Abnormal bowel wall attenuation patterns

Abnormal bowel wall attenuation patterns on CT scan can be grouped under five categories:

The first three patterns are seen on contrast studies.

White enhancement

It is defined as uniform enhancement of thickened bowel wall which is greater than or equal to the venous opacification.

Common differentials include:

• inflammatory bowel disease
• vascular disorder

Gray enhancement

It is defined as homogeneous enhancement of thickened bowel wall that equals to the muscle enhancement. It is useful in differentiating benign from malignant diseases.

Water halo sign

It corresponds to edema in the submucosa (cf. fat halo sign where there is fat infiltrating the submucosa). It may be seen in three forms:

• outer hyperattenuating layer with inner edematous layer
• inner hyperattenuating layer with outer edematous layer
• edematous submucosa between two hyperattenuating layers (target sign)

Common differentials include:

• inflammatory bowel disease
• vascular disorder
• infectious diseases
• radiation damage

Fat halo sign

It represents infiltration of the submucosa with fat, between the muscularis and the mucosa.

It is suggestive of inflammatory bowel disease, but may be seen in normal adults.

Black attenuation

It is synonymous with pneumatosis and the causes include:

• trauma
• ischemia
• infection