphae with right-angle branching
• C. Yeast forms in tissue
• D. Capsule around hyphae

Answer: (A)

Septate hyphae with acute-angle branching. Aspergillus forms narrow, hyaline hyphae that are divided by regular cross-walls (septations) and tend to branch dichotomously at sharp angles, typically around 45 degrees. This histologic pattern is a classic clue for invasive aspergillosis in tissue. In contrast, other fungi show different morphologies: mucorales have broad, largely non-septate hyphae with wide, near-right-angle branching; yeasts appear as rounded cells (budding forms in Candida, encapsulated yeasts in Cryptococcus) rather than slender hyphae. So the combination of septations plus acute-angle branching is the best indicator of Aspergillus in tissue.