PMC9152448_01
Photographs from gross postmortem examination of a 2.5-year-old, female spayed, Australian Shepherd dog that had a 2-month history of tetraparesis, progressive lethargy, and severe pain. The bone marrow and trabecular bone from both femurs were replaced and expanded by multifocal to coalescing pale tan, soft, nodules ranging from pinpoint to 2.0 cm in diameter (arrows).
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F1
Grossly, the head of both humeri and femurs (Figure 1), and the L7-S1 intervertebral joints were red, roughened, and fragmented with exposure of the subchondral bone.
Photomicrographs of sections of the femur (A,B) and lymph node (C,D) obtained from the dog in Figure 1. (A) The marrow space was largely effaced and replaced by multifocal to coalescing granulomatous cellular infiltrate (H&E; bar = 9 mm). (B) Higher magnification of the granulomas from A (dashed square). The granulomas were centered on extensive areas of lytic necrosis (white arrowhead) and dissected by myriad macrophages and epithelioid macrophages, numerous multinucleated giant cells with up to 10 nuclei, and moderate numbers of lymphocytes, plasma cells, and lesser neutrophils (asterisk; H&E; bar = 200 mum). (C) The lymph node architecture was completely replaced by similar cellular infiltrates. Numerous intralesional, intracellular and extracellular, negatively stained, non-pigmented, septated with parallel walls, acute angle branching hyphae measuring 3-6 mum in width with polar bulbous projections measuring 7-13 mum in width (arrowheads; H&E; bar = 50 mum). (D) Hyphal mats were positively stained with Gomori methenamine-silver stain (arrows) (bar = 100 mum). Occasionally, yeast forms measuring 7-15 mum were present (arrowhead) among hyphae (arrow) (inset; bar = 20 mum).
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F2
The necrotic areas contained myriad intralesional, intracellular and extracellular, negatively stained, non-pigmented, septate acute angle branching hyphae with parallel walls measuring 3-6 mum in width with polar bulbous projections measuring 7-13 mum in width (Figures 2A-C). Hyphae positively stained with Gomori methenamine-silver (GMS) and Periodic acid-Schiff (PAS) stains (Figure 2D). The granulomas were surrounded by epithelioid macrophages, numerous multinucleated giant cells with up to 10 nuclei, and moderate numbers of lymphocytes, plasma cells, and fewer neutrophils (Figure 2C).