Ureteroenteric Fistula

Ureteroenteric fistula is an abnormal communication between the ureter and the bowel (colon, ileum or rectum). It is rare. The term is also used for leakage at the ureteroenteric anastomosis of a urinary diversion, which is managed on the same principles.

It is dangerous because urine and bowel contents mix, causing recurrent pyelonephritis, sepsis and metabolic acidosis.

Pathophysiology. Causes:

• Crohn disease and diverticulitis, with an inflammatory mass eroding into the ureter.
• Pelvic malignancy and radiotherapy.
• Previous surgery (colorectal, gynaecological, vascular, urinary diversion).
• Ureteric stones, long term stents and trauma.
• Appendiceal or pelvic abscess and tuberculosis.

When the ureter drains into bowel, the intestinal mucosa absorbs urinary chloride and ammonium and loses bicarbonate. This produces hyperchloraemic, non-anion-gap metabolic acidosis with hypokalaemia.

Recurrent or persistent pyelonephritis, flank pain, fever and rigors, with enteric organisms in the urine (Escherichia coli, Enterococcus, Klebsiella, anaerobes). Large volume diarrhoea, weakness and drowsiness from acidosis and hypokalaemia. Faecal matter or gas in the urine is less common, because the bladder is usually not involved. Features of the underlying cause (change in bowel habit, weight loss, previous radiotherapy) may be present.

Sepsis with obstruction, severe acidosis, or deterioration in renal function needs urgent treatment.

• Venous blood gas, electrolytes, creatinine. Pattern: low bicarbonate, high chloride, normal anion gap, low potassium.
• Urine and blood cultures. Polymicrobial growth with enteric organisms supports the diagnosis.
• CT urography with delayed phase, with oral or rectal contrast. Contrast moving from ureter to bowel, or oral contrast in the ureter, confirms the fistula.
• Retrograde or antegrade pyelography through a nephrostomy shows the tract. Ureteroscopy defines the opening and allows biopsy.
• Colonoscopy or ileoscopy with biopsy for Crohn disease and malignancy. MRI of the pelvis for complex disease.
• Diuretic renography for split function.

Differential diagnosis.

• Enterovesical fistula
• Ureterovaginal or ureterocutaneous fistula
• Ureteric stricture with infection
• Pyelonephritis with obstruction
• Anastomotic stricture after urinary diversion
• Bowel injury with urinoma

• Sepsis: ceftriaxone 2 g intravenously once daily with metronidazole 500 mg intravenously every 8 hours, adjusted to cultures. Drain abscesses under imaging control.
• Divert urine from the fistula: percutaneous nephrostomy, with or without antegrade stent. A stent that bridges the defect may allow small fistulae to heal, with a bladder catheter in place.
• Acidosis: oral sodium bicarbonate 1 g (12 mmol) three times daily, titrated to serum bicarbonate over 22 mmol/L, and potassium replacement. Monitor creatinine and fluid balance, and use intravenous fluids when oral intake is poor.
• Optimise nutrition and treat the cause. Crohn disease needs joint gastroenterology review for medical therapy before surgery.
• Definitive surgery after sepsis and nutrition are controlled:
  • Resect the diseased bowel, close the bowel defect and repair or reimplant the ureter, with an omental or vascularised interposition.
  • Long ureteric defects need ileal interposition, psoas hitch with Boari flap, or autotransplantation.
  • Defunctioning stoma for faecal contamination, radiation damage or immunosuppression.
  • Nephrectomy for a non-functioning kidney (function under about 10 to 15%).
• Malignant fistula: palliative diversion by nephrostomy or stent, with oncological treatment.
• Leak at a diversion anastomosis: nephrostomy, ureteric stent across the anastomosis, and drainage, with revision for failure.

Monitoring. Daily bicarbonate, potassium and creatinine while acidotic. Nephrostogram before tube removal, then ultrasound and renography at 3 months. Surveillance for stricture for at least 1 year.

Referral and escalation. Refer to urology and colorectal surgery, with gastroenterology for Crohn disease. Urgent referral for sepsis, severe acidosis, obstruction or acute kidney injury.