Mural attenuation in normal small bowel and active inflammatory Crohn's disease on CT enterography: location, absolute attenuation, relative attenuation, and the effect of wall thickness.

Objective: The purpose of our study was to measure relative and absolute wall attenuations and wall thickness in normal small bowel on contrast-enhanced CT enterography and to study the efficacy of relative attenuation, absolute attenuation, and wall thickness in distinguishing normal from active inflammatory Crohn's disease of the terminal ileum.
Materials and Methods: Using a case-control study design, we reviewed 630 CT enterography examinations, of which 191 were normal and 36 had active inflammatory Crohn's disease in the terminal ileum. In healthy individuals, wall thickness and attenuation in distended and collapsed loops were measured in the duodenum and four abdominal quadrants. Wall thickness and attenuation were also measured in the terminal ileum. All measurements of intraarterial attenuation were taken at the same slice level. In the examinations of patients with Crohn's disease, only terminal ileum wall thickness and attenuation as well as arterial attenuation at the same slice level were measured. Normal segments were compared with a linear model. Terminal ileum data were fit to a multivariate logistic regression model.
Results: Relative attenuation and absolute attenuation in the normal distended and collapsed duodenum and left upper quadrant were significantly greater than in all other segments (p < 0.001 and < 0.048 for relative attenuation and p < 0.001 and < 0.032 for absolute attenuation, respectively). Relative attenuation and wall thickness models and absolute attenuation and wall thickness models discriminated normal from active terminal ileum Crohn's disease significantly better than the same measurements without wall thickness (p = 0.017 and 0.001, respectively). When the bowel wall is > 3 mm, a relative attenuation cutoff of 0.5 is 89% sensitive and 81% specific.
Conclusion: In normal small bowel, when wall measurement is taken into account, the duodenum and jejunum have a greater relative attenuation and absolute attenuation than other segments. Relative attenuation and absolute attenuation with wall thickness models discriminate normal from active terminal ileum Crohn's disease better than the same measurements without wall thickness.