Can Conventional and Diffusion-Weighted MR Enterography Biomarkers Differentiate Inflammatory from Fibrotic Strictures in Crohn's Disease?

The role of molecular imaging in detecting fibrosis in Crohn's disease

Fibrosis is a pathological process that occurs due to chronic inflammation, leading to the proliferation of fibroblasts and the excessive deposition of extracellular matrix (ECM). The process of long-term fibrosis initiates with tissue hypofunction and progressively culminates in the ultimate manifestation of organ failure. Intestinal fibrosis is a significant complication of Crohn's disease (CD) that can result in persistent luminal narrowing and strictures, which are difficult to reverse. In recent years, there have been significant advances in our understanding of the cellular and molecular mechanisms underlying intestinal fibrosis in inflammatory bowel disease (IBD). Significant progress has been achieved in the fields of pathogenesis, diagnosis, and management of intestinal fibrosis in the last few years. A significant amount of research has also been conducted in the field of biomarkers for the prediction or detection of intestinal fibrosis, including novel cross-sectional imaging modalities such as positron emission tomography (PET) and single photon emission computed tomography (SPECT). Molecular imaging represents a promising biomedical approach that enables the non-invasive visualization of cellular and subcellular processes. Molecular imaging has the potential to be employed for early detection, disease staging, and prognostication in addition to assessing disease activity and treatment response in IBD. Molecular imaging methods also have a potential role to enabling minimally invasive assessment of intestinal fibrosis. This review discusses the role of molecular imaging in combination of AI in detecting CD fibrosis.

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 have bowel strictures develop, which exhibit varying degrees of inflammation and fibrosis. Differentiation of the distinct inflammatory and fibrotic components of strictures 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 extramural complications and associated mesenteric abnormalities. Although promising data have been reported for a range of novel imaging biomarkers for detection of fibrosis and quantification of the degree of fibrosis, 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 review, we highlight the clinical relevance of identifying fibrosis in Crohn disease, review the histopathologic aspects of strictures in Crohn disease, summarize the 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 given to emerging quantitative biomarkers.

Imaging of Strictures in Crohn's Disease

Crohn's disease (CD) is a chronic inflammation of the digestive tract, and it frequently affects young patients. It can involve any intestinal segment, even though it frequently affects the distal ileum. Up to 80% of patients with CD present with inflammatory behavior, and 5% to 28% develop stricturing disease. Based on the predominant mechanism causing them, strictures can be categorized as inflammatory, fibrotic, or mixed. Determining the relative amounts of inflammation and fibrosis in a stricture can influence treatment decisions. Imaging is an extremely useful tool in patients with small bowel stricturing CD to confirm the diagnosis and to evaluate disease characteristics, usually using CT or MRI. The aim of this paper is to describe how imaging can evaluate a patient with small bowel CD stricture.

Evaluating the diagnostic accuracy of magnetic resonance imaging in distinguishing strictures in Crohn's disease: a systematic review and meta-analysis

PURPOSE

This systematic review and meta-analysis sought to assess the diagnostic accuracy of magnetic resonance imaging (MRI) in distinguishing fibrotic from inflammatory strictures in Crohn's disease (CD) patients.

METHODS

A rigorous and systematic exploration of five key databases yielded studies that met predefined criteria. Data were extracted for a comprehensive meta-analysis using MetaDiSC and MetaDTA software, providing diagnostic accuracy measures. The Quality Assessment of Diagnostic Accuracy Studies 2 (QUADAS-2) tool was utilized for evaluating the methodological quality and potential bias within the studies.

RESULTS

The systematic review involved the evaluation of 7437 records, culminating in the inclusion of 22 studies. In detecting fibrotic strictures in CD patients, MRI exhibited a pooled sensitivity of 85.20% (95% CI: 76.10-91.20%) and specificity of 96.00% (95% CI: 87.80-98.70%). For differentiating fibrotic strictures from inflammatory stenosis, the sensitivity was 81.5% (95% CI: 70.2-89.20%), and the specificity was 97.2% (95% CI: 90.0-99.3%). In terms of assessing the severity of strictures, sensitivity stood at 90.4% (95% CI: 78.1-96.1%) and specificity at 89.4% (95% CI: 57.4-98.2%). The consistency of the diagnostic accuracy was observed across different geographical locations and the various reference tests applied in the studies.

CONCLUSIONS

The results of this meta-analysis underscore the robust diagnostic accuracy of MRI in detecting fibrotic strictures, distinguishing between fibrotic and inflammatory strictures, and evaluating stricture severity in CD patients. These findings support the integration of MRI into standard diagnostic protocols for patients with CD. Further large-scale, multicenter trials are warranted to confirm these results and to identify any potential limitations associated with the application of MRI in this clinical setting.

How to Evaluate Fibrosis in IBD?

