Fistulae between the upper urinary tract and the GI systems are rare. Iatrogenic injury is the most common etiology of renoalimentary fistula, although various pathologic processes in either organ system may lead to fistulization.  Most renoalimentary fistulae are iatrogenic, secondary to percutaneous nephrostomy tube placement, although penetrating and blunt trauma, malignancy (particularly colon, renal, and transitional cell cancer), foreign body ingestion, and inflammatory processes (usually secondary to stones, infection, or diverticular disease) are occasionally implicated in renoalimentary fistulae.
Renoalimentary fistula has also been reported as a complication of percutaneous radiofrequency ablation and laparoscopic cryoablation. As more patients with small renal tumors are now undergoing these advanced forms of tumor treatment, surgeons should be mindful of renoalimentary fistula as a potential complication of them. [2, 3, 4]
If recognized early, many iatrogenic renoalimentary fistulae may be treated conservatively, eliminating the need for surgery. Chronic renoalimentary fistulae are more likely to require surgery.
History of the Procedure
Hippocrates is credited for the first reported case of renoalimentary fistula in 460 BC. Renoalimentary fistulae began to be recognized more commonly in the mid 1800s and were predominantly due to renal tuberculosis (TB). A distant second cause was pyelonephritis due to infection with other organisms.  With the exception of pyelonephritis in conjunction with stone disease, infectious causes of renoalimentary fistula diminished with advancements in antitubercular and antimicrobial therapy. As a result, renoalimentary fistulae became much less common between 1950 and 1980, with malignancy being the primary etiology.
With the advent of minimally invasive renal surgery, the incidence of renoalimentary fistulae, specifically iatrogenic renoalimentary fistula, has increased. Despite the increase, this phenomenon remains quite rare.
Renoalimentary fistulae may involve any portion of the GI tract that has an abnormal connection with the kidney. The resulting drainage of urine into the GI tract, GI contents into the urinary tract, or both can lead to diarrhea, urinary tract infections, and various electrolyte abnormalities.
Renoalimentary fistulae comprise fewer than 1% of fistulae between the urinary and intestinal tracts, the vast majority of which are colovesical fistulae.
Most renoalimentary fistulae are iatrogenic, secondary to percutaneous nephrostomy tube placement, percutaneous radiofrequency ablation, or laparoscopic cryoablation. Trauma, foreign body ingestion, malignancy (particularly colon, renal, and transitional cell cancer), and inflammatory processes (usually secondary to stones, infection, or diverticular disease) have also been implicated in some cases.
The kidneys and their associated structures are normally separated from the enteric system by the peritoneum, Gerota fascia, and perirenal fat. Consequently, renoalimentary fistulae tend to occur where these structures are manipulated, attenuated, or absent. Fistulization between the renal collecting system and the gut is more common in individuals who are thin or who are nutritionally debilitated. Renoalimentary fistulae are also more likely to develop in patients who have undergone renal surgery.
Renocolic fistulae are the most common type of renoalimentary fistulae.
All of the following have been implicated in renoalimentary fistulae:
Long-standing calculi leading to obstruction and abscess formation 
Ingestion of foreign bodies (eg, toothpicks, coins, nasogastric tubes)
Traumatic injury to the renal collecting system or the gut 
A case report has described a sinus tract between the appendix and renal collecting system secondary to appendicitis. 
The most common iatrogenic cause of renoalimentary fistula is the inadvertent placement of a percutaneous nephrostomy tube through the colon. Generally, this occurs because the colon is posteriorly displaced and may even contain a retrorenal component. This anomalous anatomy is more common on the left than the right and is seen more frequently in females than in males. A retrorenal colon is more commonly encountered at the caudal aspect of the kidney.
Fistulae following radiofrequency ablation or cryoablation are likely secondary to unrecognized bowel injury (colon or duodenum) in close approximation to the lesion being treated and are usually not discovered until follow-up imaging is performed unless they become clinically symptomatic (see CT image below). Tumor recurrence may also play a role in fistula formation following therapy.
Another common iatrogenic cause of renoalimentary fistulae is the breakdown of anastomotic suture lines when renal and bowel surgery are performed simultaneously. Such procedures are commonly used to treat locally advanced transitional cell carcinoma of the bladder or ureter that requires intestinal interposition for urinary diversion. Patients with neurogenic bladder dysfunction or congenital abnormalities of the urinary tract may also undergo intestinal reconstruction and be at risk for fistula formation. See images below.
Ingestion of a foreign body is most likely to lead to a pyeloduodenal fistula as a result of the foreign object lodging in the duodenum with resultant inflammatory reaction that involves the duodenum and posteriorly adjacent renal pelvis.
Cutaneous extension of the fistula is reported in 10% of cases.
The clinical presentation of a patient with a renoalimentary fistula varies. Patients may present with just abdominal pain and fever. However, in many cases, the presence of fecaluria, pneumaturia, biliuria, recurrent urinary tract infection (UTI), or watery diarrhea may be noted. Evidence of sepsis with fever and leukocytosis is common. The presence of peritoneal signs demands immediate surgical exploration.
When caused by percutaneous nephrostomy tube placement, gas and enteric contents may drain through the tube, while voided urine may or may not appear normal.
Renoalimentary fistulae due to radiofrequency ablation or cryoablation have been discovered on routine follow-up imaging and have been mostly asymptomatic.
If peritonitis is present, immediate surgical exploration is mandated. If the patient is stable, elective resection of the fistula following mechanical and antibiotic bowel preparation is preferred.
An exception is renoalimentary fistulae caused by iatrogenic injury to the bowel during percutaneous nephrostomy placement. If the injury is recognized early and the patient does not display signs of peritonitis, the accepted treatment is to pull back the percutaneous tube so that it drains the renal pelvis without maintaining the fistulous connection with the colon. Conservative management has been successful in asymptomatic renoalimentary fistulae following minimally invasive procedures.
The kidneys are paired retroperitoneal structures with several layers of investing tissue planes that separate them from the peritoneal contents. The retroperitoneal colonic segments are usually anterior to the kidneys, and the duodenum abuts the right kidney medially and anteriorly, rendering these bowel segments susceptible to fistula formation within the kidney.
Patients with renoalimentary fistulae due to cancer may not heal and may develop further complications such as systemic sepsis, severe electrolyte abnormalities, and even death. The ability to completely resect the tumor at the site of the fistula is a key element to success.
If the patient is severely malnourished, the chance of successful repair is decreased significantly. If the patient is not acutely ill from the fistula, repair should be delayed until nutritional status improves. Bowel rest and parenteral nutrition may be necessary to accomplish this goal, particularly if the patient has a gastric or small-intestine fistula.
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