Urinothorax

Urinothorax is a pleural effusion containing urine, caused by obstructive uropathy or urinary tract injury. It is rare, and under recognised, since the effusion is usually ipsilateral to the injured kidney, and is often attributed to heart failure.

Causes are obstructive uropathy (stones, prostatic enlargement, tumour, retroperitoneal fibrosis, neurogenic bladder), blunt or penetrating trauma, and iatrogenic injury (percutaneous nephrolithotomy, renal biopsy, lithotripsy, urological and gynaecological surgery, renal transplantation, nephrostomy, ureteric stent displacement). It is more common on the right side and in men, but it can be bilateral.

Pathophysiology. Urine leaks from a ruptured calyx or ureter into the retroperitoneum (urinoma), then moves into the pleural space through lymphatics and diaphragmatic defects, driven by the pressure gradient between the abdomen and the chest. Raised urinary tract pressure from obstruction causes the leak.

Breathlessness, pleuritic pain or cough, with flank or abdominal pain, haematuria, reduced urine output or signs of obstruction in some. Many have only respiratory symptoms. Examination shows a unilateral effusion. The pleural fluid may smell of urine.

Fever, sepsis or rising creatinine need urgent assessment, since infected obstructed urine is an emergency.

• Pleural fluid: a transudate by usual criteria (protein under 30 g/L), with an acidic pH (often under 7.4, as low as 5.5), glucose similar to serum, and a pleural fluid to serum creatinine ratio above 1.0 (often several times higher), which is the key test.
• An absent urine smell or an alkaline pH does not exclude it, particularly with urinary infection.
• Ultrasound or CT of the urinary tract: hydronephrosis, perinephric urinoma, calyceal rupture, stones or tumour. CT urography or nuclear imaging (technetium DTPA or MAG3 scan) can show the leak.
• Retrograde pyelography or antegrade study when the site must be defined.
• Renal function, urinalysis and culture, and electrolytes.
• Pleural fluid culture and cell count to exclude empyema.

Differential diagnosis.

• Heart failure effusion
• Nephrotic syndrome or cirrhotic hydrothorax
• Peritoneal dialysis hydrothorax (high glucose)
• Chylothorax or other abdominal source effusion
• Parapneumonic effusion
• Pancreaticopleural fistula

• Relieve the obstruction or repair the leak: ureteric stent (double-J, 6 to 8 French), percutaneous nephrostomy, urethral or suprapubic catheter for bladder outflow obstruction, or surgery for stones and strictures. The effusion usually resolves within days to 2 weeks after drainage.
• Thoracentesis for respiratory distress, but a chest drain is not usually needed once the urinary tract is decompressed.
• Antibiotics for infection, directed by culture (for example ciprofloxacin 500 mg twice daily or ceftriaxone 2 g intravenously daily), and drainage for empyema.
• Manage the cause: alpha blocker (tamsulosin 400 micrograms daily) for prostatic obstruction, definitive stone treatment, and tumour therapy.
• Avoid nephrotoxic drugs, and monitor renal function and electrolytes (potassium, bicarbonate) in obstruction.

Complications and prognosis. Resolves rapidly when the urinary leak is closed, and recurs if obstruction persists. Prognosis depends on the underlying cause and kidney function.

Monitoring. Daily creatinine and fluid balance during decompression, chest radiograph or ultrasound at 1 week, and renal imaging at follow up.

Referral and escalation. Refer urgently to urology or interventional radiology for obstruction, and to nephrology for renal failure.