Prospective evaluation of MR enterography as the primary imaging modality for pediatric Crohn disease assessment

Abstract

Objective: The objectives of this study were prospective evaluation of MR enterographic accuracy for detecting Crohn disease imaging features in pediatric patients, compared with a CT reference standard, as well as determination of MR enterographic accuracy for detecting active bowel inflammation and fibrosis using a histologic reference standard.

Subjects and methods: The study group for this blinded prospective study included 21 pediatric subjects with known Crohn disease scheduled for clinical CT and histologic bowel sampling for symptomatic exacerbation. All subjects and their parents gave informed consent to also undergo MR enterography. CT and MR enterography examinations were independently reviewed by two radiologists and were scored for Crohn disease features. All bowel histology specimens were reviewed by a single pathologist for the presence of active mucosal inflammation and mural fibrosis, followed by correlation of imaging and histologic findings.

Results: All 21 subjects underwent MR enterography and histologic sampling, 18 of whom also underwent CT. MR enterography had high sensitivity for detecting Crohn disease imaging features (e.g., bowel wall thickening, mesenteric inflammation, lymphadenopathy, fistula, and abscess) compared with CT, with individual sensitivity values ranging from 85.1% to 100%. Of a total of 53 abnormal bowel segments with correlation of MRI and histologic findings, MR enterography showed 86.7% accuracy (90.0% sensitivity and 82.6% specificity) for detecting active inflammation (p < 0.001). The accuracy of MR enterography for detecting mural fibrosis overall was 64.9%, compared with histology, but increased to 83.3% (p < 0.05) for detecting fibrosis without superimposed active inflammation.

Conclusion: MR enterography can substitute for CT as the first-line imaging modality in pediatric patients with Crohn disease, on the basis of its ability to detect intestinal pathologic abnormalities in both small and large bowel as well as extraintestinal disease manifestations. Additionally, MR enterography provides an accurate noninvasive assessment of Crohn disease activity and mural fibrosis and can aid in formulating treatment strategies for symptomatic patients and assessing therapy response.

Fig. 1

MR enterography and CT depiction of Crohn's imaging features. Representative image pairs from CT (a-d) and MR-E (e-h) studies demonstrate wall thickening of small bowel (a, e arrowheads) and colon (b, f arrowheads), lymphadenopathy (a, d arrows), intersphincteric fistula formation (d, h arrows), and iliopsoas abscesses (c, g arrows).

Fig. 2

MR enterographic detection of active inflammation and fibrosis. Imaging is depicted from abnormal small bowel segments (arrows) in 2 subjects, the first demonstrates bowel wall T2 hyperintensity (a) early mucosal enhancement (b) and later progressive transmural enhancement (c) suggestive of active inflammation, while the second demonstrates bowel wall T2 hypointensity (e) and minimal wall enhancement (f) that does not increase with time (g) suggestive of fibrosis. Histological assessment of corresponding surgical excision specimens confirms the MR findings, with active inflammation characterized by neutrophilic invasion of the mucosal glands (d) and submucosal collagen deposition indicative of mural fibrosis (h).

Fig. 3

Superimposed active inflammation can obscure MR enterographic detection of bowel wall fibrosis. Representative T2-weighted (a, d) and T1 fat-suppressed post-contrast (b, e) images from 2 subjects demonstrate focal small bowel wall thickening, T2 hyperintensity, and marked mural enhancement suggestive of active inflammation. Corresponding histology images (c and f) demonstrate mucosal inflammation (c, asterisk) superimposed upon submucosal fibrosis (c, “Fib”) as well as a large intramural abscess (f, “Abs”).