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case_images: Right lateral view of the abdomen. Note the over-distended urinary bladder, the cranial margins appear irregular and thickened (black arrow); a radiotransparent spot is notable in the middle of the urinary bladder (white arrow)
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case_images: Abdominal radiographs (right laterolateral and ventrodorsal projection) showed an over-distended urinary bladder with irregular cranial margins and the presence of a small radiotransparent area in the urinary bladder lumen, compatible with air (Figure 1).
case_images: Abdominal ultrasound findings. Longitudinal scan after urethral catheterisation and distension with 0.9% saline solution. (a) An irregular, rounded 4.6 x 4.2 x 4 cm lesion arises from the apex and the dorsal wall of the urinary bladder. (b) The trigone and the urethra appear normal
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case_images: On abdominal ultrasound, the urinary bladder lumen was entirely occupied by the presence of a mass of mixed echogenicity (Figure 2a); mild bilateral pyelectasia (1 mm) was also detected. The cat was sedated, and the urethra was catheterised and the urinary bladder distended with sterile 0.9% saline solution for better evaluation: an irregular vascularised lesion measuring 4.6 x 4.2 x 4.0 cm arising from the cranial and dorsal wall of the urinary bladder was observed (Figure 2b); the urethra and the trigone were not involved.
case_images: (a) Gross aspect of the urinary bladder and mass during surgery: note the thickened urinary bladder wall and the presence of a pedunculated mass that was filling the urinary bladder. (b) Gross examination: the mass measured 6.0 x 4.5 x 3.2 cm, had a fibroelastic consistency and was white to pinkish in colour; the surface is characterised by the presence of erosion and haemorrhages
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case_images: A ventral cystotomy was performed to examine the bladder mucosa and the mass appeared pedunculated and extended from the craniodorsal wall of the urinary bladder into the lumen (Figure 3a).
case_images: Microscopic findings. (a) Section of the urinary bladder mass characterised by a proliferation of spindle cells irregularly arranged in interwoven and concentric bundles. In the central part of the lesion a degenerative mucinous area is observed (haematoxylin and eosin, x 4). (b) High magnification of the spindle cell pattern intertwined with a minimal deposition of amorphous eosinophilic extracellular matrix; in the right upper corner, vessels of small and medium size are observed (haematoxylin and eosin, x 10)
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case_images: The cells appeared irregularly arranged in interwoven and concentric bundles (Figure 4a,b); moderate infiltration of neutrophils, plasma cells and lymphocytes, and eight mitoses per HPF at x 10 magnification were observed.
case_images: Immunohistochemical staining with vimentin: note the diffuse positive staining of the cytoplasm (x 10)
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case_images: Thermo Fisher Scientific), S-100 protein (Mouse S-100 Ab-1; Thermo Fisher Scientific), glial fibrillary acidic protein (rabbit antiglial fibrillar acidic protein, 1:500; Dako), smooth muscle actin (Perossidasi DAB detection; Dako) and desmin (Desmin Ab-2; Thermo Fisher Scientific). The neoplastic cells stained strongly positive for vimentin only (Figure 5).