## Distinguishing Aspergillosis from Mucormycosis ### Morphological Hallmark **Key Point:** The most reliable discriminator between these two molds is hyphal morphology under microscopy and histology. | Feature | Aspergillus | Mucormycosis | |---------|-------------|---------------| | **Septation** | Septate hyphae | Non-septate (coenocytic) hyphae | | **Branching angle** | Acute angle (45°) | Right angle (90°) | | **Diameter** | 2–4 μm | 6–30 μm (much wider) | | **Angioinvasion** | Less common; vascular occlusion | Hallmark feature; tissue necrosis | | **Tissue reaction** | Minimal necrosis | Extensive necrosis with black eschar | ### Clinical Context **High-Yield:** In tissue sections or culture, Aspergillus shows **thin, regularly septate hyphae with acute-angle (45°) branching**. Mucormycosis shows **broad, non-septate hyphae with right-angle (90°) branching**. **Clinical Pearl:** While both are opportunistic in immunocompromised patients (neutropenia, hematologic malignancy, transplant), the **morphology is the gold standard for differentiation**. Mucormycosis is angioinvasive and causes tissue necrosis (black eschar in rhinocerebral disease); Aspergillus is less angioinvasive and more likely to cause chronic cavitary lung disease or fungal balls. ### Why Morphology Wins - **Septate, acute-angle branching** = Aspergillus (correct answer) - Non-septate, right-angle branching = Mucormycosis - Both can cause rapid dissemination, but morphology is the fastest, most specific discriminator in culture and histology. [cite:Robbins 10e Ch 8]
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