Cutaneous nerve sheath tumours, non-infectious polycystic kidney disease, renal granulomas, nephrocalcinosis and crystals: Incidental pathological findings in pond-living goldfish (Carassius auratus, Linnaeus)

In an adult male goldfish (Carassius auratus, Linnaeus), an unusual combination of diseases was detected. The owner noted a bilateral, asymmetrical distention of the abdomen, multiple cutaneous masses and an altered swimming behaviour over the course of time; diagnostic work-up was not requested and euthanasia elected. Grossly, the cutaneous masses were whitish, discrete, extremely friable. Histologically, the dermis was multifocally expanded by moderately cellular, unencapsulated neoplastic tissue, composed of dermal spindle cells. The celomic cavity opening revealed a gelatinous multicystic mass, corresponding to the kidney, which replicated several cysts compressing the residual parenchyma. Histologically, sparse, late-stage granulomas, basophilic intratubular deposits and crystals were also detected. No mycobacterial DNA was detected in tissue with granulomas. No parasites were detected in the histological sections examined. Diagnoses of cutaneous nerve sheath tumours, polycystic kidney disease, renal late-stage granulomas, nephrocalcinosis and crystals were formulated. The authors had proposed to recapitulate each single condition.