Patients present with varying degrees of respiratory distress depending on the amount of fluid that has accumulated .
The etiology of urinothorax can be dichotomised as either due to obstructive uropathy or due to trauma (including iatrogenic post-surgical trauma) to the urinary system . Urinothoraces are most often seen alongside urinoma, whereby the urine is thought to traverse the diaphragm into the pleural space . Although the pathophysiology of this remains unclear, there are two leading theories: either urine travels through lymphatic drainage into the pleural space, or retroperitoneal urine moves into the peritoneal cavity and then travels directly into the pleural space via a direct transdiaphragmatic passage along a pressure gradient .
The fluid in a urinothorax is usually a transudate but biochemically, often has a low pH and a high LDH and hence may be misclassified as being exudative as per Light's criteria . However, the most important biochemical feature is the pleural fluid creatinine-to-serum creatinine ratio which is >1, with an average of 1.09–19.80 .
Chest radiographic appearance of a urinothorax is often indistinguishable form that of another cause of pleural effusion . It is reported that urinothorax secondary to obstructive uropathy usually results in bilateral effusions, while those caused by trauma to the urinary tract lead to a unilateral effusion , however, there have been numerous case-reports finding the opposite .
Again, the appearance of urinothorax on chest CT is indistinguishable from another cause of pleural effusion. However, abdominal CT is useful to detect the cause of the urinothorax . Many case reports describe later performing renal scintigraphy to confirm a urine leak .
Treatment and prognosis
The exact management strategy will depend on underlying etiology . However, the urinothorax should be drained if symptomatic and a urology consult sought .