Fluid Conundrum: Unraveling a Case of Urinothorax

Introduction: Pleural effusion of extra-vascular origin (PEEVO) is an effusion that does not originate from the pleural vasculature. Urinothorax, an infrequent form of PEEVO, is the leakage of urine into the pleural cavity due to obstructive uropathy, iatrogenic, or blunt trauma to the genitourinary (GU) system. We report a case of urinothorax occurring after nephrostomy. Case Description: A 74-year-old male with prior bilateral (B/L) obstructing renal calculi and ureteral stents presented with oliguria and acute renal failure. A nephrostogram showed severe right hydronephrosis and occluded ureteral stent. The stent was removed, and a nephrostomy tube was placed. Persistent hematuria led to tube exchange and stone removal, which revealed a large blood clot in the renal pelvis. The procedure was complicated by bleeding and limited visualization. Post-operatively, the patient developed transient hemorrhagic shock, managed with blood transfusions. A CT scan revealed right hydronephrosis, blood in the collecting system, and a new large right pleural effusion. A CT-guided chest tube drained 2L of serosanguinous fluid. Analysis showed the fluid was transudative, ruling out a hemothorax. The fluid had elevated creatinine (5) and low pH (7.0). The ratio of pleural fluid to serum creatinine (PF/SCr) >1. A renal angiogram revealed active bleeding from the right interlobar artery, which was later embolised. Discussion: Urinothorax develops rapidly, presenting with dyspnea and chest pain. Raised intraperitoneal or retroperitoneal pressure leads to the direct flow of urine through diaphragmatic pores or indirectly via the retroperitoneal and pleural lymphatics. Identifying anatomic defects like reno-pleural fistulas and urinomas is crucial to prevent recurrence. Biochemically, urinothorax is a transudative effusion with characteristically low pH (<7.40). The glucose and protein content are low. A PF/SCr >1 is the hallmark of urinothorax, with >90% sensitivity. Renal scintigraphy can detect urine migration into the pleural space if imaging is inconclusive. This patient likely sustained an iatrogenic injury to the renal system and interlobar artery, which led to leakage of urine and blood into the retroperitoneal space, resulting in a urinothorax. This rare but underdiagnosed entity must be an important consideration for new onset pleural effusion following GU procedures or obstructive uropathy.