S3899 Fistulizing Crohn's Disease Causing Hydroureteronephrosis From External Compression by an Ileocolonic Fistula

Introduction: Fistula formation occurs in 20%-50% of patients with Crohn’s disease (CD). These most commonly occur as external fistulas (perianal or enterocutaneous) whereas internal fistulas account for only one third of cases. We present a case of an ileocolonic fistula causing acute kidney injury (AKI) from external compression of a ureter. Case Description/Methods: A 38-year-old-man with fistulizing CD, diagnosed in 2014 and previously treated with mesalamine monotherapy, presented with worsening abdominal pain. Computed tomography enterography revealed a fistula between the distal ileum and sigmoid colon, along with a fistula involving the distal ileum alone. There was moderate to severe right hydroureteronephrosis adjacent to inflammatory changes from the fistulas. There was mild wall thickening of the terminal ileum (TI). The findings are suggestive of external compression of the ureter from the ileocolonic fistulas. The patient was managed with right ureteral stent placement and initiated on steroids with subsequent improvement in renal function. Outpatient follow up with initiation of anti-TNF therapy was recommended. Discussion: AKI from a ureteral obstruction is a serious sequelae of inflammatory bowel disease. In CD, this can occur from active inflammation of bowel adjacent to the ureters, fistula or abscess formation causing external compression on the ureter, or from stones within the ureter. TI inflammation in CD impairs calcium absorption leading to hyperoxaluria, a risk factor for nephro/ureteronlithiasis. Treatment of the obstruction involves surgical placement of ureteral stents, or resection of the fistula or affected bowel in addition to medical management. In fistulizing CD, advanced therapies with anti-TNF agents and immunomodulators are typically used. Anti-interleukin antibody agents may also be an option in non-responders. There is little/no role in mesalamine for treatment in CD involving more than the left colon and this can precipitate AKI from acute interstitial nephritis or minimal change disease. Imaging should be pursued in all CD patients with AKI to evaluate for ureteral obstruction. Prompt diagnosis and management are essential to prevent irreversible renal damage.