ABSTRACT
Urinothorax is an uncommon thoracic complication of genitourinary (GU) tract disease, which is most frequently caused by obstructive uropathy, but may also occur as a result of iatrogenic or traumatic GU injury. It is underrecognized because of a perceived notion as to the rarity of the diagnosis and the absence of established diagnostic criteria. Urinothorax is typically described as a paucicellular, transudative pleural effusion with a pleural fluid/serum creatinine ratio >1.0. It is the only transudate associated with pleural fluid acidosis (pH < 7.40). When the pleural fluid analysis demonstrates features of a transudate, pH <7.40 and a pleural fluid/serum creatinine ratio >1.0, a confident clinical diagnosis of urinothorax can be established. A technetium 99m renal scan can be considered a confirmatory test in patients who lack the typical pleural fluid analysis features or fail to demonstrate evidence of obstructive uropathy that can be identified via conventional radiographic modalities. Management of a urinothorax requires a multidisciplinary approach with an emphasis on the correction of the underlying GU tract pathology, and once corrected, this often leads to a rapid resolution of the pleural effusion.