Presence of fistulas as predictor of stenoses in Crohn's disease

Introduction: Fistulas belong to the most frequent complications in Crohn's disease. In patients suffering from fistulizing Crohn's disease we often observed the presence of concomitant stenoses or significant luminal narrowing in the small or large bowel, suggesting a causal relation. By analyzing retrospective data of patients with fistulas from our IBD center cohort we searched for a concomitant presence of stenoses or luminal narrowing. Methods: We screened the medical records of all patients who presented with Crohn's disease at our IBD-center since 1998. Patients having presented with fistulizing disease were selected for analysis, if the presence of fistulas was confirmed or diagnosed by physical examination, magnetic resonance (MR), or ileocolonoscopy. Furthermore, data on the status of the small and large bowel lumen were collected if ileocolonoscopy, MR enteroclysis technique, or surgery was performed within 6 months before or after the description of the fistulas. Significant luminal bowel narrowing was defined as stenosis, failure to pass the endoscope over the narrowed segment, or a reduction of the luminal diameter of more than 10mm over a length of more than 3cm. Results: Among 771 patients since 1998 with Crohn's disease at our IBD-center at the University of Munich, 333 patients presented with fistulazing or stricturing course of disease. 145 of the 333 patients suffering from one or more fistulas and 223 with stenoses could be analyzed retrospectively. Aside from perianal fistulas (n=50; 30.7%), entero-enteral (n=79; 48.5%), entero-cutaneous (n=18; 11.0%), entero-vesical (n=10; 6.1%) and entero-vaginal fistulas (n=6; 3.7%) were described. In 134 of overall 223 patients with stricturing disease, stenoses were found in the terminal ileum. Based on the patients presenting with fistulas, signs of coexisting significant luminal bowel narrowing were described in 125 (86.0%) patients with fistulas. In adverse, in 125 of 223 (56%) patients with stricturing disease fistulas appeared. 40 of 50 patients with perianal fistulas had a significant luminal narrowing. Interestingly; of these 40 patients, 14 had a stenosis in the terminal ileum as the only sign of luminal narrowing (35.0%), and in none of these patients a fistula track could be followed back to the terminal ileum. Conclusion: The fact that in patients with Crohn's disease and fistulas, in more than 80% significant luminal bowel narrowing was found, suggests a causal relation. Since some stenoses were found without any spatial contact to the fistulas, an increased intraluminal pressure at the site of the narrowed segment together with an impaired barrier function may favour the formation of fistulas by fluid flux through the bowel wall. If prospective studies in patients presenting with newly found fistula confirm this correlation, future fistula therapies have to be directed more towards the stenoses and not primarily to the fistulas.