[Massive pleural effusion secondary to hydronephrosis]

The most frequent causes of pleural effusion are congestive heart failure, advanced cirrhosis and nephrotic syndrome. In some rare cases urine can be found accumulated in the pleural compartment, being this entity denominated urinotorax. This phenomenon is generally considered secondary to an urinary obstruction or to an urinoma on the same side as the effusion through mechanisms not yet clarified. Given that it is a benign condition, easily resolved by clearing the obstruction of the urinary tract and that there is little information about it in the literature, we report a case of a massive pleural effusion secondary to hydronephrosis.