Comparison of hydrogen peroxide instillation with Goodsall's rule for fistula-in-ano

Background : Identification of the internal opening is an essential step in the management of fistula‐in‐ano. The predictive accuracy of Goodsall’s rule is compared with instillation of hydrogen peroxide for fistulas‐in‐ano. Methods : Thirty‐five patients (32 male, three female; median age 42 years; range: 6 months–70 years) were studied. Hydrogen peroxide solution was injected into the external opening of the fistula track and effervescence was observed at the internal opening within the anal canal. A fistula track was either excised or incised. Setons were placed within high fistulas. Results : There were 24 simple fistulas, compared to 11 complex fistulas (horseshoe, n = 4; abscess, n = 4). Eighteen external openings were anterior and 17 were posterior. Thirty‐four of 35 (97%) internal openings were identified. Only 20 internal openings were in accordance with Goodsall’s rule (positive predictive value: 59%). Predictive accuracy was greater for anterior external openings (13 of 18 (72%)) versus posterior external openings (six of 17 (41%); P = 0.016). For recurrent fistulas, seven of 17 fistula tracks had an internal opening in accordance with Goodsall’s rule, resulting in a positive predictive value of 41%. (Positive predictive value: anterior 67%vs posterior 12.5%; P = 0.0009.) Conclusion : The overall predictive accuracy of Goodsall’s rule was poor chiefly because of poor predictive accuracy in posterior and recurrent fistulas. The use of Goodsall’s rule alone in decision‐making before surgical intervention is not recommended.