[Analysis of risk factors for postoperative recurrence and fecal incontinence in complex anal fistula based on MRI anatomic features].

Objective: To investigate the surgical risk stratification of complex anal fistula based on magnetic resonance imaging (MRI) anatomical features, analyze the independent risk factors for postoperative recurrence and anal incontinence, and provide evidence for individualized treatment. Methods: This was a retrospective observational study. Clinical data of patients with complex anal fistula who underwent preoperative MRI and surgical treatment at two tertiary hospitals (Affiliated Hospital of Nanjing University of Chinese Medicine and Taicang Affiliated Hospital of Nanjing University of Chinese Medicine) between January 2016 and December 2021 were collected retrospectively. Patients were included if their follow-up time was ≥12 months. Exclusion criteria were: (1) anal fistula caused by specific etiologies such as tuberculosis, rectal cancer, radiotherapy, or immunodeficiency; (2) missing surgical data; (3) history of previous anal fistula surgery; and (4) preoperative anal function impairment. Fistula anatomical features were quantified based on MRI (including the vertical distance from the highest point of the main tract to the anal verge, number and location of abscesses, and anatomical spaces involved). Multivariate logistic regression analysis was employed to identify independent predictors for fistula recurrence and anal incontinence. Results: A total of 509 patients with complex anal fistula were included in the analysis, comprising 421 males (82.7%). The median follow-up was 30 (range, 18-61) months. The recurrence rate was 13.6% (69/509), and the incidence of anal incontinence was 11.2% (57/509). Univariate and multivariate analyses revealed that concomitant single abscess (OR=5.311, 95%CI: 2.443-11.540, P<0.001), multiple abscesses (OR=9.501, 95%CI: 3.933-22.950, P<0.001), and the vertical distance from the highest point of the main tract to the anal verge (per 1 cm increase, OR=1.816, 95%CI:1.187-2.779,P=0.006) were independent risk factors for postoperative recurrence. Furthermore, the vertical distance from the highest point of the main tract to the anal verge (per 1 cm increase) was the sole independent risk factor for postoperative anal incontinence (OR=1.556, 95%CI:1.253-1.935, P<0.001). Conclusions: The risks of postoperative recurrence and anal incontinence in complex anal fistula are primarily influenced by the complexity of the fistula structure, specifically the presence of concomitant abscesses and the depth of the main fistula tract.