Case Report: Uroenteric Fistula in a Pediatric-en-bloc Kidney Transplant Manifests as Deceptive Watery Diarrhea and Normal Anion Gap Acidosis

Abstract

Introduction: The diagnosis of a post-surgical uroenteric fistula can be challenging and may be delayed for months after symptoms begin. A normal anion gap metabolic acidosis has been reported in up to 100% of patients after ureterosigmoidostomy, and bladder substitution using small bowel and/or colonic segments. Here, we describe a rare case of a pediatric patient who developed a uroenteric fistula from the transplant ureters into the small bowel, after an en-bloc kidney transplantation resulting in profound acidosis and deceptive watery diarrhea. Case Presentation: The patient is an 8-year-old girl with end stage kidney disease (ESKD) secondary to focal segmental glomerulosclerosis. Through a right retroperitoneal approach, she underwent a right native nephrectomy and a pediatric deceased donor en-bloc kidney transplant including two separate ureters. One month later, she had a renal allograft biopsy for suspected rejection. During the week after the biopsy, she experienced abdominal pain followed by watery diarrhea and metabolic acidosis requiring continuous bicarbonate/acetate infusions. An extensive gastro-intestinal evaluation for the cause of the diarrhea including endoscopy was inconclusive. The urine output decreased to <500 ml daily; although, the kidney function remained normal. After 2 weeks of unexplained watery diarrhea a magnetic resonance urogram with contrast was performed which demonstrated extravasation of urine from both ureters with fistulization into the small bowel. She underwent corrective surgery which identified the fistulous tract, which was resected and both ureters were re-implanted. The diarrhea and acidosis resolved, and she has maintained normal renal allograft function for over 1 year. Conclusion: An important aspect in the early diagnosis of a uroenteric fistula is the sudden onset of severe hyperchloremic metabolic acidosis that results when urine is diverted into the intestinal tract. The mechanism is similar to that described in cases of urinary diversions and/or bladder augmentation using the intestine. Important diagnostic tools are the measurements of solute excretion and pH in the urine as compared to the "watery diarrhea" or bowel output. Summary: We describe a case of a uroenteric fistula in a pediatric-en-bloc kidney transplant patient that went undiagnosed for almost 3 weeks due to the deceptive nature of the watery diarrhea which was actually urine. A uroenteric fistula should be considered in the differential diagnosis of diarrhea and hyperchloremic metabolic acidosis as a complication of kidney transplant. The simultaneous comparison of stool and urine pH and solute excretions may lead to the diagnosis, appropriate imaging and surgical intervention.

Keywords: CFTR-SLC26; non-anion gap acidosis; pediatric-en-bloc transplant; urinary diarrhea; uroenteric fistula.

Figure 1

Timeline from deceased pediatric donor en-bloc kidney transplant (DDKT), renal allograft biopsy with subsequent development of uroenteric fistula which manifested as normal anion gap acidosis and watery diarrhea which was diagnosed by magnetic resonance imaging urogram (MRU), followed by surgical repair and discharge after 8 weeks of hospitalization. The daily fluid balance with urine and stool volumes are color coded.

Figure 2

3D magnetic resonance urogram (MRU) images show a urinoma to small bowel fistula. (A) Shows the 2 ureters of the pediatric-en-bloc kidney transplant draining into a 8.6 × 3.9 × 1.1 cm fluid collection (labeled “Urinoma”) located in the right lateral abdominal wall. The connection between the distal ureters at the base of the collection is shown (short arrow). (B) Shows the urinoma has developed a fistulous tract (magenta highlight labeled “Fistula”) which drains into the proximal small bowel limb where the excreted contrast is seen progressively filling the bowel. (C) This sequence shows a cross-section of the tiny fistula (red arrow). Note that the bright urine in the urinoma is seen starting to mix with the fluid in the adjacent bowel (curved arrows), in contrast to the otherwise dark bowel contents throughout the rest of the image. (D) This 3D maximum intensity projection shows the location of the urinoma along the right abdominal wall which is filling the markedly dilated bowel with fluid which is urine.

Figure 3

Schematic of the uroenteric fistula with differential urine pH and solutes from the bladder and bowel urines taken concurrently when in metabolic balance maintained by parenteral buffer therapy at 10–12 mmol/kg/day as sodium/ potassium acetate. H₂O, Water; HCO₃, Bicarbonate; NaCl, Sodium chloride; (NH₂)₂CO, Urea; NH₃, ammonia; CO₂, carbon dioxide; NH₄Cl, ammonium chloride; CFTR-SLC26, Cystic fibrosis-chloride transporter-soluble carrier family 26; Na-K ATPase, Sodium-potassium adenosine triphosphatase; NHE3, sodium-hydrogen exchanger 3; Uosm, urine osmolarity; FeCl, Fractional excretion of chloride.