A study on validity of Goodsall's rule in accurately predicting the course of anal fistulous tract; comparison with MRI and surgical findings

Background: Fistula-in-ano is a granulation tissue lined tract that opens deeply in the anal canal or rectum and superficially on the perianal skin. Most of these fistulae are formed from ano rectal abscess which burst spontaneously. The secondary causes of fistula in ano include conditions such as Crohn’s disease, Tuberculosis and Carcinoma rectum. Fistula in ano can be broadly classified into Anterior and Posterior, Low lying or High Fistula in ano as well as Simple and Complex fistula in ano. Goodsall’s rule depicts the relationship of the external opening of the fistula with the course of fistulous tract. The three main radiological imaging techniques that are used in evaluating perianal fistulas include contrast fistulography, endorectal ultrasonography and magnetic resonance imaging(MRI). Our aim was to assess the accuracy of Goodsall’s rule in predicting the course of anal fistulae and its reliability for evaluating patients presenting with Fistula in ano. We also correlated the clinical and intra-operative findings with that of Magnetic Resonanace(MR) Fistulogram to know whether MR Fistulogram can be used selectively for evaluating Complex Fistula in Ano
Methods: This was a Prospective Mono-centric Observational Study conducted at the General Surgery department of Apollo Main Hospital Chennai, from August 2022 to December 2023. The final study sample after considering the inclusion and exclusion criteria was 67. Various parameters such as demographic details, clinical symptoms, characteristics of fistula were studied and comparison was done between the clinical and intra operative findings as well as the imaging findings.
Results: Out of the 67 patients with Fistula in ano, 56 (83.6%)were males and 11 (16.4%) were females. Out of the 67 patients, 43(64.2%) had pain, 46(68.7%) had perianal swelling, 59(88.1%) people had complaints of discharge per anum. Antrior fidtula in ano was observed (43.3%) and a posterior opening was observed in 38 (56%). The fistulous tract was found to be simple in 42(62.69%) and complex in 25(37.31%). The overall predictive accuracy of Goodsall’s rule was 71.6%, The predictive accuracy was 75.86% with anterior fistula in ano and 68.42% with posterior fistula in ano. MRI was able to accurately delineate the course of the tract in 92.5%. MR fistulogram had a sensitivity of 93.8% (95% CI) - 93.8% (91.4% - 96.2%)
Conclusion: We conclude that the overall accuracy of Goodsall's rule in predicting the course of the fistulous tract is 72% and the predictive accuracy was high for anterior fistulae and complex fistulae. Goodsall's rule can thus be used as tool for the pre operative evaluation of patients with fistula in ano and also can help in assessing the necessity of MR fistulogram in complex cases.