Urinothorax

Urinothorax (pl. urinothoraces) means urine in the fluid-filled cavity that surrounds the lungs. It is an extremely rare cause of pleural effusion. It is secondary to obstructive uropathy whereby urine forms a collection in the pleural cavity. The urine arrives in the pleural space either retroperitoneally (under the peritoneum) under the posterior diaphragm, or via the retro peritoneal lymphatics. It remains a rare, possibly under-diagnosed, differential in the case of transudative pleural effusion. Respiratory symptoms are usually mild.

Symptoms

The defining characteristics of people affected by urinothorax are poorly defined. Symptoms include difficulty breathing, abdominal pain, chest pain, and reduced urination.

Causes

It is either caused by an obstruction (obstructive uropathy), caused by trauma, or iatrogenic. Traumatic cases tend to occur on one side, while obstructive cases tend to be bilateral.

Diagnosis

The pleural fluid is most often straw-colored, and it has a distinct smell like ammonia. Primary factors for diagnosing urinothorax include low protein and high LDH content. Low glucose levels and acidity are also described, but not reliable ways to diagnose or rule out urinothorax.

The most important chemical diagnostic factor of the fluid is that the ratio of creatinine to serum is more than 1 and usually more than 10.

Treatment

Treatment mainly consists of relieving urinary obstruction if it is present. If respiratory symptoms are minimal or nonexistent, thoracentesis may not be needed, as urinothoraces can resolve on their own in some cases after resolution of the underlying condition.