Background: Urinothorax, a rare cause of transudative pleural effusion, develops as a result of obstructive uropathy. This type of effusion resolves when the obstruction is removed. The biochemical analysis of pleural effusion has been performed in a few cases. Nephrolithiasis, a common disorder, is a rare cause of urinothorax. We present a case of urinothorax secondary to bilateral nephrolithiasis together with the biochemical data of the pleural effusion.
Case Report: A 37-year-old woman was admitted to our hospital with the complaints of dyspnea and left-sided pleuritic pain. She had previously undergone bilateral pyelolithotomy. A chest radiograph revealed a moderate left-sided pleural effusion. Diagnostic thoracentesis was performed and biochemical analysis of the pleural fluid revealed that the pH value, glucose level, and protein level were very low, and the LDH level and pleural fl uid-serum creatinine ratio were high. Localized hypodense fl uid collection resembling urinoma was seen on computed tomography of the abdomen. Urinary extravasation from the upper pole of the left kidney to the pleural space was demonstrated by renal scintigraphy. Bilateral percutaneous nephrolithotomy and antegrade endopyelolithotomy were performed at the same time. Pleural effusion resolved completely in a short period of time after the operation, without any medical treatment.
Conclusions: Although urinothorax is rarely seen, it should be considered in the diagnosis of patients with pleural effusion and nephrolithiasis. High LDH levels in pleural fl uid may cause misdiagnosis and unnecessary diagnostic procedures in patients that does not have creatinine level analysis. Alternative parameters should be used to differentiate exudates from transudates when urinothorax is suspected.

Keywords: Pleural Effusion, nephrolithiasis, transudate, Urinothorax