Internal Fistulas Discovered on Cross-Sectional Imaging Predict Future Intra-Abdominal Abscesses

Background and Aims: Internal fistulas found on cross-sectional imaging (CSI) performed during routine care of patients with Crohn’s disease (CD) are often considered incidental findings. This study aimed to assess outcomes in patients with internal fistulas on CSI. Methods: This is a single tertiary care center, retrospective case-control study of CD outcomes. Patients who had magnetic resonance enterography or computer tomography enterography performed between 2007 and 2017 were included. Electronic medical record data up to 2017 were included as variables in logistic regression analysis. CSI was scored by 3 abdominal radiologists blinded to the electronic medical record. Results: Subjects included 199 CD patients: 63 patients (cases) had internal fistulas on index scan and 136 had no internal fistula. The cases and controls were well-matched for age, race, smoking status, body mass index, and years of disease. During follow-up, cases had a more complicated disease course with higher incidence of intra-abdominal abscess formation (19.1% vs 3.7%; P < .001) and abdominal surgery (44.4% vs 24.3%; P < .001). Patients with fistula were more likely to require surgery (odds ratio 4.96, P < .001) and to develop intra-abdominal abscess (odds ratio 6.05, P < .001). The index scan of cases was more likely to demonstrate inflammation (95.2% vs 39.7%; P < .001) and stricture (27.0% vs 7.35%; P < .001) than controls though the presence of an internal fistula was the only independent variable predictive of intra-abdominal abscess. Conclusion: CD patients with internal fistulas identified by CSI have worse disease outcomes. Presence of internal fistula is the only independent risk factor for future intra-abdominal abscess regardless of the patient’s symptoms.