Fistula development after anal abscess drainage-a multicentre retrospective cohort study

PURPOSE: Anal abscesses are common and, despite correct treatment with surgical drainage, carry the risk of developing fistulas. Studies identifying risk factors for the development of anal fistulas are sparse. This study aimed to identify the risk factors for anal fistulas after anal abscess surgery.

METHODS: This was a multicentre, retrospective cohort study of patients undergoing acute surgery for anal abscesses in the Capital Region of Denmark between 2018 and 2019. The patients were identified using ICD-10 codes for anal abscesses. Predefined clinicopathological factors and postoperative courses were extracted from patient records.

RESULTS: A total of 475 patients were included. At a median follow-up time of 1108 days (IQR 946-1320 days) following surgery, 164 (33.7%) patients were diagnosed with an anal fistula. Risk factors for developing fistulas were low intersphincteric (OR 2.77, 95CI 1.50-5.06) and ischioanal (OR 2.48, 95CI 1.36-4.47) abscesses, Crohn's disease (OR 5.96, 95CI 2.33-17.2), a history of recurrent anal abscesses (OR 4.14, 95CI 2.47-7.01) or repeat surgery (OR 5.96, 95CI 2.33-17.2), E. coli-positive pus cultures (OR 4.06, 1.56-11.4) or preoperative C-reactive protein (CRP) of more than 100 mg/L (OR 3.21, 95CI 1.57-6.71).

CONCLUSION: Several significant clinical risk factors were associated with fistula development following anal abscess surgery. These findings are clinically relevant and could influence the selection of patients for specialised follow-up, facilitate expedited diagnosis, and potentially prevent unnecessarily long treatment courses.