Target Sign
Bowel Inflammation

General Considerations

• Three concentric circles formed by the layers of the bowel wall in inflammatory disease of the bowel and seen on contrast-enhanced CT
• The inner and outer rings of high attenuation are presumed to represent hyperemia of the mucosa and muscularis propria and/or serosa, respectively
• The middle low attenuation ruing is presumed to represent submucosal edema which produces thickening of the bowel wall
• Best seen during late arterial, early venous phase
• Originally described with Crohn disease, it can be seen in any inflammatory disease of the bowel, including
  • Ulcerative colitis
• C. Difficile colitis
• Ischemic bowel disease
• Radiation-induced colitis

Clinical Findings

• Depend on underlying cause

Imaging Findings

• Most common CT finding in inflammation of the bowel is bowel wall thickening
• Intensity of enhancement correlates with severity of disease 

Target Sign. Contrast-enhanced axial CT of lower abdomen in patient with Crohn disease demonstrates three concentric circles (red circle) representing hyperemic mucosa and muscularis/serosa as inner and outer high density rings and submucosal edema in the central, low density ring.
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The Target Sign: Bowel Wall.  Ahualli, J. February 2005  Radiology, 234, 549-550.