Urinothorax Secondary to Pyelonephritis With Obstructing Ureteric Calculi: A Rare Cause of Pleural Effusion.

Urinothorax is a rare cause of pleural effusion resulting from the presence of urine in the pleural space due to disruption of the urinary tract or obstructive uropathy. Only a limited number of cases have been reported in the literature to date. It is an underrecognized condition frequently delayed in diagnosis when respiratory symptoms predominate over genitourinary complaints. Prompt recognition is essential, as management must be directed at the underlying uropathy rather than the pleural effusion itself. We report a case of urinothorax secondary to pyelonephritis with obstructing ureteric calculi in a 30-year-old man who presented with progressive breathlessness and required admission to the intensive care unit. Admission arterial blood gas analysis demonstrated metabolic acidosis with inadequate respiratory compensation (pH 7.29, partial pressure of arterial carbon dioxide 38 mmHg, bicarbonate 17 mEq/L, partial pressure of arterial oxygen 62 mmHg, and lactate 3.2 mmol/L). Noncontrast computed tomography of the chest and abdomen demonstrated right-sided ureteric calculi with mild hydroureteronephrosis, perinephric fat stranding, and fluid collections extending from the perinephric and posterior pararenal spaces cranially toward the right pleural cavity, consistent with urinary extravasation. Pleural fluid analysis demonstrated markedly elevated urea (135 mg/dL) and creatinine (6.9 mg/dL), yielding a pleural fluid-to-serum creatinine ratio of 2.65, confirming the diagnosis of urinothorax. Pleural fluid pH was 7.25, consistent with the characteristically low pH seen in urinothorax. Both urine and pleural fluid cultures grew multidrug-resistant Escherichia coli, and the patient was treated with meropenem. Bilateral double-J stenting led to progressive recovery in renal function (serum creatinine 2.6 mg/dL on admission, improving to 1.5 mg/dL by day 4) and successful weaning from respiratory support. This case highlights the importance of clinical suspicion for urinothorax in patients with unexplained unilateral pleural effusion in the context of urinary tract pathology and reinforces that early biochemical pleural fluid analysis can direct timely, appropriate management.