Fat Halo Sign

An abdominal CT finding consisting of a thickened bowel wall
with three layers: an innermost layer corresponding to the mucosa, surrounded by a layer of fatty attenuation, which is in turn surrounded by the muscularis propria and serosa. Described as typical of inflammatory bowel disease—Crohn’s disease and ulcerative colitis—it has also been reported as an acute finding in graft-versus-host disease and cytoreductive surgery