Abdominal ultrasound in the assessment of extent and activity of Crohn's disease: clinical significance and implication of bowel wall thickening.

Aims: The aim of this study was to evaluate the relevance of ultrasound (US) in assessing disease extent and activity in a series of patients with quiescent or active Crohn's disease (CD). In particular, the study was aimed at evaluating whether US may be useful in distinguishing between active disease and bowel wall thickening (BWT) due to fibrosis.
Patients and Methods: A series of consecutive patients with ileal, ileo-colonic, or colonic CD previously studied with x-ray and/or endoscopy, underwent abdominal US. The following parameters were also determined in these patients: CD activity index (CDAI), erythrocyte sedimentation rate, C reactive protein, length of disease, previous surgical resection, and number of recurrences. The relationship between BWT and the aforesaid parameters was assessed by means of univariate and multiple regression analysis.
Results: Overall sensitivity and specificity of US for the assessment of anatomical distribution of CD were 89% and 94%, respectively, and there was also a significant correlation between the extent of ileal disease measured by US and that determined by small bowel x-ray. By univariate analysis, statistically significant correlations were found between BWT, CDAI, and biological indices of inflammation (erythrocyte sedimentation rate and C reactive protein), although all the correlation coefficients were low with values not exceeding 0.40, and among these, backward multiple regression analysis identified only CDAI, along with ileo-colonic localization, as the subset of predictive variables of bowel wall thickness. However, both predictions were rather weak and accounted for only 20% of the variability of the BWT. In addition, a significant relationship was found between disease US extent and clinical or biochemical disease activity. However, in a subgroup of patients characterized by quiescent disease and high BWT, CD was complicated by higher prevalence of strictures, as detected by radiological and endoscopic examinations, and more frequent surgical outcome than others.
Conclusions: Abdominal US is an accurate method for determining the abdominal distribution of CD and appears to be accurate in detecting and evaluating the disease length of ileal lesions. In contrast, despite a weak but significant correlation between BWT and clinical and biochemical parameters, the usefulness of US as an index of disease activity seems to be fairly limited. However, a high BWT in quiescent patients suggests the presence of fibrosis, which is poorly responsive to steroid treatment.