Abstract
CASE SUMMARY: A 5-year-old female spayed domestic shorthair cat was presented with haematuria, pollakiuria and stranguria of 2 months' duration, and a firm non-painful mass in the urinary bladder was palpated. Abdominal radiographs showed thickening and irregular cranial margins of the urinary bladder wall. Abdominal ultrasound showed a vascularised mass of mixed echogenicity almost entirely occupying the urinary bladder lumen. During explorative laparotomy, the mass appeared pedunculated and was totally excised. Histopathology was characterised by infiltration of the mucosal, submucosal and muscular layers by proliferated atypical mesenchymal cells; immunochemistry confirmed the diagnosis of fibrosarcoma. The cat was discharged with normal urination 5 days after surgery. The owner declined any imaging follow-up but reported the cat to be free of any clinical signs at 16 months after surgery. RELEVANCE AND NOVEL INFORMATION: To the best of our knowledge, this is the first case of primary fibrosarcoma of the urinary bladder in the cat. Fibrosarcoma should be included in the differential diagnosis of urinary bladder neoplasia.