Figure 7b. Sigmoiditis in a 77-year-old woman after radiation therapy. (a) Contrast-enhanced CT scan shows concentric edematous wall thickening of the sigmoid colon with preservation of colonic layering (arrows). There is proliferation and linear infiltration of the prerectal fat plane. (b) Frontal image from a barium enema examination shows tapered narrowing of the sigmoid colon (arrows).