Table 1. Morphologic Features of Filamentous Fungi in the GI Tract.

Organism	Primary Geographic Distribution	Morphologic Features	Host Reaction	Major Differential Diagnoses
Aspergillus species (e.g. fumigatus, flavus, and niger)	Worldwide	Hyphae- Septate Uniform width Branching-Regular Acute angles Conidial head formation in cavitary lesions	Ischemic necrosis with angioinvasion Acute inflammation Occasionally granulomatous	Mucormycosis Fusarium
Candida albicans; Candida tropicalis	Worldwide	Mixture of budding yeast and pseudohyphae; occasional septate hyphae Yeast forms are Gram positive	Usually suppurative, with variable necrosis and ulceration Occasionally granulomatous Occasional angioinvasion	Trichosporon (produces arthrocondia; disseminated disease in iron overload with immunosuppression especially AML; causes positive Cryptococcal latex agglutination test)
Candida (Torulopsis) glabrata	Worldwide	Budding yeast No hyphae No “halo” effect Yeast forms are Gram positive	Similar to other Candida species	Histoplasma Cryptococcus
Mucormycosis	Worldwide, associated with diabetics more than any other mycosis	Hyphae-Pauciseptate Ribbon-like Thin walls Branching-Haphazard	Similar to Aspergillus	Similar to Aspergillus
Basidiobolomycosis	Saudi Arabia, Africa, Parts of Asia; Arizona	Similar to mucor; fewer organisms, “cellophane ball” appearance	Eosinophilia, necrosis, granulomas, Splendore-Hoeppli reaction to organisms Produces mass	Mucor
Fusarium	Worldwide	Similar to Aspergillus; hyphae constricted at sites of origin	Similar to Aspergillus	Aspergillus Mucor
Phaeo-hyphomycosis (Dematiaceous Fungi)	Worldwide; associated with immuno-suppression	Pigmented; hyphae are closely septate and constructed at septations. Budding and vesicular swellings may be present.	Granulomatous inflammation with associated giant cells, necrosis, and dense fibrosis	Chromo-blastomycosis