To investigate the incidence and risk factors of anal fistula after surgery for acute perianal abscess, and to establish and validate a nomogram model for predicting the risk of anal fistula in the early postoperative period.

A total of 144 patients with acute perianal abscess admitted to Xi'an Central Hospital Affiliated to Xi'an Jiaotong University from January 2023 to January 2025 were enrolled as the research subjects, including 104 males and 40 females, aged 21-79 years (mean age 50.77±6.23 years). All patients were categorized into an anal fistula group (n=44) and a non-anal fistula group (n=100) according to whether anal fistula was diagnosed within 3 months after surgery. Clinical data of all patients were collected, including gender, age, body mass index (BMI), smoking history, drinking history, hypertension, constipation, diabetes mellitus, hypertension, abscess size, location and depth, preoperative fever history, preoperative antibiotic use, history of abscess and origin of pathogenic bacteria. Variables with P<0.05 in univariate analysis were included in the multivariable Logistic regression model to identify independent risk factors. A nomogram prediction model was constructed based on statistically significant indicators, and model validation was completed.

The incidence of anal fistula was 30.6% (44/144). There were no statistically significant differences in age, BMI, smoking history, drinking history, hypertension, abscess size, constipation, preoperative fever history, abscess location and preoperative antibiotic use between the anal fistula group and the non-anal fistula group (P>0.05). However, statistically significant differences were found in gender, diabetes mellitus, depth of abscess, pathogenic bacteria origin and history of abscess between the two groups (P<0.05). Logistic regression analysis showed that male gender, diabetes mellitus, depth of abscess, intestinal origin of pathogenic bacteria, and history of abscess were independent risk factors for anal fistula after surgery for acute perianal abscess (P<0.05). The concordance index (C-index) of the nomogram model for predicting the risk of anal fistula after acute perianal abscess surgery was 0.844, indicating good discrimination. The calibration curve was close to the ideal reference line, and the predicted values were generally consistent with the observed values. Receiver operating characteristic (ROC) curve analysis showed that the area under the curve (AUC) was 0.945 (95%CI: 0.915-0.979), suggesting that the nomogram model had favorable predictive discrimination.

Male gender, diabetes mellitus, depth of abscess, intestinal origin of pathogenic bacteria, and history of abscess are independent risk factors for anal fistula after acute perianal abscess surgery. The nomogram model may provide a useful reference for the early clinical identification of high-risk patients and for optimizing treatment decisions, although external validation is still needed.