Computed tomography enterography and magnetic resonance enterography in the diagnosis of Crohn's disease

Abstract

Imaging of the small bowel is complicated by its length and its overlapping loops. Recently, however, the development of crosssectional imaging techniques, such as computed tomography enterography (CTE) and magnetic resonance enterography (MRE) has shifted fundamental paradigms in the diagnosis and management of patients with suspected or known Crohn's disease (CD). CTE and MRE are noninvasive imaging tests that involve the use of intraluminal oral and intravenous contrast agents to evaluate the small bowel. Here, we review recent advances in each cross-sectional imaging modality, their advantages and disadvantages, and their diagnostic performances in the evaluation of small bowel lesions in CD.

Keywords: Crohn disease; Inflammatory bowel diseases; Magnetic resonance imaging; Tomography, spiral computed.

Fig. 1

Coronal CT enterography images using different types of neutral enteric contrast agents. CT enterography using polyethylene glycol (middle) and sorbitol (right) distends the small bowel effectively, while CT enterography using water (left) distends the small-bowel loops suboptimally.

Fig. 2

An axial CT enterography image using diluted gastrografin as a positive enteric contrast agent. Marked bowel wall thickenings (arrows) are present at the distal ileum. However, mucosal enhancement is completely obscured by the high-attenuation intraluminal positive contrast agent (^*).

Fig. 3

CT enteroclysis. A coronal CT enteroclysis image with the marked and uniform distension of entire small-bowel loops, including the jejunum (^*) and the ileum (•). Note the nasojejunal catheter inserted in the stomach (arrow) and the duodenum (arrowhead).

Fig. 4

Three-dimensional reconstruction CT images of the small bowel. (A) Sagittal multiplanar reconstruction CT images demonstrate wall thickening with luminal narrowing (arrows) with fibrofatty proliferation (^*) in the descending colon of a patient with CD. (B) Arterial phase, maximum intensity projection images in different patients depict the marked engorgement of the mesenteric vessels (comb sign) (^*) supplying the involved bowel segment. (C) A transparent volume-rendering CT enteroclysis image using air as a negative contrast agent clearly demonstrates longitudinal ulceration and shortening (arrows) on the mesenteric border of the ileum, and pseudosacculation (arrowheads) on the anti-mesenteric border. (D) A virtual enteroscopy image from the same patient also shows longitudinal ulceration and a fold deformity (arrows) in the ileum.

Fig. 5

Low-dose CT enterography images obtained using 100 kVp and 150 mAs in a 17-year-old boy with suspected CD. (A) An enteric phase CT image reconstructed using the conventional filtered back projection algorithm, had suboptimal image quality at the pelvic cavity because of severe noise. (B) However, the CT image reconstructed using an iterative reconstruction algorithm demonstrates a dramatic reduction in image noise, and shows multifocal enhancing wall thickening (arrows) in the distal ileum. The patient was diagnosed with CD on the basis of colonoscopic biopsy.

Fig. 6

A 15-year-old boy with CD and elevated inflammatory markers. (A-C) Magnetic resonance enterography images using (A) true fast imaging with steady-state precession (TrueFISP) (B) half-Fourier acquisition single-shot turbo spin-echo (HASTE), and (C) postcontrast T1-weighted 3-dimensional spoiled gradient recalled (SPGR) fat-saturated sequences show marked and asymmetric ileal wall thickening (arrows). Note the marked engorgement of the adjacent mesenteric vessels (comb sign) (^*) on the TrueFISP sequence (A) and marked enhancement on the postcontrast T1-weighted sequence (C), indicating active inflammation.

Fig. 7

A 15-year-old boy with CD. (A) Axial half-Fourier acquisition single-shot turbo spin-echo (HASTE) and (B) postcontrast T1-weighted magnetic resonance enterography images show marked distal ileal circumferential wall thickening with strong transmural hyperenhancement (arrowheads), consistent with active inflammation. (C) Axial diffusion-weighted image demonstrates the high signal intensity (arrowheads) associated with the involved ileum, suggesting the restricted diffusion of water within the distal ileum because of active inflammation.

Fig. 8

CT findings of active inflammation in CD. (A) An axial CT image shows bowel wall thickening (arrows) with bilaminar mural stratification and mucosal hyperenhancement. (B) A coronal CT image of a different patient demonstrates trilaminar mural stratification (arrows) with mucosal and serosal hyperenhancement. Note the dilated vasa recta (^*) or comb sign in the mesentery, A B indicating active disease.

Fig. 9

Chronic CD with submucosal fat deposits (arrows) in several small bowel loops.

Fig. 10

Reversible and irreversible strictures in CD. (A) A reversible stricture. The axial CT image demonstrates the narrowing of the bowel lumen caused by bowel wall edema with mural hyperenhancement and mural stratification (arrows), indicating that the stricture is not yet fibrotic. (B) An irreversible stricture. The axial CT image shows an abrupt luminal narrowing of the jejunum (arrows) with homogeneous and weak enhancement. The patient underwent jejunal segmental resection, and final histopathology confirmed chronic fibrotic strictures associated with CD (not shown).

Fig. 11

A 38-year-old man with CD. The axial CT image clearly depicts an enteroenteric fistula (arrow) in the right lower quadrant area.

Fig. 12

Fibrofatty proliferation in a 26-year-old man with active CD. The axial CT image shows a marked proliferation of fat (^*) at the medial aspect of the inflamed ascending colon (A). Note the paucity of fat around the normal descending colon (D).

Fig. 13

An anal fistula and perianal abscess in a 27-year-old man with CD. (A) An axial CT image shows a large perianal abscess (^*) just next to the anus (a). However, the anal fistula itself is not apparent on the CT image. (B) In contrast, serial T2-weighted magnetic resonance images clearly depict an anal fistula itself (arrows), which connects the anal lumen (a) and perianal abscess (^*).