(Radiographics. 2002;22:1107-1109.)
© RSNA, 2002
Invited Commentary • Author's Response
Michael Federle, MD
Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, Pennsylvania
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Commentary
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The preceding article by Wittenberg and colleagues (1) is a useful assimilation and organization of observations that have been made by numerous investigators over the past 20 years. The combination of the information categorized into the attenuation spectrum of the bowel wall and the morphologic criteria presented in the tables will help radiologists more confidently suggest a specific cause for bowel wall thickening recognized on CT scans.
I take exception, however, to their "Category 1: White Attenuation," which is said to represent intense contrast enhancement of the majority ofthe thickened bowel wall, with shock bowel being the prototypic example. Over the years, I have seen dozens of cases of shock bowel and hundreds of cases of idiopathic inflammatory bowel disease on CT scans, and I have never recognized "white" enhancement of the submucosal portion of the bowel wall. In shock bowel, first described in adults by Mirvis and colleagues in 1994 (2), the mucosa enhances extremely brightly, but the submucosa is edematous and more closely approximates the "water halo sign" in my experience (Figure). Because the mucosa is thickened and the bowel lumen is usually not distended in acute trauma victims, the bowel wall might appear to be enhancing diffusely, especially if inappropriately thick CT collimation (>7 mm) is used. However, since the authors are basing their classification scheme on the appearance of the submucosa, it seems inappropriate to create a unique category for intense mucosal enhancement.
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Figure. Shock bowel. On an enhanced CT scan of a 20-year-old man who was hypotensive following a motor vehicle crash, the wall of the small bowel is thickened. The mucosal layer enhances brightly, but the submucosal layer is of near water attenuation.
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There is a genuine cause of a "white" bowel wall that does not appear in the algorithmic approach described by Wittenberg et al. Acute bowel wall hematoma (usually caused by blunt trauma, instrumentation, or anticoagulation) will appear hyperattenuated relative to normal bowel wall and muscle on unenhanced CT scans, especially if the images are viewed at narrow window settings.
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References
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- Wittenberg J, Harisinghani MG, Jhaveri K, Varghese J, Mueller PR. Algorithmic approach to CT diagnosis of the abnormal bowel wall. RadioGraphics 2002; 22:1093-1109.[Abstract/Free Full Text]
- Mirvis SE, Shanmuganathan K, Erb R. Diffuse small-bowel ischemia in hypotensive adults after blunt trauma (shock bowel): CT findings and clinical significance. AJR Am J Roentgenol 1994; 163:1375-1379.[Abstract/Free Full Text]
Author’s Response
Jack Wittenberg, MD
Division of Abdominal Imaging and Intervention, Massachusetts General Hospital, Boston, Massachusetts
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Response
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I welcome and respect the comments of a noted abdominal imager such as Dr Federle and hope that any disagreement and controversy that follows becomes a stimulus for further investigation. From my perspective, inquiry into understanding CT manifestations of anatomic and pathophysiologic alterations in gastrointestinal disease is unfortunately taking a back seat to solid organ investigation. Since CT has become the imaging technique of choice for many gastrointestinal complaints, efforts at pursuing greater fundamental understanding are critical.
The white attenuation pattern is, as we acknowledged in our article, the most difficult to assess confidently because stratification clues and precise quantitative measurements are absent. Either Hounsfield unit measurement or visual comparison with the attenuation of associated veins provides, at present, our best assessment. The dispute in the case of shock bowel may be in part a sampling error, since we may not have had as extensive an experience as Dr Federle. However, review of the article cited by Federle reveals at least four illustrations of homogeneous bright wall enhancement of well-distended bowel. Because our CT protocol includes scans obtained at thinner (5-mm) collimation, we do not believe our observation can be explained by a tissue sampling difference. As with most diagnoses, more than one diagnostic category is possible. On the other hand, our experience with Crohn disease and ulcerative colitis is extensive enough for us to defend the assignment of the white attenuation pattern to both. That is not to say that a water or fat halo sign is not more common, but rather that all these patterns may be present in either disease. In fact, all three enhancement patterns may be seen simultaneously. If a fat halo sign is regarded as a sign of chronicity, do the other two signs represent different phases of activity, and if so, what level of activity?
We further would like to emphasize that the classification scheme is not solely based on the altered enhancement pattern of the submucosa. The abnormal stratification findings may well be dictated by altered dynamics predominantly in either or both the "mucosa" or "muscularis propria" layers. In fact, since these boundaries within the intestinal wall have not been precisely defined with CT, it is best to either use the histologic boundary labels in quotation marks or simply refer to them as inner, middle, or outer layers. If we could define boundaries with CT, then perhaps we can further refine differential diagnostic or even prognostic opinions. Clearly, there is much yet to be done.
Related Article
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Algorithmic Approach to CT Diagnosis of the Abnormal Bowel Wall
- Jack Wittenberg, Mukesh G. Harisinghani, Kartik Jhaveri, Jose Varghese, and Peter R. Mueller
RadioGraphics 2002 22: 1093-1107.
[Abstract]
[Full Text]
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