Resolution of nonurine transudative pleural effusion in a cat after removal of a hydronephrotic kidney.

CASE DESCRIPTION A 3-year-old spayed female Bengal cat was evaluated because of a history of bilateral pleural effusion and hydronephrosis of the right kidney. CLINICAL FINDINGS Cytologic analysis of a pleural fluid sample revealed characteristics of a pure transudate with a high percentage of lymphocytes. Results of fluid biochemical testing were not consistent with urine or chyle. Serum biochemical analysis and echocardiography yielded no evidence of hypoalbuminemia or high hydrostatic pressure secondary to cardiac disease. Abdominal ultrasonography revealed hydronephrosis of the right kidney and hydroureter of the right ureter. TREATMENT AND OUTCOME Exploratory laparotomy with nephrectomy of the right kidney was performed. At the time of surgery, there was no evidence of communication between the retroperitoneal space and thoracic cavity. No other treatments were performed. No evidence of pleural fluid accumulation was detected 1 week after surgery, and no recurrence of clinical signs associated with pleural effusion was observed for >1 year after surgery. CLINICAL RELEVANCE Transudative, or nonchylous lymphatic, pleural effusion secondary to intraabdominal disease, but independent of a low plasma protein concentration, is uncommon in veterinary medicine. This case emphasized that urinary tract obstruction should be considered as a differential diagnosis for cats with pleural effusion when more common disorders are not identified. Even without evidence of direct communication between the abnormal kidney or retroperitoneal space and the pleural space, removal of the hydronephrotic kidney appeared curative.