Validation of a novel imaging-guided and anatomy-based classification system for anorectal fistulas: a retrospective clinical evaluation study

Purpose: This study was conducted to evaluate the validity of a new imaging-guided, anatomy-based classification of anorectal fistulas in defining disease severity and predicting surgical outcomes. Methods: This multicenter, retrospective cohort study analyzed data from patients with perianal fistulas who underwent surgery between 2017 and 2023. All patients underwent preoperative 3-dimensional endoanal ultrasound, with adjunctive magnetic resonance imaging performed if ultrasound indicated a complex fistula. Imaging examinations were retrospectively evaluated to categorize fistulas according to the Garg classification and the newly proposed classification system. The new classification included 6 severity grades based on the characteristics of the primary tract: submucosal, intersphincteric, low transsphincteric, high transsphincteric, multiple, and suprasphincteric/extrasphincteric. Each grade was further subdivided into 3 subtypes (A, B, C) based on the extension of secondary tracts. Results: When compared with the new classification, the Garg classification demonstrated a slightly lower ability to predict the feasibility of fistulotomy in simple fistulas (94.2% vs 99.1%; Fisher exact test, P=0.006). A strong positive correlation was found between the surgery failure rate and the severity grade of the new classification (Spearman rho, 0.90; P<0.001), whereas the Garg classification showed a nonsignificant positive correlation with surgical failure rate (Spearman rho, 0.90; P=0.08). Conclusion: The new imaging-guided, anatomy-based classification of anorectal fistulas demonstrates high accuracy in defining disease severity. It represents a valuable tool for preoperative grading of anal fistulas, standardizing the reporting of diagnostic imaging, and improving the communication of findings among healthcare professionals.