PMC5415299_01
Protothecal lesion left fore: progressive increase in size over 5 months, from (a) when first noticed, through to (b) and then (c), the day of surgery. (d) At 3 months after surgery, the main pad remains, and there is a space where the lesion and the two toes were removed
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The cat had developed a new cutaneous mass between the metacarpal pad and digital pads of the left thoracic limb (Figure 1a). Despite monotherapy with this triazole antifungal, both algal lesions continued to expand, especially the left forelimb lesion (Figure 1). On the left forepaw, an amorphous mass (2.2 cm diameter) was present with a broad base of attachment to the metacarpal pad, expanding cranially between digits three and four (Figure 1c). The distal epiphyses of metacarpal bones two and three were removed with Rongeurs to allow the skin of the dorsum of the paw to be directly opposed to the remaining pad without undue tension over bony prominences (Figure 1d).
Squamous cell carcinoma that likely arose within a Bowenoid in situ carcinoma: multiple densely packed trabecular of dysplastic epidermal/basaloid like cells infiltrate from an ulcerated surface into the dermis
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Squamous cell carcinoma was diagnosed but with features suggesting the lesion may have arisen within a Bowenoid in situ carcinoma (Figure 2).
Left fore biopsy: the epidermis is indicated by an asterisk. Multiple-to-coalescing infiltrates of macrophages and neutrophils within the dermis
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These were positive with both periodic acid-Schiff and silver staining (Figures 3 and 4).
High power view of lesion shown in Figure 3. The arrows indicate some of the spherical bodies within macrophages, and the inset shows staining of these bodies with Grocott's methenamine silver stain
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These were positive with both periodic acid-Schiff and silver staining (Figures 3 and 4).
(a) Fine-needle aspirate preparation stained with Diff-Quik of left fore lesion showing macrophages, some multinucleate (arrow) containing large numbers of spherical algal bodies. (b) Unstained suspension of a cultured colony of Prototheca wickerhamii organisms. Note spherical spores containing variable numbers of sporangia
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Subsequent cytological examination of a fine-needle aspirate (FNA) made from the left forelimb mass, undertaken to improve the morphological detail of the organisms, showed large numbers of macrophages (some multi-nucleate) that contained moderate to sometimes large numbers of thinly encapsulated, spherical, granular organisms (3-10 microm diameter), some of which contained smaller internal spherical structures (Figure 5a). When examined microscopically, the colonies contained large numbers of spherical, thinly encapsulated spore-like structures (2-7 microm diameter) (Figure 5b).