Retroperitoneal granuloma in a cat caused by <i>Nocardia brasiliensis</i> resulting in bilateral ureteral entrapment and unilateral hydronephrosis

Nocardia infections in cats most commonly present as subcutaneous wounds, or less commonly, as pneumonia, purulent pleurisy and disseminated disease. Abdominal involvement is rarely reported, and to date, localised retroperitoneal infection has only been reported in people. This report describes a five-year-old domestic shorthair cat living in Canberra, Australia, that presented with a two-month history of pyrexia and inappetence progressing to anorexia. Ultrasonography showed a large retroperitoneal mass incorporating both ureters. Euthanasia was elected because of the guarded prognosis. Necropsy examination revealed the mass to be comprised of extensive pyogranulomatous inflammation with fibrosis, Splendore-Hoeppli phenomenon and filamentous Gram-positive bacteria. Culture and MALDI-TOF mass spectrometry identified the causative agent as Nocardia brasiliensis. N. brasiliensis is commonly diagnosed as a cause of cutaneous nocardiosis in Australian human patients, but to date has only been reported in one cat from the United States and one dog from Australia. A treatment approach that might have been used in such a case is provided even though the cat's owners elected not to proceed with surgical intervention.