Pseudodematiaceous Fungi in Rhinosinusal Biopsies: Report of 2 Cases With Light and Electron Microscopy Analysis

Abstract

The diagnosis of a mycosis is often established through a biopsy, which allows to differentiate invasive and non-invasive lesions, and also to identify hyaline and dematiaceous fungi. However, pigmented fungal elements that do not correspond to dematiaceous fungi, which we have called pseudodematiaceous, can occasionally be present in biopsies. Herein, we present 2 cases of mycosis caused by pseudodematiaceous fungi in rhinosinusal biopsies. A new classification for fungi identified in biopsies is proposed, dividing them into 3 groups: hyaline, dematiaceous, and pseudodematiaceous.

Keywords: Pseudodematiaceous fungi; biopsy; classification; dematiaceous fungi; hyaline fungi.

Figure 1.

Case 1: Light microscopy findings. (A) Necrotic and hemorrhagic tissue with abundant pigmented hyphae (hematoxylin-eosin 100×, original magnification). (B) Hyphae with pigmented cytoplasm (hematoxylin-eosin 400×, original magnification). (C) Coenocytic hyphae with hyaline and granular pigmented cytoplasm forms; note the absence of pigmentation of its cell wall (hematoxylin-eosin 400×, original magnification).

Figure 2.

Case 1: Electron microscopy findings. (A) Necrotic tissue with a coenocytic hyphae (blue arrows) showing a floccular and slightly granular electron-dense cytoplasm (uranyl acetate, lead citrate 6000×, original magnification). (B) Coenocytic hyphae, note the cytoplasm (C), the plasmatic membrane (red arrow), and the multilayered cell wall (CW) with intense and variable electron density (uranyl acetate, lead citrate 43 000×, original magnification).

Figure 3.

Case 2: Light microscopy findings. (A) Thick, regular hyphae, some slightly pigmented (hematoxylin-eosin 400×, original magnification). (B) Regular thick hyphae and pigmented cell wall in longitudinal section (hematoxylin-eosin 100×, original magnification). (C) Thick pigmented cell wall hyphae in cross-section (hematoxylin-eosin 100×, original magnification).

Figure 4.

Case 2: Electron microscopy findings. (A) Well-defined hyphae (blue arrows); note its cytoplasm (C), cell wall (CW), and a clear central artifactual band (A) (uranyl acetate, lead citrate 6000×; original magnification). (B) Hyphae CW with trilaminar architecture; the external is thinner and highly electron-dense and corresponds to melanin granules (M) (uranyl acetate, lead citrate 43 000×; original magnification).