EP409 - A Novel Simplified Classification System for Complex Anal Fistulas that Affects Management

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Purpose/Background: Complex anal fistulas can be difficult to categorize and manage. In our clinic we utilize a standardized approach with a modified advancement flap technique, usually after placement of seton drain for 6 weeks. We have noticed that there is a certain type of fistula that is particularly difficult to treat. Here we describe this type of fistula and compare it with a simpler type.

Methods/Interventions: All consecutive cases of anal fistulas treated by advancement flap repair by one surgeon (JC) between 2022 and 2024 were reviewed. Pouch fistulas and anovaginal fistulas were excluded. We have divided transphincteric cryptoglandular fistulas into Types 1 and 2. Type 1 fistulas are those with a relatively narrow track, a small internal opening, and minimal granulations, where symptoms and inflammation settle after seton placement. Type 2 fistulas have wide tracks full of granulations, with wide internal openings (≥10 mm), and are often horseshoe. They tend to be severely symptomatic with pain and copious drainage that do not improve with setons or tube drains. The only way to approach these fistulas is to close or at least narrow the internal opening to minimize bacterial ingress, looking at least to heal by stages. This means that flaps are performed under suboptimal circumstances. Fistulas were categorized prospectively. Healing was defined as lack of pain and discharge at 4 months, with closure of the external openings.

Results/Outcomes: There were 43 patients with 44 fistulas that underwent a total of 50 surgeries. Detailed demographic and clinical characteristics are presented (Table). Eighteen patients had prior repair before being referred. Internal openings were anterior in 25 and posterior in 19 (1 patient had 2 fistulas, one anterior and one posterior). All the 44 primary surgeries were advancement flap repairs. Half (22) of the fistulas were type 1 and half (22) were type 2. The table shows data stratified according to our classification. Initial healing rate was lower in Type 2 fistulas, but symptoms were often improved, and the number of external tracks reduced. 4 patients with Type 2 fistulas that failed the primary surgery underwent a total of 6 follow-up surgeries; 3 healed. The total healing rate after all interventions was 90% for Type 1 and 82% for Type 2, respectively (p=0.41).

Conclusion/Discussion: Anal fistulas with large internal openings and granulation-filled tracks sometimes fail primary flap repair, because seton drainage doesn’t improve the inflammation. An initial flap repair may achieve healing but if it doesn’t, the situation is usually improved, and healing can occur after a second flap. The cause of the large internal opening is not clear but may be associated with multiple abortive attempts at repair.