The EXTENT Study: Results From an International Expert Delphi Consensus to Define Ultrasonographic Parameters for Measuring Bowel Damage in Crohn's Disease

Background & Aims: A primary aim in managing Crohn's disease (CD) is preventing bowel damage. The Lémann index (LI) quantifies structural bowel damage using magnetic resonance enterography (MRE) or computed tomography enterography (CTE) and, for colonic CD, colonoscopy. Intestinal ultrasonography (IUS) provides a noninvasive imaging alternative, although its role in LI assessment remains unexplored. This study aimed to establish a consensus on parameters and acquisition protocol for scoring small bowel and colonic damage using IUS in evaluating the LI. Methods: Thirty international experts in IUS and/or MRE participated in a 3-round Delphi process. Participants provided feedback and rated statements on IUS parameters and acquisition protocol in 2 online rounds. During the final in-person round, unresolved items were discussed and voted upon. Statements with at least 80% agreement were accepted. Results: Twenty-two statements reached a consensus: 10 defined IUS parameters for stricturing and penetrating lesions for scoring LI-IUS, and 12 addressed optimal IUS cineloop acquisition for centralized review. No consensus on IUS equivalents for grade 1 stricturing lesions in the small bowel and colon was reached. Conclusions: Ultrasonographic equivalents for assessing small bowel and colonic damage in CD were derived to align with the validated LI criteria for MRE and colonoscopy. These statements mark the first phase of the EXTENT project, supporting the potential use of IUS in clinical practice and disease modification trials as an alternative tool for bowel damage assessment. The lack of consensus on grade 1 stricturing lesions suggests further exploration of IUS parameters is required. Clinical Relevance: This study supports intestinal ultrasonography as a promising tool for assessing bowel damage in Crohn's disease, providing an alternative to magnetic resonance imaging/computed tomography and colonoscopy. Implementing intestinal ultrasonography could diminish patient discomfort and expand its use in clinical practice and trials. However, the Lémann index-intestinal ultrasonography needs to be validated in the ongoing prospective multicenter EXTENT study (ClinicalTrials.gov, Number: NCT06647823).