Urinothorax: a new approach

The presence of urine in the pleural space (urinothorax) is a rarely recognized cause of pleural effusion. To date, only 58 cases have been reported. In this article the features of urinothorax are analyzed, and clinical and biochemical characteristics are reviewed in order to propose a classification, founded on pathogenic criteria, that will be useful in achieving the diagnosis.

Recently reported cases of urinothorax provide a more detailed description of the biochemical characteristics that allow a better understanding of this entity.

Urinothorax can be divided into two categories: (1) obstructive urinothorax, due to bilateral obstructive uropathy; and (2) traumatic urinothorax, due to unilateral traumatic injury of the urinary system, mostly iatrogenic. In patients with urinothorax, the pleural effusion usually has the biochemical characteristics of a transudate, with a pH lower than 7.30 and a pleural fluid/serum creatinine ratio higher than 1. These characteristics are not always present, however, and individually are shared by a significant number of pleural effusions of different etiology.