Comparison of hydrogen peroxide instillation with Goodsall's fule 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.