Contemporary Imaging Assessment of Strictures and Fibrosis in Crohn Disease, With Focus on Quantitative Biomarkers: From the AJR Special Series on Imaging of Fibrosis.

Patients with Crohn disease commonly develop bowel strictures, which exhibit varying degrees of inflammation and fibrosis. Differentiation of strictures' distinct inflammatory and fibrotic components is key for the optimization of therapeutic management and for the development of antifibrotic drugs. Cross-sectional imaging techniques, including ultrasound, CT, and MRI, allow evaluation of the full thickness of the bowel wall, as well as of extramural complications and associated mesenteric abnormalities. Although promising data have been reported for a range of novel imaging biomarkers for fibrosis detection and quantification of fibrosis degree, these biomarkers lack sufficient validation and standardization for clinical use. Additional methods, including PET with emerging radiotracers, artificial intelligence, and radiomics are also under investigation for stricture characterization. In this article, we highlight the clinical relevance of identifying fibrosis in Crohn disease, review histopathologic aspects of strictures in Crohn disease, summarize morphologic imaging findings of strictures, and explore contemporary developments in the use of cross-sectional imaging techniques for detecting and characterizing intestinal strictures, with attention to emerging quantitative biomarkers.