Pleural Effusion Secondary to Obstructive Uropathy: A Case of Urinothorax

Urinothorax is a rare type of pleural effusion and usually the result of genitourinary tract disease. An accurate and early diagnosis is crucial as resolution of the underlying pathology is the mainstay of treatment. We report the case of a 69-year-old man who was admitted to the Internal Medicine ward due to obstructive acute kidney injury of unknown origin. The patient was submitted to urinary catheterization and to right percutaneous nephrostomy. Two weeks after admission he developed a large left pleural effusion; a left urinoma was also visible on computed tomography. After thoracentesis, pleural fluid analysis demonstrated a paucicellular transudate with pH <7.40 and pleural fluid/serum creatinine ratio >1.0. The diagnosis of urinothorax was made and further study allowed the diagnosis of prostate cancer as the aetiology of the obstruction. When bilateral percutaneous nephrostomy was performed, resolution of the urinothorax and normalization of renal function occurred. LEARNING POINTS: Urinothorax is a rare and possibly under-recognized cause of transudative pleural effusion; over the last five decades, fewer than 60 cases have been reported in the English literature worldwide. Diagnosis of urinothorax depends upon a high index of clinical suspicion and on pleural fluid analysis, but imaging can also support the diagnosis, for example by showing the presence of a urinoma. Clinicians should recognize urinothorax early in its clinical course as favourable outcomes are often achieved after correction of the underlying genitourinary tract pathology.