External validation of the modified Parks classification of cryptoglandular anal fistula to predict failure of healing: the protocol for a retrospective analysis

There are multiple surgical options such as fistulotomy and fistulectomy to treat anal fistula (AF), yet treatment failure rates can be as high as 50%. In 1976, Parks et al classified AF into inter-sphincteric, trans-sphincteric, supra-sphincteric, and extra-sphincteric based on sphincter anatomy. This system overlooks complex features, which prompted Emile et al to incorporate risk factors into a modified version. In this retrospective cohort study, the external validity of this new classification will be investigated. A retrospective cohort design will be used and patients with cryptoglandular anal fistula who had preoperative MRI will be consecutively enrolled. Patients will be categorized according to the modified Parks classification. We will use descriptive analysis to describe imaging and clinical data. Moreover, logistic regression will be employed to develop a predictive model for recurrence. A P <0.05 will be considered significant, and the results will be reported with 95% confidence intervals (CI), if applicable. The study was approved by the institutional ethics committee. Patient with cryptoglandular AF often experience recurrent disease. Modified Parks classification integrates risk factors to guide management. This retrospective study is the first to externally validate Parks classification using MRI findings.