In this review, we will describe the importance of fibrosis in inflammatory bowel disease (IBD) by discussing its distinct impact on Crohn's disease (CD) and ulcerative colitis (UC) through their translation to histopathology. We will address the existing knowledge on the correlation between inflammation and fibrosis and the still not fully explained inflammation-independent fibrogenesis. Finally, we will compile and discuss the recent advances in the noninvasive assessment of intestinal fibrosis, including imaging and biomarkers. Based on the available data, none of the available cross-sectional imaging (CSI) techniques has proved to be capable of measuring CD fibrosis accurately, with MRE showing the most promising performance along with elastography. Very recent research with radiomics showed encouraging results, but further validation with reliable radiomic biomarkers is warranted. Despite the interesting results with micro-RNAs, further advances on the topic of fibrosis biomarkers depend on the development of robust clinical trials based on solid and validated endpoints. We conclude that it seems very likely that radiomics and AI will participate in the future non-invasive fibrosis assessment by CSI techniques in IBD. However, as of today, surgical pathology remains the gold standard for the diagnosis and quantification of intestinal fibrosis in IBD.

DWI ratios: New indexes for Crohn's disease activity at magnetic resonance enterography?

BACKGROUND

The aim of the study was to provide radiologists and clinicians a rapid tool for assessment of intestinal inflammation in Crohn's disease (CD) patients through quantification of diffusion-weighted imaging (DWI) signal intensity while performing magnetic resonance enterography (MRE).

MATERIALS AND METHODS

A monocentric retrospective study was conducted between September 2018 and July 2021 on CD patients who underwent MRE. Two radiologists measured signal intensity on DWI scans at the highest b-value (800 s/mm²) within pathologic intestinal walls, lymph nodes, spleen and psoas muscle and calculated the relative ratios. Spearman, Mann-Whitney and Jonckheere-Terpstra tests were applied for estimating correlation among ratios, significant differences between the two patient groups and determining the trend in relation to endoscopic classes. Wilcoxon's and Cronbach's alpha tests were employed for comparison of DWI measurements and ratios between the two observers.

RESULTS

Fifty-nine patients were enrolled in the study. In the non-surgical group, correlation has been found among Simple Endoscopic Score for Crohn's Disease (SES-CD) classes and the different ratios: bowel/spleen (p = 0.034), bowel/psoas (p = 0.008) and bowel/lymph node (p = 0.010). Within the surgical group, positive correlation was found only between bowel/lymph node ratio and bowel/psoas ratio (p = 0.014). The J-T test demonstrated an increasing monotonic trend for bowel/psoas ratio and bowel/lymph node ratio and SES-CD classes. Inter-reader evaluation demonstrated no statistical differences for DWI measurements and high degree of concordance for the final ratios.

CONCLUSION

DWI ratios correlate with endoscopic classes in non-surgical patients and have inter-observer reproducibility.

The Role of Magnetic Resonance Enterography in Crohn’s Disease: A Review of Recent Literature

Inflammatory bowel disease (IBD) is the term used to identify a form of chronic inflammation of the gastrointestinal tract that primarily contemplates two major entities: ulcerative colitis (UC) and Crohn’s disease (CD). The classic signs are abdominal pain and diarrhoea that correlate with the localization of gastro-enteric disease, although in this pathology extraintestinal symptoms may coexist. The diagnosis of CD relies on a synergistic combination of clinical, laboratory (stool and biochemical), cross-sectional imaging evaluation, as well as endoscopic and histologic assessments. The purpose of this paper is to prove the role of imaging in the diagnosis and follow-up of patients with CD with particular focus on recent innovations of magnetic resonance enterography (MRE) as a pivotal diagnostic tool, analysing the MRE study protocol and imaging features during the various phases of disease activity and its complications.

Diagnostic Accuracy of Magnetic Resonance Enterography for the Evaluation of Active and Fibrotic Inflammation in Crohn’s Disease

Background

Despite the success of standard magnetic resonance enterography (MRE) in detecting Crohn’s disease (CD), characterization of strictures and, thus, therapy guidance is still limited. The aim of the study was to determine diagnostic accuracy of MRE in detecting or ruling out active inflammation and identifying fibrotic lesions in patients with terminal ileal CD with histopathology as reference.

Methods

Sixty-seven consecutive patients (median age 32 years, range 19–79 years) with terminal ileal CD were retrospectively enrolled between January 2015 and October 2020. The median interval between MRE and surgery was 9 days (range 0–86 days). Sensitivity, specificity, positive and negative predictive value (PPV and NPV, respectively), and area under the curve (AUC) with 95% confidence intervals (CIs) were calculated for the MRE-based AIS (acute inflammation score) using the histopathology of surgical specimens as the reference standard.

Results

Sensitivity, specificity, PPV, and NPV for detecting or ruling out active inflammation were 100% (CI, 0.94–1.00; 0.44–1.00; 0.93–1.00; 0.31–1.00) using an AIS cut-off of >4.1. AUC was 1.00 (CI, 1.00–1.00; p < 0.01). In all patients with fibrotic changes only and no active inflammation, AIS was <4.1. Interobserver agreement was substantial (κ = 0.65, p < 0.01).

Conclusion

Our study has shown an excellent diagnostic performance of the MRE-based AIS for determining whether active inflammation is present or lesions are due to chronic changes in ileal CD using the histopathology of surgical specimens as reference. These findings indicate that the MRE-based AIS allows a better determination of the inflammatory stage of terminal ileal CD, which facilitates the decision to perform surgery.