Urinothorax Secondary to Obstructive Uropathy: A Rare Cause of Pleural Effusion.

Urinothorax is an exceptionally rare cause of pleural effusion characterized by the abnormal accumulation of urine in the pleural space, typically secondary to genitourinary trauma or obstructive uropathy. We report the case of a 54-year-old male who presented with acute right-sided chest pain, colicky abdominal pain, and rapidly worsening respiratory distress. Serial imaging demonstrated a rapidly refilling massive loculated pleural effusion alongside a 3.3 cm right pelviureteric junction calculus, causing moderate hydroureteronephrosis. Ultrasound-guided thoracentesis yielded an exudative fluid with a distinct uriniferous odor. Simultaneous pleural fluid and serum creatinine levels were 0.98 mg/dL and 0.8 mg/dL, respectively, yielding a diagnostic ratio of 1.22. Despite the absence of definitive radiological evidence of a retroperitoneal urinoma or urinary extravasation, the diagnosis of urinothorax was confirmed. The patient achieved complete resolution following repeated therapeutic aspirations, right percutaneous nephrolithotomy, and double-J stenting. This case underscores that urinothorax can present with an atypical exudative profile and without classic radiological findings. Clinicians must maintain a high index of suspicion in patients presenting with rapidly accumulating pleural effusions and concurrent obstructive uropathy, relying on the pleural fluid-to-serum creatinine ratio for definitive diagnosis.