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Science to Practice |
Department of Radiology, Indiana University School of Medicine, Indiana University Hospital 0279, 550 North University Blvd, Indianapolis, IN 46202, dmaglint@iupui.edu
ABSTRACT
Summary: Endoscopy is frequently used as the reference standard in the evaluation of inflammation. However, endoscopy enables visualization of the mucosa only, has a limited reach, and has difficulty in anatomic orientation. Therefore, it is not a stand-alone diagnostic procedure. Imaging is needed if one is to visualize the entire intestinal wall, define the extent of disease, and categorize disease subtypes. Bodily et al in this issue of Radiology have described an objective, more reliable, and hopefully reproducible method of measuring active inflammation of a segment of bowel by quantifying mural enhancement in patients examined with CT enterography. Their results showed good correlation with ileoscopic and histologic findings of active inflammation.
THE SETTING
An imaging-based classification of Crohn disease subtypes has been described (1). Although the imaging features of each Crohn disease subtype are objective and reproducible, an imaging-based classification system has not been validated scientifically. In this issue of Radiology, Bodily et al (2) report a post hoc analysis of data in patients who underwent computed tomographic (CT) enterography and ileoscopy with or without biopsy. This analysis was performed both to determine if quantitative measures of small-bowel mural attenuation (after administration of contrast material) and thickness correlate with endoscopic and histologic findings of small-bowel inflammation and to estimate the performance of these measures in predicting the active inflammatory subtype of Crohn disease (2).
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Before they evaluated the different variables, Bodily et al (2) validated existing software for use in measuring both mural attenuation after contrast administration and bowel wall thickness in a series of bowel wall phantoms. These tools were then used in each CT enterography data set to quantify the variables that were then compared with a reference-standard assessment of Crohn disease activity. Quantitative measurements of terminal ileal mural attenuation had the highest sensitivity for predicting the presence of active inflammatory disease, with a sensitivity of 80% in patients with definite active Crohn disease and a sensitivity of 69% in patients with probable active Crohn disease. In multivariate models, small-bowel wall thickness was found to not be a significant variable after mural attenuation was taken into account. For predicting active inflammation in Crohn disease, quantitative measures of mural attenuation exceeded the performance of an experienced gastrointestinal radiologist by about 10%.
THE PRACTICE
Clinical use:
Objective measures of Crohn disease inflammatory activity are needed to justify the use and evaluate the effectiveness of recently introduced therapies, as well as to diminish interobserver variability and improve interpretive accuracy. It is hoped that CT enterography will allow reproducible measurements of wall attenuation (enhancement) in all segments of the small bowel, because measuring this variable is difficult when a segment of bowel is collapsed or spastic. In early Crohn disease, spasm of the abnormal segment is the initial response that can potentially limit assessment of mural enhancement at CT enterography. Although Bodily et al (2) found that wall thickness and attenuation were significant variables in univariate analyses, spasm may explain why measurement of small-bowel wall thickness was not a significant variable after mural attenuation was considered. In a recent prospective study (3), CT enteroclysis was compared with ileoscopy with biopsy in a small group of patients. These authors found that not only mural enhancement but also wall thickness were significant variables in predicting active inflammation. Wall thickness was a statistically significant finding in patients with active inflammation compared with patients with inactive Crohn disease.
Future opportunities and challenges:
Diagnostic costs for Crohn disease can be considerable, especially given the cycle of repeat testing caused by the low diagnostic yield of commonly used diagnostic procedures (4). It therefore behooves radiologists to use imaging procedures with high diagnostic accuracy and predictive values. In Crohn disease, more than one subtype of the disease process may be present in a segment or in multiple adjacent segments in the same patient. The active inflammatory disease subtype may coexist with fibrostenotic disease or the fistulizing subtype in another segment (1). Patients with active inflammation respond to a range of medical therapies, some of which may adversely affect segments with stenosis and may not be effective with fistulizing disease subtypes. Reliable imaging staging results considered in the context of clinical and endoscopic information can guide therapy. Although the Crohn disease activity index is accepted as the clinical standard, it has limitations. Accurate radiologic staging is therefore important in managing Crohn disease (1).
References
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  T. A. Jaffe, A. M. Gaca, S. Delaney, T. T. Yoshizumi, G. Toncheva, G. Nguyen, and D. P. Frush Radiation Doses from Small-Bowel Follow-Through and Abdominopelvic MDCT in Crohn's Disease Am. J. Roentgenol., November 1, 2007; 189(5): 1015 - 1022. [Abstract] [Full Text] [PDF]
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 D. D. T. Maglinte and J. E. Huprich Invited Commentary * Author's Response. RadioGraphics, May 1, 2006; 26(3): 657 - 662. [Full Text] [PDF]
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