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Background and Aims: Perianal fistuliing Crohn's disease [PFCD] is an aggressive phenotype of Crohn's disease defined by frequent relapses and disabling symptoms. A novel consensus classification system was recently outlined by the TOpCLASS consortium, which seeks to unify disease severity with patient-centred goals but has not yet been validated. We aimed to apply this to a real-world cohort and to identify factors that predict transition between classes over time., Methods: We identified all patients with PFCD and at least one baseline and one follow-up pelvic MRI [pMRI]. TOpCLASS classification, disease characteristics, and imaging indices were collected retrospectively at time periods corresponding with respective MRIs., Results: We identified 100 patients with PFCD, of whom 96 were assigned TOpCLASS Classes 1-2c at baseline. Most patients [78.1%] started in Class 2b, but changes in classification were observed in 52.1% of all patients. Male sex [72.0%, 46.6%, 40.0%, p = 0.03] and prior perianal surgery [52.0% vs 44.6% vs 40.0%, p = 0.02] were more frequently observed in those with improved class compared to unchanged and worsened class. Baseline pMRI indices were not associated with changes in classification; however, greater improvements in mVAI, MODIFI-CD, and PEMPAC were seen among those who improved. Linear mixed effect modelling identified only male sex [-0.31, 95% CI -0.60 to -0.02] with improvement in class., Conclusion: The TOpCLASS classification highlights the dynamic nature of PFCD over time. However, our ability to predict transitions between classes remains limited and requires prospective assessment. Improvement in MRI index scores over time was associated with a transition to lower TOpCLASS classification., (© The Author(s) 2024. Published by Oxford University Press on behalf of European Crohn’s and Colitis Organisation. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Anal fistula is a common cause of chronic irritation to both patients and surgeons. Treatment failure rates may be decreased by a good appreciation of normal anorectal anatomy and fistula pathoanatomy, as well as a wide and practical knowledge of the possible treatment regimens. The various treatment options available for acute abscesses as well as simple and complex anal fistulae are presented and discussed. Identification of the patient at risk of postoperative anal incontinence or of the difficult or high fistula may allow treatment in a specialized proctology unit.

This paper presents the application of a classification of anal fistulas to an unselected consecutive series of 793 patients treated for this condition at St Mark's Hospital from 1968 to 1973 inclusive. The fistulas were divided into five categories on their anatomical relationships: superficial (16 per cent), intersphincteric (54 per cent), trans-sphincteric (21 per cent), suprasphincteric (3 per cent) and extrasphincteric (3 per cent), with the remaining cases multiple or unclassified (3 per cent). There was good correlation between the categories and presentation, physical signs and treatment of the fistulas. Two hundred and forty-nine patients had potentially difficult fistulas. Follow-up of these patients revealed healing of almost all the fistulas, but the functional results were less satisfactory (incontinence of loose stool in 17 per cent and of flatus in 25 per cent, soiling in 31 per cent).

A classification of anal fistulas is presented, which is the result of an analysis of 400 cases treated over the past 15 years, based on the pathogenesis of the disease and the normal muscular anatomy of the pelvic floor. Four main types were found but numerous variations of each occur, which are described. It is hoped that this will alert the surgeon to the various complex situations that he may encounter.