Histopathology Findings in Neonatal Aspergillosis
On histopathology, neonatal aspergillosis characteristically demonstrates septate hyphae with dichotomous (acute angle) branching, typically invading tissue with evidence of angioinvasion and tissue necrosis. 1
Microscopic Characteristics
The hallmark histopathologic features include:
- Septate hyphae with dichotomous branching at acute angles (typically 45 degrees), which distinguishes Aspergillus from other fungal pathogens 1, 2
- Hyphae diameter of 3-6 micrometers, appearing relatively uniform throughout the tissue specimen 1
- Angioinvasion is a characteristic feature, with fungal elements invading blood vessel walls, leading to thrombosis and tissue infarction 1
Tissue Response Patterns
The inflammatory response varies based on the neonate's immune status:
- Tissue necrosis and hemorrhagic infarction are prominent features due to the angioinvasive nature of Aspergillus 1
- Minimal inflammatory response may be present in severely immunocompromised neonates with neutropenia 1
- Acute inflammatory infiltrate with neutrophils may be seen in neonates with intact immune function 1
Site-Specific Considerations in Neonates
Cutaneous involvement is more common in neonates compared to older children and adults, requiring special attention to skin biopsy specimens 1:
- Primary cutaneous aspergillosis in neonates shows fungal invasion of the dermis and subcutaneous tissue 3
- Ulcerating skin lesions with underlying necrosis are characteristic 3
- The extremely thin and vulnerable epidermal layer in premature neonates facilitates fungal invasion 3
Diagnostic Confirmation
Culture confirmation from tissue specimens is essential to differentiate Aspergillus from other filamentous fungi (such as Fusarium or Scedosporium), as histopathology alone cannot definitively distinguish between these organisms 1, 2:
- Tissue specimens should be sent for both histopathology and fungal culture 1, 2
- Species identification is important as Aspergillus fumigatus and A. flavus are the most common species in neonates 1
Common Pitfalls
The most critical pitfall is assuming all septate branching hyphae represent Aspergillus, as other hyaline molds can appear identical on histopathology 1, 2. Always obtain culture confirmation to guide appropriate antifungal therapy, as some organisms (like Scedosporium) may be resistant to standard anti-Aspergillus agents 2.
Blood cultures have limited utility and are typically negative even in disseminated neonatal aspergillosis, so tissue diagnosis remains the gold standard 1, 2.