Teenager with poorly controlled inflammatory bowel disease Axial CT with contrast of the abdomen shows a thick-walled mass that is filled with air and oral contrast that is located medial to the oral contrast-filled thickened ascending colon and above the right psoas muscle. An extensive amount of inflammatory change is seen in the mesenteric fat in the right lower quadrant. The diagnosis was Crohn disease with a fistula to an abscess above the right psoas muscle.