VALIDATE-PERIANAL: an international real-world multi-centre exploratory validation of the TOpClass definition of a radiologically healed fistula in perianal fistulising Crohn’s disease

OBJECTIVES: Radiological healing on MRI is the ultimate therapeutic goal in Class 2a perianal fistulising Crohn's disease (pfCD). The TOpClass consortium recently defined radiological healing (TOpClass-RH) by the absence of T2 hyperintensity, a completely fibrotic fistula tract, and the absence of contrast enhancement when used. This study aimed to validate TOpClass-RH in real-world clinical practice. MATERIALS AND METHODS: VALIDATE-PERIANAL was a retrospective, multi-centre international study. Patients with pfCD with a baseline MRI scan showing active disease and follow-up MRI evidence of radiological fistula healing between 2021 and 2023 were identified. Paired scans were independently reviewed by three gastrointestinal radiologists using TOpClass-RH criteria, with consensus adjudication. A minimum of 12 months of clinical follow-up was required. The primary outcome was sustained clinical remission; secondary outcomes included inter-rater reliability (Cohen's kappa) and rates of proctectomy and stoma formation. RESULTS: Of 977 patients screened, 40 with pfCD met the inclusion criteria;14/40 (35%) fulfilled TOpClass-RH criteria. Sustained clinical remission was achieved in 93% of TOpClass-RH patients. Clinical recurrence occurred in 1/14 (7%) of TOpClass-RH patients versus 8/26 (30.8%) in the non-RH group (RR 4.3 [0.60-31.0], p = 0.12), with a median follow-up of 28 months. Inter-rater reliability was excellent (κ 0.89-0.95). There was a trend toward lower rates of proctectomy and stoma formation in the TOpClass-RH group. CONCLUSION: TOpClass-RH was associated with sustained clinical remission, although the study was underpowered to detect statistically significant differences. The definition demonstrated excellent inter-rater reliability, supporting TOpClass-RH as a clinically meaningful radiological endpoint for trials and diagnostic stratification in pfCD. Larger prospective studies are required. CRITICAL RELEVANCE STATEMENT: This study validates the TOpClass criteria for defining a radiologically healed fistula in perianal Crohn's disease, providing radiologists with practical pearls, pitfalls, and illustrative figures that advance clinical radiology practice and research application in MRI interpretation and trial standardisation. KEY POINTS: The TOpClass definition provides an internationally agreed and standardised MRI-based criteria for identifying a radiologically healed fistula in perianal Crohn's disease. 93% of patients who met the TOpClass criteria for a radiologically healed fistula achieved sustained clinical remission, with excellent inter-rater reliability. The TOpClass criteria offer a potential benchmark for clinical trials, where a radiologically healed fistula represents the aspirational gold standard, associated with long-term remission in perianal fistulising Crohn's disease.