What is the target sign?
On CT, the “target” sign, also known as mural stratification, refers to visualization of a bright soft tissue attenuation inner layer (representing mucosa, lamina propria, and hypertrophied muscularis mucosae, sometimes with hyperemia), a dark low-attenuation middle layer (representing edematous submucosa), and sometimes a bright soft tissue attenuation outer layer (representing muscularis propria and serosa); the alternating layers correspond to the rings of a target. On MRI, a similar bright-dark-bright pattern is seen on contrast-enhanced fat-suppressed T1-weighted images, whereas a dark-bright-dark pattern is seen on T2-weighted images, because fluid and edema are high in signal intensity on T2-weighted images.
This sign is not specific for a particular disease condition but is highly specific for the diagnosis of nonneoplastic disease (edema, infection, inflammation, ischemia) when encountered in the small bowel.
However, this specificity for nonneoplastic disease does not hold when it is encountered in the stomach, as scirrhous carcinoma may also have a “target” sign.
