1. Introduction

Perianal fistulising Crohn’s disease (pfCD) is a distinct and debilitating phenotype seen in around one-third of patients with Crohn’s. Clinical trials in perianal fistulising Crohn’s disease (pfCD) are increasingly using MRI criteria as a primary endpoint but there is heterogeneity in the radiological definition of a healed perianal fistula that currently limits our ability to perform meaningful meta-analyses of studies. Our aim is to standardise outcomes through generation of an international consensus definition of a radiologically healed fistula.

2. Methods and analysis

This international Delphi consensus study employs a two-part strategy.

The first is a systematic review to identify a longlist of variables used to define radiological healing in pfCD. MRI-based indices used to score fistula severity and healing will be assessed for their methodological quality using COSMIN (Consensus-based Standards for the selection of health Measurement Instruments). The systematic review protocol will be conducted using COSMIN methodology and reported using PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) and has been prospectively registered on PROSPERO (CRD42024504334).

The second part will be an online Delphi consensus, guided by the results of the systematic review. Radiologists, gastroenterologists, and colorectal surgeons with expertise in the management of pfCD will be invited to take part in two to three rounds of online surveys. Once an a priori threshold of >80% agreement is reached on individual radiological components used to define ‘healing’ and ‘healed’, a final meeting of key stakeholders will be organised to generate a consensus definition of a healed fistula.

3. Ethics and dissemination

The study has been deemed exempt from a formal Research Ethics committee review as no patients will participate directly in the consensus process, given the technical nature of the research question. The study is registered with the local R&D department (Reference RD24/007). Publication of this study will help standardise radiological endpoint measurement in clinical trials of pfCD and improve the synthesis and meta-analysis of comparative studies.