PMC8186119_01
(a) Laterolateral and (b) dorsoventral view of the thorax: residual bilateral pleural effusion (arrows) and soft tissue opacity (arrowhead) in the dorsocaudal area of the left hemithorax are noted
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T10-T13. The cranial margins of the mass were rounded and well-defined, while the caudal margins were superimposed with the left diaphragmatic crus (Figure 1).
(a) Volume-rendering sagittal reconstruction and (b) dorsal reconstruction of the diaphragmatic mass. A large, ring-enhancing, soft tissue mass arising from the left crus is shown (arrowheads); the mass is causing ventral compression of the stomach (arrow)
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The mass protruded cranially into the thoracic cavity, displacing the left caudal lung lobe and compressing the thoracic caudal segment of the oesophagus; caudally, the mass also compressed the fundus and body of the stomach, and the left medial and left lateral hepatic lobes (Figure 2).
(a) Cytological smear of undifferentiated pleomorphic sarcoma, with round cells interspersed with giant multinucleated cells and spindle-shaped cells. Romanowsky quick stain, x 20 magnification. Inset: a giant cell with multiple nuclei. Romanowsky quick stain, x 40 magnification. (b) Macroscopic appearance of the neoplasm after fixation in formalin. In cross section, the neoplasm is multilobular, embedding the diaphragm (asterisks), whitish and with multifocal necrotic haemorrhagic areas
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The sample was highly cellular and composed of spindle-shaped cells interspersed with giant multinucleated cells and round cells; the result was consistent with a malignant mesenchymal neoplasia (Figure 3a). In section, it was whitish and with necrotic haemorrhagic areas (Figure 3b).
Photomicrographs of feline undifferentiated pleomorphic sarcoma: (a) interlacing bundles of spindle cells mixed with multinucleated giant cells were shown. Haematoxylin and eosin stain, scale bar 50 microm. (b) A thin fibrovascular stroma, stained in blue, is present between the bundles of spindle cells. Masson's trichrome stain, scale bar 50 microm. (c) In another area where the fibrovascular stroma was moderate, the myofibroblasts were positive with antibody anti-alpha-smooth muscle actin. Immunohistochemistry, scale bar 50 microm. (d) Giant cells showed mild and focal positivity with anti-Iba-1 antibody. Immunohistochemistry, scale bar 50 microm
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Multinucleated giant cells with distinct cell borders, abundant eosinophilic cytoplasm and around 20 nuclei were present, and cells ranged from 20 to 50 microm in diameter (Figure 4a). Masson's trichrome staining was useful to highlight the collagen stroma present in the neoplasm (Figure 4b). The myofibroblasts present in the fibrovascular stroma were alpha-SMA positive (strong and cytoplasmic positivity in 100% of myofibroblast cells) (Figure 4c). Multinucleated giant cells were also slightly positive for Iba-1 (Figure 4d), as well as some rare round histiocytoid cells present in the neoplasia (weak and cytoplasmic positivity in around 10% of cells).