Assessment of Crohn's disease-associated small bowel strictures and fibrosis on cross-sectional imaging: a systematic review

Abstract

Patients with Crohn's disease commonly develop ileal and less commonly colonic strictures, containing various degrees of inflammation and fibrosis. While predominantly inflammatory strictures may benefit from a medical anti-inflammatory treatment, predominantly fibrotic strictures currently require endoscopic balloon dilation or surgery. Therefore, differentiation of the main components of a stricturing lesion is key for defining the therapeutic management. The role of endoscopy to diagnose the nature of strictures is limited by the superficial inspection of the intestinal mucosa, the lack of depth of mucosal biopsies and by the risk of sampling error due to a heterogeneous distribution of inflammation and fibrosis within a stricturing lesion. These limitations may be in part overcome by cross-sectional imaging techniques such as ultrasound, CT and MRI, allowing for a full thickness evaluation of the bowel wall and associated abnormalities. This systematic literature review provides a comprehensive summary of currently used radiologic definitions of strictures. It discusses, by assessing only manuscripts with histopathology as a gold standard, the accuracy for diagnosis of the respective modalities as well as their capability to characterise strictures in terms of inflammation and fibrosis. Definitions for strictures on cross-sectional imaging are heterogeneous; however, accuracy for stricture diagnosis is very high. Although conventional cross-sectional imaging techniques have been reported to distinguish inflammation from fibrosis and grade their severity, they are not sufficiently accurate for use in routine clinical practice. Finally, we present recent consensus recommendations and highlight experimental techniques that may overcome the limitations of current technologies.

Keywords: Crohn’s disease; fibrosis.

Figure 1

Transabdominal ultrasonography, CT and MR enterography demonstrating a distal ileal stricture. (A) Ultrasound image depicting the three core items for stricture diagnosis wall thickness (W, bracket), luminal narrowing (L, bracket) and prestenotic dilation (D, double arrow). (B–D) CT enterography demonstrating a distal ileal stricture with imaging findings of active inflammation and partial small bowel obstruction. (B) Coronal image demonstrating a distal ileal stricture with wall thickening, luminal narrowing and mural stratification and hyperenhancement (large white arrow). Active inflammatory Crohn’s disease is also present in the terminal ileum (arrowhead), as is a short segment jejunal stricture (small white arrow). (C) Enlarged axial image through distal ileal stricture better demonstrates luminal narrowing and increased wall thickness (W, bracket). (D) Sagittal image through distal ileal stricture shows prestenotic bowel dilation (D, arrows) and luminal narrowing within the stricture (L, bracket). (E–G) MR enterography demonstrating a distal ileal stricture with imaging findings of active inflammation. (E) Coronal half-Fourier single-shot fast spin echo (HASTE) shows ileal stricture with wall thickening and luminal narrowing (large white arrow) with upstream dilation (D, arrows). (F) Axial HASTE shows cross section through the stricture demonstrating increased wall thickness and how wall thickening is measured (W, white bracket). (G) Postcontrast axial 3D volumetric interpolated breath hold examination (VIBE) shows wall thickening and mural stratification and hyperenhancement, indicating inflammation with luminal narrowing (L, bracket). The three core items for stricture diagnosis are increased wall thickness, luminal narrowing and prestenotic dilation. CTE, CT enterography; MRE, MR enterography.

Figure 2

Proposed ranges for key items used for stricture detection in cross-sectional imaging modalities. US, ultrasound.