Ureteral obstruction and hydronephrosis in a cat associated with retroperitoneal infarction

A 9-month-old cat was presented for routine vaccination before rehoming. Physical examination revealed a palpable mass in the cranial abdomen. The right kidney was severely enlarged (6 cm × 4 cm) on plain abdominal radiographs, and failed to opacify normally during intravenous urography. Ultrasonography demonstrated a hydronephrotic right kidney. During exploratory coeliotomy, a retroperitoneal mass was identified, adherent to the caudal edge of the right kidney, enveloping the ureter and blocking urine outflow. The ureter caudal to the mass was of normal size. Right ureteronephrectomy was performed; the mass was subsequently freed from adhesions to the caudal vena cava and sublumbar muscles and excised. Histopathological examination revealed the mass to be composed of both normal and necrotic adipose tissue and fibrous tissue surrounding the ureter and a thrombosed, recanalised vessel. This appearance was consistent with an area of infarction and fibrosis with obstruction of the ureter. The cat was clinically well 3 months postoperatively.