Recurrent hydronephrosis and spontaneous renal rupture caused by lymphoplasmacytic inflammation in a cat

A seven-year-old male cat that was previously diagnosed with - and treated for - left hydronephrosis due to suspected idiopathic proteinaceous materials in the renal pelvis, presented with a short history of anorexia and vomiting. The abdominal ultrasound revealed bilateral hydronephrosis, and the intravenous pyelography showed a moderate amount of free fluid in the retroperitoneal space at 48 hours. After the nephrectomy, the gross examination of the right kidney revealed a very thin capsule with urine leakage, and the right renal pelvis showed small, black deposits. The histopathology of the right kidney revealed hydronephrosis with compression atrophy, necrosis of the renal cortex/medulla, and a moderate lymphoplasmacytic inflammation. The crystallographic analysis revealed that the black deposits were composed of 100% protein and no minerals. The cat was diagnosed with hydronephrosis and spontaneous renal rupture caused by proteinaceous pelvic materials, secondary to the idiopathic renal lymphoplasmacytic inflammation. In addition to revealing the possibility that immune-mediated renal disease can induce spontaneous renal rupture in cats, this case report demonstrates the utility of imaging for diagnosing and monitoring hydronephrosis, detecting urine leakage, and planning surgery.