Algorithmic Approach to CT Diagnosis of the Abnormal Bowel Wall

Abstract

Computed tomography demonstrates intestinal wall abnormalities that can be analyzed by categorizing attenuation changes in the intestinal wall and transposing morphologic characteristics learned from barium studies. These attenuation patterns include white, gray, water halo sign, fat halo sign, and black. The white pattern represents avid contrast material enhancement that uniformly affects most of the thickened bowel wall. If the bowel wall is enhanced to a degree equal to or greater than that of venous opacification in the same scan, it should be classified in the white attenuation pattern. Common diagnoses with this pattern include idiopathic inflammatory bowel diseases and vascular disorders. The gray pattern is defined as a thickened bowel wall with limited enhancement whose homogeneous attenuation is comparable with that of enhanced muscle. This pattern is used to differentiate between benign and malignant disease, but it is the least specific of the patterns and should be combined with morphologic observations. The water halo sign indicates stratification within a thickened bowel wall that consists of either two or three continuous, symmetrically thickened layers. Common diagnoses with this sign include idiopathic inflammatory bowel diseases, vascular disorders, infectious diseases, and radiation damage. The fat halo sign refers to a three-layered target sign of thickened bowel in which the middle or "submucosal" layer has a fatty attenuation. Common diagnoses with this sign include Crohn disease in the small intestine and idiopathic inflammatory bowel diseases in the colon. Black attenuation is the equivalent of pneumatosis, and this pattern is commonly seen in ischemia, infection, and trauma.

CT enteroclysis/enterography findings in drug-induced small-bowel damage

“…In Type 3, the mucosal layer is enhanced reflecting hyperaemia, and the submucosal layer is not enhanced reflecting oedema. 9,10 These intramural multilayered structures are called "target sign". Therefore, the mucosal damage was more severe in long-term users (Type 2) than in short-term users (Type 1).…”

Benign Diseases of the Colon and Rectum (incl. CT colonography)

“…Note that these signs overlap each other, making an exact diagnosis difficult and sometimes impossible. However, the absence of diverticula within the affected segment and the presence of shoulder formation are strong indicators for cancer In the large bowel, inflammation typically leads to bowel wall thickening, with or without mural stratification, which is the ability to distinguish the different layers of the colonic wall on crosssectional imaging [26,27]. Various inflammatory bowel diseases differ in their primary location within the GI tract, length of segmental involvement, degree of wall thickening, mural enhancement pattern, and extraintestinal involvement.…”

Imaging of Ischemia, Obstruction and Infection in the Abdomen

“…23). The "fat halo sign" is similar but occurs when the submucosa demonstrates fat deposition, though it predominantly occurs in ulcerative colitis 90 .…”

“…Bowel wall thickness, bowel wall attenuation, degree of wall thickening, symmetry of wall thickening, length of segment involved and associated findings such as stranding, lymphadenopathy and abscess are key factors which aid in delineating etiology 41,90 .…”