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Pathology of  Pseudallescheriasis

Dr Sampurna Roy MD




Pseudallescheria boydii is the most frequent etiologic agent of eumycotic mycetoma and is an occasional agent of otomycosis, keratitis, endophthalmitis, meningitis, brain abscess and osteomyelitis.

This micrograph depicts a number of mycelia with attached conidia of the fungual organism Pseudallescheria boydii. (CDC Public Health Image Library)

This fungus can be isolated from clinical specimens in either of the two forms: 

- The asexual (anamorphic) form, designated Scedosporium (formerly Monosporium) apiospermum, and

- The sexual (telemorphic) form, designated Pseudallescheria (formerly Allescheria and Petriellidium) boydii.

By convention, the disease is named for the sexual form.

Pseudallescheria boydii can colonize preexisting pulmonary cavities and form intracavitary fungus balls that resemble those produced by the Aspergillus species.

The intracavitary mycelium consists of amorphous hyphal aggregates or of contact, concentrically laminated and intertwined hyphae.

Invasive pulmonary and disseminated pseudallescheriosis are rare opportunistic infections that occur preferentially in patients treated for acute leukemia who are granulocytopenic.

Invasive lesions are infarctive as a consequence of mycelial invasion of blood vessels, but abscesses have also been reported.

Disseminated pseudallescheriasis frequently involves the brain, thyroid gland, heart, and kidneys.

In tissue sections, the hyphae of Pseudallescheria boydii resemble those of the Aspergillus species.

The septate hyphae, 2 to 5 micrometer wide, branch in a dichotomous but haphazard pattern and may produce vesicles, truncated terminal conidia, and terminal or intercalated chlamydoconidia.

Hyphal vascular invasion is conspicuous in the invasive and disseminated lesions.

Because the morphologic features of the hyphae in tissue sections closely resemble those of aspergillosis, the diagnosis is best confirmed by culture or immuno-flourescence.


Further reading:

Pseudallescheriasis in the 21st century.

Pseudallescheriasis of the Lung and Central Nervous System

Cerebral Pseudallescheriasis Due to Pseudallescheria

Pulmonary pseudallescheriasis

Pseudallescheriasis: a summary of patients from 1980-2003 in a tertiary care center

Mucormycosis, pseudallescheriasis, and other uncommon mould infections

Pseudallescheriasis as an aggressive opportunistic infection

Disseminated subcutaneous nodules caused by Pseudallescheria boydii in an atopic patient.

Case report. Atypical cutaneous pseudallescheriosis refractory to antifungal agents.

A case of cutaneous pseudallescheriosis resembling sporotrichosis




Dr Sampurna Roy  MD

Consultant  Histopathologist (Kolkata - India)






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