Laboratory Studies
Findings from skin biopsy with special staining for fungus, such as with periodic acid-Schiff or methenamine silver stain, can be supportive or suggestive of Aspergillus infection, but other fungi may appear nearly identical in histopathologic sections.
Tissue, sputum, or blood culturing is usually performed, but the results may be negative or unreliable because Aspergillus is a common laboratory contaminant. If truly present in tissue, Aspergillus is a rapidly growing fungus that can be isolated in culture within 1-3 days, but longer incubation times may be required if the inoculum is very small. Molecular and genomic laboratory testing with polymerase chain reaction combined with DNA microarray could be used to detect Aspergillus species. [11] It is recommended to use molecular techniques in conjunction with culture or staining. [12] Bronchoalveolar lavage fluid could be tested using quantitative polymerase chain reaction in combination with colony-forming assays. [13] Molecular and genomic assays are increasingly important in the sensitivity and specificity of detecting aspergillosis.
In disseminated disease, the serum galactomannan assay can be used in conjunction with cultures and/or histologic examination. Galactomannan, an Aspergillus cell wall constituent, can be detected by enzyme-linked immunosorbent assay with an approximate sensitivity of 81% and specificity of 89%. [14]
Imaging Studies
Chest radiography can help in diagnosing a primary pulmonary infection, or it can confirm the presence of a fungal ball. CT scanning or MRI may help reveal fungal abscesses in the brain.
Histologic Findings
In tissue sections, narrow septate hyphae with delicate chitinous walls, bubbly blue cytoplasm, and acute-angle branching can be demonstrated, especially with special staining. Keep in mind that on sectioning, other fungi may appear to have acute-angle branching and Aspergillus species may appear to have more of a right-angle branching. Primary cutaneous infection often involves a granulomatous reaction in the dermis and the formation of multinucleated giant cells. Hematogenous disease is usually characterized by numerous branching hyphae surrounding and, occasionally, eroding into blood vessel lumens.
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Primary cutaneous aspergillosis at a site of an intravenous catheter in a boy with leukemia.
