INTRODUCTION: Urinothorax defined as, urine in the pleural space is a rare cause of unilateral transudative pleural effusion occurring in patients with obstructive uropathy. The scarcity of reported cases may be, due to low index of suspicion or transient nature of the effusion that escapes detection following urinary diversion.
CASE PRESENTATION: A 70-year-old woman presented to the emergency department with progressive dyspnea and swelling of the abdomen. She had diabetes mellitus and thyrotoxicosis, which were satisfactorily controlled with medication. Physical examination of the chest revealed dull percussion and decreased breath sounds over the left hemithorax. Chest radiograph showed a moderately large pleural effusion (Fig 1). Thoracocentesis was performed which removed 500 ml of yellowish fluid, and analysis revealed the fluid to be a transudate as LDH was 151 U/L and total protein < 30 g/L with simultaneous serum LDH 738 U/L (upper limit 380) and total protein 59 U/L. Albumin gradient was 14, fluid pH was 7.2, and the pleural fluid to serum creatinine ratio was > 1 (234 / 210). Ultrasonography of the kidneys showed parenchymal disease with a 7.3 by 6.4-cm mass in the lower pole of right kidney that was suggestive of tumor. Mild dilatation of the right pelvicalyceal system was detected but there was with no peri-nephric fluid collection. MRI confirmed the findings without evidence of intrabdominal metastasis or lymphadenopathy (Fig 2). Pleuroscopy performed for staging showed normal pleura and left lung, and guided pleural biopsy as well as fluid were, negative for malignant cells. She was advised for surgery but declined, and was discharged home with a small-bore pleural catheter connected to drainage bag (Fig 3).
DISCUSSIONS: Urinothorax was first described by Corriere in 1968, and has since been associated with obstructive uropathy, trauma, surgical ureteral manipulation, retroperitoneal inflammatory or malignant processes, renal biopsy, and renal transplantation. Two mechanisms have been proposed which could either be cephalad extension of urinoma with rupture into the pleural space or via lymphatic connections between the peritoneum and the pleural space.[1,2] Thus urinothorax is more commonly observed to occur ipsilateral to the site of pathology although contralateral effusion has been described. [1, 2] Pleural fluid develops within hours of the precipitating event and dissipates quickly once the obstruction is relieved. Diagnosis of urinothorax therefore depends on the presence of underlying obstructive uropathy and a triad of 1) transudate, 2) low pH < 7.3, and 3) pleural fluid / serum creatinine >1..
CONCLUSION: In our patient, the urinothorax was contralateral to the renal mass, which had caused mild pelvicalyceal dilatation. There was no peri-renal fluid to suggest urinoma, and this atypical manifestation would support the latter theory where the pleural effusion, which is urine, traverses across the diaphragm via lymphatics and collects in the contralateral pleural space as a result of negative intrapleural pressure.  Lemon and Higgins have demonstrated elegantly in dogs that there are lymphatics which allow for passage of fluid from the peritoneal to the pleural cavity, and such anatomic similarities exist in man where the lower posterior intercostal lymphatic vessels descend on either side of the vertebral column through the diaphragm to the cisterna chyli before entering the thoracic duct. Treatment of urinothorax empathizes on the relief of urinary tract obstruction, and in our patient it would imply nephrectomy. However since she declined surgery, it was within reason to palliate her with a long-term indwelling pleural catheter. She died 7 months later.
DISCLOSURE: Lai Mun Looi, None.